Recent tragedies involving the collapse of several large and prominent buildings have brought international attention to the subject of progressive collapse, and the field of structural engineering is actively investigating ways to better protect structures from such catastrophic failures. One focus of these investigations is the behavior and performance of shear tab connections in steel structures during progressive collapse events. The shear tab, a simple connection, is typically modeled as a perfect pin in standard design, but in progressive collapse analysis, a much more accurate model of its true behavior and limits is required. This report documents the development of a simple yet accurate shear tab model and its use in understanding the behavior and limits of shear tab connections in column removal scenarios. Particular attention is paid to the connections’ axial force limit state, an aspect of behavior that is typically unimportant in standard design. / text

The lowland Maya site of Ceibal, Guatemala, had a long history of occupation, spanning from the Middle Preclassic Period through the Terminal Classic (1000 BC to AD 950). The Ceibal-Petexbatun Archaeological Project has been conducting archaeological investigations at this site since 2005 and has obtained 154 radiocarbon dates, which represent the largest collection of radiocarbon assays from a single Maya site. The Bayesian analysis of these dates, combined with a detailed study of ceramics, allowed us to develop a high-precision chronology for Ceibal. Through this chronology, we traced the trajectories of the Preclassic collapse around AD 150–300 and the Classic collapse around AD 800–950, revealing similar patterns in the two cases. Social instability started with the intensification of warfare around 75 BC and AD 735, respectively, followed by the fall of multiple centers across the Maya lowlands around AD 150 and 810. The population of Ceibal persisted for some time in both cases, but the center eventually experienced major decline around AD 300 and 900. Despite these similarities in their diachronic trajectories, the outcomes of these collapses were different, with the former associated with the development of dynasties centered on divine rulership and the latter leading to their downfalls. The Ceibal dynasty emerged during the period of low population after the Preclassic collapse, suggesting that this dynasty was placed under the influence from, or by the direct intervention of, an external power.

In order to optimize limited infrastructure, many power systems are frequently operated close to critical, or bifurcation, points. While operating close to such critical points can be economically advantageous, doing so increases the probability of a blackout. With the continued deployment of Phasor Measurement Units (PMUs), high sample rate data are dramatically increasing the real time observability of the power grids. Prior research has shown that the statistics of these data can provide useful information regarding network stability and associated bifurcation proximity. Currently, it is not common practice for transmission and distribution control centers to leverage the higher order statistical properties of PMU data. If grid operators have the tools to determine when these statistics warrant control action, though, then the otherwise unused statistical data present in PMU streams can be transformed into actionable information. In order to address this problem, we present two methods that aim to gauge and improve system stability using the statistics of PMU data. The first method shows how sensitivity factors associated with the spectral analysis of the reduced power flow Jacobian can be used to weight and filter incoming PMU data. We do so by demonstrating how the derived participation factors directly predict the relative strength of bus voltage variances throughout a system. The second method leverages an analytical solver to determine a range of "critical" bus voltage variances. The monitoring and testing of raw statistical data in a highly observable load pocket of a large system are then used to reveal when control actions are needed to mitigate the risk of voltage collapse. A simple reactive power controller is then implemented that pushes the stability of the system back to a stable operating paradigm. Full order dynamic time domain simulations are used in order to test this method on both the IEEE 39 bus system and the 2383 bus Polish system. We also compare this method to two other, more conventional, controllers. The first relies on voltage magnitude signals, and the second depends only on local control of a reactive power resource. This comparison illustrates how the use of statistical information from PMU measurements can substantially improve the performance of voltage collapse mitigation methods.

Through large sculptural works that are often caricatures of representational objects, my work explores the complicated moments and tangled histories of childhood Jewish schooling in Winnipeg and travels to Israel and Palestine as an adult. My thesis exhibition Collapse, as well as most of my graduate work, examines my investigation through manmade constructions that control and restrict or unite and connect the movement of others. Sculptures about a destroyed bridge’s imagined longing for exotic places, a giant onion serving as a resuscitation mechanism against tear gas or a construction crane to Armageddon are some examples of work that explore the poetry I find in dichotomies, and serve as a series of recollections that negotiate experiences beyond full understanding.

The ensemble Kalman filter (EnKF) is a reliable data assimilation tool for high-dimensional meteorological problems. On the other hand, the EnKF can be interpreted as a particle filter, and particle filters (PF) collapse in high-dimensional problems. We explain that these seemingly contradictory statements offer insights about how PF function in certain high-dimensional problems, and in particular support recent efforts in meteorology to 'localize' particle filters, i.e. to restrict the influence of an observation to its neighbourhood.

Thesis advisor: Yvette Kuiper / 40Ar/39Ar single-grain total-fusion ages of muscovite and biotite and one 40Ar/39Ar furnace step-heating age of hornblende from the Tadmuck Brook Schist, Nashoba Formation, and Ball Hill mylonite zone are used to reconstruct the late tectonic and metamorphic history of the Nashoba terrane in eastern Massachusetts. The data fall into three age populations. Age population I (~376-330 Ma) is interpreted as cooling after a migmatization event in the Nashoba terrane, population II (~300 Ma) may be associated with normal movement on the Clinton-Newbury fault, and population III (~267 Ma) is possibly related to cooling of the Rocky Pond Granite. No younger Alleghanian overprint was observed. / Thesis (MS) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

O organismo apresenta diversas reações integradas em resposta à injúria, com o objetivo de restaurar a homeostase. Dentre esses mecanismos, destaca-se a resposta inflamatória, já que sem ela a injúria que acometeu o organismo dificilmente seria resolvida. Todo procedimento cirúrgico representa uma injúria para o organismo. As técnicas cirúrgicas minimamente invasivas tendem a gerar respostas deletérias mais brandas aos animais; as cirurgias torácicas envolvem, porém, um trauma adicional caracterizado pelo colapso pulmonar, que se faz necessário mesmo nas técnicas minimamente invasivas. Foram realizados em humanos diversos estudos que avaliam as vantagens desta técnica em relação à toracotomia; na espécie eqüina, a toracoscopia vem sendo aplicada na rotina hospitalar desde a década de 80 e relatos afirmam ser um procedimento cirúrgico seguro. No entanto, não foram descritos dados referentes à resposta inflamatória decorrente deste procedimento. Desta forma, este estudo visou avaliar a resposta inflamatória sistêmica e local decorrente da técnica, na qual a indução e redução do colapso pulmonar foram feitas de maneira controlada. Foram utilizados 12 eqüinos hígidos, de raça e idade variadas, de ambos os sexos. Os animais foram divididos em dois grupos, submetidos à toracoscopia com duração de 30 e 60 minutos (grupos 1 e 2, respectivamente). As pressões intratorácicas foram controladas em todos os procedimentos, permitindo controle da indução e redução do colapso pulmonar, diminuindo assim a ocorrência de pneumotórax residual. Amostras de sangue, líquido pleural e lavado bronco alveolar foram coletadas antes do procedimento (M1), e duas (M6), seis (M7) e 24 horas (M8) após o início do colapso pulmonar. Estas foram usadas para avaliação da resposta inflamatória por meio de mensuração da produção de espécies reativas de oxigênio (ERO) pelas células presentes em cada tipo de amostra, utilizando-se como metodologia a citometria de fluxo, e para a quantificação de citocinas por ELISA (IL-1β) ou por ensaio biológico (TNF-α e IL-6). Para análise dos resultados foi considerada a possível influência dos fatores grupo e momento experimental em cada uma das variáveis estudadas. Os valores de burst oxidativo apresentados pelas células das amostras em questão não sofreram influência dos fatores avaliados. Não foi possível avaliar a variação dos níveis de IL-1β pela metodologia aplicada. Os níveis de TNF-α sofreram influência estatisticamente significativa do fator momento experimental nas amostras de lavado broncoalveolar e líquido pleural, sendo que M6 apresentou maiores níveis desta citocina; não foi observada influência desses fatores nos níveis plasmáticos da mesma. Em relação a IL-6, foi observada influência do fator momento experimental nas amostras de plasma e lavado broncoalveolar, e de ambos os fatores nas amostras de líquido pleural, sendo que os níveis dessa citocina apresentaram um padrão de aumento mais tardio que o apresentado pelo TNF-α. Concluímos que o colapso pulmonar induzido por infusão de gás CO2 em eqüinos hígidos provocou uma reação inflamatória localizada na cavidade torácica, em que não foram observadas diferenças significativas entre os dois grupos experimentais. Assim, a cirurgia torácica videoassistida em eqüinos com até 60 minutos de duração pode ser indicado sem que fatores oriundos da técnica cirúrgica agravem a enfermidade. Uma vez que não foi observada influência dos fatores estudados nos valores de pressão intratorácica, acreditamos que a metodologia aplicada foi adequada para a realização da técnica, provendo adequado controle e redução da ocorrência de pneumotórax residual, que somente foi observado nos casos onde ocorreu pneumotórax bilateral durante o procedimento cirúrgico. / Organisms present several integrative reactions to injury, aiming at the reestablishment of homeostasis. Among these mechanisms is the inflammatory reaction, for without it the initial injury would hardly be solved. Every surgical procedure represents an injury for living organisms. Minimally invasive surgical techniques tend to induce milder negative reactions in animals; nonetheless, thoracic surgery leads to an additional trauma characterized by lung collapse, required even in minimally invasive surgical techniques. Several human studies have assessed the advantages of this technique compared to thoracotomy; in horses, the use of thoracoscopy has increased in routine procedures since the 1980s, and reports point to the safety of its usage. Nevertheless, no data regarding the inflammatory reaction induced by this procedure has been reported. In this matter, our study aimed at the evaluation the local and systemic inflammatory response associated with this technique, in which the induction and reduction of lung collapse were carefully controlled. 12 healthy horses of varied breeds, age, and of both genders were used. Animals were divided in two groups, and submitted to thoracoscopy for 30 or 60 minutes (groups 1 and 2, respectively). Intrathoracic pressure was controlled in every procedure, allowing the induction and reduction of lung collapse, reducing the chance of residual pneumothorax. Samples of blood, pleural fluid, and bronchoalveolar fluid were harvested before the procedure (M1), and two (M6), six (M7) and twenty-four hours (M8) after the onset of lung collapse. These samples were employed for the evaluation of the inflammatory reaction through measurement of reactive oxygen species (ROS) by cells present in each sample, using flow cytometry, and for cytokine quantification by ELISA (IL-1β) or bioassay (TNF-α and IL-6). For the analysis of our results the factors group and experimental timepoint were considered for every variable studied. Values of oxidative burst displayed by cells in each sample did not depend on the factors analyzed. Variation of IL-1β levels could not be detected by the methods employed here. Levels of TNF-α were statistically influenced by the factor experimental timepoint in pleural fluid and bronchoalvolar fluid, and the highest levels of this cytokine were observed in M6; no influence of these factors on its plasmatic levels was observed. Regarding IL-6, we found an influence of the factor timepoint in samples of plasma and bronchoalveolar fluid, and an influence of both factors in samples of pleural fluid, being the highest levels of this cytokine found later than the TNF-α peak. We conclude that the lung collapse induced by CO2 in healthy horses caused an inflammatory reaction restricted to the thoracic cavity, without significant differences between groups 1 and 2. Thus, video-assisted thoracic surgery in horses lasting up to 60 minutes can be recommended leads to no signs of direct negative effects of the technique that could worsen the patient condition. Since we found no influence of either factor studied on values of thoracic pressure, we conclude that the methods employed for the surgery were adequate, supplying sufficient control over the occurrence of residual pneumothorax, observed only in cases of bilateral pneumothorax during the procedure.

Earthquakes represent a serious threat to the safety of masonry structures, with failure of these constructions under the influence of seismic action generally occurring via specific, well-documented collapse mechanisms. Analysis and assessment of these collapse mechanisms remains a challenge - while most analysis tools are time-consuming and computationally expensive, typical assessment methods are too simplified and often tend to underestimate the dynamic resistance of the structures. This dissertation aims to bridge the gap between the two through the development of a computational tool for the seismic collapse assessment of masonry structures, which uses rocking dynamics to accurately capture large displacement response, without compromising on computational efficiency. The tool could be used for rapid evaluation of critical mechanisms in a structure in order to prioritise retrofit solutions, as well as for code-based seismic assessment. The framework of the tool is first presented, wherein the rocking equations of motion are derived for a range of different collapse mechanisms, for any user-defined structural geometry, using as a starting point a geometric model of the structure in Rhino (a 3D CAD software). These equations of motion are then exported for solution to MATLAB. As a number of collapse mechanisms take place above ground level, a methodology to account for ground motion amplification effects is also proposed, while in the case of comparison of multiple different mechanisms, an algorithm to automatically detect critical mechanisms is presented. These developments make it possible to rapidly conduct a seismic analysis of structures with complicated three-dimensional geometries. However, the rocking equations of motion utilised thus far assume that the interfaces between the masonry macro-elements are rigid, which is not the case in reality. Thus, a flexible interface model is introduced, where the interfaces are characterised by a finite stiffness and compressive strength. This modelling strategy results in an inward shift of the rocking rotation points, and expressions are derived for these shifting rotation points for different interface geometries. The rocking equations of motion are also re-derived to account for the influence of the continuously moving hinges. However, the new equations tend to be highly non-linear - especially in the case of more complex collapse mechanisms. Thus to reduce computational burden, the semi-flexible interface model is proposed, which accounts for the shifting hinges in a more simplified manner than its fully-flexible counterpart. These new analytical models enable more accurate prediction of the seismic response of real-world structures, where interface flexibility tends to have a significant influence on dynamic response, while material damage in the form of crushing of the masonry also reduces dynamic resistance. The ability of the tool to be used for both seismic analysis and assessment is finally demonstrated by using it to perform a rocking dynamics-based analysis as well as a code-based seismic assessment of the walls of a historic earthen structure.

This thesis examines and identifies the problems of shape collapse in large deformation image registration. Shape collapse occurs in image registration when a region in the moving image is transformed into a set of near zero volume in the target image space. Shape collapse may occur when the moving image has a structure that is either missing or does not sufficiently overlap the corresponding structure in the target image. We state that shape collapse is a problem in image registration because it may lead to the following consequences: (1) Incorrect pointwise correspondence between different coordinate systems; (2) Incorrect automatic image segmentation; (3) Loss of functional signal. The above three disadvantages of registration with shape collapse are illustrated in detail using several examples with both real and phantom data. Shape collapse problem is common in image registration algorithms with large degrees of freedom such as many diffeomorphic image registration algorithms. This thesis proposes a shape collapse measurement algorithm to detect the regions of shape collapse after image registration in pairwise and group-wise registrations. We further compute the shape collapse for a whole population of pairwise transformations such as occurs when registering many images to a common atlas coordinate system. Experiments are presented using the SyN diffeomorphic image registration algorithm and diffeomorphic demons algorithm. We show that shape collapse exists in both of the two large deformation registration methods. We demonstrate how changing the input parameters to the SyN registration algorithm can mitigate the collapse image registration artifacts.

Doctor of Philosophy / Steam reconditioning to recover collapse, in mid to low density eucalypt species, has been known for over ninety years. The current industrial practices for steam reconditioning have largely been based on a few older studies, which were often poorly documented and based on very small sample sizes. On top of this, many local practices and ‘rules of thumb’ have developed over time, many of which have a questionable scientific basis. This thesis was undertaken to more rigorously investigate and fundamentally understand collapse recovery, and try to optimise its application. The most obvious variable that kiln operators have control over is the moisture content of the timber prior to steam reconditioning. Experiments were undertaken to generate a range of moisture gradients (ranging from minimal to more industrially realistic) to evaluate the effect of moisture content on collapse recovery. An optimal moisture content for the core of the boards was found to be between about 18–20%, although there was no statistical difference in recoveries between about 17–25% moisture content. Below 15% moisture content recovery dropped off severely and intra-ring internal checking closure was incomplete, while at 25% moisture content an increased level of normal shrinkage, due to the early removal of drying stresses, was the main drawback. Above a core moisture content of about 35% incomplete closure of intra-ring internal checks was again observed. There was little evidence of re-collapse occurring in these high moisture content samples. Previously established relationships between density and collapse and drying rate were again generally observed in these experiments. However, for the first time an effect of collapse in reducing the fitted drying diffusion coefficients was also observed. It was also observed that, provided the moisture content of the board was in the critical range, most of the collapse recovery was achieved in the time it took to get the core of the board up to the steaming temperature of close to 100°C. This suggests that for most thicknesses a conservative reconditioning period of two hours at temperature is all that is required. This recommended shortening of the reconditioning cycle could dramatically increase the throughput of timber through the steam reconditioning chambers. Alternatively, it could mean that where modern final drying kilns are being used, the reconditioning treatment could be carried out within the final drying kiln. A finite element model was developed to demonstrate the mechanism by which collapse recovery occurs. The theory tested was that the elastic component that stores the energy to restore the shape of the deformed cell is primarily found in the S1 and S3 layers. In contrast, the inelastic component is primarily found in the S2 layer. The model generated here provided limited support for this theory.