This study explores how aggregate representations of student-contributed content were used in whole-class discussions to scaffold scientific inquiry in two middle school science classrooms. Working together as a knowledge community, students contribute scaffolded observations concerning HelioRoom and WallCology, room-sized “Embedded Phenomena” simulations, using tablet computers. These observations are collected and represented in aggregate form, and are the focus of teacher-led whole-class discussions. This thesis examines the efficacy of these aggregate designs for advancing students’ and teachers’ engagement in and understanding of the object of scientific inquiry, their usefulness for constructing relational models, and the interaction patterns that arise from their use. Findings suggest that aggregate representations of binary relationships that use tallies are well-suited for learning activities that have directed outcomes, such as constructing a relationship network. Aggregate representations that highlight gaps in data, and areas of agreement and disagreement in the data can be effective tools fostering productive discourse in classrooms.

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Aggregate signature schemes combine the digital signatures of multiple users on different messages into one single signature. The Boneh-Gentry-Lynn-Shacham (BGLS) aggregate signature scheme is one such scheme, based on pairings, where anyone can aggregate the signatures in any order. We suggest improvements to its current chosen-key security model. In particular, we argue that the scheme should be resistant to attackers that can adaptively choose their target users, and either replace other users' public keys or expose other users' private keys. We compare these new types of forgers to the original targeted-user forger, building up to the stronger replacement-and-exposure forger. Finally, we present a security reduction for a variant of the BGLS aggregate signature scheme with respect to this new notion of forgery. Recent attacks by Joux and others on the discrete logarithm problem in small-characteristic finite fields dramatically reduced the security of many type I pairings. Therefore, we explore security reductions for BGLS with type III rather than type I pairings. Although our reductions are specific to BGLS, we believe that other aggregate signature schemes could benefit from similar changes to their security models.

Past research documents a positive link between momentum and firm-level default risk, yet this anomaly is not connected to default risk at the macro level. Namely, there is no documented momentum during recessions, when default is higher on average. In the first essay, "Momentum and Aggregate Default Risk," we attempt to resolve this puzzle by analyzing momentum pro ts over time, conditional on both business cycles and unexpected changes in aggregate default risk. First, we show that momentum is driven by shocks to aggregate default, rather than general economic conditions such as expansions and recessions. Using the Fama and MacBeth procedure, we find that a conditional default shock factor is priced and can explain a large portion of the total momentum returns. Second, we provide a risk-based explanation for this anomaly by linking the returns of momentum portfolios to shareholder recovery during financial distress. We find that losers have higher recovery (i.e., shareholders have high bargaining power) on average, and, as a result, have relatively lower risk in high default states of the world. Therefore, loser stocks have a lower risk premium and lower expected returns in worsening aggregate default conditions, leading to the observed momentum. This effect is more pronounced among stocks of firms with low credit ratings. Our results help to reconcile the seemingly contradictory evidence documented by previous studies and o er a rational explanation for the momentum anomaly. In the second essay, "Sources of Momentum in Bonds," we study the relationship between momentum in bond returns and aggregate default. We document that momentum in corporate bonds occurs mainly during periods of high default shocks and is driven by losers. Supporting this result, we find that conditional default risk is priced in the cross-section of corporate bond portfolios. Motivated by these findings, we develop a theoretical model connecting bond momentum returns to the ability of bondholders to recover value in financial distress. Specifically, we find that losers have relatively higher recovery potential and, therefore, become less risky when high default shocks occur. Thus, losers have lower expected returns in high default shocks, leading to the observed conditional momentum. Further, US government bonds, with default risk approaching zero, feature no momentum, however this anomaly prevails in sovereign bonds with positive default risk, consistent with our main results.

Uncertainty is inherent in many novel and important applications such as market surveillance, information extraction sensor data analysis, etc. In the recent a few decades, uncertain data has attracted considerable research attention. There are various factors that cause the uncertainty, for instance randomness or incompleteness of data, limitations of equipment and delay or loss in data transfer. A probabilistic threshold range aggregate (PRTA) query retrieves summarized information about the uncertain objects in the database satisfying a range query, with respect to a given probability threshold. This thesis is trying to address and handle this important type of query which there is no previous work studying on. We formulate the problem in both discrete and continuous uncertain data model and develop a novel index structure, asU-tree (aggregate-based sampling-auxiliary U-tree) which not only supports exact query answering but also provides approximate results with accuracy guarantee if efficiency is more concerned. The new asU-tree structure is totally dynamic. Query processing algorithms for both exact answer and approximate answer based on this new index structure are also proposed. An extensive experimental study shows that asU-tree is very efficient and effective over real and synthetic datasets.

Thesis (M. Eng.), Memorial University of Newfoundland, 1998. / Bibliography: leaves 196-202.

Thesis (M.S. in Engineering)--University of Texas at Austin, 2006. / Includes bibliographical references.

Made available in DSpace on 2014-06-11T19:32:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-04-17Bitstream added on 2014-06-13T20:42:51Z : No. of bitstreams: 1 santos_ad_dr_bauru.pdf: 5050501 bytes, checksum: 953944123d570eb83506e96c96c8073d (MD5) / Os cimentos odontológicos a base de Cimento Portland, vêm desde a década passada sendo exaustivamente analisados em pesquisas científicas. Comercialmente como exemplo, temos o ProRoot MTA (Tulsa Dental, Oklahoma - USA) e o MTA-Angelus (Angelus Soluções Odontológicas, Londrina - Brazil). Ambos possuem inúmeras qualidades, porém tem inadequado tempo de presa e uma consistência que dificulta o seu manuseio por parte dos clínicos. O Grupo Vidros e Cerâmicas da UNESP - Ilha Solteira desenvolveu um cimento com as mesmas aplicações clínicas do MTA. Estudos recentes mostram que este material (denominado CER), possui propriedades físico-químicas semelhantes àquelas apresentadas pelo MTA. Atualmente tem-se tentado utilizar o cimento MTA como cimento obturador endodôntico, porém, características físicas dificultam seu uso para este fim. A proposta deste trabalho foi mostrar o desenvolvimento de um novo cimento obturador endodôntico, partindo da formulação do CER e testar algumas propriedades físico químicas deste material, tendo como comparação o cimento endodôntico comercial Sealer 26® (Dentsply Ind. E Com. Ltda., Petrópolis-Brazil). Os resultados obtidos mostraram que o cimento CEOE comparado com o Sealer 26®, tem um tempo de presa menor, maior liberação de íons, maior dureza e semelhante adesividade, solubilidade e selabilidade. / In the last decade, the dental cements based on Portland cement have been exhaustively investigated scientifically. Commercially is available the ProRoot MTA (Tulsa Dental, Oklahoma - USA) and MTA-Angelus (Angelus Soluções Dental, Londrina - Brazil) cements. In spite of the excellent physical, chemical and biological properties, one of the main disadvantages with using MTA is its extended setting time and difficult handling. Recently, the Glass and Ceramics group developed an experimental cement with the same clinical applications of MTA. Recent investigations showed that this material (entitled CER) it has physico-chemical properties similar those of the MTA. At present its biological properties are being investigated. One of the principal functions of the MTA is to seal the communications between the root and extern surface of the teeth. Recent studies have been showing that the physical characteristics of the MTA make difficult his use as root-filling cement. The purpose of this study was to developed new endodontic cement based on the formulation of the CER material. The properties evaluate in this study were: setting time, ions release, adhesion, hardness, solubility and sealing ability. The obtained results were compared with the Sealer 26® (Dentsply Ind. e Com. Ltda, Petrópolis-Brazil).

Grasslands throughout the world including those in British Columbia have been severely reduced and altered by agricultural production and inappropriate livestock grazing practices. Ongoing degradation of rangelands is a worldwide problem, currently affecting about 680 million hectares of rangelands. Studies on development and application of criteria and indicators for forests and grasslands are often lacking, or have been done on a limited number of sites with relatively narrow ranges of climate and soil type. This study aims to (i) quantify the relationships among soil/vegetation properties known to be affected by grazing to easily-assessed indicators, used in the existing health assessment systems, that do not require laboratory analyses or time consuming measurement, and (ii) to evaluate impacts of grazing on soil aggregate stability on the rough fescue grasslands of the southern interior of British Columbia. During the growing seasons of 2006 and 2007, soil and vegetation properties were measured on nine open grassland sites with a potential natural plant community dominated by rough fescue (Festuca campestris Rydb.) in the southern interior of British Columbia. Each site had at least one area excluded from grazing and all units were classified into different seral stages according to the amount of rough fescue present on the land. Rough fescue cover was found to be a useful indicator of the presence of functioning recovery mechanisms. Percent exposed mineral soil was found to be a sensitive indicator of the degree of soil stability and watershed function, as well as an indicator of the integrity of nutrient cycles and energy flows in rough fescue grasslands. Percent Junegrass cover was not as sensitive an indicator as percent exposed mineral soil, but has general overall strength with many health measures.. Only the 1-2 mm aggregate size class was closely related to most soil and vegetation properties, showing that it is more sensitive than the other aggregate stability parameters to soil and vegetation properties. The results from this study can help rangeland managers and ranchers in determining the rangeland health in their area as well as help researchers understand that only a certain number of parameters need to be assessed. / Land and Food Systems, Faculty of / Graduate