Thesis (B.S.)--University of California, Berkeley.

Inaug.-Diss.--Ludwig-Maximilians Universität, Munich.

A top tree data structure solves one of the most general variants of a well- studied dynamic trees problem consisting in maintenance of a tree along with some aggregated information on paths or in individual trees, possibly in a mutable way, under operations of inserting and removing edges. It provides a simple interface separated from both an internal top tree structure representing a hierarchical partitioning of the graph, and a driver ensuring its depth to be logarithmic, which has a crucial role for the efficiency of the data structure. The driver proposed in this thesis is based on biased trees, combining techniques used in the worst-case version of link/cut trees and in the amortized driver for top trees: An input forest is decomposed into heavy paths and interleaving vertices, all of them being represented by biased trees connected together to form exactly the top tree structure. The driver is meant to be a more efficient alternative to the originally proposed one, and a comparably efficient alternative to the driver proposed by Werneck; there is a room for their experimental comparison.

Trees are large, biologically complex multi-cellular organisms that have adapted to terrestrial growth. This places specific demands on their physiology such as the ability to transport water over long distances and the ability to withstand extreme mechanical forces. Wood formation (xylogenesis) is the development of the secondary vascular system within trees, which mainly addresses these two physiological needs. Xylogenesis is a highly ordered developmental process, consisting of a number of overlapping yet distinct developmental phases. These phases are strictly regulated through a combination of biochemical signalling networks and gene expression regulation.<ul> <li>microRNAs (miRNAs) are endogenous non-coding, small (~22 nt) RNAs that function predominantly as negative regulators of gene expression at the post-transcriptional level. They have been implicated in the regulation of plant developmental processes, including determining cell fate in the apical meristem and timing of developmental events such as flowering and leaf morphogenesis. miRNAs have recently been found to have regulatory roles in plants placed under various conditions of abiotic stress such as drought, mechanical stress, cold and high levels of salinity.</li></ul> Trees placed under mechanical stress produce a specialised form of wood called reaction wood. Reaction wood is referred to as tension wood in angiosperms, as it forms on the outside of a bent trunk or branch in order to correct for the non-vertical growth. The formation of tension wood requires extensive reprogramming of wood development processes. This makes tension wood induction an ideal tool to study and refine our understanding of wood development. Recently, miRNA regulation has been implicated in the control of normal and tension wood formation in trees, but the full extent to which miRNAs are involved in tension wood induction is not known. To identify miRNAs potentially involved in the regulation of normal and tension wood development in fast-growing Eucalyptus plantation trees, real-time quantitative polymerase chain reaction (RT-qPCR) and Northern blot analyses were performed for a number of conserved and putatively novel Eucalyptus miRNAs. A total of 12 miRNAs representing 12 distinct miRNA families were profiled, including three novel miRNAs that are putatively specific to Eucalyptus trees. To more fully understand miRNA function in terms of tree development, the abundance profiles of the selected miRNAs were first determined at the whole-tree level. Of the conserved miRNAs profiled, five (miR160, miR166, miR167, miR172, miR408) were found to have abundance profiles consistent with their predicted roles in plant development. At the whole-tree level, miR90, putatively novel to Eucalyptus, was predominately expressed in the mature leaves and flowers. miR90 may target a MADS-box transcription factor which is not required for mature leaf and flower growth. miR408, a regulator of the expression of a plastocyanin gene involved in lignin polymerisation, was expressed at low levels in the immature and mature xylem, where cell lignification is most prominent. In the tension wood, miR166, a known regulator of wood development and miR408 displayed similar increasing abundance over time in tension wood xylem. These profiles support their potential role in wood development. miR160 and miR167, which target auxin response factors responded early to bending stress, with their abundance reaching maximum levels six hrs post-induction before decreasing again. This is consistent with the observed role of auxin response factors as a mechanism to rapidly respond to stimuli, such as bending. The miRNAs abundance profiles generated in this study suggest that some miRNAs do indeed play a role in normal and tension wood development, though not necessarily directly. These results provide further insights into the complex nature of miRNA regulation and their hypothesised roles in wood development. The miRNAs highlighted herein are strong candidates for further functional studies as their abundance profiles and predicted targets are consistent with roles in wood development. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Genetics / unrestricted

This dissertation examined the participation of eight lower-achieving readers in two intermediate-level elementary classrooms (one fourth- and one fifth-grade) during group discussions about literary texts. The purpose of the investigation was to determine the extent to which lower-achieving readers (defined as students who had persistent struggles to attain minimum scores on state, district, and classroom assessments in reading) displayed discourse features that indicated the students' high-level thinking during heterogeneous and homogeneous (by reading level) discussions about literary texts. Several characteristics of discourse indicate high-level thinking, including but not limited to: generalizations, analyses, speculations, affective responses, inter-textual connections, and elaborated explanations. A secondary purpose was to describe what happened when lower-achieving readers, their peers, and teachers engaged in group discussions about text. / A multiple case study design was used in this investigation. Data were collected between October 2005 and May 2006. Data sources included: field notes collected from participant observation, transcripts and indices of student and teacher interviews, transcripts and indices of audiotaped and videotaped discussions and reading lessons, and students' writing assignments and other artifacts. Multiple strategies were used to analyze the data, including analytic induction and descriptive statistical techniques. A discourse analysis coding scheme was used to determine the extent to which lower-achieving readers likely used high-level thinking about literary texts during group discussions. / The findings revealed focal students used the discourse of discussion as a tool to comprehend text in two ways. The students used the discourse about texts as intellectual scaffolds for their own thinking and transformation in understanding of the texts. In addition, the discussions created authentic opportunities for students to explore reading comprehension strategies (e.g., meanings of new words, visualizing the story). This means students drew on their knowledge of comprehension strategies and incorporated them into their discussions to reason about the texts without explicit instruction from the teacher. Focal students both evoked and heard others refer to and talk about the comprehension strategies during discussions. Moreover, an important contextual foundation of the discussions that seemed to relate to the focal students' thoughtful responses, or those that suggested the students went beyond recalling the literal details of the stories, was the use of the discourse to problem-solve about the meaning of the texts. Finally, in respect to the students' writing assignments that often followed the discussions about the texts, lower-achieving readers made use of the ideas of the discussions in their writing. / Regarding high-level thinking during discussions, the lower-achieving readers' discourse suggested that they thought in high-level ways about texts during discussions, and that they thought in high-level ways to the same extent or nearly the same extent as their peers did in the same discussions about texts. The one major difference in their talk about texts related to the instances of elaborated explanations or instances when students stated a position and explained their thoughts about the position with more than one reason or with evidence from the text. Higher-achieving readers produced significantly more 'elaborated explanations' during discussions than the lower-achieving readers in this study. / From a theoretical perspective, this investigation extends our understanding of lower-achieving readers' use of discursive practices that influence thinking and reasoning about text. From pedagogical perspectives, the findings suggest teachers might need to understand ways to encourage a kind of discourse that elicits genuine problem-solving about the meanings of text. Likewise, teachers might need to understand the discourse features that indicate high-level thinking to model and discuss the features in their work with lower-achieving readers during discussions about literary texts.

Thesis (M.S.)--University of North Texas, Aug., 2007. / Title from title page display. Includes bibliographical references.

Thesis (M.Sc.)--Acadia University, 2001. / Includes bibliographical references (leaves 42-51). Also available on the Internet via the World Wide Web.

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The objective of this study is to examine large-scale spatial patterns of tree growth and climatic variation and to investigate the possible role of climate in determining tree growth patterns over space. This study represents one of the first uses of geostatistical methods to extract information about the spatial variation of climate from tree rings in western North America. It is also one of the first uses of data in spatial series to study the relationships of spatial variations between climate and tree growth. Geostatistics analyzes the spatial structure of the variables by assuming that adjoining data are correlated with each other over space and that the particular relationship expressing the extent of spatial correlation can be analytically and statistically captured in a function. It is applied to both June Palmer Drought Severity Index (PDSI) and ring-width index data from western North America. One basic assumption of applying geostatistics in this study is that the spatially uncorrelated small-scale variations are insignificant and represent background noise in large-scale dendroclimatic studies. The statistical relationships between the spatial variations of June PDSI and ring-width index are studied by simple scatter diagrams and correlation analysis. This is done in terms of yearly variations and variations of spatial patterns. Both of them support the contention that the large-scale spatial variations in ring-width index data can be used to infer the spatial variations of climate variables. Based upon the results of this research it can be concluded that geostatistics is a viable method to characterize the spatially correlated variations in dendroclimatology. By applying geostatistics to data sets, information about the spatial variations of climate contained in tree-ring data are enhanced, and the large-scale variations of climate are emphasized. The analysis of yearly relationships over space is particularly useful for identifying statistical relationships between climate and tree growth in a geographic region. The main factors of climate controlling ring-width index are identified as well as the less frequent limiting events. Once the statistical relationships are validated, they can be used to infer the spatial variations of past climate from variations in tree-ring index.

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