Numerical Stability of Lanczos Methods

The Lanczos algorithm for matrix tridiagonalisation suffers from strong numerical instability in finite precision arithmetic when applied to evaluate matrix eigenvalues. The mechanism by which this instability arises is well documented in the literature. A recent application of the Lanczos algorithm proposed by Bai, Fahey and Golub allows quadrature evaluation of inner products of the form $\psi^\dagger g(A) \psi$. We show that this quadrature evaluation is numerically stable and explain how the numerical errors which are such a fundamental element of the finite precision Lanczos tridiagonalisation procedure are automatically and exactly compensated in the Bai, Fahey and Golub algorithm. In the process, we shed new light on the mechanism by which roundoff error corrupts the Lanczos procedureComment: 3 pages, Lattice 99 contributio

Investigation of Metal and Organic Contaminant Distributions and Sedimentation Rates in Backwater Lakes along the Illinois River

Systematic sub-sampling of sediment cores in sections of uniform thickness is necessary in order to evaluate historic changes in sediment quality, to determine the vertical extent of contamination, and to measure sedimentation rates. With these objectives in mind, fourteen sediment cores were collected during March 2002 using the Illinois State Water Survey vibracorer. Concentrations of metals and total organic carbon were measured using standard techniques. Concentrations of chlorinated pesticides, phenolic compounds, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) were measured by gas chromatography/mass spectrometry (GC-MS). The concentrations of chlorinated pesticides, phenolic compounds and polychlorinated biphenyls (PCBs) were below the method detection limit in all sediment samples analyzed. However, there was a wide range in concentrations of polycyclic aromatic hydrocarbons (PAHs) which were detected in all sediment samples. Also, a wide range of metal concentrations was noted in the sediments evaluated. Lower concentrations of metals were found in the upper 0.5 m of sediment but concentrations were elevated at depths ranging from 1.0 m to 1.5 m. Sedimentation rates were estimated using cesium-137 radiometric dating on 14 vibracores. Sedimentation rates range from < 0.1 to 1.9 cm/yr, with an average of 0.9 cm/yr. These rates are comparable to those reported in previous studies.Illinois Sustainable Technology Centerpublished or submitted for publicationis peer reviewe

Robust time-optimal path tracking control of robots : theory and experiments

[v.1. Main work] -- [v.2]. Implementation detail

Serializable Isolation for Snapshot Databases

Many popular database management systems implement a multiversion concurrency control algorithm called snapshot isolation rather than providing full serializability based on locking. There are well-known anomalies permitted by snapshot isolation that can lead to violations of data consistency by interleaving transactions that would maintain consistency if run serially. Until now, the only way to prevent these anomalies was to modify the applications by introducing explicit locking or artificial update conflicts, following careful analysis of conflicts between all pairs of transactions. This thesis describes a modification to the concurrency control algorithm of a database management system that automatically detects and prevents snapshot isolation anomalies at runtime for arbitrary applications, thus providing serializable isolation. The new algorithm preserves the properties that make snapshot isolation attractive, including that readers do not block writers and vice versa. An implementation of the algorithm in a relational database management system is described, along with a benchmark and performance study, showing that the throughput approaches that of snapshot isolation in most cases

MS

thesisA sensitive assay for titration of antibodies which inhibit the metabolism of arginine by M. arthritidis was developed. Sera collected from rabbits immunized with M. arthritidis inhibited arginine metabolism when diluted 1:1600. The addition of fresh guinea pig serum enhanced the metabolic inhibition (MI) titer at least sixteen fold while heated guinea pig serum did not affect the titer of the rabbit antiserum. It was shown that rats did not produce detectable metabolic inhibiting antibodies to M. arthritidis, but did produce complement fixing antibodies in high titers. Preliminary experiments disclosed that uninoculated rats could be passively protected against an intravenous challenge of live M. arthritidis when given serum from rats that have recovered from polyarthritis. The rat serum used had a high titer of complement fixing antibodies and no detectable MI antibodies. Rats were injected intravenously with varying numbers of M. arthritidis. Rats inoculated with the larger doses of organisms developed polyarthritis to a greater extent than those injected with smaller doses. It was shown that complement fixing antibody occurred in the sera of rats inject with M. arthritidis within three days after inoculation. Sera from rats which developed polyarthritis general fixed complement at a greater dilution than sera of rats which did not develop polyarthritis. It was also shown that rats which ha recovered from polyarthritis were resistant to intravenous challenge with M. arthritidis. Only one of fourteen rats inoculated intravenously with M. arthritidis developed polyarthritis when challenged

Analysis of cytokinin-induced maize leaf developmental changes and interacting genetic modifiers

Four distinct segments define the maize leaf along the proximal-distal axis: the proximal sheath and the distal blade, which are separated by the ligule and auricle. The process of maize leaf morphogenesis, patterning and development requires the coordination of a number of proteins and hormones. The semi-dominant gain-of-function mutant Hairy sheath frayed1 (Hsf1) disrupts a number of leaf growth parameters: (i) leaves are shorter and more narrow, (ii) an increased density of macrohairs are apparent on the abaxial sheath and adaxial blade and (iii) the normal proximal-distal leaf pattern is disrupted, resulting in outgrowths, or prongs, of ectopic sheath, auricle and ligule from the margins of the normal leaf blade. The underlying cause for the Hsf1 phenotype is a missense mutation near the binding pocket of Zea mays Histidine Kinase1, a cytokinin (CK) receptor, which results in CK hypersignaling. To investigate the role of cytokinins, a class of plant growth regulatory hormones, in leaf morphogenesis and development, we conducted exogenous hormone germination assays and double mutant analysis of genes acting downstream of CK signaling. Our results confirm the Hsf1 phenotype is due to an increase in CK signaling and is more sensitive to CK. CK treatment affects leaf growth, cell identity and proximal distal patterning in a dose-dependent manner at specific developmental stages. Genetic diversity underlies CK responses in a diverse selection of CK-treated maize inbred lines, as well as in other species. Hsf1 alters proximal-distal leaf patterning in a specific manner and double mutant analysis revealed genetic interactions with genes downstream of CK signaling. Hsf1 prong formation is enhanced by dominant knotted1-like homeobox (knox) mutants and low GA levels, although knotted1 itself does not appear to be required for prong formation. Double mutants with aberrant phyllotaxy1 and tassels replace upper ears1 reveal dosage-dependent phyllotaxy effects

Independent Evolution of Leaf and Root Traits within and among Temperate Grassland Plant Communities

In this study, we used data from temperate grassland plant communities in Alberta, Canada to test two longstanding hypotheses in ecology: 1) that there has been correlated evolution of the leaves and roots of plants due to selection for an integrated whole-plant resource uptake strategy, and 2) that trait diversity in ecological communities is generated by adaptations to the conditions in different habitats. We tested the first hypothesis using phylogenetic comparative methods to test for evidence of correlated evolution of suites of leaf and root functional traits in these grasslands. There were consistent evolutionary correlations among traits related to plant resource uptake strategies within leaf tissues, and within root tissues. In contrast, there were inconsistent correlations between the traits of leaves and the traits of roots, suggesting different evolutionary pressures on the above and belowground components of plant morphology. To test the second hypothesis, we evaluated the relative importance of two components of trait diversity: within-community variation (species trait values relative to co-occurring species; α traits) and among-community variation (the average trait value in communities where species occur; β traits). Trait diversity was mostly explained by variation among co-occurring species, not among-communities. Additionally, there was a phylogenetic signal in the within-community trait values of species relative to co-occurring taxa, but not in their habitat associations or among-community trait variation. These results suggest that sorting of pre-existing trait variation into local communities can explain the leaf and root trait diversity in these grasslands