Adopting yield pillars has been considered an effective way of alleviating ground control problems and increasing production. The purpose of this research was to study the behavior of yield pillars and to develop the design criteria. After a literature review, two 2-D finite element models were developed, each following a different non-linear approach. The first model adopted the successive iteration technique incorporated with the Mohr-Coulomb yield criterion. The second followed the elastic—plastic approach, implementing a generalized Von Mises yield criterion. Extensive underground monitoring was conducted and the finite element models were compared with the field data, both yielding promising results. Three different longwall entry layouts were investigated. The yield-stable-yield pillar system was considered to be the best design. A parametric analysis was also performed. The triaxial factor and Poisson's ratio were found to be the most important material properties affecting pillar yielding. The progressive failure hypothesis for pillar design was critically examined. The analysis suggested that the formulation defining the stress distribution in the yield zone under this hypothesis may be satisfied only in extreme cases and, therefore, the actual distribution can be different. An improved equation, describing the stress distribution in the yield zone, was derived by statistically analyzing the results of finite element simulations. The latter equation fitted the observed field data better than did the original equation, and it was further developed for estimation of yield zone width. Consideration was also given to yield pillar design. Three possible yield pillar sizes were proposed in this paper. The maximum yield pillar size was considered to be twice the width of the yield zone. Based on the pressure arch concept, the minimum yield pillar size was determined by accepting that yield pillars were only supporting the rock strata under this pressure arch. A suggested yield pillar size was obtained by selecting a size which would force the peak stress at the center of the yield pillar to equal the average tributary stress. The case studies conducted in this research indicated that the predicted yield pillar sizes were reasonably accurate. / Ph. D.

A model for optimizing the assignment of maintenance actions for a piece of equipment is developed in the thesis. The model considers the detectability and the criticality of component failure in order to assign a maintenance instruction. The thesis also develops the framework for an integrated maintenance management system. The system consists of three modules. The first module is work control. It is used to prepare, schedule, and insure the execution of maintenance instructions. The second module is the equipment condition control module which monitors maintenance effectiveness and accordingly updates the maintenance instructions. The third module is cost control. This is the tool used to monitor the economical performance of the maintenance function. An equipment information system is also presented, and two futuristic maintenance proposals are introduced. The model and the integrated maintenance management system, constitute a strong tool, that equipment managers can use to optimize the maintenance function, and improve the mechanical, operational, and economical performance of equipment. / Master of Science

Newborn infants with differential patterns of fetal growth, as determined by their weight-for-length, typically display behaviors which have been conceptualized as reflecting the integrity of the infant's behavioral organization. The newborn infant's sucking is one behavior that has been hypothesized to both reflect the effects of previous experiences on behavioral organization and affect the infant's future behavioral development. In particular, the infant's pattern of sucking activity may not only reflect the integrity of the infant's nervous system, it may also alter the temporal organization of the infant's behavioral state and motor activity by increasing behavioral quiescence. The purpose of this study was to compare the sucking activity of underweight-for-length (N = 30) and average-weight-for-length (N = 30) infants and its effects on behavioral state and motor activity. Fifteen low-PI and 15 average-PI infants were randomly assigned to each of two experimental conditions. / Master of Science

In this thesis we study the model reduction problem in terms of the geometric concepts of linear system theory. By appropriate selection of reducing subspaces, useful lower-order system models can be achieved. The reducing subspaces can be chosen as parts of a system which are "most" and "least" controllable or observable; retaining, of course, the most controllable/observable subspace for model reduction. We review results showing how several measures of controllability and observability can provide this information. Balanced, Jordan canonical form, and dual GHR representations are shown to be state space realizations which naturally identify the reducing subspaces based on these measures. Several results unifying these methods are given. In another approach, we show that the reducing subspaces can be chosen such that after completing model reduction, a number of Markov parameters and time moments of the full system are retained by the reduced order model. We show how the dual GHR can be used as a tool which identifies these subspaces and state space realizations which naturally display them. Along these lines, a connection between model reduction in the state space and second-order systems is established, particularly the reduction of structures via the Lanczos algorithm. / Master of Science

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A project was conducted to determine the relative effectiveness of several antichlors in regards to their Cl₂ and ClO₂ gaseous "scrubbing" capacity. Both a pilot study as well as full scale trials were completed. Work was done on a bleach plant-packed tower scrubber system at a kraft pulp and paper mill. The pilot study was performed at pH's of 10.0 to 12.0 and therefore may have masked the scrubbing potential of two, lower pH, antichlors. Results from the full-scale trials showed that 45% Sodium Hydrosulfide (NaHS) solution, was the most efficient when compared to 42% Sodium Bisulfite (NaHSO₃) solution and CoProduct solution. A cost analysis was completed and revealed that CoProduct solution was the most cost effective of the three compounds. Other non-economic factors such as scrubber plugging tendencies, the potential for toxic gas formation, and handling difficulties should be examined before a final choice of antichlors is made. / M.S.

The calculation of critical speeds for turbomachinery with active magnetic bearings (AMBs) is of great interest due to the increasing number of applications of this new technology. The potential for increased turbomachine performance through improved AMB design has created the need for a more accurate method for predicting the system's undamped critical speeds. This thesis documents the development of a method which improves the accuracy of critical speed calculation by properly accounting for the influence of AMB sensor location on the undamped critical speeds. This investigation includes the development of an AMB modified Jeffcott model. The results from the AMB modified Jeffcott analysis give useful design guidance for the influence of the sensor location on the first and third modes of a symmetric rotor system. A more accurate solution using a transfer matrix method modified to account for AMB sensor locations is presented. The results from the transfer matrix method for an example compressor are presented showing the influence of the sensor placement on a standard undamped critical speed map. The mode shapes with sensor location at a typical design location are given to illustrate the importance of the sensor location. / Master of Science

This research examined Whole-Tree-Chip cleaning methods applicable to field operations in Pinus taeda L. (Loblolly pine) on the coastal plain of South Carolina. Objectives were: 1) to examine current and potential cleaning methods, and 2) develop and test two cleaning approaches suggested by past research. An open top chip van was modified to: a) determine the dispersion and composition of whole-tree-chip fractions by the installation of sampling buckets and floor pans and b) provide a platform for testing two cleaning systems. System one consisted of anti-clogging screens which pre-screened chips as they were discharged at the mill. It also allowed floor pans to sample the load for fines. System two utilized a radial blade blower which altered chip stream composition during loading by the Whole-Tree-Chipper. Eight trials were conducted over a six month period using a Morbark 22 chipper. Results indicated floor screens could have been more effectively positioned at the chip dump. As installed, and pin they successfully removed 1% of the load in fines chips. The best chip stream treatment involved double deflection: first from a vacuum assisted primary screen located in the van roof, and then from a passive screen located below and behind the first. This design reduced bark and fines by one-third. / Master of Science

The status of Curvularia lunata as a primary pathogen of creeping bentgrass (Agrostis palustris) has been debated in the literature for many years. The most recent and most complete evidence indicates that this fungus is a weak pathogen, colonizing only senescing tissues. In the present study, four groups of experiments were conducted: 1) The effects of five herbicides on the growth of C. lunata in vitro were determined. 2) Acute high temperature stress was evaluated as a predisposing factor in the susceptibility of creeping bentgrass to C. lunata. 3) The effects of acute high temperature stress and exposure to five different herbicides on creeping bentgrass were evaluated together and separately. 4) The potential of chronic, moderately high temperature stress and exposure to five herbicides when occurring separately and together to serve as predisposing factors on the susceptibility of creeping bentgrass to C. lunata were evaluated. It was found that effects of the herbicides on the growth of C. lunata depend on both the specific herbicide and the concentration. High temperature stress and herbicide exposure increase the colonization of creeping bentgrass by C. lunata only to the extent that these treatments produce moribund plant tissue. / Master of Science

A mathematical model for goal oriented learning in a network of neuron-like elements was developed. Using a mouse/goal box analogy, a simulation of a network with four elements was programmed in Turbo Pascal, Version 4.0 (Borland International) to test the model. Each location in the network corresponded to a particular network input. The output of the network consisted of one of four behaviors: forward, backward, left or right. The network successfully learned sequences of up to six movements in increasingly complex mazes. / Master of Science