A number of experiments were carried out to study the potential of denitrifying bacteria and reduced nitrogen compounds for control of soil-borne damping-off pathogens. Measurement of the rhizosphere pH of growing soybean roots was carried out in soil adjusted to different pH states and packed into sheet microcosms. The results showed that the rhizosphere pH of soybean was lower than the bulk soil. Nitrate reductase activity and nitrite production was then characterised for the rhizosphere of intact 14 day-old soybean roots that were incubated in nitrate substrates adjusted to different pH values under water-logged conditions. The results showed that the rate and the quantity of nitrite production increased with increasing nitrate concentration and pH in the solution. A growth room experiment was carried out to determine root colonization by denitrifying bacteria in relation to disease caused by soil-borne pathogens, which are favoured by high soil moisture (approximately -5 KPa) and low oxygen levels. Nitrite producing bacteria were isolated from soybean roots grown in Grampian (Insch) soils which had not been cropped with soybean and Thai (Phitsanulok) soils which previously had been cropped with soybean. In the first pot experiment, the nitrite producing bacteria were isolated from different root sections of 12 and 19 day-old soybean plants after 8 weeks of continuous cropping of soils with soybean (a new crop was planted every week), and using different isolation media in order to determine the genus/species composition of the denitrifying bacteria on the rhizoplane. The results showed that continuous cropping of Thai soil and Insch soil with soybean increased pre-emergence damping-off disease and decreased fresh weight yields in seedlings that did emerge. ANOVA showed significant differences between root sections for most bacterial groups monitored {Bacillus spp., Pseudomonas and Enterobacteriaceae), with regression analysis generally showing densities increasing with root age or toward the shoot base. All nitrite producing bacterial isolates were screened for antifungal activity against Macrophomina phaseolina on agar plates and between 10 and 25% of nitrite producing bacteria were found to show in vitro antagonism. In a second pot experiment, the nitrite producing bacteria were isolated from root tissue below the crown (5 cm in length) every 2 weeks of continuous cropping of soils with soybean (a new crop was planted every 2 weeks). Plate-counting was carried out to determine the population of nitrite producing bacteria while a liquid culture MPN method was used for determination of NO, N2O and N2 producing bacteria. Linear regression analysis of the incidence of pre-emergence damping-off and soybean yields in seedling that did emerge showed a highly significant negative correlation between these parameters for both soils. ANOVA showed that there was a significant difference between soil type, with the Thai soil showing higher population densities of antagonistic bacteria on soybean roots. All nitrite producing bacterial isolates were screened for antifungal activity, but the plant pathogenic fungus, Pythium ultimum, was used in this experiment. The results showed that between 10 and 40% of nitrite producing bacteria showed in vitro antagonism. However, regression analysis showed that there was no significant increase or decrease in the nitrite producing antagonistic bacterial population with continuous soybean cropping. All 900 isolates of nitrite producing bacteria isolated from the soybean rhizoplane were screened for antagonistic activity towards Pythium ultimum based on a pot trial assay in the greenhouse. As expected, very low numbers of nitrite producing bacteria showed activity against P. ultimum and only one isolate gave a significant reduction in disease incidence in pot trials. The interactive effects of nitrite producing antagonist and an Arbuscular Mycorrhizal fungus (Glomus mosseae) and Bradryrhizobium japonicum, on control of the fungal pathogens, P. ultimum or M. phaseolina were investigated in the greenhouse. The results showed that improved plant growth was obtained with certain combined inocula involving nitrite producing bacterial antagonists, Glomus mosseae and Bradryrhizobium japonicum.

A research report submitted to the Faculty of Civil and Environmental Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. 13 October, 2016 / A Passive Auto-Tuning Mass Damper with Pulley connections (PATPD) is a vibration control device that consists of a box filled with silica sand on roller supports. The silica sand provides the mass of the damper. The PATPD is connected to the structure to be controlled by a group of ropes and pulleys; it is free to move in any translational direction. The pulleys and rope transfer a driving force to the damper, caused by the movement of the structure. The mass provides an inertial force which, in addition to the driving force of pulleys, dissipates energy providing the vibration control of the structure. Firstly, the test model underwent ‘PATPD Efficiency tests’ where the model was subjected to free translational, torsional and coupled vibration both with and without damper. This procedure was then repeated for forced harmonic excitation and the control effect for both analysed. These tests aimed to demonstrate the effectiveness of the PATPD at controlling structural vibrations. The results indicate that the PATPD provided at least 99% reduction to first natural frequency Power Spectral Density (PSD) peak for all tests, with relatively minimal increases for others. The model then underwent ‘Parameter Tests’ where the damper characteristics were changed and test procedure above repeated. These tests aimed to investigate the effect of the property changes of the PATPD on its ability to control free and forced vibration. The results indicate that (a) the PATPD provided significant reduction to first natural frequency PSD peak for all tests and (b) the properties of the PATPD affected the amount of control provided to the structure thus optimization of the PATPD could result in improved control effect. The models’ ‘Dynamic Properties’ namely model mass and stiffness were changed and test procedure repeated. These tests aimed to demonstrate the auto-tuning or adaptivity of the PATPD in its ability to control free and forced vibration. The results indicate that for all tests performed the PATPD provided significant reduction to first natural frequency PSD peak for all tests, with relatively minimal increases for others. The PATPD worked over a wide frequency band and was able to adapt to frequency changes providing significant control effect. Additional forced vibration tests under specific frequencies close to and far away from the models’ natural frequency demonstrates PATPD adaptability and efficiency. In addition tests under random excitation (as could be expected for earthquake loading) demonstrated PATPD positive control effect, adaptability and efficiency. / MT2017

Ingeniero Civil Mecánico / La aplicación de la dinámica estructural en la manufactura tradicional (torneado, fresado, entre otros ) ha permitido predecir la ocurrencia de vibraciones catastróficas o chatter en la herramienta durante un proceso de corte. Esto posibilita mejorar los parámetros de corte de manera de incrementar la tasa de remoción de material (MRR) sin que dañe a la herramienta o a la pieza trabajada. El Process Damping corresponde al amortiguamiento que se agrega al sistema debido a las fuerzas de fricción que se generan en la interacción entre una de las caras de la herramienta y la superficie ondulada de la pieza de trabajo. Este amortiguamiento permite aumentar la estabilidad durante el proceso de corte a bajas velocidades. El objetivo del presente trabajo es incorporar este fenómeno a modelos numéricos de un proceso de torneado a través de parámetros de la herramienta y condiciones de operación dadas (velocidad de corte y profundidad de corte). En la primera parte de este reporte se presentan las bases teóricas para los dos modelos dinámicos desarrollados: la simulación de las vibraciones y fuerzas de corte en el dominio temporal; y un modelo en el dominio de frecuencias que permita la obtención de los diagramas de estabilidad. La principal contribución del trabajo corresponde a la incorporación de Process Damping a los dos modelos dinámicos desarrollados para el proceso de torneado. El método usado se basó en la energía disipada durante el corte, donde los dos factores más importantes para la modelación de Process Damping fueron el coeficiente de indentación y la identificación del área de penetración durante el proceso de corte. Se realizó un análisis de sensibilidad del fenómeno de Process Damping ante distintas condiciones de operación y propiedades del material y herramienta. Luego, se analizó los dos modelos para tres tests declarados desde la literatura. Por último, se estudió que las simulaciones en el dominio temporal se complementaran con el diagrama de estabilidad generado por la simulación en el dominio de frecuencias. Para cada test se analizaron los diagramas de estabilidad obtenidos, y los gráficos de desplazamiento de la herramienta y fuerzas de corte para casos específicos, donde se observó gráficamente la influencia de la fuerza de Damping en el corte. Entre el Test #1 y Test #2 se identificó el efecto del radio de punta de la herramienta en el diagrama de estabilidad, y entre el Test #3 y los otros dos Tests se analizó la diferencia del efecto de Process Damping entre el aluminio y el acero, respectivamente. Finalmente, a partir de los resultados exhibidos se validaron los dos modelos dinámicos propuestos que incluyen los efectos del Process Damping en el torneado, permitiendo predecir las zonas de estabilidad a bajas velocidades de corte para condiciones de operación dadas. El presente trabajo de investigación se realizó en el Centro de Manufactura Avanzada de la Universidad de Sheffield, en el grupo de Machining Dynamics del área de proyectos tecnológicos.

This thesis presents a new method for the controllable damping of deformable objects. The method evolves from physically based techniques; however, it allows for non-physical, but visually plausible motion. This flexibility leads to a simple interface, with intuitive control over the behaviour of the material. This method is particularly suited for strongly damped materials, which account for the majority of objects of interest to animation, since it produces non-oscillatory behaviour. This is similar to critical damping, except that it affects all modes independently. The new method is based on the minimization of a slightly modified version of total energy. This framework can be used to simulate many other physical phenomena, and therefore lends itself to coupling with other simulations. Implementation details for a simple example are given. Results are shown for varying parameters and compared to those produced by a traditional method.

In order to meet industry demands for improved productivity and part quality, machine tools must be equipped with faster and more accurate feed drives. Over the past two decades, research has focused on the development of new control strategies and smooth trajectory generation techniques. These developments, along with advances in actuator and sensor technology, have greatly improved the accuracy of motion delivery in high speed machine tools. However, further advancement is limited by the vibration of the machine’s structure. The purpose of the research in this thesis is to develop new control techniques that use active vibration damping to achieve bandwidths near the structural frequencies of machine tools, in order to provide better dynamic positioning of the tool and workpiece. Two machine tool drives have been considered in this study. The first is a precision ball screw drive, for which a pole-placement technique is developed to achieve active vibration damping, as well as high bandwidth disturbance rejection and positioning. The pole-placement approach is simple and effective, with an intuitive physical interpretation, which makes the tuning process straightforward in comparison to existing controllers which actively compensate for structural vibrations. The tracking performance of the drive is improved through feedforward control using inverted plant dynamics and a novel trajectory pre-filter. The pre-filter is designed to remove tracking error artifacts correlated to the velocity, acceleration, jerk and snap (4th derivative) of the commanded trajectory. By applying the least-squares method to the results of a single tracking experiment, the pre-filter can be tuned quickly and reliably. The proposed controller has been compared to a controller used commonly in industry (P-PI position-velocity cascade control), and has achieved a 40-55 percent reduction in peak errors during tracking and machining tests. The controller design, stability analysis, and experimental results are discussed. The second drive considered is a linear motor driven X-Y stage arranged as a T-type gantry and worktable. The worktable motion is controlled independently of the gantry using a loop shaping filter. The gantry is actuated by dual direct drive linear motors and is strongly coupled to the worktable position, which determines its inertial characteristics. A 94 Hz yaw mode is handled in the gantry control law using sensor and actuator averaging, and active vibration damping. The stability and robustness of the design are considered using multivariable frequency domain techniques. For the worktable motion along the gantry, a bandwidth of 130 Hz is achieved. The gantry crossover frequency is 52 Hz, which is 3 times higher than the bandwidth that can be achieved using independent PID controllers (16 Hz). The performance of the proposed control scheme has been verified in step disturbance (i.e., rope snap) tests, as well as tracking and contouring experiments.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 314-327).

Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s):Young S. Shin. Includes bibliographical references (p. 57). Also available online.

With the increase in complexity of modern electricity grids, the implementation of state-estimators has become a vital aspect of stability and contingency analyses for stable and secure power system operation. Transmission line reactance is an important component in the computation of state-estimators. Two models utilizing real-time synchrophasor data and ERCOT load information are proposed to compute Thevenin equivalent reactance. This thesis presents the results of implementing these methods to estimate the equivalent reactance of a transmission network between The University of Texas at Austin and The University of Texas, PanAm. / text

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