Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 350-364). Also available in electronic version.

M.Ing. (Electrical & Electronic Engineering Science) / This dissertation deals with the design and implementation of a hysteresis machine for high-speed applications. A model is introduced whereby the optimum working point of the machine can be determined. Hence it is possible to make a comparison between different rotor materials with respect to cost, specific energies and overall performance. The development of a compensator for actively controlling the phase angle of the airgap flux density, in order to reduce hunting, is discussed with reference to practical results. A technique for measuring real power in the frequency plane with the aid of a frequency spectrum analyzer, is explained. The design and evaluation of a hysteresis machine is based on practical results obtained from this measuring technique.

No description available.

The accurate control of a positioning system that exhibits scalar hysteresis requires a control strategy that incorporates compensation for the hysteresis. One approach is to develop a compensator based on an inverse hysteresis operator. This method uses an open loop control in which the inverse operation adjusts the actuator input to compensate for the hysteresis in the system. When this is accomplished, the composite operation produces a linear relationship between a reference input and the system output. The difficulty of this method lies in developing an accurate model of the hysteresis for which an inverse operator can be obtained. In this work, a system with hysteresis is modeled by a generic model based on a Preisach type operator. First, it is shown that the operator has an inverse and that both have approximations that are convergent. Then, simulation and experimental data are used to demonstrate the ability of the operator to accurately model a hysteresis relationship. This lays the foundation for then demonstrating the concept of inverse compensation. / Ph. D.

No description available.

Embryonic biopsy routinely involves the removal of one or two blastomeres in the preimplantation genetic diagnosis (PGD) procedure to determine the presence of a specific disease. The rapid development of the PGD technique and stem cell research has led to great demand for highly automated high precision equipment for cellular component micro-extraction. This thesis presents the development of an automated microsurgery system for embryo biopsy. While the ultimate objective of this research is to improve the so called “take-home-baby rate”, the primary focus of this research, however, is devoted to demonstrate the automation of the first two steps in the embryo biopsy procedure: embryo immobilization and embryo perforation with a piezoelectric actuated micro-cutter mounted on a five DOF micromanipulator. A biological embryo holding device incorporating a unique configuration of fluidic channels is designed to increase embryo mobility in order to overcome friction force while maintaining a low suction flow rate and pressure. The validity of this design is demonstrated by good qualitative agreement between the experimental and simulation results. 3D nonlinear equations of motion of a micro-needle driven longitudinally by a piezoelectric actuator are developed based on Kane’s method . The longitudinal vibration of a micro-needle results in excitation of its out-of-plane, lateral eigenmodes at low damping coefficients. The dynamic model is in good agreement with experimental observations. This model is exploited further to describe the response of an immersed glass micropipette with imbedded mercury in piezo-assisted intracytoplasmic sperm injection (ICSI). Furthermore, piezoelectric actuator dynamic nonlinearity introduced by hysteresis is addressed in this research. A new model is proposed to characterize the rate-dependent hysteresis based on Duffing's equation. A nonlinear capacitor element is incorporated into a linear second-order system to predict the relationship between an input state and a hysteretic output. The proposed hysteresis model is verified experimentally. Based on this approach, a new electromechanical piezoelectric actuator model is proposed. A vision-assisted controller for embryo perforation is proposed by implementing a vision tracking and robust autofocusing algorithm using the particle swarm optimization (PSO) method. The performance of the proposed visual-based controller demonstrated experimentally to be effective in providing accurate embryo and micro-needle 3D positioning. Finally, an automated embryo perforation with the proposed mechanical approach was conducted successfully.

Embryonic biopsy routinely involves the removal of one or two blastomeres in the preimplantation genetic diagnosis (PGD) procedure to determine the presence of a specific disease. The rapid development of the PGD technique and stem cell research has led to great demand for highly automated high precision equipment for cellular component micro-extraction. This thesis presents the development of an automated microsurgery system for embryo biopsy. While the ultimate objective of this research is to improve the so called “take-home-baby rate”, the primary focus of this research, however, is devoted to demonstrate the automation of the first two steps in the embryo biopsy procedure: embryo immobilization and embryo perforation with a piezoelectric actuated micro-cutter mounted on a five DOF micromanipulator. A biological embryo holding device incorporating a unique configuration of fluidic channels is designed to increase embryo mobility in order to overcome friction force while maintaining a low suction flow rate and pressure. The validity of this design is demonstrated by good qualitative agreement between the experimental and simulation results. 3D nonlinear equations of motion of a micro-needle driven longitudinally by a piezoelectric actuator are developed based on Kane’s method . The longitudinal vibration of a micro-needle results in excitation of its out-of-plane, lateral eigenmodes at low damping coefficients. The dynamic model is in good agreement with experimental observations. This model is exploited further to describe the response of an immersed glass micropipette with imbedded mercury in piezo-assisted intracytoplasmic sperm injection (ICSI). Furthermore, piezoelectric actuator dynamic nonlinearity introduced by hysteresis is addressed in this research. A new model is proposed to characterize the rate-dependent hysteresis based on Duffing's equation. A nonlinear capacitor element is incorporated into a linear second-order system to predict the relationship between an input state and a hysteretic output. The proposed hysteresis model is verified experimentally. Based on this approach, a new electromechanical piezoelectric actuator model is proposed. A vision-assisted controller for embryo perforation is proposed by implementing a vision tracking and robust autofocusing algorithm using the particle swarm optimization (PSO) method. The performance of the proposed visual-based controller demonstrated experimentally to be effective in providing accurate embryo and micro-needle 3D positioning. Finally, an automated embryo perforation with the proposed mechanical approach was conducted successfully.

This thesis encompasses three essays around criminal behaviour with the first one analysing the impact of programmes aimed at poverty reduction, the second one developing a theoretical model of hysteresis in crime, and the third one empirically investigating the hysteresis hypothesis in crime rates. In the first chapter I investigate the impact of conditional cash transfers (CCT) on crime rates by analysing the Brazilian Bolsa Familia, the largest CCT programme in the world, in a panel data between 2001 and 2008. The related existing economic literature analysing general welfare programmes usually ignores the crucial endogeneity involved in the relationship between crime rates and social welfare policies through poverty, since poorer regions are focused in the distribution of resources. I use the existing temporal heterogeneity in the implementation of the programme across the states to identify the causal impact of CCT programmes on poverty and criminality. The guidelines of the Brazilian programme established that the amount of resources available for each state should be based on the poverty levels in the 2000 Census. However, due to reasons unrelated to poverty levels and crime rates, some states were able to implement the programme to a greater extent more quickly than others. States that reached the level of cash transfer expenditures proposed by the guidelines of the programme more promptly had a more significant reduction in poverty rates. Similar but less robust results are found for crime rates as robbery, theft and kidnapping, while no significant effects were found for homicide and murder, indicating a weak or non-existent relationship between conditional cash transfers and crime. I also develop, to my knowledge, the first theoretical model to explicitly account for hysteresis - a situation where positive exogenous variations in the relevant economic variables have a different effect from negative variations - in both criminal behaviour and crime rates in order to fill the gap between the theoretical predictions and the empirical evidence about the efficiency of policies in reducing crime rates. The majority of the theoretical analyses predict a sharp decrease in crime rates when there are significant improvements in the economic conditions or an increase in the probability of punishment. However, the existing empirical studies have found lower than expected effects on crime rates from variations in variables related to those factors. One important consequence of hysteresis is that the effect on an outcome variable from positive exogenous variations in the determining variables has a different magnitude from negative variations. For example, if hysteresis is present in the criminal behaviour and part of the police force in a city are dismissed in a given year, resulting in an escalation in crime, a reversal of the policy in the following year by readmitting all sacked police officers in an attempt to restore the original crime levels will result in lower crime rates, but higher than the original ones, yielding an asymmetric relationship between police and crime. Hysteresis is considered in a simple framework to model illicit behaviour. At the individual level, if criminal activity is associated with intrinsic sunk costs and learning, then the cost of leaving a criminal career is higher than entering it. At the aggregate level with homogeneous agents, this is translated into a hysteresis effect that will only occur if a specific threshold is surpassed. With heterogeneous agents, this phenomenon is reinforced generating a hysteresis effect that exists for all possible values of the variable affecting the crime decision. There are multiple equilibria at both levels. In the last chapter I empirically investigate the existence of hysteresis in crime rates. To my knowledge, this is the first empirical study to consider the existence of asymmetric effects on crime from variations in the probability of punishment and in the opportunity cost of crime. More specifically, I investigate whether positive variations on variables associated to those factors, respectively police officers and average level of income, are statistically different from negative variations. Using US crime data at the state level between 1977 and 2010, I find that police force size and real average income of unskilled workers have asymmetric effects on most types of crimes. The absolute value of the average impact of positive variations in those variables on property and violent crime rates are statistically smaller than the absolute value of the average effect of negative variations. These effects are robust under several specifications. A closer inspection of the data reveals a relatively monotonic negative relationship between wages and property crime rates, as well as negative variations in police and most crime rates. However, the relationships between positive variations in law enforcement size and most crime rates are non-linear. The magnitude of the observed asymmetries supports the hypothesis of hysteresis in crime, and suggests that no theoretical or empirical analysis would be complete without careful consideration of that important feature in the relationships between crime, police and legal income. These results corroborate the argument that policy makers should be more inclined to set pre-emptive policies rather than mitigating measures.

Thesis advisor: Robert Murphy / Hysteresis, in an economic context, is the idea that periods when the unemployment rate is greater than the natural rate have the effect of raising the underlying natural rate of unemployment (or, non-accelerating inflation rate of unemployment, NAIRU) and moving it to a new higher equilibrium state. The existence of hysteresis is still a matter of dispute in modern economics.This study examines the economic and employment situation from 1980 to the present and in particular since the beginning of the most recent recession in December 2007 and demonstrates that there exists evidence of hysteresis. It then aims to predict the economic consequences for the future and offers possible solutions to the problem.Given the scale of unemployment in the present economy and the importance of crafting an appropriate policy response, an examination of unemployment through the perspective of the hysteresis theory is a valuable approach that deserves further exploration. / Thesis (BS) — Boston College, 2012. / Submitted to: Boston College. Carroll School of Management. / Discipline: Carroll School of Management Honors Program. / Discipline: Economics.

The Diesel Oxidation Catalyst (DOC) is a key component in the exhaust after-treatment system of diesel engines. In this study two aspects of a DOC were investigated: catalyst distribution and reactant species interactions. In the first part, the effect of an axial Pt distribution along a DOC was investigated by comparing a standard sample, with a homogeneous Pt distribution along the length, with a zoned sample, where the Pt was non-homogeneously distributed along the length. Temperature-programmed oxidation (TPO) and spatially-resolved gas-phase concentration measurement experiments were used to compare the CO, C3H6 and NO oxidation performance of the standard and zoned catalysts. Both catalyst types had the same total amount of Pt but different distributions. The zoned catalyst, with more Pt located in the upstream portion, showed better performance than the standard catalyst, especially at high total flow rate and when a mixture of the reactants were used. The superior performance of the zoned sample is due to a larger, localized exotherm in the upstream region, where more Pt is located, and a decrease in the self-poisoning effect downstream, where reaction light-off occurs. In addition, catalyst durability against thermal degradation was tested by exposing the whole catalyst (homogeneous aging) and part of the catalyst (heterogeneous aging) to high temperatures. In general, the zoned catalyst showed better performance than the standard catalyst after thermal aging, especially after heterogeneous aging. The reason for the superior performance of the zoned catalyst, especially after heterogeneous aging, is that the back of the catalyst, which is exposed to higher temperature, contains less Pt than the front; therefore, most of the Pt particles in the zoned catalyst were not affected by thermal aging. However, after homogeneous aging, the performance of the standard catalyst was better than the zoned catalyst at higher flow rate and temperature most likely due to the different sintering rates in the zoned sample compared to the standard one. In the second part of this research, the interactions between CO, C3H6, H2, and NO were tested over a commercial Pt/Al2O3 monolith sample by studying these reactions during ignition and extinction (warm-up and cool-down). Results showed that CO, C3H6, and NO inhibit their own oxidation and each other’s oxidation due to the self-poisoning effect and competitive adsorption over active sites. In the case of a CO + C3H6 mixture, interesting CO and C3H6 oxidation trends were observed during the extinction phase. As the C3H6 concentration increased in the mixture, the catalytic activity of CO oxidation during the extinction phase decreased until it was actually poorer than that during the ignition phase. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed different C3H6 oxidation intermediates during the extinction phase on the catalyst surface, thus blocking active sites and lowering catalyst activity.