As research into the dynamic characteristics of job performance across time has continued to accumulate, associated implications for performance appraisal have become evident. At present, several studies have demonstrated that systematic trends in job performance across time influence how performance is ultimately judged. However, little research has considered the processes by which the performance trend-performance rating relationship occurs. In the present study, I addressed this gap. Specifically, drawing on attribution theory, I proposed and tested a model whereby the performance trend-performance rating relationship occurs through attributions to ability and effort. The results of this study indicated that attributions to ability, but not effort, mediate the relationship between performance trend and performance ratings and that this relationship depends on attribution-related cues. Implications for performance appraisal research and theory are discussed.

Due to government regulations together with health and safety reasons, there are increasing demands on reducing hazardous polluting chemicals from fossil fuel power plants. Therefore, more efforts are imposed on using renewable resources such as water, wind, solar and tide to produce clean/green electricity. On top of that, there is another increasing demand from Original Equipment Manufacturers (OEMs) to operate power plants with higher load while keep the power loss to the minimum. These requirements drive conventional fluid film bearings to its mechanical and temperature limits. This calls for the development of new bearing system designs. An outstanding tribological performance such as low start-up and break-away friction, excellent resistance to chemical attack and anti-seizure properties, can be achieved by introducing compliant polymer liners. At the same time, bearings with compliant liners may alter rotor-bearing system dynamic behaviour compared to the systems with conventional white metal bearings. The research approach of this thesis is to implement compliant liner on bearing surface, impose synchronous shaft excitation and investigate the effect of bearing design parameters on bearing dynamic response. Plain cylindrical journal bearings with different compliant liner thicknesses were analysed using a FEM approach. The numerical model was compared with an in-house developed code based on the finite difference method (FDM) for a bearing operated at steady state conditions. Results obtained by the numerical models showed good agreement. After verification of the numerical model for fixed geometry journal bearings, models for tilting pad journal bearings were developed. Dynamic behaviour of the tilting pad journal bearing with three pads with line pivot geometry was compared with published data. A good agreement was obtained between the two numerical models. The effect of pad pivot geometry on bearing dynamic response was investigated. Vertical and horizontal shaft configurations were compared in terms of the effect of preload factor, radial clearance, pivot offset, and pad inclination angles. Influence of the elastic properties of compliant liners was also studied. All these factors significantly affect bearing dynamic response. It is shown how these factors should be selected to control the journal orbit sizes. Misalignments in compliant tilting pad journal bearings were analysed for load between pivots and load on pivots with consideration of thermal effects. Significant improvements in bearing performance were obtained with compliant bearings compared to white metal bearings. Furthermore, different polymer materials (PTFE, UHMWPE, pure PEEK and PEEK composite) were characterized using Frequency Response Function (FRF). It was shown that as the excitation frequency increased the equivalent stiffness was more or less constant while equivalent damping decreased exponentially. PTFE had similar equivalent stiffness compared to PEEK. As for equivalent damping, PTFE had slightly higher damping compared to PEEK or UHMWPE. Oil film thickness, oil film temperature and loads on tilting pad journal bearing were measured on 10 MW Kaplan hydroelectric power machine. Test results were compared to FEM model. It was shown that stiffness of the supporting structure may be more important to machine performance than the stiffness of the bearing alone. / <p>QC 20150409</p> / Swedish Hydropower Centre

abstract: An embedded HVDC system is a dc link with at least two ends being physically connected within a single synchronous ac network. The thesis reviews previous works on embedded HVDC, proposes a dynamic embedded HVDC model by PSCAD program, and compares the transient stability performance among AC, DC and embedded HVDC. The test results indicate that by installing the embedded HVDC, AC network transient stability performance has been largely improved. Therefore the thesis designs a novel frequency control topology for embedded HVDC. According to the dynamic performance test results, when the embedded HVDC system equipped with a frequency control, the system transient stability will be improved further. / Dissertation/Thesis / M.S.Tech Electrical Engineering 2013

Paralleling operation of DC/DC converters is widely used in today's distributed power systems. To ensure balanced output currents among paralleled power modules, current sharing control is usually necessary.Active current sharing controls with current feedback mechanism are widely used in today's power supplies. However, the dynamic performance of these current sharing control schemes are not yet clearly explored. In this work, the dynamic current sharing performance is evaluated for paralleling systems with the output impedance approach. As the representative of the terminal characteristic of a power converter, output impedance is a powerful tool to study the dynamic response under load transients. The dynamic current sharing analyses are then conducted for three different active current sharing control structures and a comprehensive comparison among them helps the designer to choose appropriate controls for different applications. On the other hand, high-frequency load transients are possible to happen for voltage regulators, which are the power supplies of microprocessors. In order to study the dynamic current sharing performance for a paralleling system when the perturbation frequency is higher than half of the switching frequency,the conventional output impedance concept needs to be extended. Due to the non-linear behavior of a switching modulator, the beat-frequency phenomenon could cause unexpected failure of a power supply when the perturbation frequency is close to the switching frequency. To address this issue, an unconventional multi-frequency model is proposed for high-frequency dynamic current sharing studies. With this model, the sideband components are possible to be included and the beat-frequency oscillations can be predicted. After that, the conventional impedance concept is expanded in the form of extended describing function, so that the terminal characteristics of paralleled converters are represented by a series of impedances. Besides the analyses, this work also proposed several solutions for the beat-frequency oscillation issue which are experimentally verified. In summary, both low-frequency and high-frequency dynamic current sharing performances are studied in this dissertation. The output impedance concept and its extension in the form of extended describing function are utilized as the tools for researches. With these powerful tools, more insights are obtained to help better design of a paralleling system. / Ph. D.

This work details the development of a stability and control module for implementation into a Multidisciplinary Design Optimization (MDO) framework for the conceptual design of conventional and advanced aircraft. A novel approach, called the Variance Constrained Flying Qualities (VCFQ) approach, is developed to include closed-loop dynamic performance metrics in the design optimization process. The VCFQ approach overcomes the limitations of previous methods in the literature, which only functioned for fully decoupled systems with single inputs to the system. Translation of the modal parameter based flying qualities requirements into state variance upper bounds allows for multiple-input control laws which can guarantee upper bounds on closed-loop performance metrics of the aircraft states and actuators to be rapidly synthesized. A linear matrix inequality (LMI) problem formulation provides a general and scalable numerical technique for computing the feedback control laws using convex optimization tools. The VCFQ approach is exercised in a design optimization study of a relaxed static stability transonic transport aircraft, wherein the empennage assembly is optimized subject to both static constraints and closed-loop dynamic constraints. Under the relaxed static stability assumption, application of the VCFQ approach resulted in a 36% reduction in horizontal tail area and a 32% reduction in vertical tail area as compared to the baseline configuration, which netted a weight savings of approximately 5,200 lbs., a 12% reduction in cruise trimmed drag, and a static margin which was marginally stable or unstable throughout the flight envelope. State variance based dynamic performance constraints offer the ability to analyze large, highly coupled systems, and the linear matrix inequality problem formulation can be extended to include higher-order closed-loop design objectives within the MDO. Recommendations for further development and extensions of this approach are presented at the end. / This material is based on research sponsored by Air Force Research Laboratory under agreement number FA8650-09-2-3938. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Air Force Research Laboratory or the U.S. Government. / Ph. D.

Propõe-se, com este trabalho, estudar numericamente se a redundância cinemática e a redundância de atuação podem ser boas alternativas para que manipuladores planares de cinemática paralela atinjam altas acelerações. Sabe-se que estes tipos de redundância promovem uma redução de singularidades do sistema robótico entre outros benefícios. No entanto, a avaliação comparativa do desempenho dinâmico de manipuladores redundantes ainda é pouco estudada. Este estudo não é trivial pois a redundância significa não somente o aumento do torque disponível, mas também que a inércia do sistema foi aumentada. A avaliação numérica deste trabalho se dará por meio do desenvolvimento de modelos cinemáticos e dinâmicos das possíveis configurações de manipuladores paralelos planares com redundância cinemática e redundância de atuação. Esta avaliação pode ser feita pela comparação entre os manipuladores redundantes e o não-redundante para desenvolver uma mesma trajetória do end-effector. Entretanto, esta avaliação é dependente da trajetória, logo esse trabalho também propõe uma avaliação através de um índice dinâmico em toda a área de trabalho dos manipuladores. / The aim of this work is to study numerically if the kinematic redundancy and the actuation redundancy can be good alternatives for parallel planar manipulators to achieve high accelerations. It is known that types of redundancy promote, among other benefits, a significant reduction in the singularities. However, the evaluation of the redundancy as a good solution to increase the dynamic performance was not studied. This study is not trivial because the redundancy means not only that there is more torque available, but also that the inertia of the system has been considerably increased. Different configurations of the redundant manipulator will be evaluated numerically through kinematic and dynamic models. This evaluation can be performed by the comparison among the non redundant manipulator and the redundant manipulators to execute the same task. This evaluation is task dependent, so this work proposes a dynamic index to desing dynamic maps over the workspace.

Propõe-se, com este trabalho, estudar numericamente se a redundância cinemática e a redundância de atuação podem ser boas alternativas para que manipuladores planares de cinemática paralela atinjam altas acelerações. Sabe-se que estes tipos de redundância promovem uma redução de singularidades do sistema robótico entre outros benefícios. No entanto, a avaliação comparativa do desempenho dinâmico de manipuladores redundantes ainda é pouco estudada. Este estudo não é trivial pois a redundância significa não somente o aumento do torque disponível, mas também que a inércia do sistema foi aumentada. A avaliação numérica deste trabalho se dará por meio do desenvolvimento de modelos cinemáticos e dinâmicos das possíveis configurações de manipuladores paralelos planares com redundância cinemática e redundância de atuação. Esta avaliação pode ser feita pela comparação entre os manipuladores redundantes e o não-redundante para desenvolver uma mesma trajetória do end-effector. Entretanto, esta avaliação é dependente da trajetória, logo esse trabalho também propõe uma avaliação através de um índice dinâmico em toda a área de trabalho dos manipuladores. / The aim of this work is to study numerically if the kinematic redundancy and the actuation redundancy can be good alternatives for parallel planar manipulators to achieve high accelerations. It is known that types of redundancy promote, among other benefits, a significant reduction in the singularities. However, the evaluation of the redundancy as a good solution to increase the dynamic performance was not studied. This study is not trivial because the redundancy means not only that there is more torque available, but also that the inertia of the system has been considerably increased. Different configurations of the redundant manipulator will be evaluated numerically through kinematic and dynamic models. This evaluation can be performed by the comparison among the non redundant manipulator and the redundant manipulators to execute the same task. This evaluation is task dependent, so this work proposes a dynamic index to desing dynamic maps over the workspace.

No description available.

The scope of this work can be summarized by three main aspects of DC-DC power converters. The first aspect is soft switching topologies to improve conversion efficiency for On-Board Converters or Point of load (POL) converters, the second aspect is load adaptive control techniques to improve all load efficiency for battery powered DC-DC converters that are applied to mobile devices, and the third aspect is dynamic performance improvement techniques to improve load transient in voltage regulators. Topologies and control techniques for DC-DC converters are presented after reviewing loads powering requirements and steady-state and transients design challenges.

Made available in DSpace on 2017-07-10T19:24:38Z (GMT). No. of bitstreams: 1 Ana Marta Soranso.pdf: 1651613 bytes, checksum: caeedf53d6994dc87ab196226a803114 (MD5) Previous issue date: 2006-07-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The objective of this work was to evaluate the dynamic performance of an agricultural tractor utilizing distilled biodiesel (50% ethylic + 50% methylic) in proportion function of biodiesel and diesel of petroleum (0 and 100%, 5 and 95%, 15 and 85%, 25 and 75%, 50 and 50%, 75 and 25% and 100 and 0%) respectively. This research was done in the area of the department of Rural Engineering of the State University Paulista -UNESP, campus of Jaboticabal - SP, located in the latitude 21º 14 28 S e longitude 48º 17 12 W, and a tractor 4x2 FWA was used, with power of 73,6 kW (100 cv) in the motor and a ballast tractor. The used biodiesel was produced the base of residual oil of fried foods. The experimental design was entirely casualized, with 7 treatments and 5 repetitions, totaling 35 observations. The results evidenced that the mixture, biodiesel and diesel, influenced the variables significantly, hourly volumetric consumption, hourly mass consumption, fuel consumption for worked area and specific fuel consumption. When the tractor operated with 100% of biodiesel (B100) the specific consumption increased 18% on average in relation to the diesel (B0). / O objetivo deste trabalho foi avaliar o desempenho dinâmico de um trator agrícola, funcionando com biodiesel destilado (50% etílico + 50% metílico), em função das seguintes proporções de biodiesel e diesel de petróleo: 0 e 100%, 5 e 95%, 15 e 85%, 25 e 75%, 50 e 50%, 75 e 25% e 100 e 0%, respectivamente. O experimento foi realizado em área do departamento de Engenharia Rural da Universidade Estadual Paulista - UNESP, campus de Jaboticabal - SP, localizado na latitude 21º 14 28 S e longitude 48º 17 12 W. Foi utilizado um trator 4x2 TDA, com potência de 73,6 kW (100 cv) no motor e um trator de lastro. O biodiesel utilizado foi produzido à base de óleo residual de fritura de alimentos. O delineamento experimental foi inteiramente casualizado (DIC), com 7 tratamentos e 5 repetições, totalizando 35 observações. Os resultados evidenciaram que a mistura, biodiesel e diesel de petróleo, influenciou significativamente as variáveis: consumo horário volumétrico, consumo horário ponderal, consumo de combustível por área trabalhada e consumo especifico. Quando o trator operou com 100% de biodiesel (B100) o consumo específico aumentou, em média, 18%, em relação ao diesel (B0).