Global ETD Search

1	Studies of the optoelectronic properties of polymer dispersed blue-phase liquid-crystal films Wang, Yun-Ya 29 August 2012 (has links) In this study, we study polymer-dispersed blue-phase liquid-crystal (PDBPLC)films. The PDBPLC film is fabricated by using BPLC instead of nematic LC in a PDLC film. The experimental results show that the PDBPLC films and can be switchable as the conventional PDLC. The polymer morphology of the PDBPLC is affected by the concentration of monomer in the BPLC/monomer mixture. The PDBPLC exhibits a good contrast ratio with monomer concentration of 39.17 wt%. The rise time of PDBPLC films decreases as the polymer concentration increases. Moreover, the results also show that a complete phase separation occurs with the exposure time of 20 minutes. For the future work, we will improve the high driving voltage and low ratio of the PDBPLC film. optoelectronic properties rise time scatter polymer liquid crystal blue phase
2	The Relationship Between Partial Discharge Current Pulse Waveforms and Physical Mechanisms Okubo, H., Hayakawa, N., Matsushita, A. 05 1900 (has links) No description available. discharge mechanisms SF gas mixtures rise time fall time
3	Time and cost overruns on high-rise building construction in Bangladesh Salam, Md January 2007 (has links) Construction projects in developing countries may suffer from time overruns, which are associated with cost overruns. This research project investigated both time and cost overruns on high-rise building projects in Dhaka, Bangladesh. Surprisingly, preliminary data analysis showed negligible cost overruns in comparison to time overruns. So, further analysis o f cost overruns was not considered in this thesis. This research project also investigated how the causes o f time-overruns can be mitigated. 72 time-overrun and 22 cost-overrun variables were identified through a literature review. These variables were taken as parameters and a personal interview survey was conducted with developers, consultants, contractors and project managers using semistructured questionnaire. A similar second survey was conducted using 22 measures, which can mitigate time- overruns. Data analysis involved the relative importance index to rank the variables, factors analysis to reduce variables to factors with minimum loss of data, stepwise regression to find links among factors in successive stages of construction process and multiple regression to explain delays in terms of factors. The main causes o f time-overruns were ‘cash flow’, ‘planning and scheduling deficiency’ and ‘design changes’. A scree graph identified 31 important variables that caused delays but factor analysis reduced these to 14 factors. Stepwise regression found no strong links among the factors to identify them as reasons for delay in successive stages of the construction project. A multiple regression model explained about 85% of the variance of the delays using eight factors. The main individual measures mitigating time-overruns were ‘improvement of cash flow’, ‘improvement o f communication and coordination among project participants’ and ‘development o f robust planning and scheduling instruments’. Factor analysis produced ten representative factors. Stepwise regression could not find strong links among factors mitigating time-overruns in successive stages of the construction project.
4	Rhythmic sensitivity and developmental language disorder in children Richards, Susan Mary January 2017 (has links) Children with Developmental Language Disorder (DLD) have difficulties in acquiring language in the absence of other neurodevelopmental issues (e.g. autism, hearing impairment) and despite growing up in an adequate language-learning environment. Previous characterisations of DLD have focused on grammatical processing, phonological memory or rapid auditory processing. This thesis approaches the language-learning difficulties of children with DLD from a novel perspective by considering the potential contribution made by differing levels of sensitivity to the rhythmic properties of language. Children with DLD have been shown to have reduced sensitivity to some of the acoustic cues present in speech which are thought to be important for rhythmic perception. Since rhythm forms the basis of language processing in early development, poorer sensitivity to language rhythm may result in later language problems. To investigate whether children with DLD demonstrate difficulties in processing language rhythm, this thesis explores five areas of language processing which could be affected by poor rhythmic sensitivity: locating word-boundaries, processing novel words, storing lexical stress patterns, representing sentence level structures and the integration of rhythm and syntax. As part of the investigation, measures were also taken of acoustic threshold sensitivity to see whether task performance related to acoustic sensitivity. A parallel strand of the study investigated whether provision of an entraining rhythm prior to task stimuli could support task performance. Three groups of children participated in the study: children with DLD, age-matched TD children (AMC) and younger, language-matched TD children (YLC). The results indicate that rhythmic manipulation of language stimuli affects task responses across the five language areas under investigation. The findings are then discussed in terms of the contribution made to our understanding of the role of rhythm in language and language disorder.
5	Superconducting Nanowire Single-Photon Detectors for Quantum Information Science Nicolich, Kathryn L. January 2021 (has links) No description available. Physics quantum information single photon detection superconductors amorphous superconductors rise time photon number resolution
6	Spectroscopic studies of X-ray laser media Pestehe, Sayyed Jalal January 2001 (has links) No description available. 539.7
7	Modelling and Control of a Dual Sided Linear Induction Motor for a scaled Hyperloop Pod / Modellering och styrning av en dubbelsidig linjär induktionsmotor för en skalenlig Hyperloop-pod Anand, Vivek January 2020 (has links) The electrification era has been marked up by an increase in volume of electric vehicles which are directly or indirectly powered by electricity. Railways, roadways and airways are being electrified as we speak at their own respective rate. In addition to that upcoming concepts for transport solution such as hyperloop also described as the fifth mode of transportation will be electrified. The current thesis work is based on developing the model and control of the propulsion system of a scaled Hyperloop pod designed by student team KTH Hyperloop representing KTH. The team competes in Hyperloop competition organized by Spacex and the goal is to achieve the highest possible speed in a given distance and track designed by SpaceX. In order to achieve the goal of being the fastest, the scaled pod uses a Double Sided Linear Induction Motor (DSLIM) as mentioned in the subsequent chapter. The motor modelling is done on Simulink and is similar to a rotary induction motor (RIM). However the presence of end effect in DSLIM makes it different from RIM and has been discussed subsequently. The control strategy uses a synchronous frame PI control for the current control and sensor based speed control for controlling the speed of the pod.The speed control output is a reference current which is used as an input to the current controller which finally gives voltage as the control output. The corresponding bandwidth for the various loops have been calculated based on motor parameters as discussed in the method section. The validation of the motor model and the corresponding controller has been discussed in the result section, where the accuracy of the controller for the designed modelled is discussed. / Elektrifieringstiden har präglats av en ökning i volym av elfordon som direkt eller indirekt drivs med el. Järnvägar, vägar och luftvägar elektrifieras just nu med deras respektive takt. Utöver det kommer kommande koncept för transportlösning som hyperloop som också beskrivs som det femte transportsättet att elektrifieras. Detta examensarbete bygger på att utveckla modellen och regleringen av framdrivningssystemet för en nedskalad Hyperloop-pod utvecklad av studentteamet KTH Hyperloop som representerar KTH. Teamet tävlar i Hyperloop-tävlingen organiserad av SpaceX och målet är att uppnå högsta möjliga hastighet på ett visst avstånd och spår framtaget av SpaceX. För att uppnå målet om att vara snabbast använder den nedskalade podden en dubbelsidig elektrisk linjär induktionsmotor (DSLIM) som nämns i det följande kapitlet. Den elektriska motormodelleringen görs i Simulink och liknar en roterande induktionsmotor(RIM). Men närvaron av ’end effect’ i DSLIM gör den annorlunda än RIM och har diskuterats därefter. Styrstrategin använder en synkron ram-PI-styrning för strömstyrning och sensorbaserad hastighetsreglering för att styra hastigheten på podden. Varvtalsstyrningsutgången är en referensström som används som en ingång till den nuvarande styrenheten som slutligen ger spänning som slutling styrning. Motsvarande bandbredd för de olika slingorna har beräknats baserat på elektriska motorparametrar som diskuterats i metodavsnittet.Valideringen av elmotormodellen och motsvarande styrenhet har diskuterats i resultatsektionen, där noggrannheten hos styrenheten för den konstruerade modellerna diskuteras. Linear Induction Motor Rotary Induction Motor Control algorithm bandwidth Synchronous frame Field weakening Inductance Resistance PI controller Magnetic flux Mutual Inductance Rise time Roterande induktionsmotor styralgorithm bandbredd synkron ram induktans moststånd PI-regulator magnetiskt flöde ömsesidig induktans stingningstid fel Linjär induktionsmotor Vehicle Engineering Farkostteknik
8	Settling-Time Improvements in Positioning Machines Subject to Nonlinear Friction Using Adaptive Impulse Control Hakala, Tim 31 January 2006 (has links) (PDF) A new method of adaptive impulse control is developed to precisely and quickly control the position of machine components subject to friction. Friction dominates the forces affecting fine positioning dynamics. Friction can depend on payload, velocity, step size, path, initial position, temperature, and other variables. Control problems such as steady-state error and limit cycles often arise when applying conventional control techniques to the position control problem. Studies in the last few decades have shown that impulsive control can produce repeatable displacements as small as ten nanometers without limit cycles or steady-state error in machines subject to dry sliding friction. These displacements are achieved through the application of short duration, high intensity pulses. The relationship between pulse duration and displacement is seldom a simple function. The most dependable practical methods for control are self-tuning; they learn from online experience by adapting an internal control parameter until precise position control is achieved. To date, the best known adaptive pulse control methods adapt a single control parameter. While effective, the single parameter methods suffer from sub-optimal settling times and poor parameter convergence. To improve performance while maintaining the capacity for ultimate precision, a new control method referred to as Adaptive Impulse Control (AIC) has been developed. To better fit the nonlinear relationship between pulses and displacements, AIC adaptively tunes a set of parameters. Each parameter affects a different range of displacements. Online updates depend on the residual control error following each pulse, an estimate of pulse sensitivity, and a learning gain. After an update is calculated, it is distributed among the parameters that were used to calculate the most recent pulse. As the stored relationship converges to the actual relationship of the machine, pulses become more accurate and fewer pulses are needed to reach each desired destination. When fewer pulses are needed, settling time improves and efficiency increases. AIC is experimentally compared to conventional PID control and other adaptive pulse control methods on a rotary system with a position measurement resolution of 16000 encoder counts per revolution of the load wheel. The friction in the test system is nonlinear and irregular with a position dependent break-away torque that varies by a factor of more than 1.8 to 1. AIC is shown to improve settling times by as much as a factor of two when compared to other adaptive pulse control methods while maintaining precise control tolerances. control position adaptive impulsive settling-time nonlinear friction pulses displacements precise tolerances log-spaced update distributed learning Coulomb Stribeck Tomizuka Yang AIC PID MRAC STR RTAI Linux FreeBSD kernel modules microcontroller convergence practical self-tuning methods techniques limit-cycles steady-state error zero stable stability bound envelope partitioned scheme lookup-table multi-point adaptation repeatable mean servo motor exponential square-law rise-time real-time log-log interpolation pro-forma curve-fit sensitivity compliance variable static dynamic response torque acceleration velocity optical encoder parameters evolution fixed-law enhanced split weighting initialization trajectory layered processes Mechanical Engineering

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