Global ETD Search

1	Geometric Filter: A Space and Time Efficient Lookup Table with Bounded Error Zhao, Yang 11 1900 (has links) Lookup tables are frequently used in many applications to store and retrieve keyvalue pairs. Designing efficient lookup tables can be challenging with constraints placed on storage, query response time and/or result accuracy. This thesis proposes Geometric filter, a lookup table with a space requirement close to the theoretical lower bound, efficient construction, fast querying speed, and guaranteed accuracy. Geometric filter consists of a sequence of hash tables, the sizes of which form a descending geometric series. Compared with its predecessor, Bloomier filter, its encoding runs two times faster, uses less memory, and it allows updates after encoding. We analyze the efficiency of the proposed lookup table in terms of its storage requirement and error bound, and run experiments on Web 1TB 5-gram dataset to evaluate its effectiveness. Geometric Filter Hash Table Lookup Table
2	Geometric Filter: A Space and Time Efficient Lookup Table with Bounded Error Zhao, Yang Unknown Date No description available. Geometric Filter Hash Table Lookup Table
3	Novel Semi-Active Suspension with Tunable Stiffness and Damping Characteristics Wong, Adrian Louis Kuo-Tian January 2012 (has links) For the past several decades there have been many attempts to improve suspension performance due to its importance within vehicle dynamics. The suspension system main functions are to connect the chassis to the ground, and to isolate the chassis from the ground. To improve upon these two functions, large amounts of effort are focused on two elements that form the building blocks of the suspension system, stiffness and damping. With the advent of new technologies, such as variable dampers, and powerful microprocessors and sensors, suspension performance can be enhanced beyond the traditional capabilities of a passive suspension system. Recently, Yin et al. [1, 2] have developed a novel dual chamber pneumatic spring that can provide tunable stiffness characteristics, which is rare compared to the sea of tunable dampers. The purpose of this thesis is to develop a controller to take advantage of the novel pneumatic spring’s functionality with a tunable damper to improve vehicle dynamic performance. Since the pneumatic spring is a slow-acting element (i.e. low bandwidth), the typical control logic for semi-active suspension systems are not practical for this framework. Most semi-active controllers assume the use of fast-acting (i.e. high bandwidth) variable dampers within the suspension design. In this case, a lookup table controller is used to manage the stiffness and damping properties for a wide range of operating conditions. To determine the optimum stiffness and damping properties, optimization is employed. Four objective functions are used to quantify vehicle performance; ride comfort, rattle space (i.e. suspension deflection), handling (i.e. tire deflection), and undamped sprung mass natural frequency. The goal is to minimize the first three objectives, while maximizing the latter to avoid motion sickness starting from 1Hz and downward. However, these goals cannot be attained simultaneously, necessitating compromises between them. Using the optimization strength of genetic algorithms, a Pareto optima set can be generated to determine the compromises between objective functions that have been normalized. Using a trade-off study, the stiffness and damping properties can be selected from the Pareto optima set for suitability within an operating condition of the control logic. When implementing the lookup table controller, a practical method is employed to recognize the road profile as there is no direct method to determine road profile. To determine the road profile for the lookup table controller, the unsprung mass RMS acceleration and suspension state are utilized. To alleviate the inherent flip-flopping drawback of lookup table controllers, a temporal deadband is employed to eliminate the flip-flopping of the lookup table controller. Results from the semi-active suspension with tunable stiffness and damping show that vehicle performance, depending on road roughness and vehicle speed, can improve up to 18% over passive suspension systems. Since the controller does not constantly adjust the damping properties, cost and reliability may increase over traditional semi-active suspension systems. The flip-flopping drawback of lookup table controllers has been reduced through the use of a temporal deadband, however further enhancement is required to eliminate flip-flopping within the control logic. Looking forward, the novel semi-active suspension has great potential to improve vehicle dynamic performance especially for heavy vehicles that have large sprung mass variation, but to increase robustness the following should be considered: better road profile recognition, the elimination of flip-flopping between suspension states, and using state equations model of the pneumatic spring within the vehicle model for optimization and evaluation. Stiffness Semi-Active Damping Lookup Table Optimization Genetic Algorithm Pneumatic Spring Tunable Mechanical Engineering
4	Novel Semi-Active Suspension with Tunable Stiffness and Damping Characteristics Wong, Adrian Louis Kuo-Tian January 2012 (has links) For the past several decades there have been many attempts to improve suspension performance due to its importance within vehicle dynamics. The suspension system main functions are to connect the chassis to the ground, and to isolate the chassis from the ground. To improve upon these two functions, large amounts of effort are focused on two elements that form the building blocks of the suspension system, stiffness and damping. With the advent of new technologies, such as variable dampers, and powerful microprocessors and sensors, suspension performance can be enhanced beyond the traditional capabilities of a passive suspension system. Recently, Yin et al. [1, 2] have developed a novel dual chamber pneumatic spring that can provide tunable stiffness characteristics, which is rare compared to the sea of tunable dampers. The purpose of this thesis is to develop a controller to take advantage of the novel pneumatic spring’s functionality with a tunable damper to improve vehicle dynamic performance. Since the pneumatic spring is a slow-acting element (i.e. low bandwidth), the typical control logic for semi-active suspension systems are not practical for this framework. Most semi-active controllers assume the use of fast-acting (i.e. high bandwidth) variable dampers within the suspension design. In this case, a lookup table controller is used to manage the stiffness and damping properties for a wide range of operating conditions. To determine the optimum stiffness and damping properties, optimization is employed. Four objective functions are used to quantify vehicle performance; ride comfort, rattle space (i.e. suspension deflection), handling (i.e. tire deflection), and undamped sprung mass natural frequency. The goal is to minimize the first three objectives, while maximizing the latter to avoid motion sickness starting from 1Hz and downward. However, these goals cannot be attained simultaneously, necessitating compromises between them. Using the optimization strength of genetic algorithms, a Pareto optima set can be generated to determine the compromises between objective functions that have been normalized. Using a trade-off study, the stiffness and damping properties can be selected from the Pareto optima set for suitability within an operating condition of the control logic. When implementing the lookup table controller, a practical method is employed to recognize the road profile as there is no direct method to determine road profile. To determine the road profile for the lookup table controller, the unsprung mass RMS acceleration and suspension state are utilized. To alleviate the inherent flip-flopping drawback of lookup table controllers, a temporal deadband is employed to eliminate the flip-flopping of the lookup table controller. Results from the semi-active suspension with tunable stiffness and damping show that vehicle performance, depending on road roughness and vehicle speed, can improve up to 18% over passive suspension systems. Since the controller does not constantly adjust the damping properties, cost and reliability may increase over traditional semi-active suspension systems. The flip-flopping drawback of lookup table controllers has been reduced through the use of a temporal deadband, however further enhancement is required to eliminate flip-flopping within the control logic. Looking forward, the novel semi-active suspension has great potential to improve vehicle dynamic performance especially for heavy vehicles that have large sprung mass variation, but to increase robustness the following should be considered: better road profile recognition, the elimination of flip-flopping between suspension states, and using state equations model of the pneumatic spring within the vehicle model for optimization and evaluation. Stiffness Semi-Active Damping Lookup Table Optimization Genetic Algorithm Pneumatic Spring Tunable Mechanical Engineering
5	A comparison between techniques for color grading in games Oldenborg, Mattias January 2006 (has links) <p>Color has been significant in visual arts for as long as the art-forms have existed. Still images and movies have long used colors and color grading effects to affect the viewer and characterize the work. In recent years attempts have been made to bring these techniques of stylizing also to interactive games. This dissertation aims to compare two different approaches of performing real-time color grading for games. Focus is put on examining the two ways from a number of different perspectives and from there draw conclusions on advantages and disadvantages of the approaches. The results show no unanimously superior approach but rather aim to break down the results in categories and attempt to explain the benefits and drawbacks in using either one of them, aiding the decision for anyone inclined to implement color grading effects in games.</p> Color grading real-time interactive games pixel shader lookup table Computer science Datalogi
6	A comparison between techniques for color grading in games Oldenborg, Mattias January 2006 (has links) Color has been significant in visual arts for as long as the art-forms have existed. Still images and movies have long used colors and color grading effects to affect the viewer and characterize the work. In recent years attempts have been made to bring these techniques of stylizing also to interactive games. This dissertation aims to compare two different approaches of performing real-time color grading for games. Focus is put on examining the two ways from a number of different perspectives and from there draw conclusions on advantages and disadvantages of the approaches. The results show no unanimously superior approach but rather aim to break down the results in categories and attempt to explain the benefits and drawbacks in using either one of them, aiding the decision for anyone inclined to implement color grading effects in games. Color grading real-time interactive games pixel shader lookup table Computer Sciences Datavetenskap (datalogi)
7	Lookup-Table-Based Background Linearization for VCO-Based ADCs Pham, Long 30 April 2015 (has links) Scaling of CMOS to nanometer dimensions has enabled dramatic improvement in digital power efficiency, with lower VDD supply voltage and decreased power consumption for logic functions. However, most traditionally prevalent ADC architectures are not well suited to the lower VDD environment. The improvement in time resolution enabled by increased digital speeds naturally drives design toward time-domain architectures such as voltage-controlled-oscillator (VCO) based ADCs. The major obstacle in the VCO-based technique is linearizing the VCO voltage-to-frequency characteristic. Achieving signal-to-noise (SNR) performance better than -40dB requires some form of calibration, which can be realized by analog or digital techniques, or some combination. A further challenge is implementing calibration without degrading energy efficiency performance. This thesis project discusses a complete design of a 10 bit three stage ring VCO-based ADC. A lookup-table (LUT) digital correction technique enabled by the "Split ADC" calibration approach is presented suitable for linearization of the ADC. An improvement in the calibration algorithm is introduced to ensure LUT continuity. Measured results for a 10 bit 48.8-kSps ADC show INL improvement of 10X after calibration convergence. linearization Lookup-table split ADC votlage controlled oscillator background calibration technique Analog to digital converter VCO-based ADC
8	Efficient digital baseband predistortion for modern wireless handsets Ba, Seydou Nourou 10 November 2009 (has links) This dissertation studies the design of an efficient adaptive digital baseband predistorter for modern cellular handsets that combines low power consumption, low implementation complexity, and high performance. The proposed enhancements are optimized for hardware implementation. We first present a thorough study of the optimal spacing of linearly-interpolated lookup table predistorters supported by theoretical calculations and extensive simulations. A constant-SNR compander that increases the predistorter's supported input dynamic range is derived. A corresponding low-complexity approximation that lends itself to efficient hardware design is also implemented in VHDL and synthesized with the Synopsys Design Compiler. This dissertation also proposes an LMS-based predistorter adaptation that is optimized for hardware implementation and compares the effectiveness of the direct and indirect learning architectures. A novel predistorter design with quadrature imbalance correction capability is developed and a corresponding adaptation scheme is proposed. This robust predistorter configuration is designed by combining linearization and I/Q imbalance correction into a single function with the same computational complexity as the widespread complex-gain predistorter. Lookup table spacing Indirect learning architecture Amplifier linearization Quadrature imbalance Digital baseband predistortion Signal processing Digital techniques Digital communications Digital telephone systems
9	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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