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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

A Computational Iteration Method to Analyze Mechanics of Timing Belt Systems with Non-Circular Pulleys

Tan, Li 10 September 2018 (has links)
Timing belt systems, usually consisting of a toothed belt and multiple pulleys, are used in many mechanical devices, especially in the internal combustion engine to synchronize the rotation of the crankshafts and the camshafts. When the system operates, the belt teeth will be transmitted by the pulley teeth meshed with them. Timing belt drives can make sure that the engine' s valves open and close properly due to their precise transmission ratio. In this thesis, a quasi-static computational model is developed to calculate the belt load distributions and the torques around pulleys for different timing belt systems. The simplest system is a two-pulley system with one oval pulley and one circular pulley. This computational model is then extended to a two-pulley system with one special-shaped pulley and finally generalized to determine the load conditions for a multi-pulley system with multiple special-shaped pulleys. Belt tooth deflections, tooth loads, belt tension distributions, friction forces, and the effect of friction hysteresis have been taken into consideration. Results of these quantities are solved by a nested numerical iteration method. Periodic torques generated by the varied radius of noncircular pulley are calculated by this computational model to cancel the undesired external cyclic torque, which will increase the life of timing belts. / Master of Science / Timing belt systems, usually consisting of a toothed belt and multiple pulleys, are used in many mechanical devices, especially in the internal combustion engine to synchronize the rotation of the crankshafts and the camshafts. When the system operates, the belt teeth will be transmitted by the pulley teeth meshed with them. Timing belt drives can make sure that the engines valves open and close properly due to their precise transmission ratio. In this thesis, a quasi-static computational model is developed to calculate the belt load distributions and the torques around pulleys for different timing belt systems. The simplest system is a two-pulley system with one oval pulley and one circular pulley. This computational model is then extended to a two-pulley system with one special-shaped pulley and finally generalized to determine the load conditions for a multi-pulley system with multiple special-shaped pulleys. Belt tooth deflections, tooth loads, belt tension distributions, friction forces, and the effect of friction hysteresis have been taken into consideration. Results of these quantities are solved by a nested numerical iteration method. Periodic torques generated by the varied radius of noncircular pulley are calculated by this computational model to cancel the undesired external cyclic torque, which will increase the life of timing belts.
42

An Examination into Technological Timing Efforts: The Performance of Firms in the Personal Computer Industry

Childers, John Stephen Jr. 29 December 2005 (has links)
This study investigates how firms navigate technological changes over time. Specifically, we determine whether firms follow a consistent strategy in regards to when they time their entry into technological waves. Resulting performance implications of these actions are also measured. The theoretical underpinnings of this study lie at the intersection of the technology literature, the learning school, firm evolutionary theory, and the resource-based view of the firm. Past studies have added clarity as to how firms behave within a single technological wave; however, investigations regarding firm actions over successive waves are needed if we are to truly understand which firm actions lead to long-term success. This study fills the research gap by investigating firm timing patterns over multiple successive waves of technology and the resulting long-term performance implications of these actions. Further, this study examines timing efforts over both competence enhancing (incremental) and competence destroying (architectural) cycles. The findings indicate that while technological follower firms are able to consistently repeat their timing strategy, technological leaders have a much more difficult time in repeating early entry timing. Repeated leadership entry was found to be difficult in both incremental and architectural cycles. Characteristics of those leaders able to repeat leadership entry are provided. While consistent entry timing was not found to impact market share, it was found to benefit firms by reducing their hazard rate. This hazard rate reduction for timing entry consistency, whether it is as a leader or as a follower, was observed during both incremental and architectural technological changes. / Ph. D.
43

The Timing and Magnitude of Monetary Reward: Testing Hypotheses from Expectancy vs. Reciprocity Theory

Lehman, Philip Kent 18 November 2003 (has links)
Social psychologists have noted that compliance strategies based on the social norm of reciprocity can be an effective tool for changing behavior (e.g., Cialdini, 2001). In contrast to expectancy-based behavior-change strategies, which offer a reward after a behavior is completed (post-behavior reward); reciprocity-based strategies present the reward first in the form of a gift (pre-behavior reward). Although there are no explicit contingencies attached to the gift, a sense of obligation to reciprocate may be a powerful motivator to comply with the request. It was hypothesized that pre-behavior rewards would be more effective than post-behavior rewards at low magnitudes of reward, and that both strategies would be effective at higher levels. This study examined effects of the timing and magnitude ($1 vs. $10) of a cash reward on compliance with a request to use a specially designed thank-you card recognizing prosocial and proenvironmental behavior. The hypotheses were not supported. The highest rate of compliance occurred in the post-behavior $10 condition, where 35.5% of participants complied, followed by post-behavior $1 (18.8%), pre-behavior $1 (12.9%) and pre-behavior $10 (8.8%). Pairwise comparisons revealed compliance in the $10 post-behavior condition was significantly higher than the rate of compliance in the $1 and $10 pre-behavior conditions, Chi-Square (1, n = 62) = 4.31, p < .05 and Chi-Square (1, n = 65) = 6.82, p < .01 respectively. The lack of evidence for the effectiveness of pre-behavior reward strategy is discussed and contrasted with previous findings. / Master of Science
44

An adaptive prefilter for timing recovery /

Amin, Amani Sabri January 1985 (has links)
No description available.
45

Delay Analysis of Digital Circuits Using Prony's Method

Fu, Jingyi J.Y. 28 July 2011 (has links)
This thesis describes possible applications of Prony's method in timing analysis of digital circuits. Such applications include predicting the future shape of the waveform in DTA(Dynamic Timing Analysis) and delay look-up table in STA(Static Timing Analysis). Given some equally spaced output values, the traditional Prony's method can be used to extract poles and residues of a linear system, i.e. to characterize a waveform using an exponential function. In this thesis, not only values but also equally spaced derivatives are tested. Still using same idea of the traditional Prony's method, poles and residues can also be extracted with those values and derivatives. The resultant poles and residues will be used to predict the output waveform in DTA analysis. The benefits brought by the using of derivatives include less simulation steps and less CPU time consuming than the regular constant step simulation. As a matter of fact, the Prony's method can precisely approximate a complicated waveform. Such property can be applied for STA analysis. The Prony's approximation can be used to precisely record an output waveform, which is used as an entry of the look-up table of STA. Since the accuracy of STA analysis relies on the accuracy of the input and output waveform in the look-up table, the accuracy of the Prony's approach is promising.
46

Delay Analysis of Digital Circuits Using Prony's Method

Fu, Jingyi J.Y. 28 July 2011 (has links)
This thesis describes possible applications of Prony's method in timing analysis of digital circuits. Such applications include predicting the future shape of the waveform in DTA(Dynamic Timing Analysis) and delay look-up table in STA(Static Timing Analysis). Given some equally spaced output values, the traditional Prony's method can be used to extract poles and residues of a linear system, i.e. to characterize a waveform using an exponential function. In this thesis, not only values but also equally spaced derivatives are tested. Still using same idea of the traditional Prony's method, poles and residues can also be extracted with those values and derivatives. The resultant poles and residues will be used to predict the output waveform in DTA analysis. The benefits brought by the using of derivatives include less simulation steps and less CPU time consuming than the regular constant step simulation. As a matter of fact, the Prony's method can precisely approximate a complicated waveform. Such property can be applied for STA analysis. The Prony's approximation can be used to precisely record an output waveform, which is used as an entry of the look-up table of STA. Since the accuracy of STA analysis relies on the accuracy of the input and output waveform in the look-up table, the accuracy of the Prony's approach is promising.
47

Delay Analysis of Digital Circuits Using Prony's Method

Fu, Jingyi J.Y. 28 July 2011 (has links)
This thesis describes possible applications of Prony's method in timing analysis of digital circuits. Such applications include predicting the future shape of the waveform in DTA(Dynamic Timing Analysis) and delay look-up table in STA(Static Timing Analysis). Given some equally spaced output values, the traditional Prony's method can be used to extract poles and residues of a linear system, i.e. to characterize a waveform using an exponential function. In this thesis, not only values but also equally spaced derivatives are tested. Still using same idea of the traditional Prony's method, poles and residues can also be extracted with those values and derivatives. The resultant poles and residues will be used to predict the output waveform in DTA analysis. The benefits brought by the using of derivatives include less simulation steps and less CPU time consuming than the regular constant step simulation. As a matter of fact, the Prony's method can precisely approximate a complicated waveform. Such property can be applied for STA analysis. The Prony's approximation can be used to precisely record an output waveform, which is used as an entry of the look-up table of STA. Since the accuracy of STA analysis relies on the accuracy of the input and output waveform in the look-up table, the accuracy of the Prony's approach is promising.
48

Exploring models of time processing : effects of training and modality, and the relationship with cognition in rhythmic motor tasks

Karampela, Olympia January 2017 (has links)
Timing can be defined as the ability to perceive temporal sequences and regulate timed behaviors. As in other animals, our ability to make accurate time estimations is crucial in order to accomplish several activities. Organisms can process time over a wide range of durations ranging from microseconds to days. In the middle of these extremes is the hundreds of milliseconds to seconds range which is important for many everyday behaviors, such as walking, speaking and dancing. Yet, how this is managed remains poorly understood. Some central issues with regard time processing in this particular time range are whether timing is governed by one, or by several different mechanisms, possibly invoked by different effectors used to perform the timing task, as well as, if cognitive capacities are also involved in rhythmic motor timing. This thesis includes three studies. Study I investigated the effects of short- term practice on a motor timing task. Analyses of the timing variability indicated that a substantial amount of learning occurred in the first hour of practice and declined afterwards, exhibiting no trend for further decrease across the remaining 60 or 210 minutes. This effect was similar across effector, amount of feedback, and interval duration. Our results suggested that training effects influenced mainly motor precision and raised the question of whether motor timing training influenced also cognitive capacities. Study II investigated the relationship between motor timing and cognition. Specifically, participants had to train a sensorimotor synchronization task (SMS) over several days, and the question was whether this training would improve cognitive performance. A near transfer effect was found between the sensorimotor synchronization task and the sustained attention task, indicating that sustained attention is involved in motor timing. Study III compared the timing variability between the eyes and the hands, as a function of four different intervals, in order to examine whether these systems are temporally controlled by the same or different mechanism(s). The results showed several positive correlations in variability, between the eye and the finger movements, which, however, were significant only for the longer intervals. In addition, they were differences in variability between the eye and the hand, for the different interval durations. In general, the pattern of results from these studies suggested that voluntary motor timing is managed by overlapping distributed mechanisms and that these mechanisms are related to systems that manage cognitive processes, such as attention. The results partially explain the well-known relationships between cognitive ability and timing.
49

Delay Analysis of Digital Circuits Using Prony's Method

Fu, Jingyi J.Y. January 2011 (has links)
This thesis describes possible applications of Prony's method in timing analysis of digital circuits. Such applications include predicting the future shape of the waveform in DTA(Dynamic Timing Analysis) and delay look-up table in STA(Static Timing Analysis). Given some equally spaced output values, the traditional Prony's method can be used to extract poles and residues of a linear system, i.e. to characterize a waveform using an exponential function. In this thesis, not only values but also equally spaced derivatives are tested. Still using same idea of the traditional Prony's method, poles and residues can also be extracted with those values and derivatives. The resultant poles and residues will be used to predict the output waveform in DTA analysis. The benefits brought by the using of derivatives include less simulation steps and less CPU time consuming than the regular constant step simulation. As a matter of fact, the Prony's method can precisely approximate a complicated waveform. Such property can be applied for STA analysis. The Prony's approximation can be used to precisely record an output waveform, which is used as an entry of the look-up table of STA. Since the accuracy of STA analysis relies on the accuracy of the input and output waveform in the look-up table, the accuracy of the Prony's approach is promising.
50

IMPLEMENTATION OF A DYNAMICALLY RECONFIGURABLE ASYNCHRONOUS PROGRAMMABLE LOGIC (DRAPL) ARCHITECTURE

RAJAGOPALAN, JAYANTHI January 2004 (has links)
No description available.

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