Browsing by Subject "Variation"
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Item Analysis and optimization of VLSI Clock Distribution Networks for skew variability reduction(Texas A&M University, 2004-11-15) Rajaram, Anand K.As VLSI technology moves into the Ultra-Deep Sub-Micron (UDSM) era, manufacturing variations, power supply noise and temperature variations greatly affect the performance and yield of VLSI circuits. Clock Distribution Network (CDN), which is one of the biggest and most important nets in any synchronous VLSI chip, is especially sensitive to these variations. To address this problem variability-aware analysis and optimization techniques for VLSI circuits are needed. In the first part of this thesis an analytical bound for the unwanted skew due to interconnect variation is established. Experimental results show that this bound is safer, tighter and computationally faster than existing approaches. This bound could be used in variation-aware clock tree synthesis.The second part of the thesis deals with optimizing a given clock tree to minimize the unwanted skew variations. Non-tree CDNs have been recognized as a promising approach to overcome the variation problem. We propose a novel non-tree CDN obtained by adding cross links in an existing clock tree. We analyze the effect of the link insertion on clock skew variability and propose link insertion schemes. The non-tree CDNs so obtained are shown to be highly tolerant to skew variability with very little increase in total wire-length. This can be used in applications such as ASIC design where a significant increase in the total wire-length is unacceptable.Item Design methodologies for variation-aware integrated circuits(2009-05-15) Samanta, RupakThe scaling of VLSI technology has spurred a rapid growth in the semiconductor industry. With the CMOS device dimension scaling to and beyond 90nm technology, it is possible to achieve higher performance and to pack more complex functionalities on a single chip. However, the scaling trend has introduced drastic variation of process and design parameters, leading to severe variability of chip performance in nanometer regime. Also, the manufacturing community projects CMOS will scale for three to four more generations. Since the uncertainties due to variations are expected to increase in each generation, it will significantly impact the performance of design and consequently the yield. Another challenging issue in the nanometer IC design is the high power consumption due to the greater packing density, higher frequency of operation and excessive leakage power. Moreover, the circuits are usually over-designed to compensate for uncertainties due to variations. The over-designed circuits not only make timing closure difficult but also cause excessive power consumption. For portable electronics, excessive power consumption may reduce battery life; for non-portable systems it may impose great difficulties in cooling and packaging. The objective of my research has been to develop design methodologies to address variations and power dissipation for reliable circuit operation. The proposed work has been divided into three parts: the first part addresses the issues related with power/ground noise induced by clock distribution network and proposes techniques to reduce power/ground noise considering the effects of process variations. The second part proposes an elastic pipeline scheme for random circuits with feedback loops. The proposed scheme provides a low-power solution that has the same variation tolerance as the conventional approaches. The third section deals with discrete buffer and wire sizing for link-based non-tree clock network, which is an energy efficient structure for skew tolerance to variations. For the power/ground noise problem, our approach could reduce the peak current and the delay variations by 50% and 51% respectively. Compared to conventional approach, the elastic timing scheme reduces power dissipation by 20% ? 27%. The sizing method achieves clock skew reduction of 45% with a small increase in power dissipation.Item Language use in East Austin, Texas(2013-08) Points, Kathleen M.; Hinrichs, Lars; Epps, Patience, 1973-This dissertation presents a study of African American and Hispanic speakers in East Austin, Texas, an area that has been historically segregated and is now experiencing rapid gentrification. The current literature is lacking research on minority participation in sound change. This dissertation contributes to redressing the deficit in this area by describing data from sociolinguistic interviews with African American and Hispanic speakers; the following questions are considered: How do social variables influence a linguistic system? How do the social pressures of gentrification influence linguistic variables? To what extent do minority speakers participate in sound changes present in the majority group's variety of English? Specifically, it considers GOOSE and GOAT fronting and the relative positions of LOT and THOUGHT. It has previously been suggested that only Anglo speakers participate in changes affecting these vowels. With regard to GOOSE and GOAT, in many varieties of Southern English, the back vowels become fronted in Anglo speech while they remain backed in African American and Hispanic speech (e.g., Thomas, 2001a). However, the findings discussed here show that African American and Hispanic speakers may front these vowels to achieve particular stylistic purposes. With regard to LOT and THOUGHT, these vowel classes have merged, or are undergoing merger, in many regions of the United States (Labov, Ash, & Boberg, 2006). In Texas, Anglo and Hispanic speakers exhibit the LOT~THOUGHT merger while African American speakers reportedly do not and in general resist the merger (Bailey, Wikle, & Sand, 1991; Bernstein, 1993; Labov et al., 2006; Thomas, 2001a). The findings presented here suggest a trend for LOT~THOUGHT moving towards merger among African American speakers in Central Texas. This is unexpected among African American speakers in Texas and in the U.S. at large. The findings presented illustrate the importance of ethnically diverse samples in describing speech. In Texas where there is a large population of Hispanic residents, we cannot claim to have a thorough knowledge of the regional variety of English without investigating minority speakers. The analysis presented here is a step towards describing a more diverse data set of regional American English.Item NONPARAMETRIC CHANGE-POINT ESTIMATION FOR OBSERVATIONS FOLLOWING A RANDOM WALK WITH DRIFT(2011-05) Tercero, Victor G.This research follows a three paper format. Abstracts of each paper are: Paper 1: Nonparametric Estimator for the Time of a Step Change in the Trend of Random Walk Models with Drift This is the first out of three concatenated research endeavors in change-point analysis for trended observations in a time series following a random walk model with drift (RWWD) where the random variable is not restricted to normality and might be heterocedastic over time. In particular, this research proposes a nonparametric change-point estimator based on clustering techniques and the median test. When a time series follows two different RWWD schemes, the estimator is used to identify the moment in time were the drift of the characteristic function changes. It employs the p-value function of the median test to determine the two partitions that give the most statistical evidence of a difference between sets. Direct application is found in the management of living systems, a model is proposed, and a numerical example is presented to demonstrate feasibility. Paper 2: Nonparametric Estimator for the Time of a Step Change in the Variation of Random Walk Models with Drift This is the second out of three concatenated research endeavors on change-point analysis for trended observations in a time series following a random walk model with drift (RWWD) where the random variable is not restricted to normality and might be heterocedastic over time. Specifically, this research employs the previously developed estimator for changes in median trend to handle changes in the variation of the trend by using an artifice employed in the construction of Conover’s test for variation. When a time series follows two different schemes of RWWD models, the estimator is used to identify the moment in time when the variation of the series changes one step away from the original scheme. It converts the problem to estimate changes in variation into a problem to estimate a change in the median. It employs the p-value function of the median test to separate the time series in two partitions where there exist the most statistical evidence of a difference between sets. A direct application is found in volatility analysis of living systems such as macroeconomic or financial systems which are known to adjust to RWWD schemes in many cases. A numerical example is presented to demonstrate methodological feasibility. Paper 3: Performance of Estimators for Change-Point in Median and Variance Based on the P-Value Function of the Median Test This is the third out of three concatenated efforts of research in change-point analysis for trended observations in a time series following a random walk model with drift (RWWD) where the random variable is not restricted to normality and might be heterocedastic over time. This paper evaluates the performance of the two p-value-based estimators that used the maximum evidence of the median test to determine the moment a time series changes its median trend and variance. Previous research developed the corresponding procedures for the change-point estimation, however, the bias and variance of those was yet to be measured for different scenarios. To evaluate the effectiveness of the estimators, the p-value-based estimators were compared with the maximum likelihood estimators for the mean and variance of normal processes. Shift size, sample size, location of the change-point, and the underlying distribution of the observations were the factors under study.Item Skeletal ontogeny of Monodelphis domestica (Mammalia: Didelphidae) : quantifying variation, variability, and technique bias in ossification sequence reconstruction(2013-12) Morris, Zachary Stephen; Rowe, Timothy, 1953-The field of evolutionary developmental biology (evo-devo) focuses on understanding the evolution of ontogeny and mechanisms of evolutionary change. Recently, taxonomic comparisons of the sequence of skeletal ossification have become prominent in evo-devo. However, most of these studies fail to consider two major issues: how the technique used to assay ossification and ontogenetic variation and variability may affect comparisons among taxa. This study focuses on the onset of ossification in the skeleton of Monodelphis domestica and quantifies the affects of variation, variability, and technique bias on reconstructions of ontogeny. Previous comparisons among mammalian taxa have used both computed tomography (CT) and clearing-and-staining (CS) to assess the presence or absence of skeletal elements (i.e., skeletal maturity). In this study, CT and CS were used on the same specimen to compare how these methods assess skeletal maturity. The comparisons of the same individual under reveal significant differences in how skeletal maturity is assessed by CT and CS techniques. Further, significant biases were recovered between techniques. CT is more likely to reveal cranial elements that CS does not, whereas CS is more likely to reveal appendicular elements that CT does not. To assess levels of variation and variability, Ontogenetic Sequence Analysis (OSA) was used to characterize the ontogeny of Monodelphis domestica. This revealed significant levels of variation with over 800 different ontogenetic pathways recovered for the onset of ossification of all skeletal elements studied. Additionally, high levels of variability were also reconstructed because the majority of specimens were found to exhibit non-modal ontogenetic sequences. This variability is more highly concentrated in the sequence of cranial ossification, suggesting potential modularity in ontogenetic variation and variability. Finally, OSA revealed that technique bias could importantly affect reconstructions of skeletal ossification sequences because no identical sequences were recovered by the CT and CS datasets. The results of this study demonstrate the importance of considering the primary nature of developmental studies, the specimen. Only by recognizing and quantifying the complexities of evo-devo research, especially natural variation and methodological biases, can more complete understandings of the evolution of ontogeny be had.Item The eastern box turtle (Terrapene carolina) in time and space(2013-05) Vitek, Natasha Slonim; Bell, Christopher J., 1966-; Rowe, Tim B; Clarke, Julia A; LaDuc, Travis JVariation is a key component of the evolutionary process. However, variation often is poorly understood within species. The eastern box turtle (Terrapene carolina) presents an excellent opportunity to study that topic because extant populations have high levels of variation in soft-tissue characters as well as morphological variation in skeletal characters. To explore patterns of spatiotemporal variation, I used geometric morphometrics to quantify shape within three datasets. First, I asked to what extent size explained total shape variation using an ontogenetic series of 101 specimens. Next, I examined to what extent subspecies were morphologically distinct and identifiable in the modern record, and to what degree they explained overall variation using a dataset of 200 modern specimens. Finally, I compared the patterns in the modern biota to those from the fossil record using the previous datasets as well as a fossil dataset of 44 Pleistocene shells of T. carolina. I found that in four views of the turtle shell (dorsal, ventral, posterior, and lateral), size significantly explains 10% - 31% of the variation in shape. Some of the characters correlated with size were historically ascribed to characters of subspecies. Studying the extent to which size explains overall variation in different subsamples of my data allowed me to discover a new way of classifying segments of a population in order to account for size in future studies. Subspecies identification also explained a statistically significant amount of overall shape variation. However, the results of assignments tests and CVAs indicated insignificant or unreliable differences. Results indicate that differences between putative subspecies are more statistically significant than they are biologically significant. They do not support the recognition of subspecies in T. carolina. The inability of statistical analyses to identify individuals of a subspecies based on shell shape means that subspecies cannot be identified in the fossil record. Some of the same relationships between shape and size are present in the fossil record and the modern biota, but other morphological patterns are unique to fossil specimens. Two of the morphotypes co-occur in the same strata, and represent a unique evolutionary pattern not seen in the modern biota.Item The syntax of questions and variation in adult and child African American English(2012-05) White-Sustaíta, Jessica Bridget; Meier, Richard P.; Green, Lisa J., 1963-; Hinrichs, Lars; Bannard, Colin; Blockley, Mary; Beavers, JohnThis dissertation is the first in-depth examination of the syntax of questions and question variation in African American English (AAE). Question syntax in AAE can vary among subject-auxiliary inversion (e.g., What did you eat?), non-inversion (e.g., Why I can’t play?), and auxiliary-less questions (e.g., What he said?). Historically, AAE question syntax, when considered at all, has been dismissed as essentially identical to mainstream English. Thus, commentary on AAE question syntax is limited to observing that auxiliaries may “delete” in auxiliary-less questions, and that subject-auxiliary inversion may be “absent” in non-inverted questions. In other words, question syntax in AAE has generally been represented as a derivation or deviation from mainstream English. In the first half of this thesis I provide a syntactic analysis of the three question types, and I argue that question variation in AAE—in contrast to question variation in MAE—is the product of true syntactic variation. I show that 1) auxiliary-less questions are not necessarily cases of deletion, but are rather generated by AAE-specific parametric settings that—due to a lack of covert movement— never call upon an auxiliary, and 2) variation among different question types is tightly constrained and predicted by grammatical factors, such as negation, auxiliary verb-type, and tense. In the second half of this thesis, I examine question patterns among AAE-speaking children based on a corpus of over 50 hours of elicited and spontaneous speech data from more than 80 AAE- and mainstream English-speaking children (ages 5-7) in a New Orleans elementary school. My analysis of these data show the following: 1) by age 5, child speakers of AAE already follow the same grammatical patterns constraining question variation that are documented in adult AAE, 2) variation is inherent to the syntax of AAE questions, and not an artifact of dialect-switching or social variation, and 3) the patterns in the children’s data support the analysis of AAE question syntax presented in the first half of this thesis.