Browsing by Subject "Variability"
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Item Development of reliable pavement models(2011-08) Aguiar Moya, José Pablo, 1981-; Prozzi, Jorge Alberto; Manuel, Lance; Walton, Michael; Machemehl, Randy B.; Yilmaz, HilalAs the cost of designing and building new highway pavements increases and the number of new construction and major rehabilitation projects decreases, the importance of ensuring that a given pavement design performs as expected in the field becomes vital. To address this issue in other fields of civil engineering, reliability analysis has been used extensively. However, in the case of pavement structural design, the reliability component is usually neglected or overly simplified. To address this need, the current dissertation proposes a framework for estimating the reliability of a given pavement structure regardless of the pavement design or analysis procedure that is being used. As part of the dissertation, the framework is applied with the Mechanistic-Empirical Pavement Design Guide (MEPDG) and failure is considered as a function of rutting of the hot-mix asphalt (HMA) layer. The proposed methodology consists of fitting a response surface, in place of the time-demanding implicit limit state functions used within the MEPDG, in combination with an analytical approach to estimating reliability using second moment techniques: First-Order and Second-Order Reliability Methods (FORM and SORM) and simulation techniques: Monte Carlo and Latin Hypercube Simulation. In order to demonstrate the methodology, a three-layered pavement structure is selected consisting of a hot-mix asphalt (HMA) surface, a base layer, and subgrade. Several pavement design variables are treated as random; these include HMA and base layer thicknesses, base and subgrade modulus, and HMA layer binder and air void content. Information on the variability and correlation between these variables are obtained from the Long-Term Pavement Performance (LTPP) program, and likely distributions, coefficients of variation, and correlation between the variables are estimated. Additionally, several scenarios are defined to account for climatic differences (cool, warm, and hot climatic regions), truck traffic distributions (mostly consisting of single unit trucks versus mostly consisting of single trailer trucks), and the thickness of the HMA layer (thick versus thin). First and second order polynomial HMA rutting failure response surfaces with interaction terms are fit by running the MEPDG under a full factorial experimental design consisting of 3 levels of the aforementioned design variables. These response surfaces are then used to analyze the reliability of the given pavement structures under the different scenarios. Additionally, in order to check for the accuracy of the proposed framework, direct simulation using the MEPDG was performed for the different scenarios. Very small differences were found between the estimates based on response surfaces and direct simulation using the MEPDG, confirming the accurateness of the proposed procedure. Finally, sensitivity analysis on the number of MEPDG runs required to fit the response surfaces was performed and it was identified that reducing the experimental design by one level still results in response surfaces that properly fit the MEPDG, ensuring the applicability of the method for practical applications.Item Effects of varying the force levels and direction of force change on accuracy and force variability in a cyclic isometric pinch force tracking task(2012-08) Park, Sangsoo; Abraham, Lawrence D.; Spirduso, WaneenThis study investigated how varying the required force level and the direction of force change produced by the thumb and index finger affect the accuracy and variability of a cyclic isometric pinch force-tracking task. Accuracy was examined by both absolute error and relative error for the minimum and maximum force levels and by root mean square error (RMSE) and normalized root mean square error (normalized RMSE) for the force direction reversals. Variability was represented by coefficient of variation of error (CVE). In this study, ‘maximum force’ was defined as the highest force level of a given target force range, and ‘minimum force’ was defined as the minimum force level of the target range. In addition, ‘force increasing to decreasing’ indicated that the track ball motion changed from increasing to decreasing, requiring the performer to exert increasing force up to the maximum force level and then decreasing force to follow the track ball moving toward the minimum force level. The phrase ‘force decreasing to increasing’ indicated the opposite force direction reversal. Eighteen healthy right handed adult volunteers (nine men and nine women; mean age ± SD, 28.3±1.22 and 26.4±1.74) participated in this study. The participants performed a cyclic isometric pinch force tracking task over three different force ranges. Force range 1 was from a minimum force of 3% of maximal voluntary contraction force (MVC) to a maximum force of 6% MVC. In force range 2, the range was from 6% to 12% MVC, and force range 3 was from 12% to 24% MVC. For each force range, five practice trials and ten actual test trials were performed. Rest periods of twenty seconds between trials and one minute between sets of trials (including between practice and actual test trials) were provided to minimize fatigue effects. Absolute error uniformly increased as a function of increasing force. However, the 3% target force level showed larger relative error compared to the 12% target force level (p < 0.05). Another finding of this study was that producing forces positioned at the minimum target level in a range yielded higher absolute error and relative error compared to the same forces when placed at the maximum target level of a different force range. In terms of the reversals, RMSE values were higher at the change from force deceasing to increasing than the opposite, as well as at higher force levels, while normalized RMSE values were greater at lower force levels. CVE was not significantly different between the two reversals in this study. This might indicate that poorer performance during the change from force decreasing to increasing could originate from the effort to maintain consistent performance and additional effort was not beneficial to increase accuracy for the change from force decreasing to increasing.Item Lithography variability driven cell characterization and layout optimization for manufacturability(2011-05) Ban, Yong Chan; Pan, David Z.; Abraham, Jacob; Touba, Nur; Lucas, Kevin; Orshansky, MichaelStandard cells are fundamental circuit building blocks designed at very early design stages. Nanometer standard cells are prone to lithography proximity and process variations. How to design robust cells under variations plays a crucial role in the overall circuit performance and yield. This dissertation studies five related research topics in design and manufacturing co-optimization in nanometer standard cells. First, a comprehensive sensitivity metric, which seamlessly incorporates effects from device criticality, lithographic proximity, and process variations, is proposed. The dissertation develops first-order models to compute these sensitivities, and perform robust poly and active layout optimization by minimizing the total delay sensitivity to reduce the delay under the nominal process condition and by minimizing the performance gap between the fastest and the slowest delay corners. Second, a new equivalent source/drain (S/D) contact resistance model, which accurately calculates contact resistances from contact area, contact position, and contact shape, is proposed. Based on the impact of contact resistance on the saturation current, robust S/D contact layout optimization by minimizing the lithography variation as well as by maximizing the saturation current without any leakage penalty is performed. Third, this dissertation describes the first layout decomposition methods of spacer-type self-aligned double pattering (SADP) lithography for complex 2D layouts. The favored type of SADP for complex logic interconnects is a two-mask approach using a core mask and a trim mask. This dissertation describes methods for automatically choosing and optimizing the manufacturability of base core mask patterns, generating assist core patterns, and optimizing trim mask patterns to accomplish high quality layout decomposition in SADP process. Fourth, a new cell characterization methodology, which considers a random (line-edge roughness) LER variation to estimate the device performance of a sub-45nm design, is presented. The thesis systematically analyzes the random LER by taking the impact on circuit performance due to LER variation into consideration and suggests the maximum tolerance of LER to minimize the performance degradation. Finally, this dissertation proposes a design aware LER model which claims that LER is highly related to the lithographic aerial image fidelity and the neighboring geometric proximity. With a new LER model, robust LER aware poly layout optimization to minimize the leakage power is performed.Item Precision pinch isometric force, force variability, accuracy, and task time among the fourth through eighth decades of life(2011-05) Herring-Marler, Trenah Lannette; Abraham, Lawrence D.; Spirduso, Waneen Wyrick; Eakin, Richard T; Griffin, Lisa; Hunter, DianaThis dissertation encompassed three studies involving precision pinch strength and 5% submaximal fine-motor control. One hundred participants (30-79 years old) were divided into 10-year categories, with 10 males and 10 females in each decade. A Manual Force Quantification System containing a platform and force-transducer apparatus, along with a computer and visual monitor, was used. Each subject performed four tasks -- maximal voluntary isometric contraction (MVIC), force-matching, tracing, and tracking -- by applying force on the transducers with the thumb and index finger while attempting to produce a desired force level or task displayed on the computer monitor. The first study measured MVIC, accuracy (rRMSE, Root Mean Square Relative Error), and force variability (Coefficient of Variation, CV) during a 5% MVIC force-matching task. The second study measured accuracy (rRMSE), task time, and group variability during a 5% MVIC tracing task. The third study measured accuracy and group variability during a 5% MVIC tracking task. Tracing and tracking were each divided into six Segments (S1-S6), three of which (S1-S3) required the increasing application of force from 50g up to 5% MVIC and the remaining three (S4-S6) requiring a release of force from MVIC down to 1% MVIC. The force-matching and force-tracking task times were scaled to each participant's MVIC, while the tracing task was performed at the participant's self-selected speed. The participants were encouraged to be accurate but also to trace the target line as quickly as possible. Declines in precision pinch strength and force control began to occur in the 70s for easier force-control tasks and in their 60s for more advanced force-tracking tasks. Men were stronger than women at all age levels. Participants in their 30s were the fastest; those in their 40s, 50s, and 60s slowed down to be accurate; and those in their 70s moved faster but were the least accurate. Three segmental factors affected error and time: low force level, releasing as opposed to applying force, and location along the target line with respect to reversal or ending points. Finally, variables for females were more heterogeneous at earlier decades than for men, and the older the age group was, the greater the variable heterogeneity was.Item Sequence stratigraphy in strike variable fluvio-lacustrine systems : evidence from Eocene Lake Uinta and modern analogs(2021-05-10) Gearon, James Hooker; Olariu, CornelThis thesis presents an outcrop-based, near depositional-strike cross section of fluvio-lacustrine interactions along the well-studied Nine Mile Canyon near Helper, Utah, highlighting the strike variability of facies and depositional environments in the Sunnyside Interval fluvio-lacustrine deposits. We utilize a new, high-resolution correlation panel to demonstrate the existence of a new lacustrine sequence stratigraphic concept: the Supply-Generated Sequence (SGS), which allows subdivision of the cyclically deposited alluvial, fluvial, and lacustrine facies in the Sunnyside Interval based on identifiable stratigraphic horizons, indicating periods of marked clastic input followed by subaqueous lake deposition. This novel conceptual framework helps address the inadequacy of previous sequence stratigraphic interpretations of the Sunnyside Interval. Conventional interpretations rely on premises regarding base level and sediment discharge that were developed for marine settings and do not apply directly to lacustrine systems because the creation and preservation of sedimentary deposits must logically occur during base-level rise in lake basins. In marine settings, base-level draw-downs are interpreted as the common causal mechanism for deltaic progradation, leaving sediment supply as a secondary consideration. In lacustrine systems, accommodation and sediment-supply are generated by water and sediment discharge routed through tributary rivers, making pulses of deposition inherently transgressive in nature. Our findings corroborate recent studies that consider the large, channelized sandstone deposits (shown to be accompanied by δ13C negative excursions) of the Sunnyside Interval to be discharge macroforms deposited during orbitally forced high-discharge early Eocene Hyperthermal events that lasted ~40 kyr. We also document the lateral complexity and discontinuity of hyperthermal sandstone event deposits and show the approximate durations of Sunnyside Interval SGSs to be 40-50 kyr, adding further evidence for the hyperthermal forcing mechanism model. We examine four previously proposed analogs of the Sunnyside Interval System, comparing basin type, morphology, lake level change, and depositional slope. We submit that the Neales River Delta in Lake Eyre, Australia is the best modern analog for the Sunnyside Interval System is due to its morphological and stratigraphic similarities. Ultimately, we characterize the Sunnyside Interval System as a “Supply-Controlled Splay-Delta” with high sediment and water supply during transitory hyperthermal events and low sediment and water supply during inter-hyperthermal periods. The depositional system acted as both a terminal splay or a fluvially dominated delta guided by the interplay of supply and accommodation in Eocene Lake Uinta.Item Trial-to-trial dynamics and learning in generalized, redundant reaching tasks(2010-08) Smallwood, Rachel Fay; Dingwell, Jonathan B.; Abraham, Lawrence D.Trial-to-trial variability in human movement is often overlooked and averaged out, but useful information can be gleaned on the brain’s control of variability. A task can be defined by a function specifying a solution manifold along which all task variable combinations will lead to goal success – the Goal-Equivalent Manifold (GEM). We selected a reaching task with variables reach Distance (D) and reach Time (T). Two GEMs were selected: a constant D/T and constant D×T. Subjects had no knowledge of the goal prior to the experiments and were instructed only to minimize error. Subjects learned the generalized tasks by reducing errors and consolidated learning from one day to the next, generalized learning from the D×T to the D/T GEM, and had interference of learning from the D/T to the D×T GEM. Variability was structured along each GEM significantly more than perpendicular to it. Deviations resulting in errors were corrected significantly more quickly than any other deviation. Our results indicate that subjects can learn generalized reaching tasks, and the brain exploits redundancy in those tasks.Item The ups and downs of variability : are fluctuating relationship appraisals always detrimental for long-term relationship outcomes?(2013-12) Morgan, Taylor Anne; Neff, Lisa A.Variability in daily relationship satisfaction has been shown to undermine future relationship well-being. The current study suggests that the relationship climate may moderate this effect. Namely, and in light of prior work showing that ignoring relationship issues can be detrimental for long-term relationship well-being, it is argued that when the relationship is characterized by more negative relationship experiences, variability in daily satisfaction may actually represent an adaptive acknowledgement of those experiences. Seventy-eight newly-married couples completed a 10-day daily diary task which assessed the variability of daily marital satisfaction, the positive and negative marital events taking place each day, and the daily coping strategies used to manage negative marital events. Spouses then reported on their global marital happiness as well as the severity of their marital problems every six months over the first two and a half years of marriage. Results revealed that when the marriage was characterized by more negative than positive marital events (i.e., a more negative marital climate), greater variability in daily satisfaction predicted initially lower levels of global marital happiness and more severe marital problems. However, greater variability in a more negative marital climate also was associated with less steep declines in global marital happiness and fewer increases in marital problems over time compared to low variability. Together, these findings suggest that variability in daily relationship satisfaction may temporarily feel unpleasant but over time may allow couples to address important relationship issues.Item Variability of relationship evaluations & physical health outcomes : testing the moderating role of implicit theories of relationships(2015-08) Morgan, Taylor Anne; Loving, Timothy J.; Neff, Lisa A.; Gleason, Marci E.; Anderson, Edward R.; Campbell, LorneVariability (i.e., greater fluctuations) of relationship evaluations over time undermines current and future relationship and individual well-being. To date, greater variability of relationship evaluations has not been linked to individual physical health, yet overall relationship quality (e.g., initial or mean levels) is a strong predictor of several markers of physical health. The aims of the current study are three-fold--first, to explore new methods of capturing intra-individual variability; second, to replicate and extend previous findings on the damaging effects of variability by examining variability's association with relationship fate and physical health outcomes; and third, to investigate the potential moderating role of individuals' general relationship beliefs on these associations. I drew from a 9-month longitudinal study of 202 individuals who were in new dating relationships at the start of study participation (M[subscript length] = 3.28 months). The study included baseline self-reports of relationship satisfaction and Implicit Theories of Relationships (ITRs) as well as bi-weekly self-reports, for a total of up to 20 assessments per individual, of relationship status (together or not) and quality (semantic differential) and physical health (shortened SF-36). A series of analyses were conducted to obtain de-trended levels of intra-individual variability and a previously understudied measure of intra-individual change in relationship evaluations over time -- temporal dependency (i.e., the extent to which one day's relationship evaluation is correlated with the previous day's evaluation). These two variables were subsequently entered into a Cox proportional hazards model to explain the effect of each on the likelihood of relationship dissolution. Both variability and temporal dependency of relationship evaluations (but not their interaction) predicted increased likelihood of experiencing relationship dissolution. Contrary to predictions, however, greater variability and temporal dependency (and their interaction) were not associated with changes in self-reported physical health over time; all three terms, however, predicted higher levels of average self-reported physical health across assessments. Finally, the hypothesized moderating effects of individuals' implicit theories of relationships were not supported. These findings emphasize the predictive power of individuals' patterns of relationship evaluations over time for relationship fate yet suggest additional research is needed to understand the association between variable relationship evaluations and health outcomes.