Variability affects the performance and power of a circuit. Along with static variations, dynamic variations, which occur during chip operation, necessitate a safety margin. The safety margin makes it difficult to meet the target performance within a limited power budget. This research explores methodologies to minimize the safety margin, thereby improving the energy efficiency of a system. The safety margin can be reduced by either minimizing the variation or adapting to the variation. This research explores three different methods to compensate for variations efficiently. First, post-silicon tuning methods for minimizing variations in 3D ICs are presented. Design methodologies to apply adaptive voltage scaling and adaptive body biasing to 3D ICs and the associated circuit techniques are explored. Second, non-design-intrusive circuit techniques are proposed for adaptation to dynamic variations. This work includes adaptive clock modulation and bias-voltage generation techniques. Third, design-intrusive methods to eliminate the safety margin are proposed. The proposed methodologies can prevent timing-errors in advance with a minimized performance penalty. As a result, the methods presented in this thesis minimize static variations and adapt to dynamic variations, thereby, enabling robust low-power operation of digital systems.

Produsente van landboukommoditeite, veral in ontwikkelende lande, word blootgestel aan prysrisiko's. Markte vir landboukommoditeite in Suid-Afrika, soos in die res van die wêreld, is die afgelope aantal jare gekenmerk deur prosesse van deregulering. Die bemarkingsrade wat aanvanklik verantwoordelik was vir die bemarking van landbouprodukte, het ontbind en produsente van landbouprodukte moes nuwe metodes vind om hulle produkte te bemark. Een van die metodes wat gebruik word, is termynkontrakte. Witmielies en geelmielies is die twee landboukommoditeite wat in die grootste hoeveelhede geproduseer word in Suid-Afrika. Witmielies en geelmielies word as twee afsonderlike kommoditeite verhandel op die termynbeurs. Witmielies word hoofsaaklik aangewend vir menslike verbruik en geelmielies vir dierevoer. Hierdie studie fokus hoofsaaklik op witmielies. Die prys van mielies word beïnvloed deur veranderinge in die vraag daarna en aanbod daarvan. Faktore wat die vraag en aanbod van mielies beïnvloed is, onder andere, oesskattings, reënval, die wisselkoers en die pryse van mielies op die buitelandse mark, veral die markte in die VSA. In Suid-Afrika vorm die invoerpariteit en uitvoerpariteit 'n band waarbinne die prys van mielies varieer. Die doel van hierdie studie is om 'n regressievergelyking te konstrueer ten einde prys van die witmielietermynkontrakte te verklaar. Die regressie-analise word deur middel van 'n foutherstellende model met outoregressiewe foutterme behartig. Die regressie-analise slaag daarin om die prys van witmielietermynkontrakte te verklaar. / Thesis (M.Com. (Economics))--North-West University, Potchefstroom Campus, 2004.

The research reported on in this thesis forms part of the foundation of a bigger research project in which an attempt is made to provide better, faster and more efficient feedback on student writing. The introduction presents the localised and international context of the study, and discusses some of the problems experienced with feedback practice in general. The introduction also gives a preview of the intended practical implementation of the research reported on in this thesis. From there on, the thesis is presented in article form with each article investigating and answering a part of two main guiding questions. These questions are: 1. Does feedback on student writing work? 2. How can feedback on student writing be implemented as effectively as possible? The abstracts for the five individual articles are as follows: Article 1 Article 1 presents a rubric for the evaluation of Computer-Assisted Language Learning (CALL) software based on international recommendations for effective CALL. The rubric is presented after a brief overview of the pedagogical and implementation fundamentals of CALL, and a discussion of what needs to be included in a needs analysis for CALL evaluation. It is then illustrated how the evaluation criteria in the rubric can be used in the design of a new CALL system. Article 2 Providing feedback on student writing is a much-debated topic. One group of researchers argues that it is ineffective and another group remains convinced that it is effective, while at ground level teachers and lecturers simply carry on “marking” texts. The author of this article contends that both arguments have valid contributions to make and uses the arguments both for and against feedback to create a checklist for effective feedback practice. Adhering to this checklist should counter most of the arguments against feedback while supporting and improving the positive arguments in favour of feedback. Article 3 This article reports on an experiment which tested how effectively standardised feedback could be used when marking L2 student writing. The experiment was conducted using a custom-programmed software tool and a set of standardised feedback comments. The results of the experiment prove that standardised feedback can be used consistently and effectively to a degree, even though some refinements are still needed. Using standardised feedback in a standard marking environment can assist markers in raising their awareness of errors and in more accurately identifying where students lack knowledge. With some refinements, it may also be possible to speed up the marking process. Article 4 This article describes an experiment in which Boolean feedback (a kind of checklist) was used to provide feedback on the paragraph structures of first-year students in an academic literacy course. The major problems with feedback on L2 writing are introduced and it is established why a focus on paragraph structures in particular is of importance. The experiment conducted was a two-draft assignment in which three different kinds of feedback (technique A: handwritten comments; technique B: consciousness raising through generalised Boolean feedback; and technique C: specific Boolean feedback) were presented to three different groups of students. The results indicate that specific Boolean feedback is more effective than the other two techniques, partly because a higher proportion of the instances of negative feedback on the first draft were corrected in the second draft (improvements), but more importantly because in the revision a much lower number of changes to the text resulted in negative feedback on the second draft (regressions). For non-specific feedback, almost as many regressions occurred as improvements. In combination with automatic analytical techniques made possible with software, the results from this study make a case for using such checklists to give feedback on student writing. Article 5 This article describes an experiment in which a series of statements, answerable simply with yes or no (labelled Boolean feedback), were used to provide feedback on the introductions, conclusions and paragraph structures of student texts. A write-rewrite assignment (the same structure as in article 4) was used and the quality of the student revisions was evaluated. The results indicate that the students who received Boolean feedback showed greater improvement and fewer regressions than students who received feedback using the traditional method. The conclusion provides a brief summary as well as a preview of the immense future research possibilities made possible by this project. / Thesis (Ph.D. (English))--North-West University, Potchefstroom Campus, 2011.

The research reported on in this thesis forms part of the foundation of a bigger research project in which an attempt is made to provide better, faster and more efficient feedback on student writing. The introduction presents the localised and international context of the study, and discusses some of the problems experienced with feedback practice in general. The introduction also gives a preview of the intended practical implementation of the research reported on in this thesis. From there on, the thesis is presented in article form with each article investigating and answering a part of two main guiding questions. These questions are: 1. Does feedback on student writing work? 2. How can feedback on student writing be implemented as effectively as possible? The abstracts for the five individual articles are as follows: Article 1 Article 1 presents a rubric for the evaluation of Computer-Assisted Language Learning (CALL) software based on international recommendations for effective CALL. The rubric is presented after a brief overview of the pedagogical and implementation fundamentals of CALL, and a discussion of what needs to be included in a needs analysis for CALL evaluation. It is then illustrated how the evaluation criteria in the rubric can be used in the design of a new CALL system. Article 2 Providing feedback on student writing is a much-debated topic. One group of researchers argues that it is ineffective and another group remains convinced that it is effective, while at ground level teachers and lecturers simply carry on “marking” texts. The author of this article contends that both arguments have valid contributions to make and uses the arguments both for and against feedback to create a checklist for effective feedback practice. Adhering to this checklist should counter most of the arguments against feedback while supporting and improving the positive arguments in favour of feedback. Article 3 This article reports on an experiment which tested how effectively standardised feedback could be used when marking L2 student writing. The experiment was conducted using a custom-programmed software tool and a set of standardised feedback comments. The results of the experiment prove that standardised feedback can be used consistently and effectively to a degree, even though some refinements are still needed. Using standardised feedback in a standard marking environment can assist markers in raising their awareness of errors and in more accurately identifying where students lack knowledge. With some refinements, it may also be possible to speed up the marking process. Article 4 This article describes an experiment in which Boolean feedback (a kind of checklist) was used to provide feedback on the paragraph structures of first-year students in an academic literacy course. The major problems with feedback on L2 writing are introduced and it is established why a focus on paragraph structures in particular is of importance. The experiment conducted was a two-draft assignment in which three different kinds of feedback (technique A: handwritten comments; technique B: consciousness raising through generalised Boolean feedback; and technique C: specific Boolean feedback) were presented to three different groups of students. The results indicate that specific Boolean feedback is more effective than the other two techniques, partly because a higher proportion of the instances of negative feedback on the first draft were corrected in the second draft (improvements), but more importantly because in the revision a much lower number of changes to the text resulted in negative feedback on the second draft (regressions). For non-specific feedback, almost as many regressions occurred as improvements. In combination with automatic analytical techniques made possible with software, the results from this study make a case for using such checklists to give feedback on student writing. Article 5 This article describes an experiment in which a series of statements, answerable simply with yes or no (labelled Boolean feedback), were used to provide feedback on the introductions, conclusions and paragraph structures of student texts. A write-rewrite assignment (the same structure as in article 4) was used and the quality of the student revisions was evaluated. The results indicate that the students who received Boolean feedback showed greater improvement and fewer regressions than students who received feedback using the traditional method. The conclusion provides a brief summary as well as a preview of the immense future research possibilities made possible by this project. / Thesis (Ph.D. (English))--North-West University, Potchefstroom Campus, 2011.

The Skynet IV satellite will provide a medium for an integrated digital communications network. This will use the packet-oriented techniques employed in many modern communications systems. One important role of the system will be to provide jam-resistant services. The advent of sophisticated electronic jammers has required the application of complex error-correcting codes and data interleaving techniques. When the satellite link forms part of a wider network, these have profound effects upon the performance of the data link protocol. This project has examined some of these effects. Terrestrial data link control protocols were found to be very inefficient, and a number of enhancements to these protocols have been proposed. An implementation of the enhanced protocols has been tested within a simulation environment. The simulator was written in Simula, an object-oriented programming language. The performance of the link was observed to be highly dependent upon the error environment presented by the underlying physical layer service (in this case a frequency-hopped spread spectrum anti-jam satellite circuit). A model of the physical layer was combined with a link layer simulator. The model used an unusual technique to reduce the computational requirements of the simulator. The project revealed that a conventional anti-jam satellite circuit is unsuitable for carriage of packetised data services. However, a number of simple changes to the protocol and error control techniques may yield a significant increase in the performance, permitting use of the service even in the harsh error environments presented by hostile jammers. These results are to be used in the specification of future satellite modems.

There is growing evidence that young adult readers frequently fail to create exhaustive textbased representations as they read. Although there has been a significant amount of research devoted to age-related effects on text processing, there has been little research concerning this so-called shallow processing by older readers. This dissertation uses eye tracking to explore age-related effects in shallow processing across different levels of text representations. Experiment 1 investigated shallow processing by older readers at the textbase level by inserting semantic anomalies into passages read by participants. Older readers frequently failed to report the anomalies, but no more frequently than did younger readers. The eye-fixation behaviour revealed that older readers detected some of the anomalies sooner than did younger readers, but had to allocate disproportionately more processing resources to looking back to the anomalies to achieve comparable levels of detection success as their younger counterparts. Experiment 2 examined age-related effects of shallow processing at the surface form by inserting syntactic anomalies into passages read by older and younger adults. Older readers were less likely to detect syntactic anomalies when first encountering them relative to younger readers and engaged in increased regressive fixations to the anomalies. However, older readers with high iii reading comprehension skill were able to use their familiarity with text content to increase their likelihood of syntactic anomaly detection. Experiment 3 investigated the role of aging on shallow processing of the temporal dimension of the situation model. No age-related differences reporting the anomalies were found. The eye-fixation behaviour revealed that older readers with high working memory capacity detected some anomalies sooner than did younger readers; however, they had to allocate increased processing resources looking back to the anomalies to achieve comparable levels of detection as younger readers. Together, the results demonstrate that older readers are susceptible to shallow processing, but no more so than younger readers when they can rely on their linguistic skill or their existing knowledge to help reduce processing demands. However, older readers appear to require additional processing time to achieve comparable levels of anomaly detection as younger readers.

Taguchi defines quality loss as the loss imposed to the consumer for each unit of deviation from the target consumer requirements. In this thesis, the effects of inspection error and rework on quality loss are studied for a nominal-the-best type quality characteristic. The distribution of the quality characteristic in a production environment where there are inspection error and a separate rework facility is investigated. 100 % inspection policy is considered. After deriving the mean and variance of the resulting distribution of the quality characteristic, the true and simulated quality loss values for a number of scenarios are calculated. Furthermore, effects of deviation of the process mean from the target and variance of the rework are studied besides inspection error and process capability through a full factor factorial experimental design. Results are discussed for possible uses as quality improvement project selection criteria.

国立情報学研究所で電子化したコンテンツを使用している。

Many statistical models, like measurement error models, a general class of survival models, and a mixture data model with random censoring, are semiparametric where interest lies in estimating finite-dimensional parameters in the presence of infinite-dimensional nuisance parameters. Developing efficient estimators for the parameters of interest in these models is important because such estimators provide better inferences. For a general regression model with measurement error, we utilize semiparametric theory to develop an unprecedented estimation procedure which delivers consistent estimators even when the model error and latent variable distributions are misspecified. Until now, root-$n$ consistent estimators for this setting were not attainable except for special cases, like a polynomial relationship between the response and mismeasured variables. Through simulation studies and a nutrition study application, we demonstrate that our method outperforms existing methods which ignore measurement error or require a correct model error distribution. In randomized clinical trials, scientists often compare two-sample survival data with a log-rank test. The two groups typically have nonproportional hazards, however, and using a log rank test results in substantial power loss. To ameliorate this issue and improve model efficiency, we propose a model-free strategy of incorporating auxiliary covariates in a general class of survival models. Our approach produces an unbiased, asymptotically normal estimator with significant efficiency gains over current methods. Lastly, we apply semiparametric theory to mixture data models common in kin-cohort designs of Huntington's disease where interest lies in comparing the estimated age-at-death distributions for disease gene carriers and non-carriers. The distribution of the observed, possibly censored, outcome is a mixture of the genotype-specific distributions where the mixing proportions are computed based on the genotypes which are independent of the trait outcomes. Current methods for such data include a Cox proportional hazards model which is susceptible to model misspecification, and two types of nonparametric maximum likelihood estimators which are either inefficient or inconsistent. Using semiparametric theory, we propose an inverse probability weighting estimator (IPW), a nonparametrically imputed estimator and an optimal augmented IPW estimator which provide more reasonable estimates for the age-at-death distributions, and are not susceptible to model misspecification nor poor efficiencies.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1982. / Bibliography: leaves 188-191. / Microfiche. / xi, 191 leaves, bound ill. 29 cm