Class D amplifiers are becoming increasingly popular in audio devices. The strongest reason is the high efficiency which makes it advantageous for portable battery-driven products. Infineon Technologies is developing products in this area, and has recently filed a patent application regarding an implementation of a part of the class D amplifier. The aim of this Master’s thesis is to evaluate a digital open-loop implementation of a class D amplifier, using the pending patent solution, and discuss the differences from an analog closed-loop implementation. The focus has been on generating a high resolution PWM signal with a relatively low clock frequency. To achieve this, a hybrid of a counter and a self-calibrating tapped delay-line are used as a pulse generator. A model of the pulse generator was developed which made it possible to study how sampling frequency and different types of quantization affected quality parameters such as THD and SNR. With the results from the model two systems were implemented and simulated in HDL and as circuit schematics. The proposed digital open-loop class D amplifier was found to be useful in voice-band applications and for music. Since the open-loop structure suffers from poor rejection of power supply ripple, either error correction or a regulated power supply is needed. If much effort is put on the different parts of the amplifier the result can be really good but, depending on other constraints on the system, it may be simpler and less time consuming to use the analog circuit with feedback to achieve hi-fi quality. In summary, the combination of a counter and a self-calibrating tapped delay-line as a pulse generator is very useful in high resolution low-power systems. To avoid errors the delay-line and calibration can be made very accurate but with the expense of higher power consumption and area. However, the technique benefits from the small and fast logic devices available in deep sub-micron process technologies, which may finally lead to an advantage in power consumption and cost over the closed-loop analog solution.

In the context of a growing social complexification, projects have evolved in the pastdecades from simple endeavours to complex and uncertain undertakings. Consequently,project complexity has emerged as an important research direction, and recently severalproject complexity frameworks have been suggested. However, little research has beendone in this area and there has been no study on the relationship of project complexity,in its holistic sense, and the risk of delay. Therefore, the study investigates the intricaterelationship between project complexity and project delay. The research is conducted inthe context of Enterprise Resource Planning system (ERP) implementation projects,which are inherently complex and often record delays. The study has a qualitative nature and adopts an inductive approach. Nine ERPimplementationprojects have been studied in order to answer the research question.Several sources of evidence (semi-structured interviews and questionnaires) have beenutilized to ensure the credibility of the research findings through triangulation. The study contributes to the research field by verifying and augmenting the existingframeworks on reasons for project delay, complexity categories and their interplay. Itwas identified that complexity in a holistic sense represents a necessary condition forproject delay. Moreover, the study showed that although ERP projects are oftenconsidered to be technically complex, their complexity stems mainly from ‘subjective’(or perceived) and ‘uncertainty’ complexity dimensions. Finally, the conceptual modelof Eden et al. (2005) was modified to reflect the findings of the study.

<p>The goal of this work is to develop a practical and comprehensive methodology to study the response and the stability of various delay differential equations (DDEs). The development of these new analysis techniques is motivated by the existence of delays in the governing equations of many physical systems such as turning and milling processes. </p><p>Delay differential equations appear in many models in science in engineering either as an intrinsic component (e.g. machining dynamics) or as a modeling decision (biology related dynamics). However, the infinite dimensionality of DDEs significantly complicates the resulting analysis from both an analytical and numerical perspective. Since the delay results in an infinite dimensional state-space, it is often necessary to use an approximate procedure to study DDEs and ascertain their stability.</p><p>Several approximate techniques appeared in literature to study the stability of DDEs. However, a large number of these techniques---such as D-subdivision, Cluster Treatment of Characteristic Roots and Continuous Time Approximation---are limited to autonomous DDEs. Moreover, the methods that are suitable for non-autonomous DDEs, e.g. the Semi-discretization approach, often result in a very large system of algebraic equations that can cause computational difficulties. Collocation-type methods, such as Chebyshev-collocation approach, have also been used to study DDEs. One major limitation of the conventional Chebyshev collocation approach is that it is strictly applicable to DDEs with continuous coefficients. An alternative approach that can handle DDEs with piecewise continuous coefficients is the Temporal Finite Element Analysis (TFEA). However, TFEA has only linear rates of convergence and is limited to h-convergence schemes. The limited rate of convergence in TFEA has prohibited its application to a wide class of DDEs such as DDEs with complicated coefficients or with distributed and multiple delays. </p><p>In this thesis, I develop a spectral element method for the stability analysis of DDEs. The spectral element method is a Galerkin-type approach that discretizes the infinite dimensional DDE into a finite set of algebraic equations (or a dynamic map). The stability of the system is then studied using the eigenvalues of the map. </p><p>In contrast to TFEA, the spectral element method was shown to have exponential rates of convergence and hp-refinement capabilities. Further, a comparison with the widely-used collocation methods showed that our approach can often yield higher rates of convergence. The higher rates of convergence of the developed approach enabled extending it to DDEs with multiple and distributed delays. I further extended this approach to calculating the periodic orbits of DDEs and their stability. </p><p>As an application of the methods developed in this thesis, I studied the stability of turning and milling models. For example, a distributed force model was proposed to characterize cutting forces in turning. The stability of the resulting delay integro-differential equation was studied using the methods developed in this study and they were shown to agree with practical observations. As another example, the stability of a milling process--- whose model contains piecewise coefficients---was investigated. The effect of multiple-flute engagement, which contributed to the complexity of the coefficients, was also investigated. The resulting stability charts revealed new stability observations in comparison to typical analysis methods. Specifically, I was able to show that unstable regions appear in what was deemed a stable region by prior analysis techniques.</p> / Dissertation

Delay is a common problem of construction sector. Recent improvements in the sector increased the competition and this led the construction projects to be more complex than before and difficult to be completed in time. This situation not only increased the delay problems, but also made the analysis of delays difficult and that caused further problems as disputes between parties to the contract. Sound knowledge in delay analysis subject is needed to enhance the solution of the delay problem in construction projects. So, this study aims to share knowledge in delay analysis issue by construction of a delay analysis ontology that provides direct and comprehensive knowledge. The constructed ontology may ease the information sharing process and provide a base for the usage of information in computers for different purposes especially in risk and claim management processes. It may enable companies to create their own knowledge bases and decision support systems that may achieve improvement in the knowledge and its usability. To meet this objective, detailed literature review on delay subject is carried out and an ontology on delay analysis issue is created. The created ontology is validated through its comparison with three different case studies.

It is a known fact that construction projects do not often complete on time due to several reasons related with the unexpected changes in the project conditions, external factors or performance of project participants. Since construction projects are unique and limited information is available at the beginning of the projects, prediction of delays is a difficult task. However, if the delays can be assessed at the early stages, their impacts might be minimized, some of the delays can even be eliminated. This study introduces a delay assessment methodology which can be used to predict delays both at the activity level and project level. Fuzzy logic and fuzzy network analysis form the basis of this methodology. A software has been developed using the proposed delay assessment methodology and a delay taxonomy developed by Bilgin (2011). Project management teams can use the developed tool to predict delays and also evaluate impacts of delays on a project`s schedule.

Delay-tolerant networks (DTNs) are dynamic networks in which senders and receivers are often completely disconnected from each other, often for long periods of time. DTNs are enjoying a burgeoning interest from the research community largely due to the vast potential for meaningful applications, e.g., to enable access to the Internet in remote rural areas, monitor animal behavioral patterns, connect participants in mobile search and rescue applications, provide connectivity in urban environments, and support space communications. Existing work in DTNs generally focuses either on solutions for very specific applications or domains, or on general-purpose protocol-level solutions intended to work across multiple domains. In this proposal, we take a more systems-oriented approach to DTNs. Since applications operating in these dynamic environments would like their connections to be supported by the network technology best suited to the combination of the communication session's requirements and instantaneous network context, we develop a middleware architecture that enables seamless migrations from one communication style to another in response to changing network conditions. We also enable context-awareness in DTNs, using this awareness to adapt communications to more efficiently use network resources. Finally, we explore the systems issues inherent to such a middleware and provide an implementation of it that we test on a mobile computing testbed made up of autonomous robots. / text

We consider a general stochastic differential delay equation (SDDE) with multiplicative colored noise. We study the limit as the time delays and the correlation times of the noises go to zero at the same rate. First, we derive the limiting equation for the equation obtained by Taylor expanding the SDDE to first order in the time delays. The limiting equation contains a noise-induced drift term that depends on the ratios of the time delays to the correlation times of the noises. We prove that, under appropriate assumptions, the solution of the equation obtained by the Taylor expansion converges to the solution of this limiting equation in probability with respect to the sup norm over compact time intervals. Next, we derive the limiting equation for the SDDE and prove a similar convergence result regarding convergence of the solution of the SDDE to the solution of this limiting equation. We see that the limiting equation corresponding to the equation obtained by the Taylor expansion is an approximation of the limiting equation corresponding to the SDDE. Finally, we study the effects of time delay on a particular model of active Brownian motion.

Data aggregation is an important technique in wireless sensor networks. The data are gathered together by data fusion routines along the routing path, which is called data-centralized routing. We propose a localized, Delay-bounded and Energy-efficient Data Aggregation framework(DEDA) based on the novel concept of DEsired Progress (DEP). This framework works under request-driven networks with realistic MAC layer protocols. It is based on localized minimal spanning tree (LMST) which is an energy-efficient structure. Besides the energy consideration, delay reliability is also considered by means of the DEP. A node’s DEP reflects its desired progress in LMST which should be largely satisfied. Hence, the LMST edges might be replaced by unit disk graph (UDG) edges which can progress further in LMST. The DEP metric is rooted on realistic degree-based delay model so that DEDA increases the delay reliability to a large extent compared to other hop-based algorithms. We also combine our DEDA framework with area coverage and localized connected dominating set algorithms to achieve two more resilient DEDA implementations: A-DEDA and AC-DEDA. The simulation results confirm that our original DEDA and its two enhanced variants save more energy and attain a higher delay reliability ratio than existing protocols.

Communication delays are common in many complex systems. It has been shown that these delays cannot be neglected when they are long enough compared to other timescales in the system. In systems of coupled phase oscillators discrete delays in the coupling give rise to effects such as multistability of steady states. However, variability in the communication times inherent to many processes suggests that the description with discrete delays maybe insufficient to capture all effects of delays. An interesting example of the effects of communication delays is found during embryonic development of vertebrates. A clock based on biochemical reactions inside cells provides the periodicity for the successive and robust formation of somites, the embryonic precursors of vertebrae, ribs and some skeletal muscle. Experiments show that these cellular clocks communicate in order to synchronize their behavior. However, in cellular systems, fluctuations and stochastic processes introduce a variability in the communication times. Here we account for such variability by considering the effects of distributed delays. Our approach takes into account entire intervals of past states, and weights them according to a delay distribution. We find that the stability of the fully synchronized steady state with zero phase lag does not depend on the shape of the delay distribution, but the dynamics when responding to small perturbations about this steady state do. Depending on the mean of the delay distribution, a change in its shape can enhance or reduce the ability of these systems to respond to small perturbations about the phase-locked steady state, as compared to a discrete delay with a value equal to this mean. For synchronized steady states with non-zero phase lag we find that the stability of the steady state can be altered by changing the shape of the delay distribution. We conclude that the response to a perturbation in systems of phase oscillators coupled with discrete delays has a sharper functional dependence on the mean delay than in systems with distributed delays in the coupling. The strong dependence of the coupling on the mean delay time is partially averaged out by distributed delays that take into account intervals of the past.

Delay is one of the most common problems in the steel construction industry. At the time of bidding steel contractors plan tasks and assign resources according to the site visits, the information given in the contract and specifications related with the project. However, as the project progresses some conditions of the work may change. These changes may affect originally planned means and methods. Finally, the affected activities cause the project total cost and duration to increase. In steel construction projects, if not managed properly in accordance with the contract, changes are likely to result in claims between the project participants. In this study, a delay analysis methodology which is based on time impact analysis is proposed. The aim of this methodology is to quantify impacts of work changes on the schedule and cost of steel construction projects and identify the responsible parties for these changes. A risk breakdown structure is presented to help decision-makers to identify probable sources of risk factors that usually result in time and cost overruns. The potential sources of change are categorized into 3 groups: contractor-related, owner-related and external factors. By using this structure, contractors may classify changes and assign the impacts of changes to the appropriate parties. The proposed methodology comprises of 3 steps: identification and quantification of delays, allocation of these delays to responsible parties and using TIA to calculate overall impact of changes on time and cost. The major benefits of this methodology are / a) its ability to handle and quantify changes in a step by step procedure, b) it provides a graphical representation of actual progress, and c) it helps decision-makers to give reliable decisions by monitoring the impact of changes during the project&amp / #8217 / s life cycle. Construction professionals may use it to apportion impact of changes in a systematic and reliable way. Moreover, reports generated by using this methodology can provide evidence during the claim management process. An application of this methodology on a steel project demonstrates the superiority of the process in explaining the dynamic nature of changes and in apportioning the impacts between different parties in a systematic way.