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1
Pennas, Dimitrios Christou. "Mode III Fracture in Advanced Engineering Materials." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486939.
Повний текст джерелаАнотація:
Delamination is a fundamental failure mode of laminated composites. When laminates are subjected to out-of-plane loading, the resin matrices between the plies often fail, resulting in ply separation or delamination failure. Such loading conditions occur in various ways and depend heavily on the load transfer mo~es in the composite structures. Delamination cracks can be visualised in the fracture mechanics sense to grow, and thus can be characterised in Mode I (opening), Mode II (shear) and Mode III (scissoring or anti-plane shear) and their combinations. __The test techniques for delamination in Mode I and Mode II, as well as mixed Mode IIII, have been well established. However, few workers have investigated the Mode III interlaminar fracture properties of composites, partly because of the experimental difficulties associated with the introduction of pure Mode III loading to the delamination crack. The aim of this study was to investigate the Mode III interlaminar fracture properties of composite materials based on both thermoplastic and thermosetting matrices, adhesive joints and bi-material samples. For this reason, both numerical and experimental methods were used. The Edge Crack Torsion (ECT) test geometry was employed in order to evaluate the Mode III response of the samples studied, as it is commonly accepted that this is the most effective technique for cllaracterising this mode of delamination. The Virtual Crack Closure Integral has also been extensively used to characterise the loading conditions at the crack tip in these samples. Once the quasi-static response of the composites were analysed, dynamic tests were undertaken to investigate the rate-sensitive behaviour of these high-performance materials. Finally, the Mode III geometry was modified to look at possible mixed-mode failure involving Mode II contributions.
2
Liljestrand, Charlotte. "Spatial mode engineering in mid-infrared optical parametric oscillators." Thesis, KTH, Laserfysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-42705.
Повний текст джерелаАнотація:
The purpose of this thesis was to investigate the possibilities of enhancing the temporal and spatial coherence of parametric devices in the mid-infrared spectrum by exploiting inherent coherence selection of Bessel beams. Several optical parametric oscillators (OPO) were constructed and characterized for various types of resonators and pump lasers. In the first part of this work an OPO was constructed out of a periodically poled KTP (PPKTP) crystal within a stable resonator. It was pumped by a Q-switched Nd:YAG laser in transversal and longitudinal single mode operation. The OPO was pumped at 1064 nm and operated at signal wavelength of 1595.9 nm with a bandwidth at FWHM of 0.2 nm and idler wavelength 3192.9 nm and bandwidth of 0.5nm at FWHM. The stable resonator was constructed out of a curved input coupler and a planar output coupler to generate a spatially coherent beam. The beam quality factor of the OPO was measured to M2=1.3 and M2=1.7 in the horizontal and the vertical direction respectively. In the second part of this work conical beams, and hence noncollinear phase matching, was used. This was done to improve and study the temporal and spatial coherence of the generated beam if the OPO is pumped by a laser operating in multiple transversal and longitudinal modes. Using noncollinear phase matching provides a possibility of generating a highly coherent signal (or idler) wave when using a pump laser which operates in multiple transversal and longitudinal modes. Usually, such pump laser makes it difficult to generate highly coherent beams since the properties, such as bandwidth and beam quality factor, of the pump laser are transferred to the generated waves. So called multimode lasers, which operate in multiple modes, can be considered inexpensive and reliable while providing high pulse energies, and they are therefore attractive as pump sources for nonlinear processes. Throughout this second part a Q-switched Nd:YAG laser operating in multiple transversal and longitudinal modes at a wavelength 1064 nm was used. Optical parametric generation (OPG) was used to compare the effects between pumping with a Gaussian wave, and collinear phase matching, and pumping with a conical, a Bessel beam and hence noncollinear phase matching. Thereafter, optical parametric oscillation was studied with collinear and noncollinear phase matching using a Fabry-Perot cavity. The OPO pumped by a Q-switched Gaussian beam, and hence using collinear phase matching had a signal wave at 1596.3 nm and a bandwidth at FWHM of 4 nm. The OPO pumped by a conical beam, hence a Bessel beam and noncollinear phase matching, had a signal wave at 1596.5 nm and a bandwidth at FWHM of 0.2 nm. Both OPOs had a beam quality factor M2~2 in horizontal and vertical direction.
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Birge, Jonathan R. (Jonathan Richards). "Methods for engineering sub-two-cycle mode-locked lasers." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53192.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 159-166).<br>We begin by presenting a method to efficiently solve for the steady-state solution of a nonlinear cavity, suitable for simulating a solid-state femtosecond laser. The algorithm directly solves the periodic boundary value problem by using a preconditioned Krylov-Newton shooting solver. The method can be applied to the design and study of mode-locked lasers, as well as the modeling of field enhancement cavities, such as those used in high harmonic generation. In contrast to the standard approach of dynamic simulation, which converges linearly, our algorithm converges quadratically to the stable solution, typically converging two to three orders of magnitude faster than the standard approach. The second major theme is the control of dispersion in mode-locked lasers. The predominant way to design dispersion compensating optics in the past has been a consideration of the integrated net group delay dispersion (GDD). We propose and implement an alternative spectral quantity based on the energy contained in phase distortions, which we term the Phase Distortion Ratio (PDR). Dispersion compensating mirrors optimized with respect to PDR generally perform significantly better than those where GDD is optimized. We demonstrate this in the design of a dispersion compensating mirror pair capable of compressing single-single pulses. In the final section, we deal with the unique challenges inherent to measuring sub-two-cycle pulses reliably and accurately. We have recently developed a technique, Two-Dimensional spectral Shearing Interferometry (2DSI), based on spectral shearing, which requires no calibration and does not disperse the pulse being measured.<br>(cont.) Our method intuitively encodes spectral group delay in a slowly changing fringe in a two-dimensional interferogram. This maximizes use of spectrometer resolution, allowing for complex phase spectra to be measured with high accuracy over extremely large bandwidths, potentially exceeding an octave. We believe that 2DSI is a uniquely cost effective and efficient method for accurately and reliably measuring few- and even single-cycle pulses. While the method is relatively recent, it is well tested and has been successfully demonstrated on several different lasers in two different groups, including one producing 4.9 fs pulses.<br>by Jonathan R. Birge.<br>Ph.D.
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Bruno, Antonio 1972. "Tearing-mode transport model in the reversed field pinch concept." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/30007.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2002.<br>Includes bibliographical references (leaves 185-188).<br>In this thesis, a self-consistent model for analyzing the transport performance of a Reversed Field Pinch (RFP)-type of thermonuclear fusion reactor has been developed. The study has been focused on determining equilibrium configurations which describe a plasma evolution dominated by particular instabilities originated by plasma electrical resistivity (tearing-, or resistive interchange, modes). The ultimate goal is to provide a model of transport scaling in an RFP which can evaluate the global parameters describing the plasma confinement performance. Starting from a magnetic field configuration essentially given by Taylor's relaxation model, the self-consistent pressure profile is determined by assuming that the ohmic heating source raises the plasma pressure until the profile is locally marginally stable to tearing modes. A critical point here is the long held belief that an RFP, because of its bad curvature, would always be unstable to tearing or resistive interchange modes; that is, no marginally stable state exists. This belief turns out to be untrue. The basis for this statement is a careful ordering of the resistive layer dynamics, showing that thermal conductivity dominates over convection and compressibility. Thus, the use of the adiabatic equation of state in earlier work is not accurate for an RFP.<br>(cont.) As a result, tearing and interchange modes can indeed be stabilized in an RFP. In this model, a proper, selfconsistent definition of tearing-mode marginality has been used as a prescription for building the pressure profile. The actual numerical determination of the marginally stable profiles can be solved by using state-of-the-art personal computers. It is worth emphasizing that there are no free parameters in the model. Point checks indicate reasonable agreement with typical experimental data. Parametric numerical studies are also shown, spanning the operational space of RFP experiments, and finally providing the tearing mode transport scaling relations for the global confinement parameters. Comparisons with experiments as well as other transport models are shown.<br>by Antonio Bruno.<br>Ph.D.
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Balucan, Phillip James 1977. "Model reduction of a set of elastic, nested gimbals by component mode selection criteria and static correction modes." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/17520.
Повний текст джерелаАнотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.<br>Includes bibliographical references (p. 112-113).<br>Model reduction techniques provide for a computationally inexpensive method for solving elastic dynamic problems with complex structures. The elastic nested gimbal problem is a problem which requires model reduction techniques as a means to reduce the dynamic equations. This is done using two methods: one technique employs mode ranking criteria to select modes which influence the dynamics of the problem the most. The second involves the use of static correction modes along with vibration modes to simulate the dynamics of this nested gimbal model. A model of the structure is described in terms of a lumped-parameter finite element model. This mathematical model of the physical system serves as the ha.sis for developing model reduction techniques for the nested gimbal problem. A truth model based on given initial conditions is used to compare the accuracy of the model reduced problem. A number of model reduction theories are described and applied to the gimbal simulation. The equations for the mode ranking techniques and the static and vibration mode analysis are developed as well as a quantitative error measure. Comparisons are made with the truth model using the mode ranking criteria base on the momentum coefficients and the frequency cutoff criteria. Test cases are also run using the static correction modes with vibration modes and static correction modes with the ranked vibration modes using momentum coefficients. The use of various static modes is discussed during the implementation of the static correction mode method. Applying the model reduction theories to a set of elastic, nested gimbals, the mode ranking criteria provides better results based on the error measure than the frequency cutoff criteria when the simulation is run using less than twenty-five modes. Using static modes along with ranked modes to represent the elastic dynamics of the problem does not provide better results than using the unranked vibration modes with the static modes. Modeling the dynamics using static correction modes with the unranked vibration modes provides the best results while using the lea.st number of modes. It is advantageous to take into account the given conditions applied to the system when reducing the model of a complex dynamic problem.<br>by Phillip James Balucan.<br>S.M.
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Manoharan, Mohan. "Combined mode I - mode III plane strain fracture toughness of two high carbon steels /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487594970651702.
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Moyer, Gordon Stanley 1961. "AN EXPERT SYSTEM FOR FAILURE MODE INVESTIGATION IN RELIABILITY ENGINEERING." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/277237.
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Chen, De-Shiou. "Sliding mode observers for automotive alternator." The Ohio State University, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=osu1384448652.
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Hosoda, Takamichi 1965. "Incorporating unobservable heterogeneity in discrete choice model : mode choice model for shopping trips." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9498.
Повний текст джерелаАнотація:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1999.<br>Includes bibliographical references (leaves 90-95).<br>In this thesis, we propose a methodology for incorporating attitudinal data in a choice model to capture unobservable heterogeneity across the population. The key features of this approach are, 1) the concept of latent attitudes, and the assumption that 2) the respondent's answers to psychometric attitudinal questions relating to the importance of attributes are manifestations of these attitudes and that 3) those attitudinal data bring sufficient information to capture unobservable heterogeneity across the population in the context of choice behavior. Each individual is probabilistically assigned to a finite number of segments according to his/her own value of latent attitudinal variable(s) as well as to threshold parameter(s) common to the population. Segment-specific parameters are estimated simultaneously. An empirical case study on shopping trip mode choice demonstrates the effectiveness of the methodology.<br>by Takamichi Hosoda.<br>S.M.
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Yin, Hang. "Mode switch for component-based multi-mode systems." Licentiate thesis, Mälardalens högskola, Akademin för innovation, design och teknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-16153.
Повний текст джерелаАнотація:
Component-based software engineering is becoming a prominent solution to the development of complex embedded systems. Since it allows a system to be built by reusable and independently developed components, component-based development substantially facilitates the development of a complex embedded system and allows its complexity to be better managed. Meanwhile, partitioning system behavior into multiple operational modes is also an effective approach to reducing system complexity. Combining the component-based approach with the multi-mode approach, we get a component-based multi-mode system, for which a key issue is its mode switch handling. The mode switch of such a system corresponds to the joint mode switches of many hierarchically organized components. Such a mode switch is not trivial as it amounts to coordinate the mode switches of different components that are independently developed. Since most existing approaches to mode switch handling assume that mode switch is a global event of the entire system, they cannot be easily applied to component-based multi-mode systems where both the mode switch of the system and each individual component must be considered, and where components cannot be assumed to have global knowledge of the system. In this thesis, we present a mechanism---the Mode Switch Logic (MSL)---which provides an effective solution to mode switch in component-based multi-mode systems. MSL enables a multi-mode system to be developed in a component-based manner, including (1) a mode-aware component model proposed to suit the multi-mode context; (2) a mode mapping mechanism for the seamless composition of multi-mode components and their mode switch guidance; (3) a mode switch runtime mechanism which coordinates the mode switches of all related components so that the mode switch can be correctly and efficiently performed at the system level; and (4) a timing analysis for mode switches realized by MSL. All the essential elements of MSL are additionally demonstrated by a case study.<br>ARROWS
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Pogaku, Sindhuja. "SOUND MODE APPLICATION." CSUSB ScholarWorks, 2017. https://scholarworks.lib.csusb.edu/etd/445.
Повний текст джерелаАнотація:
Currently there are millions of Android cell phone users. Whenever a user changes location, he/she should manually modify the sound mode (ring, vibrate, silent). So, it’s slightly inconvenient to constantly monitor whether the phone is in general or silent mode. Sometimes user might forget to switch the mobile mode and may create a disturbance in the classroom or in the work area.
To overcome this problem “Sound Mode Application” is an Android application that allows a user to automatically change the sound mode depending on his/her GPS location. Additionally, the user may activate or deactivate the application whenever need be, and user can add as many locations as required based on their daily life.
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Banerjee, Abhishek. "AlGaN/GaN based enhancement mode MOSHEMTs." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2104/.
Повний текст джерелаАнотація:
This thesis describes a new gallium nitride (GaN) based transistor technology for electronic switching applications. Conventional GaN based transistors are of the high electron mobility transistor (HEMT) type and are depletion mode devices. These are not suitable for switching applications since an extra DC supply is required to bias the device in the cut-off (off-state) region and the devices are not fail-safe, i.e. incase of malfunction a short-circuit can exist between the main DC supply and ground. Enhancement mode (E-Mode) or normally-off devices can overcome these limitations and if realized in the GaN material system would benefit from the good material properties that support large breakdown voltages and low On-resistances. Fabrication of high performace E-mode GaN devices with low On-resistance and high breakdown voltage still remains a big challenge to date. In this thesis a new method for realizing enhancement mode aluminium gallium nitride - gallium nitride (AlGaN/GaN) devices using a localized gate-foot oxidation has been described. Thermal oxidation of the AlGaN barrier layer converts the top surface/part of this layer into aluminium oxide (Al2 O3 ) and gallium oxide (Ga2O3 ), which serve as a good gate dielectric and improve the gate leakage current by several orders of magnitude compared to a Schottky gate. The oxidation process leaves a thinner AlGaN barrier which can result in normally o§ operation. Without special precaution, however, the oxidation of the AlGaN barrier is not uniform from the top but occurs at higher rates at the defect/dislocation sites. This makes it impossible to control the barrier thickness and so rendering the barrier useless. To avoid the problem of non-uniform oxidation, a thin layer of aluminum is first deposited on the barrier layer and oxidized to form aluminium oxide on top. This additional oxide layer seems to ensure uniform oxidation of the AlGaN barrier layer underneath on subsequent further oxidation. Results of the fabricated 2 um x 100 um AlGaN/GaN MOS-HEMTs with a partially oxidized barrier layer showed a threshold voltage of -0.5 V (compared to -3 V for a Schottky devive fabricated on the same epilayer structure) and a maximum drain current of 800mA/mm at high gate bias of 5 V with very little current compression. The peak extrinsic transconductance of the device is 160 mS/mm at a drain-source voltage of 10 V with a very low specific On-resistance of 9:8 ohm.mm2 and an off-state breakdown voltage higher than 42 V. Capacitance-Voltage (C-V) measurements of Al2O3 /AlGaN /GaN circular test metal-oxide-semiconductor structures were observed and measured. They exhibit no hysteresis, indicating the good quality of the thermally grown aluminium oxide for realizing AlGaN/GaN based E-Mode devices for high frequency and high power applications.
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Espinosa, Gútiez Silvia. "Theoretical explanations of I-mode impurity removal and H-mode poloidal pedestal asymmetries." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/119102.
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Thesis: Sc. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018.<br>Cataloged from PDF version of thesis. "February 2018."<br>Includes bibliographical references (pages 203-214).<br>Using high-z wall materials switches the fusion challenge from heat load handling to removing impurities. I propose the first method of measuring the radial impurity flux from currently available diagnostics. It provides a means of solving the impurity accumulation problem while providing free fueling for optimum tokamak performance. High confinement mode operation was discovered 35 years ago to almost quadruple fusion power, and later explained by turbulence reduction by sheared flows. Less than a decade ago, improved mode operation was discovered to have the same desirable property, while removing impurities and providing fueling. Thanks to the impurity radial particle flux measuring technique developed, I explain the outward radial impurity flux without invoking a (sometimes undetected) turbulent mode. This theory is supported by the observed E x B flow shear, which also explains the desired energy confinement via turbulence reduction. Stronger impurity density in-out poloidal asymmetries than predicted by the most comprehensive neoclassical models have been measured in several tokamaks around the world during the last decade, calling into question the reduction of turbulence by sheared radial electric fields in H-mode tokamak pedestals. However, these pioneering theories neglect the impurity diamagnetic drift, or fail to retain it self-consistently as proven in this thesis, while recent measurements indicate that it can be of the same order as the ExB drift. I have developed the first self-consistent theoretical model retaining the impurity diamagnetic flow and the two-dimensional features it implies due to its associated non-negligible radial flow divergence. It successfully explains collisionally the experimental impurity density, temperature and radial electric field in-out asymmetries; thus making them consistent with H-mode pedestal turbulence reduction.<br>by Silvia Espinosa Gútiez.<br>Sc. D.
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Niu, Li. "Studies of imbalance difference theory in modeling conversion between differential mode and common mode signals." Thesis, Clemson University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3680740.
Повний текст джерелаАнотація:
<p> This dissertation describes three related studies regarding the imbalance difference theory in modeling the conversion between differential mode and common mode/antenna mode signals. The topics covered are: rigorous derivation of imbalance difference theory for modeling radiated emission problems, modeling the conversion between differential mode and common mode propagation in transmission lines, and modeling the loading impedance on differential mode signals due to radiated emissions. </p><p> The imbalance difference theory describes a method for calculating the coupling between differential mode signals and common mode signals due to changes in electrical balance on a transmission line. It provides both physical insight and a simple technique for modeling the conversions between the two modes. </p><p> The first chapter presents a rigorous derivation of imbalance difference theory for modeling radiated emission problems. Although the theory has been successfully used to model a wide variety of important EMC problems over the past, it has not been rigorously derived. The derivation carefully defines the important quantities and demonstrates that imbalance difference calculations are exact provided that the differential-mode propagation is TEM and the current division factor, h, represents the actual ratio of currents on the two transmission line conductors excited by a common-mode source. This chapter also discusses the acquisition of the current division factor from 2D calculations of the cross-section of the transmission line. </p><p> The second chapter provides a rigorous development of the imbalance difference theory for three-conductor transmission lines where both the differential mode and common mode exhibit TEM propagation. It also derives expressions for the mode conversion impedances, which account for the energy converted from one mode to the other. They are essential for modeling the conversion between the two modes when they are strongly coupled. </p><p> The third chapter introduces conversion impedance to the existing imbalance difference theory model for modeling radiated emission problems, so that when the coupling between differential mode and antenna mode are strong, the imbalance difference theory can more accurately estimate the antenna mode current. </p><p> All three papers are about confirming, enriching and expanding the imbalance difference theory. The first chapter focuses on the rigorous derivation of theory for its most common application, radiated emission problems. The second chapter expands the theory to multi-conductor transmission line structure when the two modes are strongly coupled. The last chapter introduces conversion impedance to the theory in modeling radiated emission problems and improves the accuracy of the model at resonant frequencies. </p>
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El-Rifai, Khalid 1979. "Control of AFMs in contact mode." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17597.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.<br>Includes bibliographical references (leaves 71-74).<br>The Atomic Force Microscope (AFM) is a high precision surface characterization tool commonly used in Nano-technology, Bio-technology, semiconductors, MEMS, and life sciences' applications. As most versatile systems, AFM offers little guarantees on achieving repeatable satisfactory operation. This is the case as AFMs are not used to perform a single predictable task. AFM systems are feedback regulators, which rely on photodiode detector (PSD) sensing and piezoelectric actuation. The change in probe-surface contact is a disturbance created by scanning across a surface. This disturbance is to be rejected to maintain probe-surface contact and thus allow proper surface characterization. AFM feedback systems are not only required to maintain a nominal PSD output but also guarantee that the control signal used is representative of the rejected disturbance. This is due to the fact that the image of the scanned surface is created from this control voltage. These characteristics impose severe limitations on the system's operation bandwidth, repeatability, and precision. In this effort, the key characteristics and limitations of AFM operation are analyzed. Challenges due to surface variations, plant dynamics, and contact nonlinearity are presented. The closed loop response of AFM systems in single actuator as well as in dual actuator configurations is evaluated. The emphasis is on the underlying structure corresponding to each configuration and not on a particular system tuning. In this regard, the bounds on achievable performance in each configuration are contrasted for operation within the system's overall objectives.<br>by Khalid El-Rifai.<br>S.M.
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Raghavachary, Sathyanarayanan. "Combined mode I- mode III fracture toughness of a super clean rotor steel and a 0.29C, 0.83Cu steel /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487594970653911.
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Jiang, Jingwen. "Vector mode analysis of dispersion-shifted single-mode triangular-index fibers with a trench." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59953.
Повний текст джерелаАнотація:
A vector mode analysis of dispersion-shifted-mode triangular-index fibers with a trench is presented. The aspects considered are the total dispersion, splice losses and bending loss of such fibers as a function of the trench width and location, wavelength fluctuations, index difference, as well as core radius change. The presence of a trench has pronounced effects on the performance of these fibers, yielding combined advantages of dispersion-shifted and dispersion-flattened fibers, and also improves the splice loss and bending loss characteristics. Some fiber characteristics due to the presence of a trench found in this study are interesting and have not been noted previously. As for the fabrication aspect, the effects of the parameter variations on the fiber performance are examined in detail.<br>Unlike other authors' results obtained using the scalar modal fields, our formulas here derived from the vector modal fields facilitate the study of the polarization dependence of the splice and bending losses. For weakly guiding fibers with a small index gradient, the polarization dependence becomes negligible.
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Schroth, James Gregory. "Combined mode I - mode III fracture toughness of a high-strength low-alloy steel /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487260859496482.
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Peregrym, Denis. "An investigation of shallow water mode coupling effects during single mode transmission." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/39158.
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Thesis (M.S.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 1994.<br>Includes bibliographical references (p. 57-58).<br>by Denis Peregrym.<br>M.S.
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Mihoubi, Zakaria. "Mode-locked surface emitting semiconductor lasers." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/72372/.
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Optically-Pumped Vertical External Cavity Surface Emitting Lasers (OP-VECSELs) arc novel semiconductor-based lasers that have many advantages over other lasers in terms of the power scalability, good beam quality, compactness and low cost they can offer. They can be passively mode-locked with a Semiconductor Saturable Absorber Mirror (SESAM) to produce transformnm-limnited sub-300 fs pulses directly from the laser cavity with high repetition rates. This thesis describes an experimental and theoretical investigation of OP-VECSELs. A full characterization is done on a VECSEL sample to understand time physics behind its operation iii the Continuous Wave (CW) mode and in the mode—locked mode. Then. a numerical model that, for the first time, shows the role of the Optical Stark Effect (OSE) in shaping the mode-locked pulses in the approach to steady state is introduced. TIme model results are broadly consistent with observed behavior of our rriode-locked VECSELs. Here, I also report the first coherent generation and detection of terahertz radiation using all-semiconductor components. Radiation with a bandwidth of 0.8 THz has been generated using sub-500 fs pulses with an average power of 20 mW from a mode-locked VECSEL which contains InGaAs quantum wells arid an LT-GaAs/InGaAs emitter/receiver antenna in a Terahertz Time Domain Spectrometer (THz-TDS) setup. The first mode locked OP-VECSEL at 830 rim is reported here. The combination of a GaAs quantumrm well—based gain sample and SESAI\I yielded an output with an average power of 5 mW and 15 ps-long pulses at a repetition rate of 1.9 GHz. A pumping module used to drive the laser was built for this purpose by combining the output of two commercial 665 rim diode lasers.
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Melnick, Joshua Robert. "Aluminum Nitride Countour Mode Resonators." Thesis, Rochester Institute of Technology, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1591270.
Повний текст джерелаАнотація:
<p> Resonators are a major component in RF electronic products. They are used in a host of ways to filter radio signals. Modern and Future RF communications have placed high demands on the industry; requiring low power usage, wide array of applications and resistance to noise. </p><p> In this thesis, a discussion of the motivation for RF MEMS filters and basic theory is given with an explanation of the concepts of Q factor, piezoelectricity, acoustics theory, the major types of resonators (SAW, BAW, CMR or LAMB), apodization theory and techniques as well as design, simulation of CMR and BAW devices, testing and process development of aluminum nitride by RF reactive sputtering at RIT. </p><p> Finite element analysis was performed on a number of factors of aluminum nitride contour mode resonators (CMR) from piezoelectric film thickness, to electrode pitch, electrode thickness and electrode configuration; to understand the effects. First order and second order vibration modes were seen including symmetric <i>S</i><sub>0</sub>, <i>S</i><sub>1</sub> and antisymmetric <i>A</i><sub>0</sub>, <i>A</i><sub>1</sub> resonant modes in the pizeoacoustic devices and higher. A series of time dependent video simulations of SAW, BAW and LAMB wave resonators were also performed, perhaps the first of their kind. </p><p> The RF reactive sputtering deposition for aluminum nitride was developed at RIT by a fractional factorial experiment with the factors being RF power, nitrogen to argon flow rate ratios, changing the distance of the wafer to the platen from 5 to 4 cm, use of a aluminum, molybdenum or virgin silicon seed layer and chamber pressure. In nearly all cases it was found that an RF power of 1000W is the most important factor contributing to the ⟨002⟩ orientation. The decreasing of the target distance may inhibit a reaction mechanisms in the plasma resulting in a more amorphous deposition. It may be due to the increase in temperature resulting from the higher RF power that promotes the growth of ⟨002⟩ oriented aluminum nitride. A molybdenum seed layer tends to have a stronger ⟨002⟩ peak relative to aluminum and a chamber pressure of 3mT was found to exhibit a deposition that most favors the ⟨002⟩ oriented aluminum nitride. </p><p> It was found that molybdenum is not consumed in a wet etch of KOH. Molybdenum is oxidized during photo resist ashing. The Contact Vias were necessarily over retched in order to ensure complete removal of Al-N over the Bottom Electrode. </p><p> C-V measurements were done on the aluminum nitride to determine its quality, the measured extensional piezoelectric coefficient <i>d</i><sub> 33</sub> is -0.000108716 <i>nm/V</i>, which is -0.108716 <i> pm/V</i> lower than 8pm/V typically reported. The lower piezo electric coefficient measured as compared with typical values, may be due to low film density a result of the high power used in the RF reactive sputtering that was used to heat the platen to a high enough temperature to promote the?002?oriented growth of AlN. </p><p> A series of iterations were designed and S11 frequency response measured. The electrode overlap from 25 to 50 to 75μm, it does not appear to have an effect on the resonant frequency, but does increase the amplitude of the response at that die's given frequency. Increasing the anchor width from 5μm to 10μm to 20μm lowers the relative amplitude of the response therefore lowering the Q of the resonator. It may be that the increasingly wide anchor, increases the mechanical resistances within the device and thereby lowers the Q factor of the resonator. Increasing the number of electrodes increases the relative amplitude of the response. Increasing pitch from 5μm to 6μm seems to have a small effect on the resonant frequency of the devices, shifting them from 4.57 to 4.59 GHz. A quality factor was measured, with an anchor width of 5μm, pitch of 5μm, 24 electrodes and an electrode overlap of 75μm had a measured Q value of 98.8.</p>
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Rajagopal, Gopalkrishna. "Optimal mode localization in disordered, periodic structures." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36005.
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Lisboa, Osni. "Two-mode optical fiber sensors for concrete structures." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37692.
Повний текст джерелаАнотація:
An optical fiber bending sensor and a quasi-distributed optical fiber sensor, where isolated sensing regions can be designed to sense strain, bending, etc., are developed as sensor candidates for smart civil engineering materials and structures. Both sensors use two-mode fibers. With the same two-mode fibers, acousto-optic frequency shifters are developed as the main components to accomplish these sensors. Elliptical-core two-mode fibers are chosen to improve the stability and sensitivity of the sensors. A perturbation theory approach is used to investigate the sensing mechanism of the bending sensor. A system to simultaneously measure all the sensing regions of the quasi-distributed sensor is also demonstrated.<br>Because conventional polymer-based fiber coatings often do not adequately protect the fibers themselves nor the fiber sensors during their installations into the concrete or metallic structures, two different processing methods are introduced. They provide superior protection to the fibers and sensors for the installation. The first method is to coat the fiber with a thick metallic layer (aluminum or tin) using a continuous casting process. Coating thicknesses of 0.5 to 1.5 mm and length up to 3 m are presented. Using a birefrigent fiber coated with such a thick metallic layer, a sensor for dynamic load or pressure was also implemented. The second method uses the thermal spray technology for directly embedding optical fibers and sensors into or surface attaching them onto concrete and metallic plates.<br>Finally, a sol-gel based process is used for coating optical fibers with piezoelectric lead zirconate titanate films. Coating thicknesses up to 120 mum have been achieved. Piezoelectric-coated fibers can be used as in-line optical fiber signal processing components for various fiber sensors relevant for smart structure applications. As an example, an in-line fiber phase modulator is also developed. Theoretical analysis is carried out based on an axial-symmetrical multi-layer structure operated in a radially resonant configuration. The phase modulation induced by radial acoustic modes excited on optical fibers, with a coating thickness of 120 mum and length of 5.8 cm, ranges from 100 kHz to 25 MHz.
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Minelly, John D. "Field access techniques for single-mode fibres." Thesis, University of Southampton, 1989. https://eprints.soton.ac.uk/396389/.
Повний текст джерелаАнотація:
This thesis reports on the exploitation of the beam-expanding properties of tapers in single-mode fibres and on the development of a new and versatile approach to fibre polishing. A theoretical study of the fused-taper coupler explains the differences in coupling and polarisation characteristics of strongly-fused and weakly-fused couplers in terms of the difference in tunnelling capability of TE and TM polarised waves. A study of the application of glass capillary overjackets in the production of stable taper-based devices resulted in the realisation of the first practical tapered beam-expander for single-mode fibres and a class of couplers in which cut-off of the LP11 mode of the composite waveguide comprising the coupler waist induced a flattening of the wavelength characteristics of splitting ratio. The operational principles and fabrication of a single-mode fibre beam-splitter is described. This new device which operates as a LP01 mode transformer exhibits wavelength independent 50:50 power splitting. A new polishing technique in which the optical fibre is polished on a motor driven polishing wheel is reported. The polishing can be completed in less than ten minutes and polished lengths of up to 40mm are easily attainable. The technique was successfully applied to the construction of spectrally broad fibre polarisers.
25
Hill, Misha K. (Misha Kim) 1975. "A model of a fundamental-mode Lorentz force actuated flexural plate wave resonator." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80071.
Повний текст джерелаАнотація:
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.<br>Includes bibliographical references (leaves 37-38).<br>by Misha K. Hill.<br>M.Eng.
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Bondarenko, Maksym. "Master-mode set of turbulent 3D channel flow." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/66080/.
Повний текст джерелаАнотація:
Turbulent flow fields can be expanded into a series in a set of basic functions. The terms of such series are often called modes. A master-mode-set is a subset of these modes, the time-history of which uniquely determines the time history of the entire turbulent flow provided that this flow is developed. In the present work the existence of the master-mode-set is demonstrated numerically for turbulent channel flow. The minimal size of a master-mode set and the rate of the process of the recovery of the entire flow from the master-mode set history are estimated. The velocity field corresponding to the minimal master-mode set is found to be a good approximation for mean velocity in the entire flow field. Mean characteristics involving velocity derivatives deviate in a very close vicinity to the wall, while master-mode two-point correlations exhibit unrealistic oscillations. This can be improved by using a larger than minimal master-mode set. The near-wall streaks are found to be contained in the velocity field corresponding to the minimal master-mode set, and the same is true at least for the large-scale part of the longitudinal vorticity structure. A database containing the time history of a master-mode set is demonstrated to be an ecient tool for investigating rare events in turbulent flows. In particuiii lar, a travelling-wave-like object was identified on the basis of the analysis of the database. Two master-mode-set databases of the time history of a turbulent channel flow are made available online at http://www.dnsdata.afm.ses.soton.ac.uk/. The services provided include the facility for the code uploaded by a user to be run on the server with an access to the data.
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Alsumiri, Mohammed. "Sliding mode control of renewable energy generation systems." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2014521/.
Повний текст джерелаАнотація:
As a result of decades of research and innovation in the renewable energy industry, advanced technologies have been developed for both wind and solar energy conversion systems. However, there are still some aspects of the systems that need to be enhanced to enable maximum and cost effective energy conversion. Wind is emerging as an alternative source for electrical power generation. Small-scale wind power generation system applications are becoming widespread because of rising fuel prices and the demand for reducing carbon emission. For such applications, vertical axis wind turbines (VAWT) appeal due to their ability to capture wind from different directions and their low noise-pollution. Wind energy and its conversion system are studied first. The need for advanced maximum power point tracking (MPPT) controllers is discussed in literature focusing on widely implemented algorithms. Sliding mode control theory has been studied and implemented in controlling wind power generation system (WPGS). The dynamic performance of the WPGS using sliding mode control has shown improved dynamic performance, overshoot errors eliminations and higher energy conversion ratios than the widely used proportional integral (PI) control. A new approach in WPGS control strategy by development of a novel soft control strategy based on the mathematical residue theorem has been introduced. The idea of using the residue theorem is to set a soft dynamic boundary for controlled variables around a reference point, so that controlled variables lie on a point inside this boundary. The stability of the system has been ensured by following the Forward Euler method. The developed control strategy has been implemented in different control techniques of a small-scale permanent magnet synchronous generator (PMSG) based WPGS. The introduction of the new control approach based on residue theorem has further improved the energy conversion ratio by 2:5%. Moreover, a wind speed estimation algorithm is provided and implemented to the proposed controllers to overcome the wind speed measurements issues, i.e. cost and accuracy. Furthermore, an improved back-EMF observer based on residual theorem has been designed to estimate the mechanical rotor speed of the PMSG using the stator current and voltage measurements. The improved back-EMF observer has overcome the well-known limitation of the classical back-EMF at low speed observation. In addition, the wind speed has been estimated using the calculated power obtained from the PMSG voltage and current measurements as well as the estimated rotor speed. Based on the wind and rotor speeds, the tip speed ratio (TSR) is calculated and controlled to its optimal value. A MPPT controller has been developed for photovoltaic power generation systems based on a sliding mode control scheme in stand-alone configuration. The developed controller provides a solution to atmospheric conditions measurement issues and it enhances the efficiency of the PV power system. In addition, the developed controller overcomes the power oscillation around the operating point which appears in most implemented MPPT techniques. The MPPT operation is achieved by regulating the input voltage of the PV system using DC-DC boost converter topology. Moreover, a single-ended primary inductor converter (SEPIC) topology has been employed in PV power systems. The restrictions on the application of SEPIC have been solved based on sliding mode control. The efficiency of the PV system has significantly improved.
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Lounsbury, William P. "Nonlinear Multi-Mode Robust Control For Small Telescopes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1417781523.
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Vourakis, Michail. "Duct mode evaluation for traction motor outlets." Thesis, KTH, Marcus Wallenberg Laboratoriet MWL, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-290040.
Повний текст джерелаАнотація:
This study investigates duct mode propagation at outlets of traction motors, featuring an open fan air-cooled architecture. Both acoustical measurements and simulations are employed. Measurements are performed for two duct outlet geometries, a radial and a non-radial outlet, both combined with an equidistant and a non-equidistant blade fan. Specifically, six microphones are flush-mounted circumferentially at the entrance of each duct outlet (downstream of fan blade). Additionally, five microphones are placed circumferentially above the exit of each duct outlet. Measurements from both positions are utilized for circumferential mode reconstruction (CMR) of the acoustic near field. The radiated acoustic power of detected modes, from CMR analysis, is used for performance evaluation of different fan-duct outlet combinations. CMR analysis from measurements at the entrance of duct outlets, demonstrate that the non-radial duct outlet combined with an equidistant blade fan outperforms the rest combinations. The CMR analysis from measurements above the exit of duct outlets, reflects the effect of fan rotational speed. At low fan rotational speeds, the combination of the radial duct with equidistant blade fan is favorable. At high fan speeds, both outlets perform similarly with either duct outlet. The CMR analysis performed for all fan-duct outlet combinations employed, does not indicate significant acoustic coupling phenomena. Furthermore, acoustic simulation is implemented with the finite element software for acoustics, ACTRAN. The employed methodology is developed by MSC Software Corporation. Circumferential modes of different order, are injected at the entrance of the duct outlet geometry. The far field acoustic radiation, for each injected mode is calculated. A set of fifty variants of the baseline duct outlet is evaluated, with respect to major geometrical characteristics. The results accrued through finite element analysis confirm the validity of the employed methodology, on a qualitative basis. Overall, this work proposes experimental and computational methods, along with recommended practices for the evaluation of acoustic coupling in fan-duct outlet configurations.
30
Weng, Yi. "Spatial Division Multiplexed Transmission and Sensing in Few-Mode Fibers." Thesis, University of Louisiana at Lafayette, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10261316.
Повний текст джерелаАнотація:
<p> Space division multiplexing (SDM) has become a promising approach in the telecom industry to reduce the cost-per-bit of optical fiber transmission and to resolve the approaching bandwidth crunch. Meanwhile, intermodal nonlinear effects in few-mode fibers (FMF) potentially provide some novel applications along with sophisticated optical signal processing functionality. Recently, such spatial channels and modes have been applied in optical sensing applications with the returned echo analyzed for the collection of essential environmental information. The key advantages of implementing SDM techniques in optical measurement systems include the multi-parameter discriminative capability and accuracy improvement. In this dissertation, we conduct theoretical and experimental study on the SDM systems using FMFs for both optical transmission and sensing applications. </p><p> We first investigate a fast-convergence single-stage adaptive frequency-domain recursive-least-square algorithm for simultaneously compensating chromatic dispersion and differential mode group delay in a 224 Gbit/s six-mode polarization-division multiplexed 16 quadrature amplitude modulation FMF transmission system, which increases convergence speed by 53.7% over conventional frequency-domain least-mean square method, with 11% hardware complexity reduction over two-stage recursive-least square approach. </p><p> We then present an ultrafast all-optical simultaneous wavelength and mode conversion scheme based on intermodal four-wave mixing, with the capability of switching polarization and mode degeneracy orientation in FMFs. The relation among the conversion efficiency, pump power and phase matching conditions is investigated in theory analysis and simulation. The cross-polarization modulation and cross-mode modulation can be achieved, by in the best case up to 50% conversion efficiency. </p><p> Finally, a single-end FMF-based distributed sensing system that supports simultaneous temperature and strain monitoring is demonstrated via Brillouin optical time-domain reflectometry and heterodyne detection. Theoretical analysis and experimental assessment of multi-parameter discriminative measurement applied to the distributed sensors are presented, which endows with good sensitivity characteristics and can prevent catastrophic failure in many applications.</p><p>
31
Phua, Poh-Boon 1970. "Deterministic approach to polarization mode dispersion." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/26724.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Includes bibliographical references (leaves 209-224).<br>by Poh-Boon Phua.<br>Ph.D.
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Ng, Cheng Man. "Electroencephalogram analysis based on empirical mode decomposition." Thesis, University of Macau, 2011. http://umaclib3.umac.mo/record=b2493507.
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Hugo, Etienne Martin. "Automated design of multi-mode fuzzy controllers." Thesis, Stellenbosch : Stellenbosch University, 2000. http://hdl.handle.net/10019.1/51631.
Повний текст джерелаАнотація:
Dissertation (PhD)--University of Stellenbosch, 2000.<br>ENGLISH ABSTRACT: A standard fuzzy logic controller is not robust enough to guarantee consistent closed-loop
performance for highly non-linear plants. A finely tuned closed-loop response loses relevance as
the system dynamics change with operating conditions. The self-adaptive fuzzy logic controller can
track changes in the system parameters and modify the controller parameters accordingly. In most
cases, self-adaptive fuzzy logic controllers are complex and rely on some form of mathematical
plant model.
The multi-mode fuzzy logic controller extends the working range of a standard fuzzy logic
controller by incorporating knowledge of the non-linear system dynamics into the control rule-base.
The complexity of the controller and difficulty in finding control rules have limited the application
of multi-mode fuzzy logic controllers.
An automated design algorithm is proposed for the design of a multi-mode control rule-base using
qualitative plant knowledge. The design algorithm is cost function-based. The closed-loop
response, local to a domain of the non-linear state space, can be tuned by manipulation of the cost
function weights. Global closed-loop response tuning can be done by manipulation of the controller
input gains. Alternatively, a self-learning or self-adaptive algorithm can be used in a model
reference adaptive control architecture to optimise the control rule-base. Control rules responsible
for unacceptable closed-loop performance are identified and their consequences modified.
The validity of the proposed design method is evaluated in five case studies. The case studies
illustrate the advantages of the multi-mode fuzzy logic controller. The results indicate that the
proposed self-adaptive algorithm can be used to optimise a rule-base given a required closed-loop
specification. If the system does not conform to the model reference adaptive architecture then the
intuitive nature of the cost function based design algorithm proves to be an effective method for
rule-base tuning.<br>AFRIKAANSE OPSOMMING: Standaard wasige logika beheerders is nie noodwendig robuust genoeg om goeie geslote lus
werkverrigting vir hoogs nie-liniere aanlegte te waarborg nie. In Perfek ge-optimeerde beheerder se
geslote lus werkverrigting mag verswak indien die aanleg-parameters weens bedryfstoestande
verander. Self-aanpassende beheerders kan die verandering in die aanleg-parameters volg en die
beheerder dienooreenkomstig optimeer. As In reël is In self-aanpassende beheerder kompleks en
afhanklik van In wiskundige model van die aanleg.
Die multi-modus wasige logika beheerder vergroot die werksbereik van die standaard wasige logika
beheerder deur kennis aangaande die stelsel se bedryfstoestand en stelselparameters in die reël-basis
in te bou. Die aanwending van die multi-modus beheerder word tans beperk deur die struktuur
kompleksiteit en moeilike optimering van die reël-basis.
In Ge-outomatiseerde multi-modus reël-basis ontwerps-algoritme wat gebruik maak van
kwalitatiewe kennis van die aanleg en In kostefunksie word in hierdie proefskrif voorgestel. Die
geslote lus gedrag beperk tot In gebied in die toestands-ruimte kan ge-optimeer word deur die
kostefunksie gewigte te manipuleer. Die globale werkverrigting kan ge-optimeer word met die
beheerder intree aanwinste. In Self-aanpassende algoritme in In model-verwysings aanpassende
argitektuur word as altematieftot reël-basis optimering voorgestel. Reëls verantwoordelik vir swak
werkverrigting word ge-identifiseer en verbeter deur modifikasie van die reëls se gevolgtrekkings.
Die voorgestelde ontwerps-metode word deur middel van vyf gevallestudies ondersoek. Die studies
dui die voordele van die multi-modus struktuur aan. Die self-aanpassende argitektuur is In kragtige
hulpbron om In reël-basis te optimeer vir In gegewe geslote lus spesifikasie. Hierdie proefskrif toon
aan dat indien die stelsel nie aan die vereistes van In model verwysingstelsel voldoen nie, is die
kostefunksie benadering tot reël-basis ontwerp In aantreklike en intuïtief verstaanbare opsie om die
reël-basis te optimeer.
34
Chang, Hao-Chi. "Sliding mode control design based on block control principle /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486461246815228.
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Yao, Wang. "4?50G bps PAM4 System over 60km of Single-Mode Fiber." Thesis, University of Louisiana at Lafayette, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10277257.
Повний текст джерелаАнотація:
<p>In recent years, the growth demand of information transmission has promoted the development of communication technology. Many modulation methods are used in many fields, such as QPSK and OFDM, which are used in long-distance communication. In this thesis, I discussed the PAM-4, which can be used in inter-data center (<80km) links due to its better performance and lower cost. Then I tested one channel 4?50Gbps PAM-4 system and eight channels 4?50Gbps PAM-4 system with varying degrees of gain of optical amplifier and length of DCF. Finally, I discussed the performance of the two designs and figured out the factors that affect the transmission system.
36
Malhotra, Namrata. "International entry mode decisions of professional service firms, the case of engineering consulting." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0025/NQ46881.pdf.
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Jiang, Xin. "Engineering of novel single- and multi-mode infrared optical fibres for device applications." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.530831.
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Ellison, Rachel (Rachel M. ). "Mode II fracture mechanics of moso bamboo for application in novel engineering materials." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98653.
Повний текст джерелаАнотація:
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 32-34).<br>Bamboo has been used as a structural material for thousands of years. Recently there has been increasing interest in its use as a modem construction material. In this study, as part of a larger project to characterize the mechanical properties of Moso bamboo for application in the production of structural bamboo products (SBP), end-notched flexure (ENF) tests and three-point bending tests were performed to obtain the mode II interlaminar toughness (GIIc) and longitudinal Young's modulus (EL). It was found that known values for GIIc, include the pith (innermost layer) and cortex (outermost layer) of the bamboo culm in their calculations. The resulting value is, to a statistically significant degree (t = 5.0 x 10⁶), higher than that with the pith and cortex removed, as they typically will be in processing SBP. A new value, GIIc, = 630 +/- 155 J/m² , was established for specimens lacking the pith and cortex. Although no correlation was found between GIIc, and specimen density, it is suspected that a relationship does exist, and recommendations for further investigation are given.<br>by Rachel Ellison.<br>S.B.
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Pusino, Vincenzo. "High power, high frequency mode-locked semiconductor lasers." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5174/.
Повний текст джерелаАнотація:
Integrated mode-locked laser diodes are effective sources of periodic sequences of optical pulses, which have always been of great interest for a range of spectroscopy, imaging and optical communications applications. However, some disadvantages prevent their widespread use, such as the restricted tuning of their repetition rate and their output power levels never exceeding a few mW. This thesis reports on the work done to address those limitations. Two main findings are presented, the first being the generation of ultra-high repetition rate optical signals through external injection of two continuous wave signals. This mechanism is much simpler than other techniques previously proposed to increase the repetition rate of monolithic modelocked laser, and has proved successful in generating optical signals up to quasi-THz. It is based on injection of two continuous wave signals whose spacing is an integer multiple of the pulsed cavity free spectral range and whose injection wavelengths coincide with two of the monolithic laser modes. This technique allows discrete tunability of the repetition rate with a step equal to the injected cavity free spectral range, and the injected laser has been shown to lock up to a repetition rate of 936 GHz, corresponding to 26 times that of the free-running semiconductor laser (36 GHz). The presented scheme is suitable for integration, opening the way for a successful on-chip generation of ultra-high repetition rate optical signals exploiting coupled cavity phenomena. The second main finding of this thesis regards the changes induced on the pulsed operation of monolithic passively mode-locked lasers by a blue bandgap detuning applied to their saturable absorber. The quantum well intermixing technique has been used for attaining an area-selective bandgap shift on the fabricated chip, being fully postgrowth. The lasers with a detuned absorber were found to have an extended range of gain section currents and absorber voltages in which stable mode-locking operation took place. Furthermore, a comparison of mode-locked devices fabricated on the same chip, respectively with and without a bandgap detuned absorber, showed that the emitted pulses had greater peak power and were less affected by optical chirp when the bandgap of the absorbing section was shifted. A new intermixing technique has also been developed as part of this work to address some inconsistencies of the pre-existing one; the newly introduced approach has been found to provide better spatial resolution and a more precise control of the attained bandgap shift.
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Baggett, Joanne Claire. "Bending losses in large mode area holey fibres." Thesis, University of Southampton, 2004. https://eprints.soton.ac.uk/65504/.
Повний текст джерелаАнотація:
The aims of the study presented here are to develop methods of accurately predicting bend loss in arbitrary index fibres, to use these techniques to explore the potential offered by holey fibres in the large-mode-area, single-mode regime, and to place their performance in context against conventional step-index fibres. In the study presented here, numerical and experimental techniques have been developed that are capable of accurately evaluating the bending losses, the fundamental mode area and the modedness of holey fibres. Note that these techniques are also applicable to conventional solid fibres, which is essential in order to form accurate comparisons. These techniques are applied here to the problem of understanding the bending losses of large-mode-area holey fibres and are successfully used to assess the practical limits that bend loss imposes on large-mode-area holey fibres designed for single-mode operation. These properties are also evaluated for a range of equivalent conventional fibres, the results of which are used to benchmark the potential of holey fibre technology in this regime. The results of this study reveal that the performance of large-mode-area holey and conventional fibres at any given wavelength are similar, and that holey fibres offer advantages for broadband applications. Methods of improving bend loss in holey fibres are also investigated, and it is shown that more complex hole arrangements can be used to improve bend loss in a holey fibre.
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Matsas, Victor Jacob. "Passively and actively mode-locked fibre laser devices." Thesis, University of Southampton, 1993. https://eprints.soton.ac.uk/399129/.
Повний текст джерелаАнотація:
This thesis examines a number of passively and actively mode-locked fibre laser devices. The passive systems that are described incorporate the fast, saturable absorber-like action of a Kerr-type nonlinear optical switch to provide the passive mode-locking mechanism. Two such all-fibre nonlinear switches are described and analysed, namely the nonlinear optical loop mirror and the nonlinear optical gate. The mode-locked fibre laser systems based on the performance of these devices, informally known as the "Figure-of-eight" laser and the "nonlinear polarisation evolution" laser are described and characterised with respect to their modes of operation, self-starting thresholds and resonator parameters. These lasers provide a unique and convenient method for generating fundamental solitons 0.1-5 ps long. A theoretical analysis shows that the resonant loss mechanism, which is responsible for the formation of sidebands in the optical spectrum of the solitons produced by these systems, imposes a limit on the soliton pulsewidth that can be derived from a given cavity. This limit has a square-root dependence on the product of the intracavity dispersion and resonator length. The actively mode-locked fibre laser configurations that are described are 100-1000m long and form part of an investigation into their use for distributed temperature sensing. The sensing method is based on the production of spontaneous Raman backscattered radiation from the mode-locked pulse circulating within the cavity. An extended version of the Kuizenga-Siegman (K-S) analysis of active mode-locking has shown that in systems with large dispersion-length-(bandwidth)2 products there is a significant increase in the pulse durations that can be achieved. However, the accuracy of the K-S theory is also shown to be questionable when used for cavity lengths >50m. Optical time-domain reflectometry measurements on a 4km mode-locked ring laser provided strong supporting evidence for the successful use of long fibre lasers for distributed temperature sensing.
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Deng, Wenqi. "Cantilever dynamic analysis in tapping mode atomic force microscopy." Thesis, Liverpool John Moores University, 2015. http://researchonline.ljmu.ac.uk/4349/.
Повний текст джерелаАнотація:
Tapping mode atomic force microscopy (AFM) is becoming popular in the area of biology, as well as for polymer and semiconductor materials science. Unlike other AFM techniques, it only makes intermittent contact with the sample, which largely reduces any potential surface damage to soft materials, like cells and polymer. Moreover, phase image can also be obtained from tapping mode AFM besides height and amplitude image. Phase images provide extra information on the test sample in comparison with height and amplitude images. Studies have been carried out to investigate the contributions to phase shifts in tapping mode AFM using point-mass model. Results showed that the phase shift is independent of the Young’s modulus of the material; the phase shift only changes when energy dissipation occurs, such as the case with adhesion hysteresis and viscosity. However, the simple point mass model can only study the first order vibration mode of the AFM cantilever. Moreover, it does not take into account geometrical effects of the tip and the cantilever. However, correct interpretation of phase images still poses a significant challenge to the AFM community. In this study, the cantilever’s dynamic behaviour in tapping mode AFM is studied through a three dimensional finite element method. A rectangular silicon cantilever with the dimensions 240 μm length, 30 μm width, 2.7 μm thick and with a silicon tip radius of 9nm, are used in the simulation. The cantilever dimensions are the same as those of the Olympus model AC240TS cantilevers used in AFM experiments. The material properties of the silicon cantilever as used in the simulation again match those of the real cantilevers and are defined as: Young’s modulus of 170 GPa and a Poisson’s ratio of 0.28. A piezo actuator is attached to the cantilever. A sinusoidal voltage is subsequently applied to the piezo actuator in order to vibrate the cantilever. The cantilever’s dynamic displacement responses are firstly obtained via simulation under different tip-sample separations and for different tip-sample interaction forces, such as elastic force, adhesion force, viscosity force and the van der Waals force, which correspond to the cantilever’s action upon various different representative computer-generated test samples. Simulated results show that the dynamic cantilever displacement response consists of three states: free vibration, a transition state and a stable state. Phase shift, transition time, stable amplitude and frequency changes are then analysed from the dynamic displacement responses that are obtained. The phase shift of free vibration is 90o. It is found that under pure repulsive force, the phase shifts are above 90o, while the phase shifts are below 90o under pure attractive force. Also, attractive forces have the ability to decrease the phase shifts. When different interaction forces are coupled together, depending on the strength of the attractive forces, the phase shifts may suddenly drop below 90o. Finally, experiments are carried out on a real AFM system to support the findings of the simulations. Olympus model AC240TS cantilever is used in the experiment, while polyurethane (PU), polyvinyl chloride (PVC) and parafilm are used as test sample. Phase shifts were recorded by changing the setpoint ratio (setpoint ratio = setpoint amplitude/free amplitude). The phase shifts were recorded from set-point amplitudes varying from 43.6nm to 4.36nm, which have the similar trend as simulation results.
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Saravanos, Constantine. "Operational window of single-mode optical fibers." Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10834.
Повний текст джерелаАнотація:
The purpose of this Ph.D. thesis is to define the design window of single-mode dispersion-unshifted fibers. This window, defined in the mode field diameter (MFD) and cutoff wavelength (lambda c) plot is determined by the fiber properties with regards to the chromatic dispersion, the bend loss sensitivity at 1550 nm and the modal noise penalty imposed on high speed operating systems. This has been achieved by developing numerical models used to analyze the properties of optical fibers. These models were used to calculate the propagation characteristics of optical fibers and from them their physical properties, such as the dispersion and bending loss of the fundamental mode. Similar programs, used in the calculations of the LP11 mode attenuation and bend performance, determined the fiber's modal noise sensitivity and from it the upper limit of cutoff wavelength.
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Ethier, Jonathan. "MIMO antenna design using characteristic mode concepts." Thesis, University of Ottawa (Canada), 2008. http://hdl.handle.net/10393/27683.
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In this thesis we show how characteristic mode (CM) theory can be used to in the design of the antennas with the low envelope correlation coefficients preferred for MIMO antennas. This is due to the fact that the radiated fields of CMs are orthogonal over the radiation sphere. We show how a handheld device structure can be excited at various points (which form the multi-antenna ports) to ensure that each port excites a set of CMs such that the mode indices in each set are different for each antenna. It is this important result which causes the natural orthogonality properties of the CMs to be transferred to the overall radiation patterns of the multiple antennas. The CM analysis we have performed includes the effects of structure losses; it appears to be the first time that the computation of such modes have been reported. A logical and satisfying methodology for MIMO antenna design is the result. The methodology is extended to include arbitrary MIMO scattering environments using polarization sensitive generalized characteristic modes, which is the first of its kind from both the theory and methodology perspective. This design approach for MIMO antennas is not restricted to handheld devices, and can be used in a variety of applications. Lastly we discuss the various port mode theories that yield far-field orthogonality for perfect scattering environments, the application of which has already been discussed in the literature. We show succinctly that physical port symmetry yields frequency insensitive modes, but very minor symmetry breaking yields very narrow low envelope correlation bandwidth, something that is not discussed in the literature, but discussed in detail in this thesis.
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Benyhesan, Mohammad Kassim. "Current-mode CMOS hybrid image sensor." Thesis, University of Missouri - Kansas City, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1540634.
Повний текст джерелаАнотація:
<p> Digital imaging is growing rapidly making Complimentary Metal-Oxide-Semi conductor (CMOS) image sensor-based cameras indispensable in many modern life devices like cell phones, surveillance devices, personal computers, and tablets. For various purposes wireless portable image systems are widely deployed in many indoor and outdoor places such as hospitals, urban areas, streets, highways, forests, mountains, and towers. However, the increased demand on high-resolution image sensors and improved processing features is expected to increase the power consumption of the CMOS sensor-based camera systems. Increased power consumption translates into a reduced battery life-time. The increased power consumption might not be a problem if there is access to a nearby charging station. On the other hand, the problem arises if the image sensor is located in widely spread areas, unfavorable to human intervention, and difficult to reach. Given the limitation of energy sources available for wireless CMOS image sensor, an energy harvesting technique presents a viable solution to extend the sensor life-time. Energy can be harvested from the sun light or the artificial light surrounding the sensor itself. </p><p> In this thesis, we propose a current-mode CMOS hybrid image sensor capable of energy harvesting and image capture. The proposed sensor is based on a hybrid pixel that can be programmed to perform the task of an image sensor and the task of a solar cell to harvest energy. The basic idea is to design a pixel that can be configured to exploit its internal photodiode to perform two functions: image sensing and energy harvesting. As a proof of concept a 40 × 40 array of hybrid pixels has been designed and fabricated in a standard 0.5 <i>µm</i> CMOS process. Measurement results show that up to 39 <i>µW</i> of power can be harvested from the array under 130 Klux condition with an energy efficiency of 220 nJ /pixel /frame. The proposed image sensor is a current-mode image sensor which has several advantages over the voltage-mode. The most important advantages of using current-mode technique are: reduced power consumption of the chip, ease of arithmetic operations implementation, simplification of the circuit design and hence reduced layout complexity.</p>
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Rourke, Anthony. "The dynamics of multi-mode vibratory rate sensors." Thesis, University of Nottingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269689.
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Dixit, Ravindra. "Sliding Mode Observation and Control for Semiactive Vehicle Suspensions." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20011116-144808.
Повний текст джерелаАнотація:
<p>Dixit, Ravindra Krishna. Sliding Mode Observation and Control for Semiactive Vehicle Suspen-sions.(Under the direction of Dr. Greg Buckner).This thesis investigates the application of robust, nonlinear observation and control strategies,namely sliding mode observation and control (SMOC), to semiactive vehicle suspensions using amodel reference approach. The vehicle suspension models include realistic nonlinearities in thespring and magnetorheological (MR) damper elements, and the nonlinear reference models incorpo-rateskyhook damping. Since full state measurement is difficult to achieve in practice, a sliding modeobserver (SMO) that requires only suspension deflection as a measured input is developed. The per-formanceand robustness of sliding mode control (SMC), SMO, and SMOC is demonstrated throughcomprehensive computer simulations and compared to popular alternatives. The results of thesesimulations reveal the benefits of sliding mode observation and control for improved ride quality,and should be directly transferable to commercial semiactive vehicle suspension implementations.<P>
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Spindler, Henry C. (Henry Carlton) 1970. "System identification and optimal control for mixed-mode cooling." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/30334.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.<br>"September 2004."<br>Includes bibliographical references (p. 285-294).<br>The majority of commercial buildings today are designed to be mechanically cooled. To make the task of air conditioning buildings simpler, and in some cases more energy efficient, windows are sealed shut, eliminating occupants' direct access to fresh air. Implementation of an alternative cooling strategy-mixed-mode cooling-is demonstrated in this thesis to yield substantial savings in cooling energy consumption in many U.S. locations. A mixed-mode cooling strategy is one that relies on several different means of delivering cooling to the occupied space. These different means, or modes, of cooling could include: different forms of natural ventilation through operable windows, ventilation assisted by low-power fans, and mechanical air conditioning. Three significant contributions are presented in this thesis. A flexible system identification framework was developed that is well-suited to accommodate the unique features of mixed-mode buildings. Further, the effectiveness of this framework was demonstrated on an actual multi- zone, mixed-mode building, with model prediction accuracy shown to exceed that published for other naturally ventilated or mixed-mode buildings, none of which exhibited the complexity of this building. Finally, an efficient algorithm was constructed to optimize control strategies over extended planning horizons using a model-based approach. The algorithm minimizes energy consumption subject to the constraint that indoor temperatures satisfy comfort requirements. The system identification framework was applied to another mixed-mode building, where it was found that the aspects integral to the modeling framework led to prediction improvements relative to a simple model.<br>(cont.) Lack of data regarding building apertures precluded the use of the model for control purposes. An additional contribution was the development of a procedure for extracting building time constants from experimental data in such a way that they are constrained to be physically meaningful.<br>by Henry C. Spindler.<br>Ph.D.
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Haskara, ?brahim. "Sliding mode estimation and optimization methods in nonlinear control problems /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488192960166775.
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Somogyi, Chad Alexander. "Common mode voltage mitigation strategies using PWM in neutral-point-clamped multilevel inverters." Thesis, Marquette University, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1594317.
Повний текст джерелаАнотація:
<p> Over the last several decades, there has been consistent growth in the research and development of multilevel voltage-source inverter-based adjustable speed motor drives (ASDs) as a result of low cost, high reliability power semiconductors. The three-level neutral-point-clamped (NPC) ASD is a popular multilevel inverter used in low and medium voltage applications because of its ability to produce lower levels of total harmonic distortion (THD) and withstand higher voltages while preserving the rated output power compared to two-level ASDs.</p><p> As with other voltage-source inverters, three-level NPC ASDs produce common-mode voltage (CMV) that can cause motor shaft voltages, bearing currents, and excess voltage stresses on motor windings, resulting in the deterioration of motor bearings and insulation. Furthermore, the CMV and resultant currents can generate electromagnetic interference that can hinder the operation of sensitive control electronics. In this thesis, three carrier-based, three-level pulse-width-modulation (PWM) strategies were investigated to examine the levels of CMV, common-mode current, and <i>dv/dt</i> produced by the three-level NPC ASD. Additionally, the effects that each PWM strategy has on the THD in the output waveforms, as well as the total switching and conduction losses were analyzed through software simulation programs using a resistive-inductive load over a range of modulation indices. The first of the three methods, in-phase disposition sub-harmonic PWM (PD-SPWM), was verified experimentally using a laboratory-scale, 7.5 kVA three-level NPC ASD prototype.</p><p> It was determined that PD-SPWM produced the highest CMV amplitude of one-third the dc bus voltage, but the lowest values of differential-mode dv/dt, THD, and drive losses. The second strategy, phase-opposition (PO)-SPWM, reduced the CMV amplitude to one-sixth the dc bus voltage, at the cost of higher THD and drive losses and a doubling of the differential-mode dv/dt. The final strategy, zero common-mode (ZCM)-SPWM, was modified (MZCM-SPWM) to accommodate IGBT dead-time by delaying the output voltage transitions based on the polarity of the output currents and the direction of the commanded voltage transitions. The MZCM-SPWM method nearly eliminated all CMV pulses while maintaining comparable levels of THD, but produced twice the switching losses compared to PD- and PO- SPWM, and twice the differential-mode <i>dv/dt</i> compared to PD-SPWM.</p>