• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 3612
  • 1154
  • 886
  • 758
  • 305
  • 298
  • 183
  • 99
  • 89
  • 89
  • 89
  • 89
  • 89
  • 87
  • 86
  • Tagged with
  • 9573
  • 1098
  • 977
  • 780
  • 737
  • 733
  • 543
  • 523
  • 518
  • 467
  • 402
  • 372
  • 361
  • 351
  • 350
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
231

Photoresist-based polymer resonator antennas (PRAs) with lithographic fabrication and dielectric resonator antennas (DRAs) with improved performance

Rashidian, Atabak 09 May 2011 (has links)
<p>The demand for higher bit rates to support new services and more users is pushing wireless systems to millimetre-wave frequency bands with more available bandwidth and less interference. However at these frequencies, antenna dimensions are dramatically reduced complicating the fabrication process. Conductor loss is also significant, reducing the efficiency and gain of fabricated metallic antennas. To better utilize millimetre-wave frequencies for wireless applications, antennas with simple fabrication, higher efficiency, and larger impedance bandwidth are required.</p> <p>Dielectric Resonator Antennas (DRAs) offer many appealing features such as large impedance bandwidth and high radiation efficiency due to the lack of conductor and surface wave losses. DRAs also provide design flexibility and versatility. Different radiation patterns can be achieved by different geometries or resonance modes, wideband or compact antennas can be provided by different dielectric constants, and DRAs can be excited by a wide variety of feeding structures. Nevertheless, compared to their metallic counterparts, fabrication of DRAs is challenging since they have traditionally been made of high permittivity ceramics, which are naturally hard and extremely difficult to machine and cannot be easily made in an automatic way. The fabrication of these three dimensional structures is even more difficult at millimetre-wave frequencies where the size of the antenna is reduced to the millimetre or sub-millimetre range, and tolerances to common manufacturing imperfections are even smaller. These fabrication problems restrict the wide use of DRAs, especially for high volume commercial applications.</p> <p>A new approach to utilize the superior features of DRAs for commercial applications, introduced in this thesis, is to exploit polymer-based resonator antennas (PRAs), which dramatically simplifies fabrication due to the natural softness and results in a wide impedance bandwidth due to the low permittivity of polymers. Numerous polymer types with exceptional characteristics can be used to fulfill the requirements of particular applications or achieve extraordinary benefits. For instance, in this thesis photoresist polymers facilitate the fabrication of PRAs using lithographic processes. Another advantage derived from this approach is the capability of mixing polymers with a wide variety of fillers to produce composite materials with improved or extraordinary characteristics.</p> <p>The key contributions of this thesis are in introducing SU-8 photoresist as a radiating material, developing three lithographic methods to fabricate photoresist-ceramic composite structures, introducing a simple and non-destructive measurement method to define electrical properties of the photoresist composites, and demonstrating these structures as improved antenna components.</p> <p>It is shown that pure SU-8 resonators can be highly efficient antennas with wideband characteristics. To achieve more advantages for RF applications, the microwave properties of photoresists are modified by producing ceramic composite materials. X-ray lithography fabrication is optimized and as a result one direct and two indirect methods are proposed to pattern ultra thick (up to 2.3 mm) structures and complicated shapes with an aspect ratio as high as 36:1. To measure the permittivity and loss tangent of the resulting materials, a modified ring resonator technique in one-layer and two-layer microstrip configurations is developed. This method eliminates the requirement to metalize the samples and enables characterization of permittivity and dielectric loss in a wide frequency range from 2 to 40 GHz. Various composite PRAs with new designs (e.g. frame-based and strip-fed structures) are lithographically fabricated, tested, and discussed. The prototype antennas offer -10 dB bandwidths as large as 50% and gain in the range of 5 dBi.
232

Leveraged Plans for Measurement System Assessment

Browne, Ryan January 2009 (has links)
In manufacturing, measurement systems are used to control processes and inspect parts with the goal of producing high quality product for the customer. Modern Quality Systems require the periodic assessment of key measurement systems to ensure that they are functioning as expected. Estimating the proportion of the process variation due to the measurement system is an important part of these assessments. The measurement system may be simple, for example, with one gauge automatically measuring a single characteristic on every part or complex with multiple characteristics, gauges, operators etc. Traditional assessment plans involve selecting a random sample of parts and then repeatedly measuring each part under a variety of conditions that depend on the complexity of the measurement system. In this thesis, we propose new plans for assessing the measurement system variation based on the concept of leveraging. In a leveraged plan, we select parts (non-randomly) with extreme initial values to measure repeatedly. Depending on the context, parts with initial measurements may be available from regular production or from a specially conducted baseline study. We use the term leveraging because of the re-use of parts with extreme values. The term leverage has been used by the  proponents of the problem solving system initially proposed by Dorian  Shainin. Parts with relatively large and small values of the response  are compared to identify the major causes of the variation. There is no discussion of the theory of leveraging in the literature or its application to measurement system  assessment. In this thesis, we provide motivation for why leveraging  is valuable and apply it to measurement system  assessments. We consider three common contexts in the thesis: Simple measurement systems with one gauge, no operator effects and no external information about the process performance; Measurement systems, as stated above, where we have external information, as would be the case, for example, if the measurement system was used for 100% inspection; Measurement systems with multiple operators. For each of these contexts, we develop new leveraged assessment plans and show that these plans are substantially more efficient than traditional plans in estimating the proportion of the process variation due to the measurement system. In each case, we also provide methodology for planning the leveraged study and for analysing the data generated. We then develop another new application of leveraging in the assessment of a measurement system used for 100% inspection. A common practice is to re-measure all parts with a first  measurement outside of inspection limits. We propose using these repeated measurements to assess the variation in the measurement system. Here the system itself does the leveraging since we have repeated measurements only on relatively large or small parts. We recommend using maximum likelihood estimation but we show that the ANOVA estimator, although  biased, is comparable to the MLE when the measurement system is reliable.  We also provide guidelines on how to schedule such assessments. To outline the thesis, in the first two chapters, we review the contexts described above. For each context, we discuss how to characterize the measurement system performance, the common assessment plans and their analysis. In Chapter 3, we introduce the concept of leveraging and provide motivation for why it is effective. Chapters 4 to 7 contain the bulk of the new results in the thesis. In Chapters 4, 5 and 6, which correspond to the three contexts described above, we provide new leveraged plans, show their superiority to the standard plans and provide a methodology to help design leveraged plans. In Chapter 7, we show how to assess an inspection system using repeated measurements on initially rejected parts. In the final chapter, we discuss other potential applications of leveraging to other measurement system assessment problems and to a problem in genetics.
233

Measurement Devices for Custom Shoe Manufacturing

Besliu, Dragos 26 August 2011 (has links)
The majority of North Americans suffer from foot problems at some point in their lives. These foot problems can be divided into three domains ranging from mismatch on healthy feet, to small injuries and deformities and extreme sensitivity and deformities. A solution to these problems is the development of corrective shoes. The design of corrective shoes involves three steps: first, the measurement or digitization of the foot to create a model; second, the manipulation of the model and last creation; third, constructing the shoe with the last. This work focuses on developing a foot digitization system or scanner for each of the three problem domains. A good digitization paves the way for development of foot manipulation algorithms and last manufacturing techniques that can be applied to develop well fitting comfortable shoes. Three scanning methods were investigated in this work. The first was designed for scanning near normal feet and automatically building a 3D approximation of the plantar surface of the foot. This digitizer was successfully built and demonstrated. The second scanner was designed to scan the entire 3D surface of the foot. This scanner was built and used to extract data for building complete 3D models of the foot. The last scanner was designed to measure and modify the pressure distribution of the loaded foot on a controllable surface. This scanner is more capable in creating an optimal corrective shoe, but is more expensive. A pin matrix design was selected and subsystem prototypes were successfully produced and tested. The first two developed designs provide low cost solutions for modeling feet, for the purposes of corrective shoe and insole creation. The third design explores a method of measuring foot pressure and distributing it via control of a 3D surface upon which the foot is supported.
234

Study of microfluidic measurement techniques using novel optical imaging diagnostics

Park, Jaesung 25 April 2007 (has links)
Novel microscale velocity and temperature measurement techniques were studied based on confocal laser scanning microscopy (CLSM) and optical serial sectioning microscopy (OSSM). Two microscopic measurement systems were developed, 1) a CLSM micro particle image velocimetry (PIV) system with a dual Nipkow disk confocal unit (CSU-10), a CW argon-ion laser and an upright microscope, and 2) an OSSM micro- particle tracking velocimetry (PTV) system with an epi-fluorescence microscope and a non-designed specimen to make a three-dimensional (3-D) diffraction particle image. The CLSM micro-PIV system shows a unique optical slicing capability allowing true depth-wise resolved vector field mapping. A comparative study is presented between the CLSM micro-PIV and a conventional epi-fluorescence micro-PIV. Both have been applied to the creeping Poiseuille flows in two different microtubes of 99-µm (Re = 0.00275) and 516-µm ID diameters (Re = 0.021). The CLSM micro-PIV consistently shows significantly improved particle image contrasts, the definition of "optical slicing" and measured flow vector fields more accurately agreeing with predictions based on the Poiseuille flow fields, compared to the conventional micro-PIV. The OSSM micro-PTV technique is applied for a 3-D vector field mapping in a microscopic flow and a Brownian motion tracking of nanoparticles. This technique modifies OSSM system for a micro-fluidic experiment, and the imaging system captures a diffracted particle image having numerous circular fringes instead of an in-focus particle image. The 3-D particle tracking is based on a correlation between the 3-D diffraction pattern of a particle and the defocus distance from a focal plane. A computational program is invented for the OSSM micro-PTV, and provides a 3-D velocity vector field with a spatial resolution of 5.16 µm. In addition, a concept of nonintrusive thermometry is presented based on the correlation of the Brownian motion of suspended nanoparticles with the surrounding fluid temperature. Detection of fully three-dimensional Brownian motion is possible by the use of the OSSM, and the measured value of mean square displacement (MSD) is compared fairly well with Einstein's predictions.
235

Development of Indoor Tank Measurement Facility for Rough Surface Back Scattering

Lo, Shr-luen 11 September 2007 (has links)
This thesis intends to design a set of acoustics measurement system, it can measure the rough surface to have the scattering influence regarding the sound wave. And this set of acoustics measurement system will be able to provide the rough surface establishment function, acoustics measurement precise pinpointing for position and rough surface accurate shape data. Establishing the main environment take the Institute of Undersea Technology large experiment water tank as the system. The experiment water tank sets up XYZ table which can control the three translation directions migration. Because this experiment needs five degrees-of-freedom except for three translation directions migration and also has two axes rotary motion. In order to measure scattering field so we need to design the rotary mechanism for two axes that enables the microphone to achieve themovements in five degrees-of-freedom. In this experiment has to conformity themeasurement of laser system¡¦s rough surface position, the position of microphone shooting and receiving point, and establishes scraper position which rough surface used. In order to compare the scattering state of the shape of rough surface and the soundwave beats the rough surface after we integrate all the information, we can realize where directional sound wave beats and what¡¦s the shape of this rough surface. Except for conformity position, this equipment¡¦s localization is all by the programcontrolmotor. It can save time in adjusting position for experimenter in an effective way and itmay abridge the experiment time effectively.
236

Cancer treatment-related fatigue psychometric testing of the cancer treatment-related fatigue representation scale (CTRFRep) in patients undergoing radiation treatment for cancer /

Reuille, Kristina M. January 2009 (has links)
Thesis (Ph.D.)--Indiana University, 2009. / Title from screen (viewed on February 2, 2010). School of Nursing, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Janet L. Welch, Juanita F. Keck, Janet S. Fulton, Barbara Manz Friesth. Includes vitae. Includes bibliographical references (leaves 150-164).
237

Atlas of deep current observations for central California

Zamora, Ulysses D. January 2009 (has links) (PDF)
Thesis (M.S. in Applied Science (Physical Oceanography))--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Collins, Curt. Second Reader: Margolina, Tetyana. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: California Current, RAFOS floats, current meters, seasonal variability, mesoscale eddies, tides. Includes bibliographical references (p. 261-263). Also available in print.
238

Conjointanalyse zur Messung und Erklärung von Markenwert /

Otter, Thomas. January 2001 (has links)
Wien, WirtschaftsUniversität, Thesis (doctoral), 2001.
239

Working towards an integrative job performance taxonomy /

Wu, Hui Chin. January 2002 (has links) (PDF)
Thesis (M. Psych. Org.)--University of Queensland, 2002. / Includes bibliographical references.
240

Ex ante evaluations of data structures for end user queries : theory and two experimental tests /

Basford, Jay. January 2002 (has links) (PDF)
Thesis (M. Infm. Systems)--University of Queensland, 2002. / Includes bibliographical references.

Page generated in 0.0679 seconds