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Effects of Dissipation on Propagation of Surface Electromagnetic and Acoustic Waves

Description: With the recent emergence of the field of metamaterials, the study of subwavelength propagation of plane waves and the dissipation of their energy either in the form of Joule losses in the case of electomagnetic waves or in the form of viscous dissipation in the case of acoustic waves in different interfaced media assumes great importance. with this motivation, I have worked on problems in two different areas, viz., plasmonics and surface acoustics. the first part (chapters 2 & 3) of the dissertation deals with the emerging field of plasmonics. Researchers have come up with various designs in an efort to fabricate efficient plasmonic waveguides capable of guiding plasmonic signals. However, the inherent dissipation in the form of Joule losses limits efficient usage of surface plasmon signal. a dielectric-metal-¬dielectric planar structure is one of the most practical plasmonic structures that can serve as an efficient waveguide to guide electromagnetic waves along the metal-dielectric boundary. I present here a theoretical study of propagation of surface plasmons along a symmetric dielectric-metal-dielectric structure and show how proper orientation of the optical axis of the anisotropic substrate enhances the propagation length. an equation for propagation length is derived in a wide range of frequencies. I also show how the frequency of coupled surface plasmons can be modulated by changing the thickness of the metal film. I propose a Kronig-Penny model for the plasmonic crystal, which in the long wavelength limit, may serve as a homogeneous dielectric substrate with high anisotropy which do not exist for natural optical crystals. in the second part (chapters 4 & 5) of the dissertation, I discuss an interesting effect of extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two metal plates. Starting from the elastic properties of the ...
Date: May 2012
Creator: Nagaraj, Nagaraj
Partner: UNT Libraries

Evaluation of TBC-coated {beta}-NiAl substrates without a bond coat

Description: {beta}-NiAl substrates with various alloy additions and oxide dispersions were coated with Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} using electron beam-physical vapor deposition. Cyclic oxidation experiments (1000-1200 C) were conducted to study effect of substrate dopants such as Y and Zr on coating lifetime without the intermediate metallic bond coat layer used in conventional thermal barrier coatings. Oxidation kinetics and Al{sub 2}O{sub 3} scale microstructures were compared to those for uncoated substrates. Degradation of substrate-alumina interface by void formation was the primary mechanism leading to coating spallation. Coating lifetime was correlated to alumina scale adhesion on unocated substrates.
Date: April 1996
Creator: Pint, B. A.; Nagaraj, B. A. & Rosenzweig, M. A.
Partner: UNT Libraries Government Documents Department

The effect of thermal aging on the thermal conductivity of plasma sprayed and EB-PVD thermal barrier coatings

Description: Thermal barrier coatings (TBCs) applied to the hot gas components of turbine engines lead to enhanced fuel efficiency and component reliability. Understanding the mechanisms which control the thermal transport behavior of the TBCs is of primary importance. Electron beam-physical vapor deposition (EV-PVD) and air plasma spraying (APS) are the two most commonly used coating techniques. These techniques produce coatings with unique microstructures which control their performance and stability. The density of the APS coatings was controlled by varying the spray parameters. The low density APS yttria-partially stabilized zirconia (yttria-PSZ) coatings yielded a thermal conductivity that is lower than both the high density APS coatings and the EB-PVD coatings. The thermal aging of both fully and partially stabilized zirconia are compared. The thermal conductivity of the coatings permanently increases upon exposure to high temperatures. These increases are attributed to microstructural changes within the coatings. This increase in thermal conductivity can be modeled using a relationship which depends on both the temperature and time of exposure. Although the EB-PVD coatings are less susceptible to thermal aging effects, results suggest that they typically have a higher thermal conductivity than APS coatings before thermal aging. The increases in thermal conductivity due to thermal aging for plasma sprayed partially stabilized zirconia have been found to be less than for plasma sprayed fully stabilized zirconia coatings.
Date: May 1, 1996
Creator: Dinwiddie, R.B.; Beecher, S.C.; Porter, W.D. & Nagaraj, B.A.
Partner: UNT Libraries Government Documents Department

Development of a direct-injected natural gas engine system for heavy-duty vehicles: Final report phase 2

Description: This report summarizes the results of Phase 2 of this contract. The authors completed four tasks under this phase of the subcontract. (1) They developed a computational fluid dynamics (CFD) model of a 3500 direct injected natural gas (DING) engine gas injection/combustion system and used it to identify DING ignition/combustion system improvements. The results were a 20% improvement in efficiency compared to Phase 1 testing. (2) The authors designed and procured the components for a 3126 DING engine (300 hp) and finished assembling it. During preliminary testing, the engine ran successfully at low loads for approximately 2 hours before injector tip and check failures terminated the test. The problems are solvable; however, this phase of the program was terminated. (3) They developed a Decision & Risk Analysis model to compare DING engine technology with various other engine technologies in a number of commercial applications. The model shows the most likely commercial applications for DING technology and can also be used to identify the sensitivity of variables that impact commercial viability. (4) MVE, Inc., completed a preliminary design concept study that examines the major design issues involved in making a reliable and durable 3,000 psi LNG pump. A primary concern is the life of pump seals and piston rings. Plans for the next phase of this program (Phase 3) have been put on indefinite hold. Caterpillar has decided not to fund further DING work at this time due to limited current market potential for the DING engine. However, based on results from this program, the authors believe that DI natural gas technology is viable for allowing a natural gas-fueled engine to achieve diesel power density and thermal efficiency for both the near and long terms.
Date: March 2, 2000
Creator: Cox, G.B.; DelVecchio, K.A.; Hays, W.J.; Hiltner, J.D.; Nagaraj, R. & Emmer, C.
Partner: UNT Libraries Government Documents Department

Sampling Within k-Means Algorithm to Cluster Large Datasets

Description: Due to current data collection technology, our ability to gather data has surpassed our ability to analyze it. In particular, k-means, one of the simplest and fastest clustering algorithms, is ill-equipped to handle extremely large datasets on even the most powerful machines. Our new algorithm uses a sample from a dataset to decrease runtime by reducing the amount of data analyzed. We perform a simulation study to compare our sampling based k-means to the standard k-means algorithm by analyzing both the speed and accuracy of the two methods. Results show that our algorithm is significantly more efficient than the existing algorithm with comparable accuracy. Further work on this project might include a more comprehensive study both on more varied test datasets as well as on real weather datasets. This is especially important considering that this preliminary study was performed on rather tame datasets. Also, these datasets should analyze the performance of the algorithm on varied values of k. Lastly, this paper showed that the algorithm was accurate for relatively low sample sizes. We would like to analyze this further to see how accurate the algorithm is for even lower sample sizes. We could find the lowest sample sizes, by manipulating width and confidence level, for which the algorithm would be acceptably accurate. In order for our algorithm to be a success, it needs to meet two benchmarks: match the accuracy of the standard k-means algorithm and significantly reduce runtime. Both goals are accomplished for all six datasets analyzed. However, on datasets of three and four dimension, as the data becomes more difficult to cluster, both algorithms fail to obtain the correct classifications on some trials. Nevertheless, our algorithm consistently matches the performance of the standard algorithm while becoming remarkably more efficient with time. Therefore, we conclude that analysts can use ...
Date: August 1, 2011
Creator: Bejarano, Jeremy; Bose, Koushiki; Brannan, Tyler; Thomas, Anita; Adragni, Kofi; Neerchal, Nagaraj et al.
Partner: UNT Libraries Government Documents Department