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  • 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.
571

Studies on microporous materials

Murdoch, Morag Jessie January 2009 (has links)
Microporous titanosilicates and vanadosilicates were synthesised characterized and photoreactivity studies were carried out.  The titanosilicates synthesised were the titanosilicate pharmacosiderite and AM – 18 and the vanadosilicates were AM – 6, ETVS – 10, AM – 14 and VSH -13Na.  A variety of different techniques were used in the characterisation studies including different X-Ray methods, vibrational spectroscopy, electron microscopy, and solid state NMR spectroscopy.  The studies showed that the synthesised products were homogeneous and an insight into the structures of AM – 18 and AM – 14 was obtained. Raman spectroscopy was used to assess the levels of defects in large crystals of ETS – 10 and ETS – 4 by measuring the variation in the frequency of the Ti – O band and the width of this band.  A similar study was done on large crystals of AM – 6.  Raman spectroscopy showed that Ti – O stretching bands containing Ti(V) and Ti(IV) were present in AM – 18 structure.  The frequency of the vanadyl bands in AM – 14 indicated that it could contain vanadyl chains. Photoreactivity studies using EPR spectroscopy, on the potassium titanosilicate pharmacosiderite showed an O<sup>-</sup> species, after UV irradiation in the presence of oxygen.  When the partial pressure was reduced a superoxide and the anomalous ozonide species were observed.  On changing the cation to a proton form, a superoxide anion radical was observed but no other oxygen radicals were observed. Attempted oxidation and reduction studies on VSH – 13Na were unsuccessful and HRTEM and nitrogen adsorption studies showed that the one-dimensional channels were blocked. Oxidation and reduction studies on AM – 14 indicated that the vanadium sites were easily accessible to gas phase.
572

Naval electric weapons the electromagnetic railgun and free electron laser

Williams, Robert E. 06 1900 (has links)
Approved for public release; distribution is unlimited / Theory and simulations of the railgun and free electron laser are presented, as well as a suggestion for extending the railgun lifecycle. The theory, design, and analysis of an electromagnetic railgun using a numerical model are discussed. The effects of varying electrical pulse formations, rail materials and geometries are explored. The application of a metallurgical process to mitigate hypervelocity gouging in railgun rails is proposed. This concept, to delay the onset velocity of gouging by laser-peening rails surfaces, may significantly increase the velocity at which projectiles acceptably traverse the barrel and extend the useful life of rails. If successful, this process would apply to any pair of materials in sliding contact at high relative velocity, including rocket sled tracks and light gas guns barrels. The status of proof-of-concept tests at LLNL, UC Davis, and UT is covered. FEL simulations investigating the effect that electron beam focal point variations have on the optical mode within the undulator are presented. / Lieutenant, United States Navy
573

Transport imaging for the study of quantum scattering phenomena in next generation semiconductor devices

Bradley, Frank Mitchell 12 1900 (has links)
Approved for public release; distribution is unlimited / The minority carrier diffusion length is a critical parameter in the development of next generation Heterostructure Bipolar Transistors (HBT) and highly efficient solar cells. A novel technique has been developed utilizing direct imaging of electron/hole recombination via an optical microscope and a high sensitivity charge coupled device coupled to a scanning electron microscope to capture spatial information about the transport behavior (diffusion lengths/drift lengths) in luminescent solid state materials. In this work, a numerical model was developed to do a multi-parameter least squares analysis of transport images. Results were applied to the study of transport in materials at the forefront of device technology that are affected by quantum scattering effects, where few reliable experimental measurements exist. The technique allows for easy localization of the measurement site, broad application to a range of materials and potential industrial automation to aid electronics for terahertz devices. / Outstanding Thesis
574

High energy laser applications in a surface combatant terminal phase theater ballistic missile defense, low atmosphere propagation, and free electron laser gain

Niles, Sean P. 06 1900 (has links)
The Free Electron Laser (FEL) can provide the naval surface combatant with a directed energy weapon that can be used against a large target set. Due to space constraints in a shipboard installation, an exploration is conducted to show the feasibility of short Rayleigh length FELs using a FEL simulation. Low atmosphere engagements are discussed through the modeling of a turbulence module for laser propagation in cruise missile defense applications. In particular, this thesis explores the difficulties in engaging a short/medium range theater ballistic missile (TBM) in the terminal phase as an engagement scenario in support of littoral operations using HELCoMES, developed by SAIC, as an engagement analysis tool. A concept of operations (CONOPS) for the use of a FEL as an area TBM defensive weapon is explored, using a unitary, high explosive warhead model and extrapolations to other TBM warhead types.
575

Analysis of the failure of a vacuum spin-pit drive turbine spindle shaft

Pettitt, Jason M. 09 1900 (has links)
The Naval Postgraduate School's Rotor Spin Research Facility experienced a failure in the Spring of 2005 in which the rotor dropped from the drive turbine and caused extensive damage. A failure analysis of the drive turbine spindle shaft was conducted in order to determine the cause of failure: whether due to a material or design flaw. Also, a dynamic analysis was conducted in order to determine the natural modes present in the system and the associated frequencies that could have contributed to the failure of the shaft. It was concluded that the failure was due to low cycle fatigue, a possible stress concentration was identified, and a torsional mode was found near the speed at which failure occurred.
576

Dynamical Friction Coefficients for Plasmas Exhibiting Non-Spherical Electron Velocity Distributions

Williams, G. Bruce 08 1900 (has links)
This investigation is designed to find the net rate of decrease in the component of velocity parallel to the original direction of motion of a proton moving through an electron gas exhibiting a non-spherical velocity distribution.
577

A Study of the Decay Levels of 169/Tm69

Harris, Robert J. 12 1900 (has links)
The purpose of this investigation was to study the radiations of the 169/Tm nucleus as it de-excites after the electron capture decay of the 169/Yb. Numerous unreported gammas were present in the sample. The origins of these gamma rays were found.
578

Magnetomorphic Oscillations in Cadmium Cylinders

Hight, Ralph D. 08 1900 (has links)
The work presented here is an experimental investigation of the effect of cylindrical geometry on electrical conductivity, in which single-crystal samples of cadmium at the temperature of liquid helium are used, with the diameter on the order of the electron mean free path.
579

Experimental and Theoretical Study of Electronic Transitions in Phosphorus, Phosphoryl, and Thiophosphoryl Trichlorofluorides

McAdams, Mary Jane 05 1900 (has links)
This thesis is an investigation of the vacuum uv spectra of the phosphorus, phosphoryl, and thiophosphoryl trichlorofluorides in the region 1250 to 3000A. Assignments for absorption bands are made utilizing results from photoelectron spectra and ab initio calculations, oscillator strengths for absorption bands, and CNDO/2 molecular orbital calculations. Results from CNDO/2 calculations are compared with theoretical calculations, and experimental data are discussed with regard to the bonding in the compounds.
580

STABILITY AND SPECTROSCOPIC PROPERTIES OF NEGATIVE IONS

Behera, Swayamprabha 06 May 2011 (has links)
Negative ions play an important role in chemistry as building blocks of salts and oxidizing agents. Halogen atoms, due to their ability to attract electrons, readily form negative ions. Considerable interest exists in the design and synthesis of new negative ions called superhaogens whose electron affinities are much higher than those of halogen atoms. This thesis deals with the design of such species. Using density functional theory I have studied two classes of superhalogens. First one involves d1 transition metal (Sc, Y, La) atoms surrounded by Cl while the second one involves simple metals (Na, Mg, Al) surrounded by pseudohalogens such as CN. Geometry, electronic structure, and electron affinity of these species containing up to 5 ligands have been calculated. Studies reveal a fundamental difference between the interaction of transition and metal atoms with electronegative ligands. In addition, pseudohalogens can be used to synthesize a new class of superhalogens.

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