Physics Commons^™

Spectroscopic Constants, Lifetimes And Predissociation Rates For Bi2A(0+U), Michael W. Dolezal

Theses and Dissertations

More than 100,000 spectral features from a Bi₂(X¹ Σ⁺_g → A(0⁺_u)) absorption spectrum, encompassing 0 ≤ v' ≤ 91, 0 ≤ v" ≤ 7 and J2(A). Ground state constants, reported by Barrow et al. [1], remain unchanged. The new constants are used to redefine the A-state potential using traditional RKR methods and to set the dissociation energy at De = 29,913 cm"1, which correlates A-state dissociation products to ⁴S + ²D atoms. A pulsed dye laser apparatus was used to obtain lifetime data for Bi₂A(0⁺_u) …

Analyzing The Effects Of Meteorology On Radar Measured Index Of Refraction Structure Parameter, Jeffrey W. Budai

Theses and Dissertations

Forecasting optical turbulence is essential for the Air Force's Airborne Laser program to optimize placement of aircraft. To find bow meteorology affects C_n², the intensity of turbulence in the index of refraction, case studies of synoptically interesting times are first chosen. Correlation coefficients are then computed between radar measured C_n² and meteorological quantities. The potential for mechanically turbulent activity is looked at. In the analysis of this work, six meteorological features were found likely to affect C_n². Two features associated with affecting potential refractivity, and thus C_n², are jets …

Development Of Non-Contact Scanning Force Microscopy For Imaging In Liquid Environments, Anthony Grant

Theses

The aim of this work was to develop a non-contact mode scanning force microscope (SFM) for application to biological samples within liquid environments. Given that biological samples are particularly soft in their natural state and that a liquid is the most difficult operating environment for non-contact mode scanning force microscopy, the development of an instrument that is optimised to image biological samples in vitro presents significant challenges.

Firstly, the SFM tip to sample interaction has to be minimised either, in the worst case, to prevent the sample from being detached from its support or to maximise spatial resolution by minimising …

Characterizing And Monitoring Changes In State Of Polymers During Cure And Use -Aging, Andrew Orschel Meyer

Dissertations, Theses, and Masters Projects

Multi Angle Laser Light Scattering (MALLS) and Frequency Dependent Electromagnetic Sensing (FDEMS) provide unique characterizations of polymer systems during cure and use-aging. This research illustrates how MALLS is an extremely accurate technique for absolute characterization of macromolecules, giving molecular weight and size information that other widely used and accepted techniques are incapable of measuring. Application of MALLS to monitoring the changing state of a polyamide-11 system in a water aging environment led to the discovery of an equilibrium molecular weight which is the result of two competing reactions, hydrolysis-degradation and a newly discovered recombination-polymerization reaction. The discovery of this recombination …

Optical Studies Of Layered Inorganic Solids: A Novel Phase Transition And Energy Transfer Studies., Christie L. Larochelle

Electronic Theses and Dissertations

The optical properties of a group of dicyanoargentates(1) and dicyanoaurates( 1) have been studied. The samples include K2Na[Ag(CN)2I3, Tb[Ag(CN)2]3, Tb[Au(CN)2I3 and a series of compounds of the form Tb,Lal-,[Ag(CN)2]3 with x=0.001, 0.01 and 0.1. Additionally, a novel type of silver-gold mixed- metal sample (L~[A~,Au~-,(CN)~]~ with x=0.9 and 0.5) was synthesized and characterized. The compound K2Na[Ag(CN)2I3 has earlier been shown to exhibit a phenomenon known as luminescence thermochromism, whereby only one emission band is present at very low temperatures and very high temperatures, but a second, lower energy band is also present at intermediate temperatures. This prompted further investigation to explain …

Solid State Nmr Characterization Of Structural And Motional Parameter Distributions In Polyamidoammonium Dendrimers, Dariya Ivanovna Malyarenko

Dissertations, Theses, and Masters Projects

The characterization of narrow distributions of structural and motional parameters, and their evolution during the broad glass transition, is performed for deuterated PAMAM dendrimer salts using solid state NMR. The broadening of deuteron quadrupole echo (QE) lineshapes is consistent with the presence of narrow hydrogen bond length distribution (sigmar < 0.25 A) at the spacer amide and branching tertiary amine sites. The temperature dependent averaging of the experimental lineshapes is explained on the basis of fast planar librations in the dendrimer interior, and fast rotation and intermediate regime libration (in an asymmetric cone) of the dendrimer termini. The amplitudes of libration are temperature dependent and higher for low generation dendrimers, while librational rates show Arrhenius behavior only within the glass transition region. In this region, the width of log-normal distribution of rates increases with temperature at sites associated with chlorine counterions. The largest distributions are still less than one order of magnitude wide, unlike the dendrimer in solution or the linear polymers. Interpenetrated low generations (G < 3), uniform intermediate generations (G = 3--5) with surface network, and backfolded high generations (G > 5), are distinguished by interior and termini dynamics.;In the regime of fast motion QE lineshapes are highly sensitive to the presence of narrow structural and motional parameter distributions, and provide constraints on motional geometry independent of rates. The precise characterization of narrow log-normal rate distributions in the intermediate regime can be …

Deformation Studies Of Tungsten-Gold Contacts At The Nanometer Scale., Steven A. Smallwood

Electronic Theses and Dissertations

The deformation behavior of atomically clean, nanometer sized tungsten / gold contacts was studied at room temperature in ultra-high vacuum. An instrument that combines atomic force microscopy (AFM), scanning tunneling microscopy (STM), and field ion microscopy (FIM) into a single experimental apparatus was designed, constructed, and calibrated. A cross-hair force sensor having a spring constant of - 442 N/m was developed and its motion was monitored during indentation experiments with a differential interferometer. Tungsten tips of controlled size (12.8 nm < tip radius < 2 1.6 nm) were first shaped and characterized using FIM and then indented into a Au (1 10) single crystal to depths ranging from 1.5 nrn to 18 nm using the force sensor. Continuum mechanics models were found to be valid in predicting elastic deformation during initial contact and plastic zone depths despite our small size regime. Multiple discrete yielding events lasting < 1.5 ms were observed during the plastic deformation regime; at the yield points a maximum value for the principal shear stress was measured to be 5 + 1 GPa. During tip withdrawal, "pop-out" events relating to material relaxation within the contact were observed. Adhesion between the tip and sample led to experimental signatures that suggest neck formation prior to the break of contact. STM images of indentation holes revealed various shapes that can be attributed to the (1 1 1 ) (1 10) crystallographic slip system in gold. FIM images of the tip after indentation showed no evidence of tip damage