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The effect of temporal pulse shape on optical damage

Description: The conditions under which optical materials are susceptible to laser-induced damage is a topic which has been the subject of considerable study. Laser parameters such as wavelength and temporal pulse duration have been studied extensively. Until this work the effect of temporal pulse shape has not been considered. We present here data from a simple single-parameter model and a supporting experiment which predicts that a Flat-In-Time-pulse will produce damage at approximately 80% of the fluence of a Gaussian pulse of the same FWHM duration.
Date: August 15, 2006
Creator: Carr, C W; Trenholme, J B & Spaeth, M L
Partner: UNT Libraries Government Documents Department

Low-speckle holographic beam shaping of high-coherence EUV sources

Description: This paper describes a method to arbitrarily shape and homogenize high-coherence extreme ultraviolet sources using time-varying holographic optical elements and a scanning subsystem to mitigate speckle. In systems with integration times longer than 100 ms, a speckle contrast below 1% can be achieved.
Date: August 1, 2010
Creator: Anderson, Christopher N.; Miyakawa, Ryan H. & Naulleau, Patrick
Partner: UNT Libraries Government Documents Department

Revealing myths about people, energy and buildings

Description: In this essay we take a closer look at some energy myths, focusing on the ways energy professionals and the public alike, talk, write and teach about how energy affects the way in which we design, operate, retrofit and inhabit buildings. What myths about people, energy and buildings are current today? Who tells these myths and why do we believe them? How do myths affect our behavior? Myths are a way of understanding the world we live in. They may represent incomplete understanding, or be based on premises that are scientifically not valid, but they help us understand and explain how the world works, and we shape our behavior accordingly.
Date: May 1, 2000
Creator: Diamond, R. & Moezzi, M.
Partner: UNT Libraries Government Documents Department

Sculpting the shape of semiconductor heteroepitaxial islands: fromdots to rods

Description: In the Ge on Si model heteroepitaxial system, metal patterns on the silicon surface provide unprecedented control over the morphology of highly ordered Ge islands. Island shape including nanorods and truncated pyramids is set by the metal species and substrate orientation. Analysis of island faceting elucidates the prominent role of the metal in promoting growth of preferred facet orientations while investigations of island composition and structure reveal the importance of Si-Ge intermixing in island evolution. These effects reflect a remarkable combination of metal-mediated growth phenomena that may be exploited to tailor the functionality of island arrays in heteroepitaxial systems.
Date: June 20, 2006
Creator: Robinson, J.T.; Walko, D.A.; Arms, D.A.; Tinberg, D.S.; Evans,P.G.; Cao, Y. et al.
Partner: UNT Libraries Government Documents Department

The Extinction Toward the Galactic Bulge from RR Lyrae Stars

Description: The authors present mean reddenings toward 3525 RR0 Lyrae stars from the Galactic bulge fields of the MACHO Survey. These reddenings are determined using the color at minimum V-band light of the RR0 Lyrae stars themselves and are found to be in general agreement with extinction estimates at the same location obtained from other methods. Using 3256 stars located in the Galactic Bulge, they derive the selective extinction coefficient R{sub V,VR} = A{sub V}/E(V-R) = 4.2 {+-} 0.2. this value is what is expected for a standard extinction law with R{sub V,BV} = 3.1 {+-} 0.3
Date: November 7, 2007
Creator: Kunder, A; Popowski, P; Cook, K & Chaboyer, B
Partner: UNT Libraries Government Documents Department

Characterization of the effect of short pulse exposure on laser damage size, morphology, and conditioning in wide band gap materials

Description: The first objective of this proposal was to develop a fundamental understanding of how short-pulse (100 ps to 1 ns) laser parameters affect conditioning and damage initiation in KDP and DKDP crystals. In this study we experimentally determine the effect of short-pulse laser parameters including pulse duration, pulse shape, and fluence on conditioning effectiveness, pinpoint damage density, pinpoint size, and pinpoint morphology in crystals. Based on the experimental results we developed empirical models, which give insight into the underlying physics of energy deposition from short-pulse lasers in KDP and DKDP crystals. The second objective of this proposal was to explore the mechanisms by which energy is deposited during damage in SiO{sub 2}. We have measured how laser parameters such as pulse duration, pulse shape, wavelength, and fluence are relevant to energy deposition, for initiation and growth on the surface of SiO{sub 2} optics.
Date: February 7, 2008
Creator: Carr, C. W.
Partner: UNT Libraries Government Documents Department

Development of diagnostics for high-energy petawatt pulses

Description: Applications accessed by high energy petawatt (HEPW) lasers require complete, single-shot characterization of pulse spatial, temporal, and energy characteristics. We describe techniques that enable single-shot characterization of the temporal shape and pulse contrast of HEPW pulses with >10{sup 8} dynamic range over a ns-temporal window. Approaches to measure pulse durations that span two orders of magnitude will be discussed. Finally, we describe a novel implementation of spectrally dispersed two-beam interferometry for measurement of the phase difference between two HEPW pulses. This technique can be applied to dispersion and B-integral measurements in a HEPW system, as well as to achieve precise timing of nanosecond pulses. Lastly, spectrally dispersed interferometry represents an ideal technique to enable coherent addition of HEPW pulses for production of ultrahigh intensities.
Date: June 15, 2006
Creator: Jovanovic, I; Hernandez, J; Appel, G; Barker, D; Betts, S; Brewer, W et al.
Partner: UNT Libraries Government Documents Department


Description: The longitudinal bunch profile acquisition system at RHIC was recently upgraded to allow on-line measurements of the bunch spectrum, and collision vertex location and shape. The system allows monitoring the evolution of these properties along the ramp, at transition and rebucketing, and at store conditions. We describe some of the hardware and software changes, and show some applications of the system.
Date: July 5, 2004
Creator: VAN ZEIJTS,J.
Partner: UNT Libraries Government Documents Department

Rhodium Nanoparticle Shape Dependence in the Reduction of NO by CO

Description: The shape dependence of the catalytic reduction of NO by CO on Rhodium nanopolyhedra and nanocubes was studied from 230-270 C. The nanocubes are found to exhibit higher turnover frequency and lower activation energy than the nanopolyhedra. These trends are compared to previous studies on Rh single crystals.
Date: July 13, 2009
Creator: Renzas, J.R.; Zhang, Y.; Huang, W. & Somorjai, G.A.
Partner: UNT Libraries Government Documents Department

Probing the Geometry of Warped String Compactifications at the LHC

Description: Warped string compactifications, characterized by the nonsingular behavior of the metric in the infrared (IR), feature departures from the usual anti?de Sitter warped extra dimensions. We study the implications of the smooth IR cutoff for Randall-Sundrum- (RS-)type models. We find that the phenomenology of the Kaluza-Klein gravitons (including their masses and couplings) depends sensitively on the precise shape of the warp factor in the IR. In particular, we analyze the warped deformed conifold, find that the spectrum differs significantly from that of RS, and present a simple prescription (a mass-gap ansatz) that can be used to study the phenomenology of IR modifications to 5D warped extra dimensions.
Date: May 28, 2007
Creator: Walker, Devin; Shiu, Gary; Underwood, Bret; Zurek, Kathryn M. & Walker, Devin G. E.
Partner: UNT Libraries Government Documents Department

Perceived Attractiveness and Personality Attributes: A Gender and Racial Analysis

Description: Subjects rated 12 female body shapes with respect to their physical attractiveness, and the extent to which they would be expected to possess various personality characteristics. The shapes were varied using 3 levels of overall weight and 4 levels of body shapeliness. The sample was modified to control for socioeconomic factors and results are based on 297 undergraduates from Caucasian, African American, and Hispanic racial backgrounds. Loglinear analyses revealed that men and women, regardless of racial background, rated shapely underweight females as most physically attractive, sexy, and ideal for a woman, followed by normal weight figures of similar proportion. African Americans, women in particular, judged the shapely normal weight figures more favorably than the other subjects. Multidimensional scaling and subsequent frequency analyses showed that those figures judged as most attractive, sexy, and ideal were also expected to be fairly emotionally stable, and most successful and interpersonally competitive, but least faithful, kind, and family-oriented. Overweight female shapes, while rated as least physically attractive, sexy, and emotionally stable, were expected to be most family-oriented, kind, and faithful. Shapely normal weight figures were judged to be attractive and sexy, and were assumed to possess a moderate amount of the personality traits in question. The results suggest that Caucasian and Hispanic subjects prefer shapely underweight women, while African Americans, particularly women, find shapely underweight and shapely normal weight women to be physically appealing. African American women also rate shapely normal weight women favorably with respect to personality traits. This perceptual difference may help inoculate them from developing eating disturbances and account for the low prevalence rate of eating disorders in African Americans compared to women of other racial backgrounds. It is suggested that future research identify those beliefs, values or behaviors that seem to inoculate African American women from developing eating disorders. Once identified, ...
Date: May 2000
Creator: Olby, Brian C.
Partner: UNT Libraries

Thermomechanical characterization of nickel-titanium-copper shape memory alloy films

Description: In an effort to develop a more extensive model for the thermomechanical behavior of shape memory alloy (SMA) films, a novel characterization method has been developed. This automated test has been tailored to characterize films for use in micro-electromechanical system (MEMS) actuators. The shape memory effect in NiTiCu is seen in the solid-state phase transformation from an easily deformable low-temperature state to a 'shape remembering' high-temperature state. The accurate determination of engineering properties for these films necessitates measurements of both stress and strain in microfabricated test structures over the full range of desired deformation. Our various experimental methods (uniaxial tensile tests, bimorph curvature tests and diaphragm bulge tests) provide recoverable stress and strain data and the stress-strain relations for these films. Tests were performed over a range of temperatures by resistive heating or ambient heating. These measurements provide the results necessary for developing active SMA structural film design models.
Date: October 31, 2000
Creator: Seward, K P; Ramsey, P B & Krulevitch, P
Partner: UNT Libraries Government Documents Department

Final Report: FG02-01ER-45906 - A novel class of artificially modulated magnetic multilayers based on magnetic shape memory alloys

Description: The temperature dependent micromagnetic behavior, structural phase transitions, magnetic transition, and the dynamics of phase transitions have been investigated using magnetic shape memory alloys. Results provide a novel concept of ‘polymagnets’. In thin film form the number of martensite variants is greatly reduced. A new technique to study dynamics of magnetic phase transitions has been developed applicable to bulk, thin films or multilayers. Transition pathways in magnetic shape memory alloys are as follows: Structural transitions followed by magnetic transition on cooling, and magnetic transition followed by structural transition on heating. The anisotropy of exchange spring mulilayers is greatly sensitive to substrate constraints, and shows a marked rotational hysteresis at lower temperatures. Results also show that a large reduction in coercivity of multilayers is a direct result of broadening of domain wall width by interlayer magnetostatic interactions.
Date: June 20, 2005
Creator: Chopra, H. D.
Partner: UNT Libraries Government Documents Department

Final Technical Report: Nanostructured Shape Memory Alloys

Description: With this grant we explored the properties that result from combining the effects of nanostructuring and shape memory using both experimental and theoretical approaches. We developed new methods to make nanostructured NiTi by melt-spinning and cold rolling fabrication strategies, which elicited significantly different behavior. A template synthesis method was also used to created nanoparticles. In order to characterize the particles we created, we developed a new magnetically-assisted particle manipulation technique to manipulate and position nanoscale samples for testing. Beyond characterization, this technique has broader implications for assembly of nanoscale devices and we demonstrated promising applications for optical switching through magnetically-controlled scattering and polarization capabilities. Nanoparticles of nickel-titanium (NiTi) shape memory alloy were also produced using thin film deposition technology and nanosphere lithography. Our work revealed the first direct evidence that the thermally-induced martensitic transformation of these films allows for partial indent recovery on the nanoscale. In addition to thoroughly characterizing and modeling the nanoindentation behavior in NiTi thin films, we demonstrated the feasibility of using nanoindentation on an SMA film for write-read-erase schemes for data storage.
Date: July 28, 2005
Creator: Crone, Wendy; Drugan, Walter; Ellis, Arthur & Perepezko, John
Partner: UNT Libraries Government Documents Department

Shape trends and triaxiality in neutron-rich odd-mass Y and Nbisotopes

Description: New level schemes of Y and Nb isotopes are proposed based on measurements of prompt gamma rays from 252Cf fission at Gammasphere. Shape trends regarding triaxiality and quadrupole deformations are studied.
Date: September 28, 2004
Creator: Luo, Y.X.; Rasmussen, J.O.; Gelberg, A.; Stefanescu, I.; Hamilton, J.H.; Ramayya, A.V. et al.
Partner: UNT Libraries Government Documents Department

Methods for Analyzing Electric Load Shape and its Variability

Description: Current methods of summarizing and analyzing electric load shape are discussed briefly and compared. Simple rules of thumb for graphical display of load shapes are suggested. We propose a set of parameters that quantitatively describe the load shape in many buildings. Using the example of a linear regression model to predict load shape from time and temperature, we show how quantities such as the load?s sensitivity to outdoor temperature, and the effectiveness of demand response (DR), can be quantified. Examples are presented using real building data.
Date: May 12, 2010
Creator: Price, Philip
Partner: UNT Libraries Government Documents Department