Open Access. Powered by Scholars. Published by Universities.®
- Keyword
-
- Active noise control (2)
- Noise (2)
- Acoustic (1)
- Acoustic energy density (1)
- Annealing (1)
-
- Apertured beam (1)
- Atom-photon collisions (1)
- Band gap (1)
- Bell's Inequality (1)
- Bell's Theorem (1)
- Binary alloys (1)
- COMSUBS (1)
- Compositional stability (1)
- Conversion efficiency (1)
- Cooling fan (1)
- Cooling fans (1)
- DC-bias (1)
- David Mermin (1)
- Delta scuti (1)
- Density calculations (1)
- Diffusion (1)
- Directional (1)
- Domain average (1)
- ED (1)
- Electromagnetic scattering (1)
- Equilibrum calculations (1)
- FIREBALL (1)
- FePt (1)
- Feedback (1)
- Ferroelectric perovskites (1)
- Publication
- Publication Type
Articles 1 - 16 of 16
Full-Text Articles in Entire DC Network
Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson
Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson
Theses and Dissertations
Electromagnetic scattering from a rough two dimensional homogeneous scatterer has been computationally modeled. The scatterer is intended to simulate reflection from a two interface multilayer. The rough scatterer was created from Gaussian random points centered about an ideal interface. The points were connected with a third order spline interpolant which accounts for correlation between neighboring surface atoms. The scalar electric field integral equation (EFIE) and magnetic field integral equation (MFIE) were solved using the Nystrom method to obtain the reflected intensity as a function of observation angle. Verification of the accuracy of the code was obtained by means of comparison …
Ordering Tendencies In The Binary Alloys Of Rh, Pd, Ir, And Pt: Density Functional Calculations, Gus L. W. Hart, Brian Kolb, Stefan Müller, David B. Botts
Ordering Tendencies In The Binary Alloys Of Rh, Pd, Ir, And Pt: Density Functional Calculations, Gus L. W. Hart, Brian Kolb, Stefan Müller, David B. Botts
Faculty Publications
The binary alloys of Rh, Pd, Ir, and Pt are important because of their high catalytic potential. We report in this paper that the Rh1-xIrx and Rh1-xPtx systems, long thought to phase separate at low temperatures, actually exhibit miscibility over the entire concentration and temperature range. We find low critical ordering temperatures, indicating that long-range order is unlikely to be observed experimentally. These results are compared with previous theoretical predications for the other binary alloys of Rh, Pd, Ir, and Pt and with calculations performed here on the Pt1-xIrx and Pd1-xIrx systems. We discuss these results and investigate the mechanisms …
Fourier Spectroscopy Of Ultrashort Laser Pulses, Scott D. Bergeson, Justin Peatross
Fourier Spectroscopy Of Ultrashort Laser Pulses, Scott D. Bergeson, Justin Peatross
Faculty Publications
We describe a Fourier-transform spectrometer appropriate for use in an undergraduate optics laboratory. The modular design, which uses off-the-shelf equipment, is suitable for determining the spectra of ultrashort pulsed and continuous light sources. The spectrometer does not require equal step sizes for the motion of the mirror. An algorithm interpolates the phase of both a reference and an unknown light beam at equal intervals before performing the Fourier transform. The interferometer scan and the phase and spectral analysis are performed in a few seconds, making the apparatus a useful tool for teaching concepts of temporal coherence and Fourier spectroscopy.
Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter
Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter
Theses and Dissertations
Measurements in a reverberation chamber use spatially averaged squared pressure to calculate sound absorption, sound power, and other sound measurements. While a reverberation chamber provides an approximation of a diffuse sound field, variations in the measurements introduce uncertainty in measurement results. Room qualification procedures require a sufficient number of source-receiver locations to obtain suitable measurements. The total acoustic energy density provides greater spatial uniformity than squared pressure, which requires fewer source-receiver positions to produce similar or better accuracy in measurement results. This paper explores the possibility of using energy density in place of squared pressure, using methods outlined in current …
Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green
Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green
Theses and Dissertations
Feedback active noise control (ANC) has been applied as a means of attenuating broadband noise from a small axial cooling fan. Such fans are used to maintain thermal stability inside of computers, projectors, and other office equipment and home appliances. The type of low-level noise radiated from axial cooling fans has been classified as harmful to productivity and human well being. Previous research has successfully implemented feed-forward ANC, targeting specific narrow-band fan noise content related to the blade passage frequency (BPF) of the fan. The reference signal required for a feed-forward algorithm limits its ability to attenuate much of the …
Mesoscopic Domain Average Engineering Simulations Of Ferroelectric Perovskites Compared With Multidomain Group Theoretical Predictions, Brandon J. Keith, Dorian M. Hatch
Mesoscopic Domain Average Engineering Simulations Of Ferroelectric Perovskites Compared With Multidomain Group Theoretical Predictions, Brandon J. Keith, Dorian M. Hatch
Faculty Publications
Engineered, multidomain ferroelectrics are of current interest for mechatronic and optical applications. Previously [D. M. Hatch et al., J. Appl. Phys. 94, 5220 (2003)], we presented a set of tables/symmetry rules showing all possible domain average engineered multidomain structures arising from [100]-, [110]-, and [111]-ordering ferroelectric transitions from a Pm[overline 3]m perovskite structure. In this work we test those predictions against three-dimensional mesoscopic fast quench simulations under various electric/stress field combinations and find excellent agreement with multidomain group theory. These simulations use a Langevin strain-displacement/polarization evolution strategy and are important to developing processing conditions for materials with precise domain structures.
Understanding Dc-Bias Sputtered Thorium Oxide Thin Films Useful In Euv Optics, William R. Evans, Sarah C. Barton, Michael Clemens, David D. Allred
Understanding Dc-Bias Sputtered Thorium Oxide Thin Films Useful In Euv Optics, William R. Evans, Sarah C. Barton, Michael Clemens, David D. Allred
Faculty Publications
We use spectroscopic ellipsometry to determine the optical constants of seven thin-film ThO2 samples deposited by radio-frequency sputtering, thickness ranging between 24 and 578 nm, for the spectral range of 1.2 to 6.5. We used a hollow-cathode light source and vacuum monochromator to measure constants at 10.2 eV. None of the deposition parameters studied including DC-bias voltages successfully increased the n of (that is, densify) thoria films. The value of n at 3.0 eV is 1.86 ± 0.04. We find compelling evidence to conclude that the direct bad gap is at ~5.9 eV, clarifying the results of others, some of …
Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson
Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson
Theses and Dissertations
Previous work has shown that active noise control is a feasible solution to attenuate tonal noise radiated by small axial cooling fans, such as those found in desktop computers. One such control system reduced noise levels of a baffled 80-mm fan in the free field with four small loudspeakers surrounding the fan. Due to industry specified spatial constraints, a smaller fan and speaker configuration was desirable. The smaller configuration maintains similar control performance, further facilitating practical implementation of the control system. The smaller control system employs a smaller fan running at a higher speed. Different loudspeaker configurations for control exist …
A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose
A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose
Theses and Dissertations
The detection of variable stars in open clusters is an essential component of testing stellar structure and evolution theories. The ability to detect low-amplitude variability among cluster members is directly related to the quality of the photometric results. Point Spread Function (PSF) fitting is the best method available for measuring accurate magnitudes within crowded fields of stars, while high-precision differential photometry is the preferred technique for removing the effects of atmospheric extinction and variable seeing. In the search for new variable stars among hundreds or thousands of stars, the Robust Median Statistic (RoMS) is proven more effective for finding low-amplitude …
Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter
Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter
Theses and Dissertations
We studied the wurtzite to rock salt phase transition in gallium nitride ( GaN ). Using the mapping algorithm of COMSUBS we found 435 possible mechanisms for this transition. We then used FIREBALL to do density functional theory calculations and found enthalpy barrier heights for the transition pathway. We used this to determine the mechanisms that are the most favorable for GaN. The most favorable mechanisms for GaN are those that break no bonds during the phase transition. The bond-preserving mechanisms involve bilayer sliding of (010) hexagonal plane in the plus or minus [100] hexagonal direction.
Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix
Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix
Theses and Dissertations
Highly directive loudspeakers have long been important tools for sound system designers, experimental acousticians, and many other professionals in the audio industry. They allow sound engineers to more easily manipulate the radiation pattern of their loudspeakers to accommodate the purpose of the venue. Many commercially available products, while exhibiting good directivity at mid and high frequencies, generally lack control in the low frequency range. A new method for controlling the radiation pattern of a loudspeaker at low frequencies has been developed and modeled extensively. Prototypes have been built and tested in an anechoic chamber. Results from computer modeling and experimental …
Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter
Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter
Theses and Dissertations
We investigate the spatial evolution of an intense laser pulse as it generates high-order harmonics in a long gas cell, filled with 80 torr of helium. A thin foil separates the gas-filled region of the cell from a subsequent evacuated region. The exit plane of the gas cell can be scanned along the laser axis so that the evolution of the laser throughout the focus can be observed (full scanning range of 9 cm). We constructed an apparatus that images the laser radial energy profile as it exits the cell. The high harmonics, odd orders ranging from 45 to 91, …
Compositional Stability Of Fept Nanoparticles On Sio2/Si During Annealing, Richard R. Vanfleet, B. Yao, R. V. Petrova, K. R. Coffey
Compositional Stability Of Fept Nanoparticles On Sio2/Si During Annealing, Richard R. Vanfleet, B. Yao, R. V. Petrova, K. R. Coffey
Faculty Publications
The loss of Fe due to oxidation or diffusion into the substrate can prevent the successful preparation of well-ordered, stoichiometric, FePt nanoparticles. In this work we report the composition changes during annealing observed for small (<10 nm) FePt nanoparticles on thermally grown SiO2 layers on Si wafer substrates. Additionally, we describe the use of a controlled reducing gas mixture, Ar+H2+H2O, to reduce the loss of Fe.
The Violation Of Bell's Inequality In A Deterministic But Nonlocal Model, Stephanie Allred Magleby
The Violation Of Bell's Inequality In A Deterministic But Nonlocal Model, Stephanie Allred Magleby
Theses and Dissertations
This thesis investigates the violation of Bell's Inequality through the use of nonlocal measurement schemes as encapsulated in a quasi-deterministic toy model. This toy model, called the Q Box, is reminiscent of Mermin's Box in that it describes a system that appears to be deterministic yet produces the statistics of a quantum type system. [1] The workings of the Q Box are detailed both as a thought experiment and as a computer simulation. Nonlocal measurement protocols similar to those which generate a violation of Bell's Inequality in the Q Box are also applied to Mermin's Box, with comparable results. [1] …
Compact Solid-State Laser Source For 1s-2s Spectroscopy In Atomic Hydrogen, Scott D. Bergeson, N. Kolachevsky, J. Alnis, T. W. Hansch
Compact Solid-State Laser Source For 1s-2s Spectroscopy In Atomic Hydrogen, Scott D. Bergeson, N. Kolachevsky, J. Alnis, T. W. Hansch
Faculty Publications
We demonstrate a compact solid-state laser source for high-resolution two-photon spectroscopy of the 1S-2S transition in atomic hydrogen. The source emits up to 20 mW at 243 nm and consists of a 972 nm diode laser, a tapered amplifier, and two doubling stages. The diode laser is actively stabilized to a high-finesse cavity. We compare the new source to the stable 486 nm dye laser used in previous experiments and record 1S-2S spectra using both systems. With the solid-state laser system, we demonstrate a resolution of the hydrogen spectrometer of 6×10^11, which is promising for a number of high-precision measurements …
Finding The Radial Parallel Temperature Profile In A Non-Neutral Plasma Using Equilibrium Calculations On Experimental Data, Grant W. Hart, Bryan G. Peterson
Finding The Radial Parallel Temperature Profile In A Non-Neutral Plasma Using Equilibrium Calculations On Experimental Data, Grant W. Hart, Bryan G. Peterson
Faculty Publications
In 1992, Eggleston et al. [D. L. Eggleston et al., Phys. Fluids B 4, 3432 (1992)] reported on a technique for measuring the radial temperature profile in a pure-electron plasma confined in a Malmberg-Penning trap by partially dumping the plasma onto a charge collector at the end of the trap. For short plasmas and short confining rings, the assumptions in their paper are violated and a more general calculation is needed. This paper presents a variation of the standard equilibrium calculation to find the temperature profile of a pure-electron plasma. Eggleston's shortcut "evaporation" temperature method is found to require a …