Silicon has the highest theoretical capacity of any known anode material, and silicon coated carbon nanotubes (Si-CNTs) have shown promise of dramatically increasing battery capacity. However, capacity fading with cycling and low rate capability prevent widespread use. Here, three studies on differing aspects of these batteries are presented. Here, three studies on differing aspects of these batteries are presented. The first examines the rate capability of these batteries. It compares the cycling of electrodes hundreds of microns thick with and without ten micron access holes to facilitate diffusion. The holes do not improve rate capability, but thinner coatings of silicon do improve rate capability, indicating that the limiting mechanism is the diffusion through the nanoscale bulk silicon. The second attempts to enable stable cycling of anodes heavily loaded with silicon, using a novel monolithic scaffolding formed by coating vertically aligned carbon nanotubes (VACNTs) with nanocrystalline carbon. The structure was only able to stabilize the cycling at loadings of carbon greater than 60% of the electrode by volume. These electrodes have volume capacities of ~1000 mAhr/ml and retained over 725 mAhr/ml by cycle 100. The third studies the use of an encapsulation method to stabilize the solid electrolyte interphase (SEI) and exclude the electrolyte. The method was only able to stabilize cycling at loadings below 5% silicon, but exhibits specific capacities as high as 3000 mAhr/g of silicon after 20 cycles.

An alternative pressure-sensor based method for estimating the acoustic intensity, the phase and amplitude gradient estimation (PAGE) method, is presented. This method is similar to the finite-difference p-p (FD) method, in which the intensity is estimated from pressure measurements made using an array of closely spaced microphones. The PAGE method uses the same hardware as the FD method, but does not suffer from the frequency-dependent bias inherent to the FD method. Detailed derivations of the new method and the traditional FD method are presented. Both methods are then compared using two acoustic fields: a plane wave and a three monopole system. The ability to unwrap the phase component of the PAGE method is discussed, which leads to accurate intensity estimates above previous frequency limits. The uncertainties associated with both methods of estimation are presented. It is shown that the PAGE method provides more accurate intensity estimates over a larger frequency bandwidth. The possibility of using a higher-order least-squares estimation with both methods is briefly demonstrated. A laboratory experiment designed to validate the PAGE method was conducted. The preliminary results from this experiment are presented and compared to analytical predictions. Finally, the application of the PAGE method to a static rocket test firing is presented. The PAGE method is shown to provide accurate intensity estimates at frequencies that are higher than possible with just the FD method.

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Modern problems in astrophysics tend to require large, complex computational frameworks to solve many aspects of the system simultaneusly. Calculation of the energy production through nuclear reactions is typically one of those aspects. The use of standard nuclear burning algorithms will take up the majority of the computational time with all but the smallest of networks. The explicit asymptotic method has shown promise in computing large networks faster than existing methods in various environments while retaining accuracy. The purpose of this thesis is to show that this method can be successfully used to solve complex systems using a network of realistic size in a reasonable amount of time, and to investigate some problems in the flame propagation for a Type Ia, which have never been investigated with a realistic network.

The field of biological acoustics has witnessed a steady increase in the research into overtone singing, or “throat-singing,” in which a singer utilizes resonance throughout the vocal tract to sing melodies with the overtones created by a vocal drone. Recent research has explored both how a singer vocalizes in order to obtain rich harmonics from a vocal drone, as well as how further manipulations of the vocal apparatus function to filter and amplify selected harmonics. In the field of phonetics, vowel production is quantified by measuring the frequencies of vocal tract resonances, or formants, which a speaker manipulates to voice a particular vowel. Thus, an investigation of throat singing is closely linked to human speech production. Formants are usually detected in vowel spectra obtained using Fast Fourier Transform algorithms (FFTs). An alternative method that provides much higher frequency resolution is external excitation of the vocal tract and measurement of the pressure response signal at the mouth’s opening, which can be used to calculate the acoustic impedance spectrum. We demonstrate the use of such an “acoustic impedance meter” to measure the formant frequencies of common vowels as well as the oscillatory modes of simple resonant pipe systems. The impedance meter accurately measures fundamental pipe modes and a variety of formant frequencies with an uncertainty of 1 Hz. Finally, we assess how the impedance meter may be used to measure the unique resonances achieved by qualified throat singers.

This research is an analysis of the explosive seed dispersal of Impatiens pallida fruit. Data was taken using high-speed video and analyzed using LoggerPro video analysis software. From the videos we discerned a qualitative model for dehiscence, a description of how the process unfolds, and from our data we deduced quantitative values for the velocity, momentum, and energy of the system. We were also able to glean a lower bound of Young’s modulus E of the fruit tissue. These results and the tools of analysis that generate them are the foundation for the development of a theoretical model of the plants motion. Our results also provide insights into Impatiens pallida’s evolutionary history by explaining its seed dispersal mechanism. A secondary benefit of this research is providing ecologist’s with new tools to analyze ultra-rapid movements in plants and fungi. These tools of analysis will assist in defining a plant’s or fungi’s evolutionary context and the ecological significance rapid motion plays.

Blazars exhibit the most extreme variability of the class of objects known asactive galactic nuclei (AGN). They are characterized by a featureless continuum, high polarization, and variability at all wavelengths and timescales. The amplitude of optical variations can range from less than 0.1 magnitude on the timescale of minutes to hours, to greater than 5.0 magnitudes on timescales of months to years, and gamma-ray variability amplitudes can span a range of as much as three orders of magnitude in a time-scale as short as a few days. These characteristics are consistent with a supermassive black hole accreting matter at the heart of the host galaxy. However, the observed properties of these objects don't necessarily reflect the intrinsic properties because the emissions have been modified by cosmological distances. The variability of these blazars, which have very different redshifts, have been investigated using several different analytical approaches; i.e. structure function analysis, variability index analysis, and light curve analysis. By transforming observed measurements into the rest frame of the source, the intrinsic properties of the variability can be compared. These variability characteristics of blazars, as seen in their rest frame, and as a function of state, will be discussed in reference to their general characteristics and classification schemes.

This work is a description of the Visible to near Infrared Spectrograph system for the CHARA array. The CHARA Array is a 6-telescope interferometer at the Mount Wilson Observatory in the mountains north of Pasadena, California. It combines the light from the 1-meter telescopes, and measures the visibility of the resulting interference fringes, which gives information about the source intensity distribution on the sky. The resolution of the instrument is proportional to the telescope separation, or baseline, divided by the wavelength. The VIS system operates in the 600-1000~nm wavelength range, a factor of 3 to 4 shorter than the standard operating wavelength at CHARA, 2.13 um. An introduction to interferometry is given, with a description of the CHARA Array. The effects of diffraction through the system combined with atmospheric turbulence are described, and the results of a computer model given. The VIS system design is described, and results of the first fringe data are presented, including system visibility and throughput estimates.

The structural properties of the group III-nitrides including AlN, Ga1-xMnxN, GaN:Cu, and InN were investigated by Raman spectroscopy. Absorption and photoluminescence spectroscopy were utilized to study the optical properties in these materials. The analysis of physical vapor transport grown AlN single crystals showed that oxygen, carbon, silicon, and boron are the major impurities in the bulk AlN. The Raman analysis revealed high crystalline quality and well oriented AlN single crystals. The absorption coefficient of AlN single crystals were assessed in the spectral range from deep UV to the FIR. The absorption and photoluminescence analysis indicate that, in addition to oxygen, carbon, boron, and silicon, contribute to the optical properties of bulk AlN crystals. In situ Cu-doped GaN epilayers with Cu concentrations in the range of 2x10^16 cm-3 - 5x1017 cm-3, grown on sapphire substrate by metal organic chemical vapor deposition, were investigated by Raman and PL spectroscopy. The Raman study revealed high crystalline GaN:Cu layers with minimal damage to the hexagonal lattice structure due to the Cu incorporation. A strong Cu related emission band at 2.4 eV was assigned to Cu induced optical transitions between deep Cu states and shallow residual donor states. Compensation of Cu states by residual donors and poor activation probability of deep Cu states are responsible for semi-insulating electrical conductivity. Ferromagnetic Ga1-xMnxN epilayers, grown by MOCVD with Mn concentration from x = 0 to x = 1.5, were optically investigated by Raman, PL, and transmission spectroscopy. The Raman studies revealed Mn-related Raman peaks at 300 cm-1, 609 cm-1, and 669 cm-1. Mn-related absorption and emission bands in Ga1-xMnxN were observed at 1.5 eV and 3.0 eV, respectively. The structural properties of InN layers, grown by high pressure-CVD with different free carrier concentrations, were analyzed by Raman spectroscopy. The Raman results show that the InN layers have high crystalline quality. The free carriers in layers were calculated by using the Lindhard-Mermin dielectric function taking into account finite wave vectors for various scattering processes including forbidden Frohlich, deformational potential associated with allowed electro-optic, and charge density fluctuation, mechanisms. The free carrier concentrations in the layers are below 1x10^20 cm-3.

Strong and variable X-ray emission has long been known to be a universal property of active galaxies. However, despite years of study, the exact nature of the variability remains relatively unknown. We present here results of a multi-year monitoring campaign of a sample of Seyfert galaxies (3C 120, Mkn 509, 3C 390.3, and Akn 120), carried out using the Rossi X-ray Timing Explorer (RXTE). For Mkn 509, we also present results of optical monitoring. Mkn 509 shows a strong correlation between X-ray and optical variations, with the optical leading the X-ray by 25 days. We also investigate the rms-flux relationship in our sample. The two radio loud objects in our sample (3C 120, 3C 390.3) show a clear correlation between flux and rms variability, while the two radio quiet objects (Mkn 509, Akn 120) show no such relationship. Monte Carlo simulations were used to estimate the shape of the underlying power spectrum, and we find that all of our objects have a break frequency below which the power spectrum flattens. The relationship between optical and X-ray variability is discussed, with lags occurring most likely as a result of instabilities or changes in accretion flow propagating inwards through the disk. We also discuss possible physical timescales that could be related to the break frequency, along with connections to galactic X-ray binaries.