Liberal Arts

It is well known that cavitation collapse can generate intense concentrations of mechanical energy, sufficient to erode even the hardest metals and to generate light emissions visible to the naked eye ͓sonoluminescence ͑SL͔͒. Considerable attention has been devoted to the phenomenon of "single bubble sonoluminescence" ͑SBSL͒ in which a single stable cavitation bubble radiates light flashes each and every acoustic cycle. Most of these studies involve acoustic resonators in which the ambient pressure is near 0.1 MPa ͑1 bar͒, and with acoustic driving pressures on the order of 0.1 MPa. This study describes a high-quality factor, spherical resonator capable of achieving acoustic cavitation at ambient pressures in excess of 30 MPa ͑300 bars͒. This system generates bursts of violent inertial cavitation events lasting only a few milliseconds ͑hundreds of acoustic cycles͒, in contrast with the repetitive cavitation events ͑lasting several minutes͒ observed in SBSL; accordingly, these events are described as "inertial transient cavitation." Cavitation observed in this high pressure resonator is characterized by flashes of light with intensities up to 1000 times brighter than SBSL flashes, as well as spherical shock waves with amplitudes exceeding 30 MPa at the resonator wall. Both SL and shock amplitudes increase with static pressure.

High amplitude radial pulsations of a single bubble in several glycerine and water mixtures were observed in an acoustic stationary wave system at acoustic pressure amplitudes on the order of 150 kPa at 21 to 25 kHz. Sonoluminescence, a phenomenon generally attributed to the high temperatures generated during the collapse of cavitation bubbles, was observed as short light pulses occurring once every acoustic period. These emissions could be seen to originate at the geometric center of the bubble when observed through a microscope. It was observed that the light emissions occurred simultaneously with the bubble collapse. Using a laser scattering technique, experimental radius-time curves were obtained which confirmed the absence of surface waves which are expected at pressure amplitudes above 100 kPa. From these radius-time curves, measurements of the pulsation amplitude, the timing of the major bubble collapse, and the number of rebounds were made and compared with several theories. The implications of this research on the current understanding of cavitation were discussed.

High amplitude radial pulsations of a single gas bubble in several glycerine and water mixtures have been observed in an acoustic stationary wave system at acoustic pressure amplitudes as high as 1.5 bars. Using a laser scattering technique, radius-time curves have been obtained experimentally which confirm the absence of surface waves. Measurements of the pulsation amplitude, the timing of the major bubble collapse, and the number of rebounds have been made and compared with the theory. From these data, calculations of the internal gas temperature and pressure during the collapse have been performed. Values of at least 2,000 K and 2,000 bars have been obtained using a sophisticated model of spherically symmetric bubble dynamics. Simultaneously, sonoluminescence (SL), a phenomenon discovered in 1933 and attributed today to the high temperatures and pressures generated during the collapse of the bubbles, were observed as short light pulses occurring once every acoustic period. The light emissions can be seen to originate at the geometric center of the bubble when observed through a microscope. Also, the simultaneity of the light emissions and the collapse of the bubble has been confirmed with the aid of a photomultiplier tube. This is the first recorded observation of SL generated by a single bubble. Comparisons of the measured quantities have been made to those predicted by several models. In addition, the implications of this research on the current understanding of cavitation related phenomena such as rectified diffusion, surface wave excitation and sonoluminescence will be discussed. Some possible future experiments are suggested which could further increase our understanding of cavitation bubble dynamics.

High-amplitude radial pulsations of a single gas bubble in several glycerine and water mixtures have been observed in an acoustic stationary wave system at acoustic pressure amplitudes on the order of 150 kPa ( 1.5 arm) at 21-25 kHz. Sonoluminescenee (SL), a phenomenon generally attributed to the high temperatures generated during the collapse of cavitation bubbles, was observed as short light pulses occurring once every acoustic period. These emissions can be seen to originate at the geometric center of the bubble when observed through a microscope. It was observed that the light emissions occurred simultaneously with the bubble collapse. Using a laser scattering technique, experimental radius-time curves have been obtained which confirm the absence of surface waves, which are expected at pressure amplitudes above 100 kPa. IS. Hotsburgh, Ph.D. dissertation, University of Mississippi (1990) ]. Also from these radius-time curves, measurements of the pulsation amplitude, the timing of the major bubble collapse, and the number of rebounds were made and compared with several theories. The implications of this research on the current understanding of cavitation related phenomena such as rectified diffusion, surface wave excitation, and sonoluminescence are discussed.

Single bubble sonoluminescence in an air-water system has been shown to occur along a unique surface in the acoustic pressure-ambient radius-gas concentration parameter space where the bubble is stable both in shape and in ͑average͒ size. In this paper, we show how the bubble deviates from the expected path ͑traced by the shape-instability threshold as a function of pressure͒ in order to reach the observed stability. We also present measurements of the expansion ratio (R max /R 0 ) for bubbles near the threshold for light emission. The results suggest that maximal bubble radial response is an insufficient criterion for the onset of light emission, and we present data for the dependence of the emitted light on several parameters.

Catalonia, the autonomous region of Spain has seen an increase in secessionist sentiments in recent years. While the past inclination toward independence has been centered on economic autonomy and cultural identity, there has been a recent emphasis on political independence, particularly in the times of crisis. In this thesis. I analyze the relationship between the economic changes during the period of a crisis and the public opinion about the potential Catalan secession. Specifically, it investigates the relationships between the economic change and public sentiment during the financial crisis of 2008, the political crisis of 2017, and the pandemic crisis of 2020. I hypothesized that there would be a significant relationship between the economic growth and the Catalan desire to secede during times of crisis. To test my hypothesis, I conducted a trend analysis of the percentage of agreement with questions or statements posed by the Baròmetre d’Opinió Política [Political Opinion Baro...