Robert W. M. Smith

Participation in School-Based Extracurricular Activities and Adolescent Adjustment

This paper examines the association between participation in school-based extracurricular activities (ECAs) and adolescent adjustment (drinking, marijuana use, grades, academic attitudes and academic aspirations) among students from six high schools. Three major issues were addressed: the potential confounding of selective EGA participation by better adjusted students and measures of adjustment, variability in the strength of the association between ECA participation and adjustment as a function of adolescent demographic characteristics and activity type, and the role of peers as mediators of the association between ECA participation and adjustment. Adolescents who participated in ECAs reported higher grades, more positive attitudes toward schools, and higher academic aspirations once demographic characteristics and prior adjustment were controlled. Alcohol and marijuana use were not independently associated with ECA participation. The ECA-adjustment association did not vary by demographic characteristics and did not appear to be mediated by peer characteristics. Those who participated in non-sport ECAs reported consistently better adjustment than those who did not participate in ECAs and those who participate in sports.

Regenerator‐based thermoacoustic refrigerator for ice cream storage applications

A regenerator‐based chiller has been built in the ‘‘bellows bounce’’ style [J. Acoust. Soc. Am. 112, 15 (2002)] to replace the vapor compression system in an ice cream sales cabinet. It utilizes a 6‐in.‐diam metal bellows to form a compliant cavity that contains the dynamic pressure oscillation (>50 kPa). The stiffness of the gas trapped in the bellows is resonated against the mass of the bellows‐cap and the mass of a moving‐magnet linear motor which is capable of high (>85%) electro‐acoustic efficiency. A second resonator, operated well below its natural frequency, uses the gas stiffness of a 1‐l volume nested within the bellows and the inertia of an ordinary loudspeaker cone to create the pressure difference across the regenerator that drives gas flow that is in‐phase with pressure. The mass of the cone can be adjusted to vary the multiplication factor that is typically 5%–10% greater than the dynamic pressure within the bellows. The loudspeaker cone suffers none of the hydrodynamic losses associated wi...

Sensorless control of a thermoacoustic refrigerator

A method for commanding the frequency of the signal that drives an electrodynamic sound source to maintain the coupled thermoacoustic resonator at its resonance frequency is described. The method uses only the current and voltage applied to the source terminals to select the operating frequency, thereby eliminating the need for pressure and displacement sensors used in previous phase-locked-loop frequency tracking systems. An equivalent circuit model of the coupled electro-mechanical system is used to extract piston position and pressure from the measured input current and voltage waveforms. Parameters of the electro-mechanical model can be obtained from a least-squares fit of the model using measured current, voltage, position, and force over the frequency range of interest. Parameters thus obtained are in good agreement with individual physical measurements of those same parameters. Results are presented for the implementation of this controller in a large thermoacoustic chiller.

Stability of the parametrically excited damped inverted pendulum: Theory and experiment

The parametrically driven, damped, inverted pendulum can be dynamically stabilized in particular regions of the parameter space. The impact of damping on dynamic stabilization can be stabilizing or destabilizing depending on the location in parameter space (i.e., drive frequency and amplitude). Floquet analysis and numerical simulations were used to determine the stable regions. An experiment was conducted that verifies the model. Physical explanations and simple bounding approximations are provided to summarize findings. The utility of the highly damped pendulum results are illustrated by drawing the analogy to dynamic stabilization of the Rayleigh-Taylor instability: it permits ready demonstration that dynamic stabilization is impossible in that system absent surface tension.

First audiogram for marine mammals in the open ocean and at depth: Hearing and whistling by two white whales down to 30 atmospheres

In examining the potential impact of human‐made sound on sea mammals, it was considered that whale hearing sensitivity might diminish with increasing ambient pressure. To test the effect of depth, two white whales made 885 dives to a platform at 5, 100, 200, or 300 m in the Pacific Ocean. At each stationing on the platform up to 12 min at a time, whales whistled when they heard a 500‐ms tone from a hydrophone. With increasing depth, air density increase in the middle ear, sinuses, and nasal cavity changed each whale’s whistle response, but did not attenuate hearing as it does in the aerial ear (of humans and other land mammals tested in pressure chambers) due to middle ear impedance changes. The findings support theories that sound is conducted through whale head tissues to the ear without the usual ear drum/ossicular chain amplification of the aerial middle ear. These first ever hearing tests in the open ocean demonstrate that whales hear as well at depth as near the surface, therefore, zones of influenc...

High‐efficiency 2‐kW thermoacoustic driver

A moving‐magnet electrodynamic driver will be described which is intended to maintain an acoustic resonance within a thermoacoustic air conditioner containing an inert gas mixture of helium and argon at 30 bar. It is energized by a linear motor with a Bl‐product of 41 N/A and a coil resistance of 0.24 Ω. An auxiliary spring system augments the magnetic stiffness (154 kN/m) to provide a driver mechanical resonance frequency near 60 Hz. An Inconel bellows forms a flexure seal which provides an effective piston area that maximizes electroacoustic conversion efficiency by making the Joule heating losses in the coil equal to the mechanical dissipation in the magnetic suspension. The driver’s electroacoustic conversion efficiency is predicted to be in excess of 83%. [Work supported by the Office of Naval Research.]

Fission-powered in-core thermoacoustic sensor

A thermoacoustic engine is operated within the core of a nuclear reactor to acoustically telemeter coolant temperature (frequency-encoded) and reactor power level (amplitude-encoded) outside the reactor, thus providing the values of these important parameters without external electrical power or wiring. We present data from two hydrophones in the coolant (far from the core) and an accelerometer attached to a structure outside the reactor. These signals have been detected even in the presence of substantial background noise generated by the reactors fluid pumps.

Inhibition of Rayleigh-Bénard convection through acceleration modulation for thermoacoustic devices

The ability to dynamically stabilize Rayleigh-Benard convection using acceleration modulation is of interest to groups who design and study thermoacoustic machines, as the introduction of unwanted convection can have deleterious effects on the desired operation and efficiency of the device. These performance issues caused by suspected convective instability have been seen both in traveling wave thermoacoustic refrigerators and in cryogenic pulse tube chillers. This presentation reports the results of an experiment intended to determine the vibratory, fluidic, and geometric conditions under which a small, rectangular container of statically unstable fluid may be stabilized by vertical vibration, evaluating the computational methods of R. M. Carbo [J. Acoust. Soc. Am. 135 654 (2014)]. Measurements are obtained using a long-displacement kinematic shaker of a unique design with the convecting gas characterized using both thermal transport measurements and flow visualization employing tracer particles illuminated by a diode laser light sheet phase-locked to the shaker. [Work supported by the Julian Schwinger Foundation for Physics Research, the Pennsylvania Space Grant Consortium Graduate Research Fellowship, and the Paul S. Veneklasen Research Foundation.]The ability to dynamically stabilize Rayleigh-Benard convection using acceleration modulation is of interest to groups who design and study thermoacoustic machines, as the introduction of unwanted convection can have deleterious effects on the desired operation and efficiency of the device. These performance issues caused by suspected convective instability have been seen both in traveling wave thermoacoustic refrigerators and in cryogenic pulse tube chillers. This presentation reports the results of an experiment intended to determine the vibratory, fluidic, and geometric conditions under which a small, rectangular container of statically unstable fluid may be stabilized by vertical vibration, evaluating the computational methods of R. M. Carbo [J. Acoust. Soc. Am. 135 654 (2014)]. Measurements are obtained using a long-displacement kinematic shaker of a unique design with the convecting gas characterized using both thermal transport measurements and flow visualization employing tracer particles illumina...

Using the Sound of Nuclear Energy

Abstract The generation of sound by heat has been documented as an acoustical curiosity since 1568 when a Buddhist monk reported in his diary the loud tone generated by a ceremonial rice cooker. Over the last four decades, significant progress has been made in understanding thermoacoustic processes, enabling the design of thermoacoustic engines and refrigerators. Motivated by the Fukushima nuclear reactor disaster, we have developed and tested a thermoacoustic engine that exploits the energy-rich conditions in the core of a nuclear reactor to provide core condition information to the operators without a need for external electrical power. The heat engine is self-powered and can wirelessly transmit the temperature and reactor power level by generation of a pure tone that can be detected outside the reactor. We report here the first use of a fission-powered thermoacoustic engine capable of serving as a performance and safety sensor in the core of a research reactor and present data from the hydrophones in the coolant (far from the core) and an accelerometer attached to a structure outside the reactor. These measurements confirmed that the frequency of the sound produced indicates the reactors coolant temperature and that the amplitude (above an onset threshold) is related to the reactors operating power level. These signals can be detected even in the presence of substantial background noise generated by the reactors fluid pumps.

The vibroacoustical environment in two nuclear reactors

Laboratory experiments have suggested that thermoacoustic engines can be incorporated within nuclear fuel rods. Such engines would radiate sounds that could be used to measure and acoustically-telemeter information about the operation of the nuclear reactor (e.g., coolant temperature or fluxes of neutrons or other energetic particles) or the physical condition of the nuclear fuel itself (e.g., changes in porosity due to cracking, swelling, evolved gases, and temperature) that are encoded as the frequency and/or amplitude of the radiated sound [IEEE Measurement and Instrumentation 16(3), 18–25 (2013)]. For such acoustic information to be detectable, it is important to characterize the vibroacoustical environments within reactors. We will present measurements of the background noise spectra (with and without coolant pumps) and reverberation times within the 70,000 gallon pool that cools and shields the fuel in the 1 MW research reactor on Penn State’s campus using two hydrophones, a piezoelectric projector,...