Evaluation of a multi-point method for determining acoustic impedance

An investigation was conducted to explore potential improvements provided by a Multi-Point Method (MPM) over the Standing Wave Method (SWM) and Two-Microphone Method (TMM) for determining acoustic impedance. A wave propagation model was developed to model the standing wave pattern in an impedance tube. The acoustic impedance of a test specimen was calculated from a best fit of this standing wave pattern to pressure measurements obtained along the impedance tube centerline. Three measurement spacing distributions were examined: uniform, random, and selective. Calculated standing wave patterns match the point pressure measurement distributions with good agreement for a reflection factor magnitude range of 0.004 to 0.999. Comparisons of results using 2, 3, 6, and 18 measurement points showed that the most consistent results are obtained when using at least 6 evenly spaced pressure measurements per half-wavelength. Also, data were acquired with broadband noise added to the discrete frequency noise and impedances were calculated using the MPM and TMM algorithms. The results indicate that the MPM will be superior to the TMM in the presence of significant broadband noise levels associated with mean flow

Investigating Behavioral Responses to Positive Inducements for Filing Tax Returns

A significant amount of non-compliance associated with the personal income tax is due to the taxpayers who are not “in the system,” not having filed a tax return in the recent past or perhaps ever. We use experimental laboratory methods to examine two types of positive incentives for filing tax returns: tax credits and social safety net benefits, both of which are conditional on tax filing. Our experimental design captures the essential features of the voluntary income reporting and tax assessment system used in many countries. Human participants in a controlled laboratory environment earn income through their performance in a task. The participants must then decide whether to file a tax return and, conditional upon filing, how much income to report. Taxes are paid on reported income only. Unreported income of filers may be discovered via a random audit, and the participant must then pay the owed taxes plus a fine based on the unpaid taxes; non-filers are not subject to an audit. Inducements for filing are introduced in several alternative treatments. In one treatment we introduce a social safety net (e.g., unemployment replacement income) that is conditional on past filing behavior. In a second treatment we introduce tax credits that are available either to low income participants or to all income levels, but again only to those who file a tax return. Our results suggest that a tax credit increases filing but only if the credit is targeted to low income earners. The provision of a social safety net via unemployment benefits also has a positive, albeit indirect, impact on participation. Key Words:

Inducing Private Wildfire Risk Mitigation: Experimental Investigation of Measures on Adjacent Public Lands

Increasing private wildfire risk mitigation is an important part of the larger forest restoration policy challenge. Data from an economic experiment are used to evaluate the effectiveness of providing fuel treatments on public land adjacent to private land to induce private wildfire risk mitigation. Results show evidence of “crowding out” where public spending can decrease the level of private risk mitigation. However, a policy prescription that ameliorates this crowding out is identified. Participants undertake more mitigation when fuel treatments on publicly owned lands are conditional on a threshold level of private mitigation effort and information describing each participant’s spending is provided. Key Words:

Fluctuating pressures measured beneath a high-temperature, turbulent boundary layer on a flat plate at Mach number of 5

Fluctuating pressures were measured beneath a Mach 5, turbulent boundary layer on a flat plate with an array of piezoresistive sensors. The data were obtained with a digital signal acquisition system during a test run of 4 seconds. Data sampling rate was such that frequency analysis up to 62.5 kHz could be performed. To assess in situ frequency response of the sensors, a specially designed waveguide calibration system was employed to measure transfer functions of all sensors and related instrumentation. Pressure time histories were approximated well by a Gaussian prohibiting distribution. Pressure spectra were very repeatable over the array span of 76 mm. Total rms pressures ranged from 0.0017 to 0.0046 of the freestream dynamic pressure. Streamwise, space-time correlations exhibited expected decaying behavior of a turbulence generated pressure field. Average convection speed was 0.87 of freestream velocity. The trendless behavior with sensor separation indicated possible systematic errors

Experimental validation of a two-dimensional shear-flow model for determining acoustic impedance

Tests were conducted to validate a two-dimensional shear-flow analytical model for determining the acoustic impedance of a liner test specimen in a grazing-incidence, grazing-flow environment. The tests were limited to a test specimen chosen to exhibit minimal effects of grazing flow so that the results obtained by using the shear-flow analytical model would be expected to match those obtained from normal-incidence impedance measurements. Impedances for both downstream and upstream sound propagation were generally consistent with those from normal-incidence measurements. However, sensitivity of the grazing-incidence impedance to small measurement or systematic errors in propagation constant varied dramatically over the range of test frequencies