Application of Swept-Sine Excitation for Acoustic Impedance Education

The NASA Langley Normal Incidence Tube (NIT) and Grazing Flow Impedance Tube (GFIT) are regularly employed to characterize the frequency response of acoustic liners through the eduction of their specific acoustic impedance. Both test rigs typically use an acoustic source that produces sine wave signals at discrete frequencies (Stepped-Sine) to educe the impedance. The current work details a novel approach using frequency-swept sine waveforms normalized to a constant sound pressure level for excitation. Determination of the sound pressure level and phase from microphone measurements acquired using swept-sine excitation is performed using a modified Vold-Kalman order tracking filter. Four acoustic liners are evaluated in the NIT and GFIT with both stepped-sine and swept-sine sources. Using these two methods, the educed impedance spectra are shown to compare favorably. However, the new (Swept-Sine) approach provides much greater frequency resolution in less time, allowing the acoustic liner properties to be studied in much greater detail

THE EFFECTS OF FARMLAND, FARMLAND PRESERVATION AND OTHER NEIGHBORHOOD AMENITIES ON PROXIMATE HOUSING VALUES: RESULTS OF A CONJOINT ANALYSIS OF HOUSING CHOICE

Using stated-preference data from a choice-based conjoint analysis instrument, we estimate willingness to pay for the presence of neighboring land that is dedicated to agricultural use (versus a developed land use) and for the preservation of surrounding farmland as permanent cropland. The data also elucidate how individuals balance the values associated with nearby agricultural land patterns with other key neighborhood characteristics such as neighborhood parks, housing density, commute times, school quality and neighborhood safety. The median respondent from a randomly chosen sample of Columbus, Ohio homeowners was willing to pay $843 annually to avoid immediate conversion of 10 percent of agricultural land within one mile of the house valued in the conjoint experiment while the same respondent was willing to pay$277 annually to preserve the same amount of farmland as permanent cropland. We find provision of neighborhood parks within housing developments to be a strong substitute for farmland preservation.Land Economics/Use,

What\u27s on First?: Organizing the Casebook and Molding the Mind

This study empirically tests the proposition that law students adopt different conceptions of the judge’s role in adjudication based on whether they first study intentional torts, negligence, or strict liability. The authors conducted an anonymous survey of more than 450 students enrolled in eight law schools at the beginning, mid-point, and end of the first semester of law school. The students were prompted to indicate to what extent they believed the judge’s role to be one of rule application and, conversely, to what extent it was one of considering social, economic, and ideological factors. The survey found that while all three groups of students shifted toward a belief that judges consider social, economic, and ideological factors, the degree of the shift differed in a statistically significant way depending on which torts their professors taught first. These differences persisted throughout the semester, even after they studied other torts. Further, these differences were observed even when the analysis controlled for law school ranking and were more pronounced among students attending the highest ranked schools. In interpreting the survey results, the authors employ sociologist Erving Goffman’s theory of “frame analysis” and the work of cognitive psychologists including Amos Tversky and Daniel Kahneman on “anchoring.” The Article concludes that the category of tort liability to which students are first exposed affects the “frame” or “lens” through which they view the judicial process. This frame becomes anchored and persists throughout the study of other tort categories. The lessons about the nature of the judging process learned implicitly through the professor’s choice of topic sequence may be even more important than the substantive topics themselves

Keeping Cases from Black Juries: An Empirical Analysis of How Race, Income Inequality, and Regional History Affect Tort Law

This Article presents an empirical analysis of how race, income inequality, the regional history of the South, and state politics affect the development of tort law. Beginning in the mid-1960s, most state appellate courts rejected doctrines such as contributory negligence that traditionally prevented plaintiffs’ cases from reaching the jury. We examine why some, mostly Southern states did not join this trend. To enable cross-state comparisons, we design an innovative Jury Access Denial Index (JADI) that quantifies the extent to which each state’s tort doctrines enable judges to dismiss cases before they reach the jury. We then conduct a multivariate analysis that finds strong correlations between a state’s JADI and two factors: (1) the percentage of African Americans in its largest cities, and (2) its history as a former slave-holding state. These findings suggest that some appellate courts, particularly those in the South, afraid that juries with substantial African-American representation would redistribute wealth or retaliate for grievances, struck preemptively to prevent cases from reaching them. Surprisingly, we do not find a consistent association between a state’s JADI and either income inequality or its political leanings. In other words, race and region, rather than economic class or politics, explain the failure to embrace pro-plaintiff changes that occurred elsewhere. We suggest, therefore, that states that declined to discard antiquated anti-jury substantive doctrines between the mid-1960s and the mid-1980s should acknowledge that these precedents were tainted by their predecessors’ efforts to keep tort cases from African-American jurors and refuse to accord them deference

An Atlas of Foraminifera, Ostracoda and Micro-Molluscs around Lord Howe Island and Middleton Reef

The Lord Howe seamount chain on the western margin of Zealandia some 580 km off the east coast of Australia provides a suitable habitat for the growth of the southernmost coral reefs in the Pacific Ocean. The shelves around Middleton Reef, Lord Howe Island and Balls Pyramid represent carbonate depositional environments where calcareous microfossils are common and generally well preserved. While many of the organisms were originally carried to the islands by an offshoot from the East Australian Current, thus having many species in common with eastern Australia, the islands also exhibit a number of endemic species that have evolved locally over the last 6.5 million years. The islands are now home to rich and well diversified foraminiferal, ostracod and micro-molluscan fauna, which have not been fully documented previously. This book provides an atlas of the microfossils from lagoonal, beach, shallow near-shore and deeper shelf environments around Middleton Reef, Lord Howe Island and Balls Pyramid. Many of the foraminifer and ostracod species can be directly related to the taxonomy and ecology of the foraminifer and ostracod fauna from southeastern Australian coastal and shallow marine environments that were described and illustrated by Yassini and Jones (1995). About The Book: The first section of the book provides a general introduction about the development of the seamount chain, the location of the study area, its bathymetry, morphology and sedimentary facies. It does not assume any prior knowledge of the area or any exposure to the taxonomy or ecology of these organisms. It is expected to be useful in geological, environmental and marine science studies. The main aim of this book is to provide a photographic atlas of all the recognised microfossil species from Lord Howe Island, Balls Pyramid and Middleton Reef. This will enable future researchers to reassess the assemblages and provide the basis for international comparisons with these faunas. The known depth and environmental parameters for each of the recognised species are presented in tabular form. It must be noted that this investigation is based on thanatocenose investigations and does not imply that each species necessarily lived in the environment in which it was found since it could have been affected by post-mortem transport.https://ro.uow.edu.au/uowbooks/1031/thumbnail.jp

Over-the-Rotor Liner Investigation via the NASA Langley Normal Incidence Tube

NASA Langley and Glenn Research Centers have collaborated on the usage of acoustic liners mounted very near or directly over the rotor of turbofan aircraft engines. This collaboration began over a decade ago with the investigation of a metallic foam liner. Similar to conventional acoustic liner applications, this liner was designed to absorb sound generated by the rotor-alone and rotor-stator interaction sources within the fan duct. Given its proximity to the rotor tips, the expectation was that the liner would also serve as a pressure release and thereby inhibit the amount of noise generated. Initial acoustic results were promising, but there was concern regarding potential aerodynamic penalties. Nevertheless, there were sufficient positive results to warrant further investigation. To that end, the current report presents results obtained in the NASA Langley Normal Incidence Tube for 20 acoustic liner candidates for the OTR application. The majority contain grooves at their surface, designed to minimize aerodynamic penalties caused by placing the liner in close proximity to the fan rotor tips. The intent is to assess the acoustic properties of each liner configuration, and in particular to assess the effects of including the grooves on the overall acoustic performance. An additional intent of this paper is to provide documentation regarding recent enhancements to the NASA Langley Normal Incidence Tube

A Conventional Liner Acoustic/Drag Interaction Benchmark Database

The aerodynamic drag of acoustic liners has become a significant topic in the design of such for aircraft noise applications. In order to evaluate the benefits of concepts designed to reduce liner drag, it is necessary to establish the baseline performance of liners employing the typical design features of conventional configurations. This paper details a set of experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of a number of perforate-over-honeycomb liner configurations at flow speeds of M=0.3 and 0.5. These conventional liners are investigated to determine their resistance factors using a static pressure drop approach. Comparison of the resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 Hz at source sound pressure levels of 140 and 150 dB. Educed impedance and attenuation spectra are used to determine the interaction between acoustic performance and drag

Graphical Acoustic Liner Design and Analysis Tool

An interactive liner design and impedance modeling tool comprises software utilized to design acoustic liners for use in constrained spaces, both regularly and irregularly shaped. A graphical user interface allows the acoustic channel geometry to be drawn in a liner volume while the surface impedance calculations are updated and displayed in real-time. A one-dimensional transmission line model may be used as the basis for the impedance calculations

Acoustic Liner Drag: A Parametric Study of Conventional Configurations

Interest in the characterization of the aerodynamic drag performance of acoustic liners has increased in the past several years. This paper details experiments in NASA Langley's Grazing Flow Impedance Tube to quantify the relative drag of several conventional perforate-over-honeycomb liner configurations. For a fixed porosity, facesheet hole diameter and cavity depth are varied to study the effect of each. These configurations are selected to span the range of conventional liner geometries used in commercial aircraft engines. Detailed static pressure and acoustic measurements are made for grazing flows up to M=0.5 at 140 dB SPL for tones between 400 and 2800 Hz. These measurements are used to calculate a resistance factor () for each configuration. Analysis shows a correlation between perforate hole size and the resistance factor but cavity depth seems to have little influence. Acoustic effects on liner drag are observed to be limited to the lower Mach numbers included in this investigation

Acoustic Liner Drag: Measurements on Novel Facesheet Perforate Geometries

Interest in characterization of the aerodynamic drag of acoustic liners has increased in the past several years. This paper details experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of several perforate-over-honeycomb liner configurations at flow speeds of centerline flow Mach number equals 0.3 and 0.5. Various perforate geometries and orientations are investigated to determine their resistance factors using a static pressure drop approach. Comparison of these resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 hertz at source sound pressure levels of 140 and 150 decibels. Educed impedance and attenuation spectra are used to determine the impact of variations in perforate geometry on acoustic performance