Characterization of High-Power Rocket and Jet Noise Using Near-Field Acoustical Holography

Structural fatigue, hearing damage, and community disturbances are all consequences of rocket and jet noise, especially as they become more powerful. Noise-reduction schemes require accurate characterization of the noise sources within rocket plumes and jets. Nearfield acoustical holography (NAH) measurements were made to visualize the sound field in the jet exhaust region of an F-22 Raptor. This is one of the largest-scale applications of NAH since its development in the 1980s. A scan-based holographic measurement was made using a 90-microphone array with 15 cm regular grid spacing, for four engine power settings. The array was scanned through 93 measurement positions, along three different planes in a region near 7 m from the jet centerline and 23 m downstream. In addition, 50 fixed reference microphones were placed along the ground 11.6 m from the jet centerline, spanning 30.8 m. The reference microphones have been used to perform virtual coherence on the measurement planes. Statistically-optimized NAH (SONAH) has been used to backpropagate the sound field to the source region for low frequencies, and to identify jet noise characteristics. Ground reflection interference and other non-ideal measurement conditions must be dealt with. Details relating to jet coherence lengths and their relation to reference microphone requirements will be discussed. Preliminary results of this ongoing work will be presented. [Work supported by Air Force SBIR.

Characterization of Rocket and Jet Noise using Near-Field Acoustic Holography Methods

As rockets and jets on military aircraft become more powerful, the noise they produce can lead to structural fatigue, hearing damage, and community disturbances. Noise-reduction technologies and sound radiation prediction require accurate characterization of the noise sources within rocket plumes and jets. Near-field acoustical holography techniques were used to visualize the sound field in the region of the jet exhaust on a high-performance military jet. Holography requires a coherent measurement of the sound field, but the size of the jet made a dense measurement over the entire source region impractical. Thus, a scan-based measurement was performed, after which a partial field decomposition (PFD) procedure was used to tie together incoherent scans. Then, the effective aperture of the measurement was extended utilizing the rigid ground reflection and a processing technique called analytic continuation. Finally, the three-dimensional sound field was reconstructed using statistically-optimized near-field acoustical holography (SONAH). This is the first time such a map has been obtained for a full-scale military aircraft. [Work supported by Air Force SBIR.

The behavioural wedge

When nations fail to agree, can individual citizens make a difference? The third of our post-Copenhagen features is by Jonathan Gilligan, Thomas Dietz, Gerald T. Gardner, Paul C. Stern , and Michael P. Vandenbergh . They look at the effects that voluntary actions by individuals can have, and at the policies that can best encourage such actions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79202/1/j.1740-9713.2010.00405.x.pd

Energy and Climate Change: Key Lessons for Implementing the Behavioral Wedge

The individual and household sector accounts for roughly 40 percent of United States energy use and carbon dioxide emissions, yet the laws and policies directed at reductions from this sector often reflect a remarkably simplistic model of behavior. This Essay addresses one of the obstacles to achieving a “behavioral wedge” of individual and household emissions reductions: the lack of an accessible, brief summary for policymakers of the key findings of behavioral and social science studies on household energy behavior. The Essay does not provide a comprehensive overview of the field, but it discusses many of the leading studies that demonstrate the extent and limits of rational action. These studies can inform lawyers and policymakers who are developing measures to reduce energy use and carbon emissions and can serve as an entry point for more detailed studies of the literature. An effective response to the climate change problem will require substantial reductions in energy demand in addition to new developments in low-carbon energy supplies. The individual and household sector presents a major opportunity: the sector accounts for roughly 40% of U.S. carbon emissions and a comparable percentage of total U.S. energy production, and it is one of the most promising areas for reducing emissions. A recent analysis estimates that behavioral measures directed at this sector could reasonably be expected to reduce total US emissions by over 7% by 2020, an amount larger than the combined emissions from several of the largest-emitting industrial sectors and larger than the total emissions of France. In many cases, these emissions reductions can be achieved at less cost than the leading alternatives. Despite this opportunity, recent regulatory and policy efforts are only beginning to direct substantial attention to the individual and household sector. Findings from the social sciences provide valuable insights into how to capitalize on this opportunity, yet policymakers often have little time to develop new polices and are confronted with a barrage of often-conflicting approaches and theories. This Essay addresses the policy-making challenge by distilling the findings from a broad range of fields into several key principles for those developing energy and climate laws and policies. The principles we outline here are a starting point for policymakers working in this area. We attempt to provide insight into which principles are most relevant to law and policy, but instructions as to how to incorporate these principles are beyond the scope of this essay. The principles include only a subset of the insights from the behavioral and social science literature. In many cases, adherence to multiple principles will be necessary to develop the most effective policy design. Policymakers should consult the body of work referenced here, as well as experts in the social sciences to further their understanding of these and other principles. More extensive reviews of this literature and its relevance to energy and climate policy are also available

Scaling of Majorana Zero-Bias Conductance Peaks

We report an experimental study of the scaling of zero-bias conductance peaks compatible with Majorana zero modes as a function of magnetic field, tunnel coupling, and temperature in one-dimensional structures fabricated from an epitaxial semiconductor-superconductor heterostructure. Results are consistent with theory, including a peak conductance that is proportional to tunnel coupling, saturates at $2e^2/h$, decreases as expected with field-dependent gap, and collapses onto a simple scaling function in the dimensionless ratio of temperature and tunnel coupling.Comment: Accepted in Physical Review Letter

Digital Image Correlation Data Processing and Analysis Techniques to Enhance Test Data Assessment and Improve Structural Simulations

The NASA Shell Buckling Knockdown Factor Project (SBKF) was established in 2007 by the NASA Engineering and Safety Center (NESC) with the primary goal to develop new analysis-based buckling design factors (a.k.a. knockdown factors) and high-fidelity buckling simulations for selected launch-vehicle-like cylindrical shell structures. A series of tests are being conducted on large-scale metallic and composite cylindrical shells in order to provide validation data for these new factors and simulations. However, the validation of these new factors and simulations is quite demanding and requires test data that is commensurate with their fidelity. Traditional instrumentation, such as linear variable displacement transducers (LVDTs) and electrical-resistance strain gages serve a critical role in providing accurate displacement and strain measurements in these tests, but only allow for data to be recorded at a select number of point locations and are not sufficient to provide all the necessary validation data. Advanced measurement technologies can be used effectively to complement traditional instrumentation and gather additional data required to validate these structural simulations. In particular, three-dimensional digital image correlation (DIC) was implemented during SBKF cylinder testing to characterize the full-field displacement and strain behavior. Commercially available VIC-3DTM software and user-written data processing scripts were used to generate valuable data and insight into the complex buckling response of the cylinders that otherwise would be impossible to gather using traditional instrumentation. In addition, the measured data from DIC was used to verify measured test data obtained from other instrumentation, enhance test and analysis correlation, and help identify the root cause of anomalous test results that may have gone unexplained if only traditional instrumentation was used. Selected test results that demonstrate the use of DIC on the SBKF cylinders are presented and a portion of the data processing methods are described

Accessory renal arteries in a Caribbean population: a computed tomography based study

INTRODUCTION: The commonest variation to the classic anatomic description of renal arterial supply is the presence of accessory renal arteries. The incidence varies widely according to ethnicity. There is no data on the prevalence of these anomalies in persons of Caribbean ethnicity. METHODS: All CT scans done over two years from July 1, 2010 to June 30, 2012 were retrospectively evaluated. The anatomy of the renal arterial supply was reported from these studies and the anatomy of accessory renal arteries was documented. RESULTS: There were 302 CT scans evaluated and accessory renal arteries were present in 109/302 (36.1%) CT scans, 95% confidence interval 30.6%, 41.4%. There were 71/309 (23.5%) patients with accessory arteries on the left and 54/309 (17.9%) had them on the right (p 0.087). Of these, 16 (14.7%) patients had bilateral accessory renal arteries present. The most common origin for the accessory arteries was the abdominal aorta in 108 (99.1%) cases and in 1 case the accessory artery arose from the coeliac trunk. There were 80 left sided accessory renal arteries: 17 (21.3%) upper polar and 27 (33.8%) lower polar arteries. Of 62 right sided accessory arteries, 14 (22.6%) were upper polar and 26 (42%) were lower polar arteries. CONCLUSION: This is the first population-based report of anatomic anomalies in renal arterial supply in a Caribbean population. These are important findings that may affect vascular and urologic procedures on persons of Caribbean ethnicity

Test and Analysis Correlation of a Large-Scale, Orthogrid-Stiffened Metallic Cylinder without Weld Lands

The NASA Engineering Safety Center (NESC) Shell Buckling Knockdown Factor Project (SBKF) was established in 2007 by the NESC with the primary objective to develop analysis-based buckling design factors and guidelines for metallic and composite launch-vehicle structures.1 A secondary objective of the project is to advance technologies that have the potential to increase the structural efficiency of launch-vehicles. The SBKF Project has determined that weld-land stiffness discontinuities can significantly reduce the buckling load of a cylinder. In addition, the welding process can introduce localized geometric imperfections that can further exacerbate the inherent buckling imperfection sensitivity of the cylinder. Therefore, single-piece barrel fabrication technologies can improve structural efficiency by eliminating these weld-land issues. As part of this effort, SBKF partnered with the Advanced Materials and Processing Branch (AMPB) at NASA Langley Research Center (LaRC), the Mechanical and Fabrication Branch at NASA Marshall Space Flight Center (MSFC), and ATI Forged Products to design and fabricate an 8-ft-diameter orthogrid-stiffened seamless metallic cylinder. The cylinder was subjected to seven subcritical load sequences (load levels that are not intended to induce test article buckling or material failure) and one load sequence to failure. The purpose of this test effort was to demonstrate the potential benefits of building cylindrical structures with no weld lands using the flow-formed manufacturing process. This seamless barrel is the ninth 8-ft-diameter metallic barrel and the first single-piece metallic structure to be tested under this program

The Art of Hegel's Aesthetics. Hegelian Philosophy and the Perspectives of Art History

This volume explores one of modernity’s most profound and far-reaching philosophies of art: the Vorlesungen über die Ästhetik, delivered by Georg Friedrich Wilhelm Hegel in the 1820s. The book has two overriding objectives: first, to ask how Hegel’s work illuminates specific periods and artworks in light of contemporary art-historical discussions; second, to explore how art history helps us make better sense and use of Hegelian aesthetics. In bringing together a range of internationally acclaimed critical voices, the volume establishes an important disciplinary bridge between aesthetics and art history. Given the recent resurgence of interest in ‘global’ art history, and calls for more comparative approaches to ‘visual culture’, contributors ask what role Hegel has played within the field – and what role he could play in the future. What can a historical treatment of art accomplish? How should we explain the ‘need’ for certain artistic forms at different historical junctures? Has art history been ‘Hegelian’ without fully acknowledging it? Indeed, have art historians shirked some of the fundamental questions that Hegel raised