An assessment of propeller aircraft noise reduction technology

This report is a review of the literature regarding propeller airplane far-field noise reduction. Near-field and cabin noise reduction are not specifically addressed. However, some of the approaches used to reduce far-field noise produce beneficial effects in the near-field and in the cabin. The emphasis is on propeller noise reduction but engine exhaust noise reduction by muffling is also addressed since the engine noise becomes a significant part of the aircraft noise signature when propeller noise is reduced. It is concluded that there is a substantial body of information available that can be used as the basis to reduce propeller airplane noise. The reason that this information is not often used in airplane design is the associated weight, cost, and performance penalties. It is recommended that the highest priority be given to research for reducing the penalties associated with lower operating RPM and propeller diameter while increasing the number of blades. Research to reduce engine noise and explore innovative propeller concepts is also recommended

A review of propeller noise prediction methodology: 1919-1994

This report summarizes a review of the literature regarding propeller noise prediction methods. The review is divided into six sections: (1) early methods; (2) more recent methods based on earlier theory; (3) more recent methods based on the Acoustic Analogy; (4) more recent methods based on Computational Acoustics; (5) empirical methods; and (6) broadband methods. The report concludes that there are a large number of noise prediction procedures available which vary markedly in complexity. Deficiencies in accuracy of methods in many cases may be related, not to the methods themselves, but the accuracy and detail of the aerodynamic inputs used to calculate noise. The steps recommended in the report to provide accurate and easy to use prediction methods are: (1) identify reliable test data; (2) define and conduct test programs to fill gaps in the existing data base; (3) identify the most promising prediction methods; (4) evaluate promising prediction methods relative to the data base; (5) identify and correct the weaknesses in the prediction methods, including lack of user friendliness, and include features now available only in research codes; (6) confirm the accuracy of improved prediction methods to the data base; and (7) make the methods widely available and provide training in their use

Making the most of interference : speckle metrology and its application to cold atoms

Speckle patterns result from the interference of multiple reflections in disordered media. This is regarded as a randomization process which destroys information contained within the initial light beam and is deleterious to many optical systems. Indeed, many engineers study speckle to remove its effect. Intriguingly however, the processes that produce the speckle are entirely linear, and there is growing recognition that this complex pattern is rich in useful information on both the incident laser source and the environment, with startling potential uses. We will demonstrate our recent results [1], which show that the speckle pattern produced by light propagation in an integrating sphere can be used as a sensitive wavemeter, with a resolution below 1fm. Moreover, this can be used to stabilize the wavelength of a laser on a timescale and to a stability applicable for laser cooling of cold atoms. Reference: [1] N. K. Metzger, et al., “Harnessing speckle for a sub-femtometre resolved broadband wavemeter and laser stabilization”, Nature Communications 8, 15610 (2017)PostprintNon peer reviewe

A test of basin-scale acoustic thermometry using a large-aperture vertical array at 3250-km range in the eastern North Pacific Ocean

Author Posting. © Acoustical Society of America, 1999. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 105 (1999): 3185, doi:10.1121/1.424649.Broadband acoustic signals were transmitted during November 1994 from a 75-Hz source suspended near the depth of the sound-channel axis to a 700-m long vertical receiving array approximately 3250 km distant in the eastern North Pacific Ocean. The early part of the arrival pattern consists of raylike wave fronts that are resolvable, identifiable, and stable. The later part of the arrival pattern does not contain identifiable raylike arrivals, due to scattering from internal-wave-induced sound-speed fluctuations. The observed ray travel times differ from ray predictions based on the sound-speed field constructed using nearly concurrent temperature and salinity measurements by more than a priori variability estimates, suggesting that the equation used to compute sound speed requires refinement. The range-averaged oceansound speed can be determined with an uncertainty of about 0.05 m/s from the observed ray travel times together with the time at which the near-axial acoustic reception ends, used as a surrogate for the group delay of adiabatic mode 1. The change in temperature over six days can be estimated with an uncertainty of about 0.006 °C. The sensitivity of the travel times to ocean variability is concentrated near the ocean surface and at the corresponding conjugate depths, because all of the resolved ray arrivals have upper turning depths within a few hundred meters of the surface.This work was supported largely by the Strategic Environmental Research and Development Program through Defense Advanced Research Projects Agency ~DARPA! Grant No. MDA972-93- 1-0003. Additional support was provided at SIO by the Office of Naval Research ~ONR! through Grant No. N00014- 97-1-0258. J. Colosi wishes to acknowledge support from an ONR Young Investigator Award, from the J. Lamar Worzel Assistant Scientist Fund, and from the Penzance Endowed Fund in support of scientific staff at WHOI

Excavation of Regolith by Impinging Jets of Gas

There are many situations in nature and technology where particulate matter is excavated by a fluid jet. Such a process is often used to excavate soil or to dig wells. Air jets are often used to transport particulate matter such as powders in various industrial processes. Similar situations occur in nature, as when waterfalls scour holes in sand. In other cases, the excavation is unwanted such as when a rocket lands on the sandy or dusty surface of a planet or moon. Recent research into regolith excavation by gas jets has obtained new insights into the physical processes of that excavation, and these may lead to new advances in technology for more efficient fluid-jet excavation processes and for better control of the unwanted excavation effects of landing rockets. This talk will explain the new insights and point to future work supporting lunar exploration

Outcomes and Complications With Off-Label Use of Drug-Eluting Stents Results From the STENT (Strategic Transcatheter Evaluation of New Therapies) Group

ObjectivesThis study evaluates outcomes and complications in patients treated with drug-eluting stents (DES) for “off-label” indications.BackgroundDrug-eluting stents have been effective in randomized trials, but their safety and efficacy for off-label indications has not been well studied.MethodsThe STENT (Strategic Transcatheter Evaluation of New Therapies) Registry is the largest multicenter U.S. registry evaluating outcomes of DES. Off-label indications included ostial, left main, long, bifurcation, and in-stent restenotic lesions, saphenous vein grafts, chronic total occlusions, small or large vessels, multilesion or multivessel percutaneous coronary interventions, and ST-segment elevation myocardial infarction. Outcomes were adjusted using Cox proportional hazards regression and propensity analyses.ResultsDrug-eluting stents were used in an off-label manner in 59% of patients. The patients who received off-label treatment were more often male, had a higher incidence of prior infarction and bypass surgery, and lower ejection fractions. Off-label versus “on-label” use of DES was associated with higher rates of death, myocardial infarction, target vessel revascularization, major adverse cardiac events, and stent thrombosis at 9 months and 2 years. Off-label use of DES compared with off-label use of bare-metal stents (BMS) had lower rates of death, myocardial infarction, target vessel revascularization, and major adverse cardiac events at 9 months and 2 years and lower rates of stent thrombosis at 9 months.ConclusionsOff-label use of DES is associated with higher event rates compared with on-label use of DES, which is consistent with a higher risk clinical and lesion profile. However, event rates with off-label use of DES are lower compared with off-label use of BMS. Pending results from randomized trials, our data support the use of DES for off-label indications in selected patients