Effect of boattail geometry on the acoustics of parallel baffles in ducts

Sound attenuation and total pressure drop of parallel duct baffles incorporating certain boattail geometries were measured in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. The baseline baffles were 1.56 m long and 20 cm thick, on 45-cm center-to-center spacings, and spanned the test section from floor to ceiling. Four different boattails were evaluated: a short, smooth (nonacoustic) boattail; a longer, smooth boattail; and two boattails with perforated surfaces and sound-absorbent filler. Acoustic measurements showed the acoustic boattails improved the sound attenuation of the baffles at approximately half the rate to be expected from constant-thickness sections of the same length; that is, 1.5 dB/n, where n is the ratio of acoustic treatment length to duct passage width between baffles. The aerodynamic total pressure loss was somewhat sensitive to tail geometry. Lengthening the tails to reduce the diffusion half-angle from 11 to 5 degrees reduced the total pressure loss approximately 9%. Perforating the boattails, which increased the surface roughness, did not have a large effect on the total pressure loss. Aerodynamic results are compared with a published empirical method for predicting baffle total pressure drop

PFAS in the Drinking Water Source: Analysis of the Contamination Levels, Origin and Emission Rates

Groundwater contamination caused by the use of the aqueous film-forming foam (AFFF) containing per- and polyfluoroalkyl substances (PFAS) was investigated in southern Sweden. sigma PFAS concentrations in groundwater ranged between 20 and 20,000 ng L-1; PFAS composition was primarily represented by PFOS and PFHxS. The PFAS chain length was suggested to have an impact on the contaminant distribution and transport in the groundwater. PFAS profiling showed that the use of PFSAs- and PFCAs/FTSAs-based PFAS-AFFF can be a contributor to PFAS contamination of the drinking water source (groundwater). PFAS emission was connected to PFAS-AFFF use during the fire-training and fire-fighting equipment tests at the studied location. PFAS emission per individual fire training was (semi-quantitatively) estimated as [1.4 < 11.5 +/- 5.7 < 43.7 kg] (n = 20,000). The annual emission estimates varied as [11 < 401 +/- 233 < 1125 kg yr(-1)] (n = 1005) considering possible [2 < 35 +/- 20 < 96] individual fire-training sessions per year

Geochemical Constraints on the Structure of the Earth's Deep Mantle and the Origin of the LLSVPs

Funder: Royal Commission for the Exhibition of 1851; Id: http://dx.doi.org/10.13039/501100000700Funder: University of Cambridge; Id: http://dx.doi.org/10.13039/501100000735Funder: Geological Society of London; Id: http://dx.doi.org/10.13039/100008066Abstract: Geophysical analysis of the Earth's lower mantle has revealed the presence of two superstructures characterized by low shear wave velocities on the core‐mantle boundary. These Large Low Shear Velocity Provinces (LLSVPs) play a crucial role in the dynamics of the lower mantle and act as the source region for deep‐seated mantle plumes. However, their origin, and the characteristics of the surrounding deep mantle, remain enigmatic. Mantle plumes located above the margins of the LLSVPs display evidence for the presence of this deep‐seated, thermally and/or chemically heterogeneous mantle material ascending into the melting region. As a result, analysis of the spatial geochemical heterogeneity in ocean island basalts provides constraints on the structure of the Earth's lower mantle and the origin of the LLSVPs. In this study, we focus on the Galápagos Archipelago in the eastern Pacific, where bilateral asymmetry in the radiogenic isotopic composition of erupted basalts has been linked to the presence of LLSVP material in the underlying plume. We show, using spatial variations in the major element contents of high‐MgO basalts, that the isotopically enriched south‐western region of the Galápagos mantle—assigned to melting of LLSVP material—displays no evidence for lithological heterogeneity in the mantle source. As such, it is unlikely that the Pacific LLSVP represents a pile of subducted oceanic crust. Clear evidence for a lithologically heterogeneous mantle source is, however, found in the north‐central Galápagos, indicating that a recycled crustal component is present near the eastern margin of the Pacific LLSVP, consistent with seismic observations

Design and Development of a Deep Acoustic Lining for the 40-by 80-Foot Wind Tunnel Test Section

The work described in this report has made effective use of design teams to build a state-of-the-art anechoic wind-tunnel facility. Many potential design solutions were evaluated using engineering analysis, and computational tools. Design alternatives were then evaluated using specially developed testing techniques, Large-scale coupon testing was then performed to develop confidence that the preferred design would meet the acoustic, aerodynamic, and structural objectives of the project. Finally, designs were frozen and the final product was installed in the wind tunnel. The result of this technically ambitious project has been the creation of a unique acoustic wind tunnel. Its large test section (39 ft x 79 ft x SO ft), potentially near-anechoic environment, and medium subsonic speed capability (M = 0.45) will support a full range of aeroacoustic testing-from rotorcraft and other vertical takeoff and landing aircraft to the take-off/landing configurations of both subsonic and supersonic transports

Electromagnetic response of a static vortex line in a type-II superconductor : a microscopic study

The electromagnetic response of a pinned Abrikosov fluxoid is examined in the framework of the Bogoliubov-de Gennes formalism. The matrix elements and the selection rules for both the single photon (emission - absorption) and two photon (Raman scattering) processes are obtained. The results reveal striking asymmetries: light absorption by quasiparticle pair creation or single quasiparticle scattering can occur only if the handedness of the incident radiation is opposite to that of the vortex core states. We show how these effects will lead to nonreciprocal circular birefringence, and also predict structure in the frequency dependence of conductivity and in the differential cross section of the Raman scattering.Comment: 14 pages (RevTex

The Harris hip score: Do ceiling effects limit its usefulness in orthopedics?: A systematic review

The Harris hip score (HHS), a disease-specific health status scale that is frequently used to measure the outcome of total hip arthroplasty, has never been validated properly. A questionnaire is suitable only when all 5 psychometric properties are of sufficient quality. We questioned the usefulness of the HHS by investigating its content validity. We performed a systematic review based on a literature search in PubMed, Embase, and the Cochrane Library for descriptive studies published in 2007. 54 studies (59 patient groups) met our criteria and were included in the data analysis. To determine the content validity, we calculated the ceiling effect (percentage) for each separate study and we pooled data to measure the weighted mean. A subanalysis of indications for THA was performed to differentiate the populations for which the HHS would be suitable and for which it would not. A ceiling effect of 15% or less was considered to be acceptable. Over half the studies (31/59) revealed unacceptable ceiling effects. Pooled data across the studies included (n = 6,667 patients) suggested ceiling effects of 20% (95%CI: 18-22). Ceiling effects were greater (32%, 95%CI:12-52) in those patients undergoing hip resurfacing arthroplasty. Although the Harris hip score is widely used in arthroplasty research on outcomes, ceiling effects are common and these severely limit its validity in this field of researc

The Nordic Arthroplasty Register Association: A unique collaboration between 3 national hip arthroplasty registries with 280,201 THRs

Background and purpose The possibility of comparing results and of pooling the data has been limited for the Nordic arthroplasty registries, because of different registration systems and questionnaires. We have established a common Nordic database, in order to compare demographics and the results of total hip replacement surgery between countries. In addition, we plan to study results in patient groups in which the numbers are too small to be studied in the individual countries

Systematic review of tonsil surgery quality registers and introduction of the Nordic Tonsil Surgery Register Collaboration

Surgical quality registers provide tools to measure and improve the outcome of surgery. International register collaboration creates an opportunity to assess and critically evaluate national practices, and increases the size of available datasets. Even though millions of yearly tonsillectomies and tonsillotomies are performed worldwide, clinical practices are variable and inconsistency of evidence regarding the best clinical practice exists. The need for quality improvement actions is evident. We aimed to systematically investigate the existing tonsil surgery quality registers found in the literature, and to provide a thorough presentation of the planned Nordic Tonsil Surgery Register Collaboration. A systematic literature search of MEDLINE and EMBASE databases (from January 1990 to December 2016) was conducted to identify registers, databases, quality improvement programs or comprehensive audit programs addressing tonsil surgery. We identified two active registers and three completed audit programs focusing on tonsil surgery quality registration. Recorded variables were fairly similar, but considerable variation in coverage, number of operations included and length of time period for inclusion was discovered. Considering tonsillectomies and tonsillotomies being among the most commonly performed surgical procedures in otorhinolaryngology, it is surprising that only two active registers could be identified. We present a Nordic Tonsil Surgery Register Collaboration-an international tonsil surgery quality register project aiming to provide accurate benchmarks and enhance the quality of tonsil surgery in Denmark, Finland, Norway and Sweden.Peer reviewe

Risk factors of anterior cruciate ligament tears: Neuromuscular status

Peer reviewe