Acoustic design considerations: Review of rotor acoustic sources

It is not sufficient to optimize a rotor design in terms of a single noise level calculated for a single flight condition and a single measurement location. The various noise sources, their frequency content, amplitude, and directivity as a function of operating condition must be considered. A summary of the frequency ranges, directivity patterns and the most important operational and design parameters for major rotor noise sources is presented. It is difficult to generalize design requirements for rotor noise because the acoustic output varies so widely depending on the noise source, flight condition, measurement location, and frequency range. However, assuming the rotor must lift a fixed nominal payload and operate over a wide range of flight conditions, three general design guidelines can be stated: (1) minimize tip Mach number; (2) minimize blade thickness in the tip region; and (3) minimize gradients in the spanwise lift distribution in the tip region. Constraints on blade thickness, maximum values for hover tip Mach number, advancing tip Mach number and spanwise lift coefficient gradient will be specified during the aerodynamic, dynamic and structural optimization process. The rotor noise sources to be considered include the low frequency loading and thickness noise, and the higher frequency noise due to blade-vortex interactions (BVI). The analyses to be employed will include the comprehensive rotor analysis and design program CAMRAD and the rotor noise prediction program WOPWOP

Results of the 1986 NASA/FAA/DFVLR main rotor test entry in the German-Dutch wind tunnel (DNW)

An acoustics test of a 40%-scale MBB BO-105 helicopter main rotor was conducted in the Deutsch-Niederlandischer Windkanal (DNW). The research, directed by NASA Langley Research Center, concentrated on the generation and radiation of broadband noise and impulsive blade-vortex interaction (BVI) noise over ranges of pertinent rotor operational envelopes. Both the broadband and BVI experimental phases are reviewed, along with highlights of major technical results. For the broadband portion, significant advancement is the demonstration of the accuracy of prediction methods being developed for broadband self noise, due to boundary layer turbulence. Another key result is the discovery of rotor blade-wake interaction (BWI) as an important contributor to mid frequency noise. Also the DNW data are used to determine for full scale helicopters the relative importance of the different discrete and broadband noise sources. For the BVI test portion, a comprehensive data base documents the BVI impulsive noise character and directionality as functions of rotor flight conditions. The directional mapping of BVI noise emitted from the advancing side as well as the retreating side of the rotor constitutes a major advancement in the understanding of this dominant discrete mechanism

CMB anisotropies from acausal scaling seeds

We investigate models where structure formation is initiated by scaling seeds: We consider rapidly expanding relativistic shells of energy and show that they can fit current CMB and large scale structure data if they expand with super-luminal velocities. These acausally expanding shells provide a viable alternative to inflation for cosmological structure formation with the same minimal number of parameters to characterize the initial fluctuations. Causally expanding shells alone cannot fit present data. Hybrid models where causal shells and inflation are mixed also provide good fits.Comment: 9 pages,13 figures, revised version accepted for publication in PR

A note on area variables in Regge calculus

We consider the possibility of setting up a new version of Regge calculus in four dimensions with areas of triangles as the basic variables rather than the edge-lengths. The difficulties and restrictions of this approach are discussed.Comment: 4 pages, amstex. Revision has minor changes and more precise conclusion

Acoustic measurements from a rotor blade-vortex interaction noise experiment in the German-Dutch Wind Tunnel (DNW)

Acoustic data are presented from a 40 percent scale model of the 4-bladed BO-105 helicopter main rotor, measured in the large European aeroacoustic wind tunnel, the DNW. Rotor blade-vortex interaction (BVI) noise data in the low speed flight range were acquired using a traversing in-flow microphone array. The experimental apparatus, testing procedures, calibration results, and experimental objectives are fully described. A large representative set of averaged acoustic signals is presented

Health impact of catch-up growth in low-birth weight infants : systematic review, evidence appraisal, and meta-anaylsis

This study aimed to systematically review and appraise evidence on the short-term (e.g. morbidity, mortality) and long-term (obesity and non-communicable diseases, NCDs) health consequences of catch-up growth (versus no catch-up growth) in individuals with a history of low birth weight (LBW).We searched MEDLINE, EMBASE, Global Health, CINAHL plus, Cochrane Library, ProQuest Dissertations and Thesis, and reference lists. Study quality was assessed using the risk of bias assessment tool from the Agency for Health Care Research and Quality, and the evidence base was assessed using the GRADE tool. Eight studies in 7 cohorts (2 from high-income countries, 5 from low-middle income countries) met the inclusion criteria for short-term (mean age: 13.4 months) and/or longer-term (mean age: 11.1 years) health outcomes of catch-up growth which had occurred by 24 or 59 months. Of 5 studies on short-term health outcomes, 3 found positive associations between weight catch-up growth and body mass and/or glucose metabolism; 1 suggested reduced risk of hospitalisation and mortality with catch-up growth. Three studies on longer-term health outcomes found catch-up growth was associated with higher body mass, BMI, or cholesterol. GRADE assessment suggested that evidence quantity and quality were low. Catch-up growth following LBW may have benefits for the individual with LBW in the short term, and may have adverse population health impacts in the long-term, but the evidence is limited. Future cohort studies could address the question of the consequences of catch-up growth following LBW more convincingly, with a view to informing future prevention of obesity and NCDs

BRCA1-BARD1: the importance of being in shape

The breast cancer type-1 susceptibility protein (BRCA1) contributes to genome integrity through homologous recombinational DNA repair and by protecting stalled replication forks from nucleolytic degradation. We recently discovered that fork protection requires a conformational change of BRCA1 unimportant to homologous recombination repair, indicating separate roles for BRCA1 in these pathways

Are health assets associated with improved outcomes for hospitalised older adults? A systematic review

Objective Health assets are protective factors that support health and wellbeing, rather than risk factors that are associated with disease. This concept was developed in the community setting. In hospitalised older adults, the dominant approach has been to identify risk factors, with little examination of health assets. The purpose of this systematic review was to determine whether, in hospitalised older people, individual health assets decrease the risk of post hospital mortality, functional decline, new need for residential care, readmission or longer length of stay. Methods MEDLINE, EMBASE, CINAHL and PsycINFO were searched to identify studies examining outcomes for hospitalised older adults. Included studies examined at least one potential individual health asset, which was a psychosocial characteristic or health characteristic. Study quality was assessed, and findings are narratively described. Results Nine prospective cohort and two retrospective cohort studies were identified. subjective, functional and biological health assets were identified. Health assets were associated with decreased risk of post-hospital mortality, functional decline, new need for residential care and readmission. Conclusion The complex interplay between health status and psychological and social factors is incompletely understood. Health assets are associated with improved outcomes for hospitalised older adults. The small number of studies suitable for inclusion indicates the need for further research in this area