An extension of the local momentum theory to a distorted wake model of a hovering rotor

The local momentum theory is based on the instantaneous balance between the fluid momentum and the blade elemental lift at a local station in the rotor rotational plane. Therefore, the theory has the capability of evaluating time wise variations of air loading and induced velocity distributions along a helicopter blade span. Unlike a complex vortex theory, this theory was developed to analyze the instantaneous induced velocity distribution effectively. The boundaries of this theory and a computer program using this theory are discussed. A concept introduced into the theory is the effect of the rotor wake contraction in hovering flight. A comparison of this extended local momentum theory with a prescribed wake vortex theory is also presented. The results indicate that the extended local momentum theory has the capability of achieving a level of accuracy similar to that of the prescribed wake vortex theory over wide range variations of rotor geometrical parameters. It is also shown that the analytical results obtained using either theory are in reasonable agreement with experimental data

Sensing with magnetic dipolar resonances in semiconductor nanospheres

In this work we propose two novel sensing principles of detection that exploit the magnetic dipolar Mie resonance in high-refractiveindex dielectric nanospheres. In particular, we theoretically investigate the spectral evolution of the extinction and scattering cross sections of these nanospheres as a function of the refractive index of the external medium (next). Unlike resonances in plasmonic nanospheres, the spectral position of magnetic resonances in high-refractive-index nanospheres barely shifts as next changes. Nevertheless, there is a drastic reduction in the extinction cross section of the nanospheres when next increases, especially in the magnetic dipolar spectral region, which is accompanied with remarkable variations in the radiation patterns. Thanks to these changes, we propose two new sensing parameters, which are based on the detection of: i) the intensity variations in the transmitted or backscattered radiation by the dielectric nanospheres at the magnetic dipole resonant frequency, and ii) the changes in the radiation pattern at the frequency that satisfies Kerker's condition of near-zero forward radiation. To optimize the sensitivity, we consider several semiconductor materials and particles sizes. © 2013 Optical Society of America.B.G.-C. acknowledges support from the JAE-Doc program of the Spanish Council of Research (CSIC). This research has been funded by Ministerio de Ciencia e Innovación, through grants: Consolider NanoLight (CSD2007-00046), FIS2009-13430-C02, as well as by the Comunidad de Madrid (Microseres-CM, S2009/TIC-1476).Peer Reviewe

Modeling high-energy light curves of the PSR B1259-63/LS 2883 binary based on 3-D SPH simulations

Temporal changes of X-ray to very-high-energy gamma-ray emissions from the pulsar-Be star binary PSR B1259-63/LS 2883 are studied based on 3-D SPH simulations of pulsar wind interaction with Be-disk and wind. We focus on the periastron passage of the binary and calculate the variation of the synchrotron and inverse-Compton emissions using the simulated shock geometry and pressure distribution of the pulsar wind. The characteristic double-peaked X-ray light curve from observations is reproduced by our simulation under a dense Be disk condition (base density ~10^{-9} g cm^{-3}). We interpret the pre- and post-periastron peaks as being due to a significant increase in the conversion efficiency from pulsar spin down power to the shock-accelerated particle energy at orbital phases when the pulsar crosses the disk before periastron passage, and when the pulsar wind creates a cavity in the disk gas after periastron passage, respectively. On the contrary, in the model TeV light curve, which also shows a double peak feature, the first peak appears around the periastron phase. The possible effects of cooling processes on the TeV light curve are briefly discussed.Comment: 32 pages, 6 figues. Accepted for publication in Ap

Social participation and mortality: does social position in civic groups matter?

BACKGROUND: Social participation is known to predict longevity. However, little is known about the effect of social participation according to an individual's position in civic groups. We evaluated the influence of social position on mortality, using data from a large cohort of Japanese older adults (the AGES cohort). METHODS: Of 14,804 individuals aged 65 years and older enrolled in the AGES, 14,286 individuals were followed up for approximately 5 years from 2003 to 2008. We performed inverse probability of treatment weighted (IPTW) Cox proportional hazards regression with multiple imputation of missing values to compute hazard ratios (HR) for all-cause mortality according to the individual's position in the community organization(s) to which they belonged. We examined participation in the following civic groups: neighborhood association/senior citizen club/fire-fighting team, religious group, political organization or group, industrial or trade association, volunteer group, citizen or consumer group, hobby group, and sports group or club. The values for IPTW were computed based on demographic variables, socioeconomic status, and self-reported medical condition. RESULTS: During 22,718 person-years of follow-up for regular members of community groups and 14,014 person-years of follow-up for participants in leadership positions, 479 deaths and 214 deaths were observed, respectively. Relative to regular members, crude HR for all-cause mortality for occupying leadership positions (e.g. president, manager, or having administrative roles) was 0.72 (95 % CI:0.62-0.85). The IPTW-HR was 0.88 (95 % CI: 0.79-0.99) for participants occupying leadership positions. CONCLUSIONS: Holding leadership positions in community organization(s) may be more beneficial to health than being regular members