12,140 research outputs found
Investigation of a bearingless helicopter rotor concept having a composite primary structure
Experimental and analytical investigations were conducted to evaluate a bearingless helicopter rotor concept (CBR) made possible through the use of the specialized nonisotropic properties of composite materials. The investigation was focused on four principal areas which were expected to answer important questions regarding the feasibility of this concept. First, an examination of material properties was made to establish moduli, ultimate strength, and fatigue characteristics of unidirectional graphite/epoxy, the composite material selected for this application. The results confirmed the high bending modulus and strengths and low shear modulus expected of this material, and demonstrated fatigue properties in torsion which make this material ideally suited for the CBR application. Second, a dynamically scaled model was fabricated and tested in the low speed wind tunnel to explore the aeroelastic characteristics of the CBR and to explore various concepts relative to the method of blade pitch control. Two basic control configurations were tested, one in which pitch flap coupling could occur and another which eliminated all coupling. It was found that both systems could be operated successfully at simulated speeds of 180 knots; however, the configuration with coupling present revealed a potential for undesirable aeroelastic response. The uncoupled configuration behaved generally as a conventional hingeless rotor and was stable for all conditions tested
Heating of the molecular gas in the massive outflow of the local ultraluminous-infrared and radio-loud galaxy 4C12.50
We present a comparison of the molecular gas properties in the outflow vs. in
the ambient medium of the local prototype radio-loud and ultraluminous-infrared
galaxy 4C12.50 (IRAS13451+1232), using new data from the IRAM Plateau de Bure
interferometer and 30m telescope, and the Herschel space telescope. Previous
H_2 (0-0) S(1) and S(2) observations with the Spitzer space telescope had
indicated that the warm (~400K) molecular gas in 4C12.50 is made up of a
1.4(+-0.2)x10^8 M_sun ambient reservoir and a 5.2(+-1.7)x10^7 M_sun outflow.
The new CO(1-0) data cube indicates that the corresponding cold (25K) H_2 gas
mass is 1.0(+-0.1)x10^10 M_sun for the ambient medium and <1.3x10^8 M_sun for
the outflow, when using a CO-intensity-to-H_2-mass conversion factor alpha of
0.8 M_sun /(K km/s pc^2). The combined mass outflow rate is high, 230-800
M_sun/yr, but the amount of gas that could escape the galaxy is low. A
potential inflow of gas from a 3.3(+-0.3)x10^8 M_sun tidal tail could moderate
any mass loss. The mass ratio of warm-to-cold molecular gas is >= 30 times
higher in the outflow than in the ambient medium, indicating that a
non-negligible fraction of the accelerated gas is heated to temperatures at
which star formation is inefficient. This conclusion is robust against the use
of different alpha factor values, and/or different warm gas tracers (H_2 vs.
H_2 plus CO): with the CO-probed gas mass being at least 40 times lower at 400K
than at 25K, the total warm-to-cold mass ratio is always lower in the ambient
gas than in the entrained gas. Heating of the molecular gas could facilitate
the detection of new outflows in distant galaxies by enhancing their emission
in intermediate rotational number CO lines.Comment: A&A, in pres
The clustering and bias of radio-selected AGN and star-forming galaxies in the COSMOS field
Dark matter haloes in which galaxies reside are likely to have a significant
impact on their evolution. We investigate the link between dark matter haloes
and their constituent galaxies by measuring the angular two-point correlation
function of radio sources, using recently released 3 GHz imaging over $\sim 2 \
\mathrm{deg}^2z<1b = 1.5
^{+0.1}_{-0.2}z=0.62b = 2.1\pm 0.2b =
2.9 \pm 0.3b = 1.8^{+0.4}_{-0.5}z \sim 0.7M_{h} \sim 3-4
\times 10^{13}h^{-1}_{\odot}M_{h} \sim 1-2 \times
10^{13}h^{-1}_{\odot}z \ge 1z<1$.Comment: 20 pages, 10 figures, 1 table, accepted by MNRA
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