10,855 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
RISK AND SUSTAINABLE AGRICULTURE: A TARGET-MOTAD ANALYSIS OF THE 92-YEAR "OLD ROTATION"
Target-MOTAD was used to assess the risks and returns of sustainable cotton crop rotations from Auburn University's 92-year "Old Rotation." Study results analyze rotations of continuous cotton, with and without winter legumes; two years of cotton-winter legumes-corn, with and without nitrogen fertilization; and three years of cotton-winter legumes-corn and rye-soybeans double-cropped. Ten years of observations on deviations from target income were used to identify optimal sustainable rotation(s). Study results suggest that diversification in rotations, as well as in crops, results in the least risk for a given level of target income.Risk and Uncertainty,
Influence of antisymmetric exchange interaction on quantum tunneling of magnetization in a dimeric molecular magnet Mn6
We present magnetization measurements on the single molecule magnet Mn6,
revealing various tunnel transitions inconsistent with a giant-spin
description. We propose a dimeric model of the molecule with two coupled spins
S=6, which involves crystal-field anisotropy, symmetric Heisenberg exchange
interaction, and antisymmetric Dzyaloshinskii-Moriya exchange interaction. We
show that this simplified model of the molecule explains the experimentally
observed tunnel transitions and that the antisymmetric exchange interaction
between the spins gives rise to tunneling processes between spin states
belonging to different spin multiplets.Comment: 5 pages, 4 figure
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
Temperature dependence of the coercive field in single-domain particle systems
The magnetic properties of Cu97Co3 and Cu90Co10 granular alloys were measured
over a wide temperature range (2 to 300K). The measurements show an unusual
temperature dependence of the coercive field. A generalized model is proposed
and explains well the experimental behavior over a wide temperature range. The
coexistence of blocked and unblocked particles for a given temperature rises
difficulties that are solved here by introducing a temperature dependent
blocking temperature. An empirical factor gamma arise from the model and is
directly related to the particle interactions. The proposed generalized model
describes well the experimental results and can be applied to other
single-domain particle system.Comment: 7 pages, 8 figures, revised version, accepted to Physical Review B on
29/04/200
Testing Magnetic Field Models for the Class 0 Protostar L1527
For the Class 0 protostar, L1527, we compare 131 polarization vectors from
SCUPOL/JCMT, SHARP/CSO and TADPOL/CARMA observations with the corresponding
model polarization vectors of four ideal-MHD, non-turbulent, cloud core
collapse models. These four models differ by their initial magnetic fields
before collapse; two initially have aligned fields (strong and weak) and two
initially have orthogonal fields (strong and weak) with respect to the rotation
axis of the L1527 core. Only the initial weak orthogonal field model produces
the observed circumstellar disk within L1527. This is a characteristic of
nearly all ideal-MHD, non-turbulent, core collapse models. In this paper we
test whether this weak orthogonal model also has the best agreement between its
magnetic field structure and that inferred from the polarimetry observations of
L1527. We found that this is not the case; based on the polarimetry
observations the most favored model of the four is the weak aligned model.
However, this model does not produce a circumstellar disk, so our result
implies that a non-turbulent, ideal-MHD global collapse model probably does not
represent the core collapse that has occurred in L1527. Our study also
illustrates the importance of using polarization vectors covering a large area
of a cloud core to determine the initial magnetic field orientation before
collapse; the inner core magnetic field structure can be highly altered by a
collapse and so measurements from this region alone can give unreliable
estimates of the initial field configuration before collapse.Comment: 43 pages, 9 figures, 4 tables. Accepted by the Astrophysical Journa
- …