125 research outputs found
Acoustic characteristics of 1/20-scale model helicopter rotors
A wind tunnel test to study the effects of geometric scale on acoustics and to investigate the applicability of very small scale models for the study of acoustic characteristics of helicopter rotors was conducted in the United Technologies Research Center Acoustic Research Tunnel. The results show that the Reynolds number effects significantly alter the Blade-Vortex-Interaction (BVI) Noise characteristics by enhancing the lower frequency content and suppressing the higher frequency content. In the time domain this is observed as an inverted thickness noise impulse rather than the typical positive-negative impulse of BVI noise. At higher advance ratio conditions, in the absence of BVI, the 1/20 scale model acoustic trends with Mach number follow those of larger scale models. However, the 1/20 scale model acoustic trends appear to indicate stall at higher thrust and advance ratio conditions
Large magnetoresistance using hybrid spin filter devices
A magnetic "spin filter" tunnel barrier, sandwiched between a non-magnetic
metal and a magnetic metal, is used to create a new magnetoresistive tunnel
device, somewhat analogous to an optical polarizer-analyzer configuration. The
resistance of these trilayer structures depends on the relative magnetization
orientation of the spin filter and the ferromagnetic electrode. The spin
filtering in this configuration yields a previously unobserved
magnetoresistance effect, exceeding 100%.Comment: 3.5 pages, 3 figures, submitted to Appl. Phys. Let
A new type of temperature driven reorientation transition in magnetic thin films
We present a new type of temperature driven spin reorientation transition
(SRT) in thin films. It can occur when the lattice and the shape anisotropy
favor different easy directions of the magnetization. Due to different
temperature dependencies of the two contributions the effective anisotropy may
change its sign and thus the direction of the magnetization as a function of
temperature may change. Contrary to the well-known reorientation transition
caused by competing surface and bulk anisotropy contributions the reorientation
that we discuss is also found in film systems with a uniform lattice
anisotropy. The results of our theoretical model study may have experimental
relevance for film systems with positive lattice anisotropy, as e.g. thin iron
films grown on copper.Comment: 7 pages, 4 figures, accepted for publication in EPJ
Observation of band structure and density of states effects in Co-based magnetic tunnel junctions
Utilizing Co/AlO/Co magnetic tunnel junctions (MTJs) with Co
electrodes of different crystalline phases, a clear relationship between
electrode structure and junction transport properties is presented. For
junctions with one fcc(111) textured and one polycrystalline (poly-phase and
poly-directional) Co electrode, a strong asymmetry is observed in the
magnetotransport properties, while when both electrodes are polycrystalline the
magnetotransport is essentially symmetric. These observations are successfully
explained within a model based on ballistic tunneling between the calculated
band structures (DOS) of fcc-Co and hcp-Co.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
- …