6,418 research outputs found
A laser velocimeter flow survey above a stalled wing
A laser velocimeter operating in the backscatter mode was used to survey the flow about a stalled wing installed in the Langley V/STOL tunnel. Mean velocities and magnitudes of velocity fluctuations were calculated from measurements of two orthogonal components of velocity. Free shear mixing layers above and below a large separated flow region were defined. Velocity power spectra were calculated at two points in the flow field. The flow-field survey was carried out about a rectangular aspect-ratio-8 wing with an airfoil section. The wing angle of attack was 19.4 deg, the Mach number was 0.148, and the nominal Reynolds number was 1 x 1 million
Correlation of laser velocimeter measurements over a wing with results of two prediction techniques
The flow field at the center line of an unswept wing with an aspect ratio of eight was determined using a two dimensional viscous flow prediction technique for the flow field calculation, and a three dimensional potential flow panel method to evaluate the degree of two dimensionality achieved at the wing center line. The analysis was made to provide an acceptable reference for comparison with velocity measurements obtained from a fringe type laser velocimeter optics systems operating in the backscatter mode in the Langley V/STOL tunnel. Good agreement between laser velocimeter measurements and theoretical results indicate that both methods provide a true representation of the velocity field about the wing at angles of attack of 0.6 and 4.75 deg
Epitaxial strain modulated electronic properties of interface controlled nickelate superlattice
Perovskite nickelate heterostructure consisting of single unit cell of
EuNiO and LaNiO have been grown on a set of single crystalline
substrates by pulsed laser interval deposition to investigate the effect of
epitaxial strain on electronic and magnetic properties at the extreme interface
limit. Despite the variation of substrate in-plane lattice constants and
lattice symmetry, the structural response to heterostructuring is primarily
controlled by the presence of EuNiO layer. In sharp contrast to bulk
LaNiO or EuNiO, the superlattices grown under tensile strains exhibit
metal to insulator transition (MIT) below room temperature. The onset of
magnetic and electronic transitions associated with the MIT can be further
separated by application of large tensile strain. Furthermore, these
transitions can be entirely suppressed by very small compressive strain. X-ray
resonant absorption spectroscopy measurements reveal that such
strain-controlled MIT is directly linked to strain induced self-doping effect
without any chemical doping.Comment: Accepted in Phys. Rev.
Epitaxial growth of (111)-oriented LaAlO/LaNiO ultra-thin superlattices
The epitaxial stabilization of a single layer or superlattice structures
composed of complex oxide materials on polar (111) surfaces is severely
burdened by reconstructions at the interface, that commonly arise to neutralize
the polarity. We report on the synthesis of high quality LaNiO/mLaAlO
pseudo cubic (111) superlattices on polar (111)-oriented LaAlO, the
proposed complex oxide candidate for a topological insulating behavior.
Comprehensive X-Ray diffraction measurements, RHEED, and element specific
resonant X-ray absorption spectroscopy affirm their high structural and
chemical quality. The study offers an opportunity to fabricate interesting
interface and topology controlled (111) oriented superlattices based on
ortho-nickelates
- …