Engineering topics

Maekawa, S.

Publications and source records attributed to Maekawa, S..

6 records

DOE OSTI2014

The Ba 4d-4f giant dipole resonance in complex Ba/Si compounds

The shape of the Ba 4d–4f giant dipole resonance is studied for Ba atoms embedded inside complex Si networks covering structures consisting of Si nanocages and nanotubes, i.e. the clathrate Ba 8 Si 46 , the complex compound BaSi 6 , and the semiconducting BaSi 2 . Here, non-resonant x-ray Raman scattering is used to investigate confinement effects on the shape of the giant resonance in the vicinity of the Ba NIV, V-edge. The distinct momentum transfer dependence of the spectra is analyzed and discussed. The measurements are compared to calculations of the giant resonance within time-dependent local density approximation in the dipole limit. No modulation of the giant resonance's shape for Ba atoms confined in different local environments was observed, in contrast to the calculations. The absence of such shape modulation for complex Ba/Si compounds is discussed providing important implications for further studies of giant resonance phenomena utilizing both theory and experiment.

Sahle, Ch. J.↗

DOE OSTI2014

Thermal engineering of non-local resistance in lateral spin valves

We study the non-local spin transport in Permalloy/Cu lateral spin valves (LSVs) fabricated on thermally oxidized Si and MgO substrates. While these LSVs show the same magnitude of spin signals, significant substrate dependence of the baseline resistance was observed. The baseline resistance shows much weaker dependence on the inter-electrode distance than that of the spin transport observed in the Cu wires. A simple analysis of voltage-current characteristics in the baseline resistance indicates the observed result can be explained by a combination of the Peltier and Seebeck effects at the injector and detector junctions, suggesting the usage of high thermal conductivity substrate (or under-layer) is effective to reduce the baseline resistance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1977

Vibroacoustic response of structures and perturbation Reynolds stress near structure-turbulence interface

The interaction between a turbulent flow and certain types of structures which respond to its excitation is investigated. One-dimensional models were used to develop the basic ideas applied to a second model resembling the fuselage construction of an aircraft. In the two-dimensional case a simple membrane, with a small random variation in the membrane tension, was used. A decaying turbulence was constructed by superposing infinitely many components, each of which is convected as a frozen pattern at a different velocity. Structure-turbulence interaction results are presented in terms of the spectral densities of the structural response and the perturbation Reynolds stress in the fluid at the vicinity of the interface.

Maekawa, S.↗

NASA NTRS1977

Response of periodic beam to supersonic boundary-layer pressure fluctuations

The response of a periodic beam (modeling a periodic fuselage) to supersonic boundary-layer pressure fluctuations is analyzed on the basis of a scheme in which a decaying turbulence is treated as a superposition of frozen-pattern components, thus allowing the structural response to be similarly superposed and the advantage of frozen-pattern analysis to be maximally utilized. The fundamental solution required for the construction of the total response is one corresponding to the excitation of a frozen-pattern sinusoid. To obtain this fundamental solution, the formulation follows Mead's wave-propagation method (1971), but also takes into account the effect of freestream velocity on the same side of the turbulence excitation and the effect of a cavity on the opposite side of the excitation. As a numerical example, the spectral density of the structural response is computed and the results are compared with experimental data.

Lin, Y. K.↗

NASA NTRS1976

On some structure-turbulence interaction problems

The interactions between a turbulent flow structure; responding to its excitation were studied. The turbulence was typical of those associated with a boundary layer, having a cross-spectral density indicative of convection and statistical decay. A number of structural models were considered. Among the one-dimensional models were an unsupported infinite beam and a periodically supported infinite beam. The fuselage construction of an aircraft was then considered. For the two-dimensional case a simple membrane was used to illustrate the type of formulation applicable to most two-dimensional structures. Both the one-dimensional and two-dimensional structures studied were backed by a cavity filled with an initially quiescent fluid to simulate the acoustic environment when the structure forms one side of a cabin of a sea vessel or aircraft.

Maekawa, S.↗

NASA NTRS1976

A new look at decomposition of turbulence forcing field and the structural response

Measured cross-spectrum of a turbulence field usually shows some decay in the statistical correlation in addition to convection at a characteristic velocity. It is shown that a decaying turbulence can be decomposed into frozen-pattern components thus permitting a simpler way to calculate the structural response. This procedure also provides a relationship whereby the measured input spectra can be incorporated. The theory is applied to an infinite beam which is backed on one side by a fluid filled cavity and is exposed on the other side by the turbulence excitation. The effect of the free stream velocity is also taken into consideration.

Lin, Y. K.↗