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Results for “phase coherence”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Development of powder metallurgy 2XXX series Al alloys for high temperature aircraft structural applications

The objective of the present investigation was to improve the strength and fracture toughness combination of P/M 2124 Al alloys in accordance with NASA program goals for damage tolerance and fatigue resistance. Two (2) P/M compositions based on Al-3.70 Cu-1.85 Mg-0.20 Mn with 0.12 and 0.60 wt. pct. Zr were selected for investigation. The rapid solidification rates produced by atomization were observed to prohibit the precipitation of coarse, primary Al3Zr in both alloys. A major portion of the Zr precipitated as finely distributed, coherent Al3Zr phases during vacuum preheating and solution heat treatment. The proper balance between Cu and Mg contents eliminated undissolved, soluble constituents such as Al2CuMg and Al2Cu during atomization. The resultant extruded microstructures produced a unique combination of strength and fracture toughness. An increase in the volume fraction of coherent Al3Zr, unlike incoherent Al20Cu2Mn3 dispersoids, strengthened the P/M Al base alloy either directly by dislocation-precipitate interactions, indirectly by a retardation of recrystallization, or a combination of both mechanisms. Furthermore, coherent Al3Zr does not appear to degrade toughness to the extent that incoherent Al20Cu2Mn3 does. Consequently, the addition of 0.60 wt. pct. Zr to the base alloy, incorporated with a 774K (935 F) solution heat treatment temperature, produces an alloy which exceeds all tensile property and fracture toughness goals for damage tolerant and fatigue resistant applications in the naturally aged condition.

Chellman, D. J.↗
NASA NTRS2002

Autonomic neural control of dynamic cerebral autoregulation in humans

BACKGROUND: The purpose of the present study was to determine the role of autonomic neural control of dynamic cerebral autoregulation in humans. METHODS AND RESULTS: We measured arterial pressure and cerebral blood flow (CBF) velocity in 12 healthy subjects (aged 29+/-6 years) before and after ganglion blockade with trimethaphan. CBF velocity was measured in the middle cerebral artery using transcranial Doppler. The magnitude of spontaneous changes in mean blood pressure and CBF velocity were quantified by spectral analysis. The transfer function gain, phase, and coherence between these variables were estimated to quantify dynamic cerebral autoregulation. After ganglion blockade, systolic and pulse pressure decreased significantly by 13% and 26%, respectively. CBF velocity decreased by 6% (P<0.05). In the very low frequency range (0.02 to 0.07 Hz), mean blood pressure variability decreased significantly (by 82%), while CBF velocity variability persisted. Thus, transfer function gain increased by 81%. In addition, the phase lead of CBF velocity to arterial pressure diminished. These changes in transfer function gain and phase persisted despite restoration of arterial pressure by infusion of phenylephrine and normalization of mean blood pressure variability by oscillatory lower body negative pressure. CONCLUSIONS: These data suggest that dynamic cerebral autoregulation is altered by ganglion blockade. We speculate that autonomic neural control of the cerebral circulation is tonically active and likely plays a significant role in the regulation of beat-to-beat CBF in humans.

Non-NASA Center↗
NASA NTRS2003

Phase Sensitive X-Ray Diffraction Imaging Study of Protein Crystals

The study of defects and growth of protein crystals is of importance in providing a fundamental understanding of this important category of systems and the rationale for crystallization of better ordered crystals for structural determination and drug design. Yet, as a result of the extremely weak scattering power of x-rays in protein and other biological macromolecular crystals, the extinction lengths for those crystals are extremely large and, roughly speaking, of the order of millimeters on average compared to the scale of micrometers for most small molecular crystals. This has significant implication for x-ray diffraction and imaging study of protein crystals, and presents an interesting challenge to currently available x-ray analytical techniques. We proposed that coherence-based phase sensitive x-ray diffraction imaging could provide a way to augment defect contrast in x-ray diffraction images of weakly diffracting biological macromolecular crystals. I shall examine the principles and ideas behind this approach and compare it to other available x-ray topography and diffraction methods. I shall then present some recent experimental results in two model protein systems-cubic apofemtin and tetragonal lysozyme crystals to demonstrate the capability of the coherence-based imaging method in mapping point defects, dislocations, and the degree of perfection of biological macromolecular crystals with extreme sensitivity. While further work is under way, it is intended to show that the observed new features have yielded important information on protein crystal perfection and nucleation and growth mechanism otherwise unobtainable.

Hu, Z. W.↗
NASA NTRS1975

Periodic variations stratospheric temperature from 20-65 km at 80 deg N to 30 deg S

Results for a seasonally varying diurnal tide in temperature at Churchill are presented, and possible significant aliasing of longer period waves by this tide is discussed. A diurnal tide whose amplitude and phase are coherent throughout the year is found to have little effect on periodic amplitudes other than the long-term mean, because most rocketsonde observations are taken near the same local time each day. Errors in periodic components arising from lack of solar radiation corrections are found to be largest for the long-term mean with a small influence noted in the annual wave's amplitude. Spatial variations of the amplitudes and phases of long-period waves are examined through the use of height-latitude sections, 20-65 km, at 80 deg N to 30 deg S. The quasi-biennial oscillation and semiannual waves have tropical maxima of 2 and 3C near 30 and 40 km respectively. The annual wave's maximum is over 22C near 45 km at 70 deg N and the terannual wave's maximum is over 6C near 55 km at 80 deg N. The semiannual wave has to polar maxima: 7C near 75 deg N at 32 km and 3C above 60 km north of 35 deg N.

Nastrom, G. D.↗
DOE OSTI2026

Instantaneous difference frequency locking observed during toroidicity-induced Alfvén eigenmode coupling in the DIII-D tokamak

In magnetic confinement fusion, toroidicity-induced Alfvén eigenmodes (TAEs) are well-studied, weakly stable solutions of the linearized ideal magnetohydrodynamic equations. Driven unstable by suprathermal populations of energetic particles, TAE pose a key vulnerability to the confinement of high-energy alpha particles generated by fusion reactions. Hence, it is paramount to understand TAE dynamics if a working reactor is to be realized. In this work, we detect and characterize signatures of nonstationary nonlinear coupling between TAE using a novel, time-resolved bispectral analysis; results are supported by analytic signal of band-passed data. Crucially, a stationary phase relationship between two TAE and a nascent low frequency fluctuation is observed precisely when the triple product of magnetic fluctuation amplitudes is enhanced. Local mode number and frequency spectrum, gleaned from beam-emission spectroscopy, corroborates simultaneous satisfaction of nonlinear matching conditions, and provides a tool to identify theorized pathways of energy transfer, e.g. TAE parametric instability.

bispectral analysis↗
DOE OSTI2026

Quantum Computing Algorithms and Applications for Coherent and Strongly Correlated Chemical Systems

This project advanced quantum algorithms, quantum information theory, strongly correlated electronic structure methods, molecular quantum materials, and exciton transport imaging in coherent condensed phase systems. Across the award period, the team developed new methods for open-quantum-system simulation, Hamiltonian learning, state tomography, reduced-density-matrix and contracted-quantum eigensolver approaches, and quantum diagnostics for device capability and openness.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1973

Multiple scattering theory of radiative transfer in inhomogeneous atmospheres.

In this paper we treat the multiple scattering theory of radiative transfer in plane-parallel inhomogeneous atmospheres. The treatment presented here may be adopted to model atmospheres characterized by an optical depth dependent coherent scattering phase function. For the purpose of illustration we consider the semi-infinite medium in which the absorption property of the atmosphere is characterized by an exponential function. The methodology employed here is the extension of the case treated previously by the author for homogeneous atmospheres.

Kanal, M.↗
NASA NTRS1975

Airloads near the open port of a one-meter airborne telescope

An infrared telescope is mounted in a cavity in the fuselage of a C-141 airplane. The cavity is sealed off from the rest of the fuselage and can be opened to the outside for viewing. A retractable porous spoiler is installed ahead of the opening to inhibit cavity resonance. The paper presents the mean pressures, pressure fluctuations, spectra, phase, and coherence of the pressures in the cavity and on the fuselage near the cavity, along with pertinent acceleration and torque information for the aircraft structure and telescope. It is shown that a moderate spoiler extension controls resonance in normal flight attitudes and produces a cavity environment with approximately the same turbulence intensity as an attached turbulent boundary layer.

Buell, D. A.↗
NASA NTRS1977

Fluctuating loads on the flap surfaces of an externally-blown-flap configuration

An experimental program to obtain the fluctuating loads on the surfaces of a triple-slotted externally-blown-flap powered-lift STOL configuration was conducted. A large model of a wing/flap system and a TF-34 medium bypass ratio engine was investigated. Measurements of the fluctuating pressure, static pressure, and surface temperature resulting from the jet impingement were obtained at several locations on the surfaces of the second and third flaps. Fluctuating pressure data include overall level, power-spectral density (PSD), cross-correlation coefficient, coherency, and phase angle of the cross power-spectral density. These data indicate that more than one mechanism contributes to the fluctuating pressure levels on the flaps. In the immediate area above the intersection of the engine centerline and the flap, low frequency pressures dominate the overall fluctuating pressure levels. In other areas, such as below this intersection and outboard on the flaps, the PSD curve reaches a peak value at a Strouhal number ranging from 0.22 to 0.45.

Schoenster, J. A.↗
NASA NTRS1978

A ring-source model for jet noise

A model consisting of two ring sources was developed to study the direct radiation of jet noise in terms of correlation, coherence, and phase and also to aid in solving the inverse radiation problem of determining the noise source in terms of far-field measurements. The rings consist of discrete sources which are either monopoles or quadrupoles with Gaussian profiles. Only adjacent sources, both within the rings and between rings, are correlated. Results show that from the far-field information can be used to determine when the sources are compact or noncompact with respect to the acoustic wavelength and to distinguish between the types of sources. In addition, from the inverse radiation approach, the center of mass, the location and separation distance of the ring, and the diameters can be recovered.

Maestrello, L.↗
NASA NTRS1977

Performance of DPSK with convolutional encoding on time-varying fading channels

The bit error probability performance of a differentially-coherent phase-shift keyed (DPSK) modem with convolutional encoding and Viterbi decoding on time-varying fading channels is examined. Both the Rician and the lognormal channels are considered. Bit error probability upper bounds on fully-interleaved (zero-memory) fading channels are derived and substantiated by computer simulation. It is shown that the resulting coded system performance is a relatively insensitive function of the choice of channel model provided that the channel parameters are related according to the correspondence developed as part of this paper. Finally, a comparison of DPSK with a number of other modulation strategies is provided.

Mui, S. Y.↗
NASA NTRS1977

Alloy design with oxide dispersoids and precipitates

The mechanical behavior of particle-strengthened alloys is reviewed. On the basis of this knowledge, it is concluded that second-phase particles, coherent or incoherent, can enhance the flow strength, creep resistance, and stress-rupture life of alloys. Unfortunately, particles are usually not beneficial alloy-design elements if enhanced uniaxial ductility, plane-strain ductility, stress-rupture ductility, and toughness are called for. Such properties as fatigue-crack propagation resistance appear to require, for example, both high strength and high ductility, a situation which can come to pass only when the perennial conflict between strength and ductility is resolved in particle-strengthened systems in particular and in any other material system in general. Wherever possible, the role of coherent and incoherent particles in alloy design is distinguished.

Tien, J. K.↗
NASA NTRS1978

Evaluation of aero Commander propeller acoustic data: Static operations

Acoustic data are analyzed from a series of ground tests performed on an Aero Commander propeller-driven aircraft with an array of microphones flush-mounted on one side of the fuselage. The analyses were concerned with the propeller blade passage noise during static operation at several different engine speeds and included calculations of the magnitude and phase of the blade passage tones, the amplitude stability of the tones, and the spatial phase and coherence of the tones. The results indicate that the pressure field impinging on the fuselage represents primarily aerodynamic (near field) effects in the plane of the propeller at all frequencies. Forward and aft of the propeller plane aerodynamic effects still dominate the pressure field at frequencies below 200 Hz; but at higher frequencies, the pressure field is due to acoustic propagation from an equivalent center located about 0.15 to 0.30 blade diameters inboard from the propeller hub.

Piersol, A. G.↗
NASA NTRS1979

Field measurement of penetrator seismic coupling in sediments and volcanic rocks

Field experiments were conducted to determine experimentally how well a seismometer installed using a penetrator would be coupled to the ground. A dry lake bed and a lava bed were chosen as test sites to represent geological environments of two widely different material properties. At each site, two half-scale penetrators were fired into the ground, a three-component geophone assembly was mounted to the aft end of each penetrator, and dummy penetrators were fired at various distances to generate seismic signals. The recorded signals were digitized, and cross-spectral analyses were performed to compare the observed signals in terms of power spectral density ratio, coherence and phase difference. The analyses indicate that seismometers deployed by penetrators will be as well coupled to the ground as are seismometers installed by conventional methods for the frequency range of interest in earthquake seismology, although some minor differences were observed at frequencies near the upper limit of the frequency band.

Nakamura, Y.↗
NASA NTRS1979

Field Measurements of Penetrator Seismic Coupling in Sediments and Volcanic Rocks

Field experiments were conducted to determine how well a seismometer installed using a penetrator would be coupled to the ground. A dry-lake bed and a lava bed were chosen as test sites to represent geological environments of two widely different material properties. At each site, two half-scale penetrators were fired into the ground, a three-component geophone assembly was mounted to the aft end of each penetrator, and dummy penetrators were at various distances to generate seismic signals. These signals were detected by the penetrator-mounted geophone assembly and by a reference geophone assembly buried or anchored to surface rock and 1-m from the penetrator. The recorded signals were digitized, and cross-spectral analyses were performed to compare the observed signals in terms of power spectral density ratio, coherence, and phase difference. The analyses indicate that seismometers deployed by penetrators will be as well coupled to the ground as are seismometers installed by conventional methods for the frequency range of interest in earthquake seismology.

Nakamura, Y.↗
NASA NTRS1979

Evaluation of aero commander propeller acoustic data: Taxi operations

The acoustic data from ground tests performed on an Aero Commander propeller driven aircraft are analyzed. An array of microphones flush mounted on the side of the fuselage were used to record data. The propeller blade passage noise during operations at several different taxi speeds is considered and calculations of the magnitude and phase of the blade passage tones, the amplitude stability of the tones, and the spatial phase and coherence of the tones are included. The measured results are compared to theoretical predictions for propeller noise and various evaluations which reveal important details of propeller noise characteristics are presented.

Piersol, A. G.↗
NASA NTRS1979

Direct and inverse problems in radiation of sound from discrete random sources on two coaxial rings

An analytical model consisting of two ring sources of sound is developed to study the direct radiation in terms of correlation, coherence, and phase and also to aid in solving the inverse-radiation problem of determining the noise source in terms of farfield measurements. The rings consist of discrete sources which are either monopoles or quadrupoles with Gaussian autocorrelations. Only adjacent sources, both within and between the rings, are correlated. Results show that from the farfield information one can determine when the sources are compact or noncompact with respect to the acoustic wavelength and distinguish between the types of sources. In addition, from the inverse-radiation approach one can recover the center of mass, the location and separation distance of the ring, and the respective diameters.

Maestrello, L.↗