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Results for “phase stability”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

X-band uplink feedcone capabilities, components, and layout

Two new X-(7.2 GHz up, 8.4 GHz down) and S-band (2.1 to 2.3 Ghz) common aperture (XSC) feedcones are being added to the DSS 45 and DSS 65 34-Meter Efficiency Antennas. These new feedcones are modifications of the existing SXC feedcone design incorporating a new high power (20-kW) X-band transmitter. The modified Antenna Microwave Subsystem design also incorporates two additional X-band low noise amplifiers and greater phase stability performance to meet both the increased stability requirements for Galileo gravity wave experiments and requirements for spacecraft navigation near the Sun. A third XSC will be constructed for DSS 15 later.

Marlin, H.↗
NASA NTRS1987

Aperture-synthesis interferometry at optical wavelengths

The prospects for applying aperture-synthesis interferometry to the optical domain are reviewed. The radio examples such as the VLA provide a model, since the concepts are equally valid for radio and optical wavelengths. If scientific problems at the milliarc-second resolution level (or better) are to be addressed, a space-based optical array seems to be the only practical alternative, for the same reasons that dictated array development at radio wavelengths. One concept is examined, and speculations are offered concerning the prospects for developing real systems. Phase-coherence is strongly desired for a practical array, although self-calibration and phase-closure techniques allow one to relax the restriction on absolute phase stability. The design of an array must be guided by the scientific problems to be addressed.

Burke, Bernard F.↗
NASA NTRS1988

A fine resolution multifrequency polarimetric FM radar

A fine resolution polarimetric FM SAR was developed for optimization of polarimetric SARs and interpretation of SAR data via controlled experiments with surface-base sensors. The system is designed for collecting polarimetric data at 5.3 and 10 GHz over incidence angles from 0 to 60 deg. Features of the system include broad bandwidth to obtain fine range resolution, phase stabilization and linearization loop circuitry, and digital signal processing capability. The system is used in a research program to collect polarimetric backscatter data from artificial sea ice research and design trade-offs, laboratory and field evaluation, as well as results from experiments on artificial sea ice are presented.

Bredow, J.↗
NASA NTRS1985

Thermal Barrier Coatings. Abstracts and figures

The Thermal Barrier Coatings Workshop was held May 21 and 22, 1985, at the NASA Lewis Research Center in Cleveland, Ohio. Six sessions covered Failure Mechanisms and Life Modeling, Effects of Oxidation and Creep, Phase Stability and Microstructural Aspects, Nondestructive and Analytical Assessment, Coating Development, and Alternative Applications.

Source record↗
NASA NTRS1989

VLBI using a telescope in Earth orbit. I - The observations

A VLBI experiment has been conducted at a frequency of 2.3 GHz, using an antenna in Earth orbit. The observational procedure for the orbiting antenna, part of the Tracking and Data Relay Satellite System, is described. Nonstandard VLBI procedures were necessary to obtain adequate phase stability and to correlate the data. Several technical concepts necessary for a dedicated space VLBI mission were successfully tested.

Levy, G. S.↗
NASA NTRS1989

Thermal coefficient of delay for various coaxial and fiber-optic cables

Data are presented on the thermal coefficient of delay for various coaxial and fiber optic cables, as measured by the Frequency and Timing Systems Engineering Group and the Time and Frequency Systems Research Group. The measured pressure coefficient of delay is also given for the air-dielectric coaxial cables. A description of the measurement method and a description of each of the cables and its use at JPL and in the DSN are included. An improvement in frequency and phase stability by a factor of ten is possible with the use of fiber optics.

Lutes, G. F.↗
NASA NTRS1990

Energetics and crystal chemistry of Ruddlesden-Popper type structures in high T(sub c) ceramic superconductors

The formation of Ruddlesden-Popper type layers (alternating slabs of rocksalt and perovskite structures) is seen in these oxides which is similar in many respects to what is seen in the system Sr-Ti-O. However, it was observed that there are some significant differences, for example the rocksalt and perovskite blocks in new superconducting compounds are not necessarily electrically, unlike in Sr-Ti-O systems. This will certainly render an additional coulombic bonding energy between two different types of blocks and may well lead to significant differences in their structural chemistry. In the higher order members of the various homologous series, additional Cu-O planes are inserted in the perovskite blocks. In order for the unit cell to electrically neutral the net positive charge on rocksalt block (which remains constant throughout the homologous series) should be balanced by an equal negative charge on perovskite block. It, thus becomes necessary to create oxygen vacancies in the basic perovskite structure, when width of the perovskite slab changes on addition of extra Cu-O planes. Results of atomistic simulations suggest that these missing oxygen ions allow the Cu-O planes to buckle in these compounds. This is also supported by the absence of buckling in the first member of Bi-containing compounds in which there are no missing oxygen ions and the Sr-Ti-O series of compounds. Additional results are presented on the phase stability of polytypoid structures in these crystal chemically complex systems. The studies will focus on the determination of the location of Cu(3+) in the structures of higher order members of the La-Cu-O system and whether Cu(3+) ions or oxygen vacancies are energetically more favorable charge compensating mechanism.

Dwivedi, Anurag↗
NASA NTRS1991

Nonequilibrium Phase Chemistry in High Temperature Structure Alloys

Titanium and nickel aluminides of nonequilibrium microstructures and in thin gauge thickness were identified, characterized and produced for potential high temperature applications. A high rate sputter deposition technique for rapid surveillance of the microstructures and nonequilibrium phase is demonstrated. Alloys with specific compositions were synthesized with extended solid solutions, stable dispersoids, and specific phase boundaries associated with different heat treatments. Phase stability and mechanical behavior of these nonequilibrium alloys were investigated and compared.

Wang, R.↗
NASA NTRS1991

The pulse-pair algorithm as a robust estimator of turbulent weather spectral parameters using airborne pulse Doppler radar

The pulse pair method for spectrum parameter estimation is commonly used in pulse Doppler weather radar signal processing since it is economical to implement and can be shown to be a maximum likelihood estimator. With the use of airborne weather radar for windshear detection, the turbulent weather and strong ground clutter return spectrum differs from that assumed in its derivation, so the performance robustness of the pulse pair technique must be understood. Here, the effect of radar system pulse to pulse phase jitter and signal spectrum skew on the pulse pair algorithm performance is discussed. Phase jitter effect may be significant when the weather return signal to clutter ratio is very low and clutter rejection filtering is attempted. The analysis can be used to develop design specifications for airborne radar system phase stability. It is also shown that the weather return spectrum skew can cause a significant bias in the pulse pair mean windspeed estimates, and that the poly pulse pair algorithm can reduce this bias. It is suggested that use of a spectrum mode estimator may be more appropriate in characterizing the windspeed within a radar range resolution cell for detection of hazardous windspeed gradients.

Baxa, Ernest G., Jr.↗
NASA NTRS1990

Film properties of high performance semi-interpenetrating polyimide networks

Consideration is given to an approach to provide a semi-IPN in which two constituent materials have nearly the same chemical structure and polymer chain length. A reactive endcapped LARC-TPI polyamic acid having a formulated molecular weight of 20,000 is prepared and then combined with various quantities of a commercial LARC-TPI polyamic acid solution. The polyimide films of semi-IPNs are tested along with two constituent materials. The physical and mechanical properties of the polyimide films are presented. The applicability of using this approach to minimize phase separation and to maximize long-term phase stability is discussed. The concept of controlling morphology by chemistry is proven for providing LARC-TPI based semi-2-IPNs. A very long chain LARC-TPI endcapped with a nadic group exhibits physical properties almost identical to unendcapped LARC-TPI.

Gerber, M. K.↗
NASA NTRS1990

Radio science experiment of Voyager-2 spacecraft occultation by Neptune

NASA-JPL and Japan's Institute of Space and Astronautical Science collaborated at the Usuda Deep Space Center in the Voyager-2 Neptune occultation experiment. Phase information is extracted from the recorded data by means of a digital filter that can track the carrier frequency and narrow the filter bandwidth by up to 3 mHz. The results thus obtained can verify the phase-stability of the receiving system as a whole. Problems experienced by low-noise amplifiers were solved through the use of system redundancies.

Hayashi, T.↗
NASA NTRS1994

Superhumps in cataclysmic binaries. 3: V795 Herculis

We report photometry of the cataclysmic variable V795 Herculis during 1990-1994. Comparison of recent with previously published data shows that the 2.78-hr periodicity has essentially disappeared; the amplitude has diminished by a factor of at least 10. In its place, there is a low-amplitude signal near the radial-velocity (orbital?) period of 2.60 hr. During 1983-1989, the star did show an obvious 2.78-hr signal. We study the published data on this signal, together with our own data under the (questionable) assumption that the signal still exists with an amplitude too small to survive the rigors of unbiased period detection. The data are really too sparse and too poorly distributed to decide the issue of phase stability. But since the photometric signal is transient and exceeds the likely orbital period by approximately 8%, the photometric waves are likely to be yet another example of 'superhumps', the phenomenon made famous by dwarf novae in superoutburst. At high frequencies, the star shows a quasi-periodic signal with P approximately 1160 s, and possibly also a stable signal with P = 1310.2 s (or 1330.4 s, the one-day alias). The beat period between these signals could be the orbital period, or that of the vanished superhump.

Patterson, Joseph↗
NASA NTRS1995

Structure and superconductivity in (Bi(0.35)Cu(0.65))Sr2YCu2O7 and related materials

The recently reported (Bi/Cu)Sr2YCu2O7 phase has been studied by time of flight powder neutron diffraction. The proposed 1212 structure has been confirmed and refinements have shown the oxygen in the (Bi/Cu)O layer is displaced by 0.78 A from the ideal (1/2,1/2,0) site (P4/mmm space group) along /100/. Bond Valence Sum calculations have suggested oxidation states of Bi(5+) and Cu(2+) for the cations in the (Bi/Cu)O layers. The material is non-superconducting and all attempts to induce superconductivity have been unsuccessful. Work on the related material (Ce/Cu)Sr2YCu2O7 has shown the ideal Ce content to be 0.5 Ce per formula unit. The introduction of Ba (10%) onto the Sr site dramatically increases phase stability and also induces superconductivity (62 K).

Jennings, R. A.↗
NASA NTRS1996

Polymer-Induced Depletion Interaction and Its Effect on Colloidal Sedimentation in Colloid-Polymer Mixtures

In this paper we focus on the polymer-induced depletion attraction and its effect on colloidal sedimentation in colloid-polymer mixtures. We first report a small angle neutron scattering (SANS) study of the depletion effect in a mixture of hard-sphere-like colloid and non-adsorbing polymer. Then we present results of our recent sedimentation measurements in the same colloid-polymer mixture. A key parameter in controlling the sedimentation of heavy colloidal particles is the interparticle potential U(tau), which is the work required to bring two colloidal particles from infinity to a distance tau under a give solvent condition. This potential is known to affect the average settling velocity of the particles and experimentally one needs to have a way to continuously vary U(tau) in order to test the theory. The interaction potential U(tau) can be altered by adding polymer molecules into the colloidal suspension. In a mixture of colloid and non-adsorbing polymer, the potential U(tau) can develop an attractive well because of the depletion effect, in that the polymer chains are expelled from the region between two colloidal particles when their surface separation becomes smaller than the size of the polymer chains. The exclusion of polymer molecules from the space between the colloidal particles leads to an unbalanced osmotic pressure difference pushing the colloidal particles together, which results in an effective attraction between the two colloidal particles. The polymer-induced depletion attraction controls the phase stability of many colloid-polymer mixtures, which are directly of interest to industry.

Tong, Penger↗
NASA NTRS1998

X-Ray Spectral and Temporal Studies of the Ultra-Compact System X1916-05

Rossi x-ray timing Explorer (RXTE) Cycle 1 data on the ultra-compact low mass x- ray binary (LMXB) X1916-05 is analyzed. In this current report, the scientific objectives of this investigation of hard x-ray studies of bursters and the results achieved are summarized. The scientific objectives are: (1) Period of the x-ray dips in X1916-05; (2) Phase stability of the x-ray dip period; (3) Spectral break energy and its dependence on mass transfer rate; and (4) Qpos detected from this LMXB. A list of published papers resulted from this project is also included.

Grindlay, Jonathan E.↗
NASA NTRS1997

Final Report

As an ongoing project, the original proposal of implementing BFS (Bozzolo-Ferrante-Smith methods) to the process of alloy design was satisfied beyond the original expectations, as the project evolved from the original goal of backing the experimental results with theoretical and computational evidence, to the point where theoretical predictions lead the way for further experimental studies. For the first time, computer simulations were used to predict the phase stability of many component systems (four and five elements), which are currently being developed and analyzed experimentally. Similar progress was made in the area of surface structure analysis via computer simulations.

Bozzolo, Guillermo↗
NASA NTRS2004

Experimental Study of Serpentinization Reactions

Current carbonaceous chondrite parent-body thermal models [1-3] produce scenarios that are inconsistent with constraints on aqueous alteration conditions based on meteorite mineralogical evidence, such as phase stability relationships within the meteorite matrix minerals [4] and isotope equilibration arguments [5, 6]. This discrepancy arises principally because of the thermal runaway effect produced by silicate hydration reactions (here loosely called serpentinization, as the principal products are serpentine minerals), which are so exothermic as to produce more than enough heat to melt more ice and provide a self-sustaining chain reaction. One possible way to dissipate the heat of reaction is to use a very small parent body [e.g., 2] or possibly a rubble pile model. Another possibility is to release this heat more slowly, which depends on the alteration reaction path and kinetics.

Cohen, B. A.↗
NASA NTRS1992

Isoperiodic neuronal activity in suprachiasmatic nucleus of the rat

A subpopulation of neurons in the suprachiasmatic nucleus (SCN) is shown here to exhibit isoperiodic bursting activity. The period of discharge in these cells may be lengthened or the periodicity may be transiently disrupted by photic stimulation. It is suggested that many, if not all, of these cells are vasoactive intestinal polypeptide (VIP) neurons. It is shown that the ultradian periodicity of these cells, estimates of the VIP neuron population size in the SCN, effects of partial lesions on tau (period), and estimates of the phase stability of SCN-driven circadian rhythms are consistent with a strongly coupled, multioscillator model of circadian rhythmicity, in which the oscillator population constitutes a restricted subset of the SCN neuronal population.

NASA Discipline Regulatory Physiology↗