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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

High-Temperature Surface-Acoustic-Wave Transducer

Aircraft-engine rotating equipment usually operates at high temperature and stress. Non-invasive inspection of microcracks in those components poses a challenge for the non-destructive evaluation community. A low-profile ultrasonic guided wave sensor can detect cracks in situ. The key feature of the sensor is that it should withstand high temperatures and excite strong surface wave energy to inspect surface/subsurface cracks. As far as the innovators know at the time of this reporting, there is no existing sensor that is mounted to the rotor disks for crack inspection; the most often used technology includes fluorescent penetrant inspection or eddy-current probes for disassembled part inspection. An efficient, high-temperature, low-profile surface acoustic wave transducer design has been identified and tested for nondestructive evaluation of structures or materials. The development is a Sol-Gel bismuth titanate-based surface-acoustic-wave (SAW) sensor that can generate efficient surface acoustic waves for crack inspection. The produced sensor is very thin (submillimeter), and can generate surface waves up to 540 C. Finite element analysis of the SAW transducer design was performed to predict the sensor behavior, and experimental studies confirmed the results. One major uniqueness of the Sol-Gel bismuth titanate SAW sensor is that it is easy to implement to structures of various shapes. With a spray coating process, the sensor can be applied to surfaces of large curvatures. Second, the sensor is very thin (as a coating) and has very minimal effect on airflow or rotating equipment imbalance. Third, it can withstand temperatures up to 530 C, which is very useful for engine applications where high temperature is an issue.

Zhao, Xiaoliang↗
NASA NTRS1997

On the Origin and Evolution of Stellar Chromospheres, Coronae and Winds

The final report discusses work completed on proposals to construct state-of-the-art, theoretical, two-component, chromospheric models for single stars of different spectral types and different evolutionary status. We suggested to use these models to predict the level of the "basal flux", the observed range of variation of chromospheric activity for a given spectral type, and the decrease of this activity with stellar age. In addition, for red giants and supergiants, we also proposed to construct self-consistent, purely theoretical, chromosphere-wind models, and investigate the origin of "dividing lines" in the H-R diagram. In the report, we list the following six specific goals for the first and second year of the proposed research and then describe the completed work: (1) To calculate the acoustic and magnetic wave energy fluxes for stars located in different regions of the H-R diagram; (2) To investigate the transfer of this non-radiative energy through stellar photospheres and to estimate the amount of energy that reaches the chromosphere; (3) To identify major sources of radiative losses in stellar chromospheres and calculate the amount of emitted energy; (4) To use (1) through (3) to construct purely theoretical, two-component, chromospheric models based on the local energy balance. The models will be constructed for stars of different spectral types and different evolutionary status; (5) To explain theoretically the "basal flux", the location of stellar temperature minima and the observed range of chromospheric activity for stars of the same spectral type; and (6) To construct self-consistent, time-dependent stellar wind models based on the momentum deposition by finite amplitude Alfven waves.

Musielak, Z. E.↗
NASA NTRS1991

The directional dependence of magnetic fluctuations generated by cometary ion pickup

The properties of low frequency magnetic fluctuations generated by cometary ion pickup are examined by means of one-dimensional hybrid simulations, in which newborn ions are created at a constant rate. The helicity and direction of propagation of magnetic fluctuations are investigated for various cometary ion injection angles, alpha, relative to the solar wind magnetic field. The parameter eta represents the relative contribution of wave energy density propagating in the direction away from the comet, parallel to the beam. For small (quasi-parallel) injection angles, alpha is about 0 deg and eta is of order unity, while for larger (quasi-perpendicular) angles, alpha is about 90 deg and eta is about 0.5. At intermediate angles, alpha is about 60 deg, eta can vary between 0 and 1, depending on the wave number. The wave properties are consistent with the instabilities expected from linear theory.

Miller, Ronald H.↗
NASA NTRS1983

Ship waves and lee waves

Dynamics analogous to those of surface ship waves on water of finite depth are noted for the three-dimensional trapped lee wave modes produced by an isolated obstacle in a stratified fluid. This vertical trapping of wave energy is modeled by uniform upstream flow and stratification, bounded above by a rigid lid, and by a semiinfinite fluid of uniform stability whose wind velocity increases exponentially with height, representing the atmosphere. While formal asymptotic solutions are produced, limited quantitative usefulness is obtained through them because of the limitations of the approximations and the infinity of modes in the solution. Time-dependent numerical models are accordingly developed for both surface ship waves and internal and atmospheric ship waves, yielding a variety of results.

Sharman, R. D.↗
NASA NTRS1985

Planetary and Gravity Waves in the Mesosphere and Lower Thermosphere

Rocket and ground based studies of the mesosphere and lower thermosphere show that waves play an important role in the dynamics of their region. The waves manifest themselves in wind, temperature, density, pressure, ionization and airglow fluctuations in the 80-120 km height range. Rockets have enabled the density and temperature structure to be measured with excellent height resolution, while long term studies of wind motions using MST, partial reflection and meteor radars and, more recently, lidar investigations of temperature and density, have enabled the temporal behaviour of the waves to be better understood. A composite of power spectra is shown of wind motions measured near the mesopause at widely separated locations and illustrates how wave energy is distributed as a function of frequency. The spectra show three distinct parts; (1) a long period section corresponding to periods longer than 24 h; (2) a section between 12 and 24 h priod where the spectra are dominated by narrow; peaks associated with the semidiurnal and diurnal tides and (3) a section at periods less than 12 h where the spectral density decreases montonically (except for the 8 h tidal peak). The long period section is associated with transient planetary scale waves while the short period motions are caused by gravity waves.

Vincent, R. A.↗
NASA NTRS2019

A Year in the Life of GW 170817: The Rise and Fall of a Structured Jet from a Binary Neutron Star Merger

We present the results of our year-long afterglow monitoring of GW 170817, the first binary neutron star merger detected by Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo. New observations with the Australian Telescope Compact Array and the Chandra X-ray Telescope were used to constrain its late-time behaviour. The broad-band emission, from radio to X-rays, is well-described by a simple power-law spectrum with index β ∼ 0.585 at all epochs. After an initial shallow rise ∝t0.9, the afterglow displayed a smooth turnover, reaching a peak X-ray luminosity of LX ≈ 5 × 1039 erg s−1 at 160 d, and has now entered a phase of rapid decline, approximately ∝t−2. The latest temporal trend challenges most models of choked jet/cocoon systems, and is instead consistent with the emergence of a relativistic structured jet seen at an angle of ≈22◦ from its axis. Within such model, the properties of the explosion (such as its blast wave energy EK ≈ 2 × 1050 erg, jet width θc ≈ 4◦, and ambient density n ≈ 3 × 10−3 cm−3) fit well within the range of properties of cosmological short gamma-ray bursts.

Acceleration of particles↗
NASA NTRS2006

Getting a Kick Out of Numerical Relativity

Operating ground-based gravitational wave detectors and a planned instrument in space are bringing about the new field of gravitational wave astronomy. A prime source for any of these observatories is the merger of a system of two black holes. Brought together by copious losses of gravitational-wave energy, these systems merge in a burst of energy with a peak power exceeding any electromagnetic source. Observations of these sources will generate a wealth of astrophysical information, and may provide an unparalleled probe of strong-field gravitational physics, but a full interpretation of the observations will require detailed predictions from General Relativity. I will discuss recent advances in numerical simulations of binary black hole systems which are generating dramatic progress in understanding binary black hole mergers. Recent achievements include the first simulations of binary black hole systems through several orbits and merger, leading to detailed predictions for the final portion of the gravitational radiation waveforms from equal-mass mergers. For unequal-mass mergers, it has recently become possible to measure the impulsive kick imparted to the final black hole, by the asymmetry of the merger radiation. These first results announce an accelerating wave of progress soon to come from the energetic field of numerical relativity.

Source record↗
NASA NTRS2010

Demonstration of a Submillimeter-Wave HEMT Oscillator Module at 330 GHz

In this work, radial transitions have been successfully mated with a HEMT-based MMIC (high-electron-mobility-transistor-based monolithic microwave integrated circuit) oscillator circuit. The chip has been assembled into a WR2.2 waveguide module for the basic implementation with radial E-plane probe transitions to convert the waveguide mode to the MMIC coplanar waveguide mode. The E-plane transitions have been directly integrated onto the InP substrate to couple the submillimeter-wave energy directly to the waveguides, thus avoiding wire-bonds in the RF path. The oscillator demonstrates a measured 1.7 percent DC-RF efficiency at the module level. The oscillator chip uses 35-nm-gate-length HEMT devices, which enable the high frequency of oscillation, creating the first demonstration of a packaged waveguide oscillator that operates over 300 GHz and is based on InP HEMT technology. The oscillator chip is extremely compact, with dimensions of only 1.085 x 320 sq mm for a total die size of 0.35 sq mm. This fully integrated, waveguide oscillator module, with an output power of 0.27 mW at 330 GHz, can provide low-mass, low DC-power-consumption alternatives to existing local oscillator schemes, which require high DC power consumption and large mass. This oscillator module can be easily integrated with mixers, multipliers, and amplifiers for building high-frequency transmit and receive systems at submillimeter wave frequencies. Because it requires only a DC bias to enable submillimeter wave output power, it is a simple and reliable technique for generating power at these frequencies. Future work will be directed to further improving the applicability of HEMT transistors to submillimeter wave and terahertz applications. Commercial applications include submillimeter-wave imaging systems for hidden weapons detection, airport security, homeland security, and portable low-mass, low-power imaging systems

Radisic, Vesna↗
NASA NTRS2013

A First Search for Coincident Gravitational Waves and High Energy Neutrinos Using LIGO, Virgo and ANTARES Data from 2007

We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.

using LIGO↗
NASA NTRS1971

The reduction of a ""safety catastrophic'' potential hazard: A case history

A worst case analysis is reported on the safety of time watch movements for triggering explosive packages on the lunar surface in an experiment to investigate physical lunar structural characteristics through induced seismic energy waves. Considered are the combined effects of low pressure, low temperature, lunar gravity, gear train error, and position. Control measures constitute a seal control cavity and design requirements to prevent overbanking in the mainspring torque curve. Thus, the potential hazard is reduced to safety negligible.

Joseph P. Jones↗
NASA NTRS1972

Microwave device investigations

Materials, devices and novel schemes for generation, amplification and detection of microwave and millimeter wave energy are studied. Considered are: (1) Schottky-barrier microwave devices; (2) intermodulation products in IMPATT diode amplifiers; and (3) harmonic generation using Read diode varactors.

Choudhury, K. K. D.↗
NASA NTRS1972

Reformulation of quasi-linear theory.

Standard plasma quasi-linear theory is reformulated on the basis of a classical quantum derivation proceeding from the Vlasov equation and dealing only with frequency, wavenumber, and velocity. The wave amplitudes are assumed to be weakly time-dependent, and no distinction is made between growing and decaying waves. The proposed method leads to no negative diffusivity of 'fake' diffusion. By appropraite treatment of nonresonant interaction, expressions are obtained for wave energy and momentum.

Kaufman, A. N.↗
NASA NTRS1972

Alfvenic motions in the solar atmosphere.

Discussion of the amplitude of bulk velocities associated with upward-propagating Alfven waves in the lower solar atmosphere. It is shown that, for a given wave energy flux, the bulk velocities can be appreciably lower in cases when the wavelength is much larger than the scale height, than in situations where the wavelength is smaller than the scale height.

Hollweg, J. V.↗
NASA NTRS1973

Application of ERTS-1 data to the protection and management of New Jersey's coastal environment

The author has identified the following significant results. A Coastal Zone Surveillance Program has been developed in which systematic comparisons of early ERTS-1 images and recently acquired images are regularly made to identify areas where changes have occurred. A methodology for assessing and documenting benefits has been established. Quantification of benefits has been directed toward four candidate areas: shore protection, ocean outfalls, coastal land resources, and offshore waste disposal. A refinement in the change detection analysis procedure has led to greater accuracy in spotting developmental changes in the Coastal Zone. Preliminary conclusions drawn from the Shore Erosion case study indicate that in the northern test area (developed beach) erosion has occurred more often, is generally more severe, and the beach is slower to recover than in the southern test area (natural beach). From these data it appears that it may be possible to define areas most likely to experience further erosion. The assumption of continued erosion in areas that have at one time experienced severe erosion is supported by the simple fact that as a beach narrows wave energy is concentrated on a narrower beach surface. The higher energy condition subsequently results in accelerated erosion.

Yunghans, R. S.↗
NASA NTRS1973

Upper atmospheric planetary-wave and gravity-wave observations

Previously collected data on atmospheric pressure, density, temperature and winds between 25 and 200 km from sources including Meteorological Rocket Network data, ROBIN falling sphere data, grenade release and pitot tube data, meteor winds, chemical release winds, satellite data, and others were analyzed by a daily-difference method, and results on the magnitude of atmospheric perturbations interpreted as gravity waves and planetary waves are presented. Traveling planetary-wave contributions in the 25-85 km range were found to have significant height and latitudinal variation. It was found that observed gravity-wave density perturbations and wind are related to one another in the manner predicted by gravity-wave theory. It was determined that, on the average, gravity-wave energy deposition or reflection occurs at all altitudes except the 55-75 km region of the mesosphere.

Justus, C. G.↗