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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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The results of a stagnation-line analysis of the radiative heating of a phenolic-nylon ablator are reported. The analysis includes flowfield coupling with the ablator surface, equilibrium chemistry, multicomponent or binary diffusion and a coupled line and continuum radiation calculations. Users manual and operating instructions for the computer programs listed in the report are included.
Sliding friction experiments were conducted in a vacuum with binary-copper alloy riders sliding against a conventional bearing-steel surface with normal residual oxides present. The binary alloys contained 1 atomic percent of various alloying elements. Auger spectroscopy analysis was used to monitor the adhesive transfer of the copper alloys to the bearing-steel surface. A relation was found to exist between adhesive transfer and the reaction potential and free energy of formation of the alloying element in the copper. The more chemically active the element and the more stable its oxide, the greater was the adhesive transfer and wear of the copper alloy. Transfer occurred in all the alloys except copper-gold after relatively few (25) passes across the steel surface.
Comparative lab spectra and Thematic Mapper imagery investigations at 3 Tertiary calderas in southern Nevada indicate that desert varnish is absorbant relative to underlying host rocks below about 0.7 to 1.3 microns, depending on mafic affinity of the sample, but less absorbant than mafic host rocks at higher wavelengths. Desert varnish occurs chiefly as thin impregnating films. Distribution of significant varnish accumulations is sparse and localized, occurring chiefly in surface recesses. These relationships result in the longer wavelength bands and high 5/2 values over felsic units with extensive desert varnish coatings. These lithologic, petrochemical, and desert varnish controlled spectral responses lead to characteristic TM band relationships which tend to correlate with conventionally mappable geologic formations. The concept of a Rock-Varnish Index (RVI) is introduced to help distinguish rocks with a potentially detectable varnish. Felsic rocks have a high RVI, and those with extensive desert varnish behave differently, spectrally, from those without extensive varnish. The spectrally distinctive volcanic formations at Stonewall Mountain provide excellent statistical class segregation on supervised classification images. A binary decision rule flow-diagram is presented to aid TM imagery analysis over volcanic terrane in semi-arid environments.
The principal goal of our phase 1 investigation was the development of techniques and data analysis tools for pulsar searches and timing. After the launch of the Compton Observatory, we received from the Burst and Transient Source Experiment (BATSE) team one day of discriminator large area (DISCLA) data for use in the development and testing of data analysis techniques. Using this first day of data for testing and optimizing our timing tools we detected four x-ray binary pulsars, Vela X-1, Cen X-3, 4U 0115+63, and GX 301-2. Subsequently, we received four more days of data, allowing us to test our timing tools with data from a variety of days. In summary, using the tools we developed based on the first day of data that we received, we have detected 8 pulsars in 5 days of data, or roughly one quarter of the approximately 30 known x-ray binary pulsars. In addition to the pulsars listed above, we detected GX 1+4, 4U 1626-67, OAO 1657-415, and Her X-1. Many of the data analysis tools that we developed have been ported to MSFC and are being used for the analysis of BATSE data. This appendix describes some of the timing tools and presents preliminary pulse period and phase profile results.
We present the first calculations of magnetic field evolution following accretion-induced field reduction which demonstrate the possibility of subsequent surface magnetic field growth. Assuming the preaccretion field is pushed down or advected below the accreting material, we show that significant diffusion of the suppressed field back to the surface can occur within a Galactic age approximately 10(exp 10) yr. This produces surface fields characteristic of standard pulsars if the total mass transferred is below a critical value delta M(sub c) approximately 0.04 solar masses. We then show how this provides a natural explanation for the existence of old pulsars with high inferred surface dipole fields which are still observable. Using our results in conjunction with a model for accretion-induced field reduction we predict the evolution of a binary pulsar's spin and magnetic field through its postaccretion lifetime. This analysis also provides a qualitative explanation for a recent suggestion that the magnetic fields and spins of recycled pulsars have a bimodal distribution.
Three Rossi Timing Explorer (RXTE) observations were carried out for this proposal based on target of opportunity triggers derived from the All-Sky Monitor (ASM) on RXTE. We obtained short observations of 4U1636-536 (15ks) and 4U1735-44 (23ks) and a longer observation of 4U0614+091 (117ks). Our analysis of our observations of the atoll neutron star x-ray binary 4U1735-44 lead to the discovery of a second high frequency quasiperiodic oscillation (QPO) in this source. These results were published in the Astrophysical Journal Letters. The data obtained on the source 4U0614+091 were used in a comprehensive study of this source, which will be published in the Astrophysical Journal. The data from this proposal were particularly critical for that study as they lead to the detection of the highest QPO frequency every found in the x-ray emission from an x-ray binary which will be important in placing limits on the equation of state of nuclear matter.
25 1417-624 is a 57 mHz transient Be/X-ray pulsar system first discovered by SAS 3 in 1978. After the discovery outburst it was not seen again until 1994 when BATSE observed an outburst that peaked at 40 Srab (pulsed flux, 20-50 keV) and lasted 110 days, followed by a series of 5 shorter, 10-15 mCrab outbursts occurring every 42 days. Pulse timing analysis showed that these smaller outbursts began a few days after periastron passage of the system's eccentric, 42 day period orbit. Renewed activity from the source was detected by BATSE beginning in 1999 November. BATSE monitoring shows a 10 mCrab peak flux outburst lasting 10 days, followed in the next orbit by a 30 mCrab peak flux outburst, which to date has lasted 56 days. Regular monitoring with RXTE began during the 1999 November outburst and has continued in to the current outburst. The data provides good coverage of the low flux state between BATSE detections, which includes the periastron passage. Pulses are detected through this interval, showing that the source did not enter the propeller regime. The PCA monitoring from the lowest flux level, which occurs shortly before periastron, until the peak of the current outburst, show a continuous evolution of the pulse profile. These profiles contain a narrow notch feature which allow us to present a phase aligned history of this pulse evolution. We present a timing analysis of the PCA and BATSE observations that provide corrections to the binary orbit, and measurements of the torque during the observations. From the observed torque and flux we show that disc accretion is occurring in the current outburst, most probably was also occurring in the smaller outburst.
The final merger of two black holes is expected to be the strongest gravitational wave source for ground-based interferometers such as LIGO, VIRGO, and GEO600, as well as the space-based interferometer LISA. Observing these sources with gravitational wave detectors requires that we know the radiation waveforms they emit. Since these mergers take place in regions of extreme gravity, we need to solve Einstein's equations of general relativity on a computer in order to calculate these waveforms. For more than 30 years, scientists have tried to compute black hole mergers using the methods of numerical relativity. The resulting computer codes have been plagued by instabilities, causing them to crash well before the black holes in the binary could complete even a single orbit. Within the past few years, however, this situation has changed dramatically, with a series of remarkable breakthroughs. This talk will focus on new simulations that are revealing the dynamics and waveforms of binary black hole mergers, and their applications in gravitational wave detection, data analysis, and astrophysics.
The final merger of two black holes is expected to be the strongest gravitational wave source for ground-based interferometers such as LIGO, VIRGO, and GE0600, as well as the space-based interferometer LISA. Observing these sources with gravitational wave detectors requires that we know the radiation waveforms they emit. Since these mergers take place in regions of extreme gravity, we need to solve Einstein's equations of general relativity on a computer in order to calculate these waveforms. For more than 30 years, scientists have tried to compute black hole mergers using the methods of numerical relativity. The resulting computer codes have been plagued by instabilities, causing them to crash well before the black holes in the binary could complete even a single orbit. Within the past few years, however, this situation has changed dramatically, with a series of remarkable breakthroughs. This talk will focus on new simulations that are revealing the dynamics and waveforms of binary black hole mergers, and their applications in gravitational wave detection, data analysis, and astrophysics.
A systematic analysis of the effect of convection on the microstructural evolution in cast binary, ternary and commercial Al-Si based alloys.
We present results from the first three years of observations of moving group (MG) targets in the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) high-contrast imaging survey of exoplanets and disks using the Subaru telescope. We achieve typical contrasts of (is) approximately10(exp 5) at 1" and (is) approximately 10(exp 6) beyond 2" around 63 proposed members of nearby kinematic MGs. We review each of the kinematic associations to which our targets belong, concluding that five, beta Pictoris ((is) approximately 20 Myr), AB Doradus ((is) approximately 100 Myr), Columba ((is) approximately 30 Myr), Tucana-Horogium ((is) approximately 30 Myr), and TW Hydrae ((is) approximately 10 Myr), are sufficiently well-defined to constrain the ages of individual targets. Somewhat less than half of our targets are high-probability members of one of these MGs. For all of our targets, we combine proposed MG membership with other age indicators where available, including Ca ii HK emission, X-ray activity, and rotation period, to produce a posterior probability distribution of age. SEEDS observations discovered a substellar companion to one of our targets, kappa And, a late B star. We do not detect any other substellar companions, but do find seven new close binary systems, of which one still needs to be confirmed. A detailed analysis of the statistics of this sample, and of the companion mass constraints given our age probability distributions and exoplanet cooling models, will be presented in a forthcoming paper.
Geothermal plant performance is bounded by the second law efficiency, which accounts for the quantity of exergy that can be converted into useful work. This in turn is dependent on the geothermal resource temperature and the temperature of the heat sink (i.e., the ambient temperature). In this study we show that ambient temperature variability on a diurnal and seasonal basis can affect performance and cost estimations for geothermal plants. We have utilized the updated System Advisor Model (SAM) to assess nine geothermal sites with existing resource capacities across three climate zones. Our analysis shows that both evaporatively-cooled flash and air-cooled binary cycle plants are affected by temperature, with a slightly higher effect in EGS binary sites. By assuming an ambient (wet bulb) temperature baseline of 15.6 degrees C (60 degrees F) and comparing baseline results to those from site-specific data we observe up to 15% underestimation of plant performance and up to 20% overestimation of cost.
Geothermal plant performance is bounded by the second law efficiency, which accounts for the quantity of exergy that can be converted into useful work. This, in turn, is dependent on the geothermal resource temperature and the temperature of the heat sink (i.e., the ambient temperature). In this study, we show that ambient temperature variability on a diurnal and seasonal basis can affect performance and cost estimations for geothermal plants. We have utilized the updated System Advisor Model (SAM) to assess nine geothermal sites with existing resource capacities across three climate zones. Our analysis shows that both evaporatively-cooled flash and air-cooled binary cycle plants are affected by temperature, with a slightly higher effect in enhanced geothermal system binary sites. By assuming an ambient (wet bulb) temperature baseline of 15.6 degrees C (60 degrees F) and comparing baseline results to those from site-specific data, we observe up to 15% underestimation of plant performance and up to 20% overestimation of cost. These results make a case for the inclusion of location-based weather data as inputs to supply curves that are used in capacity expansion models for the prediction of future geothermal deployment scenarios.
Context. Brown dwarfs are transition objects between stars and planets that are still poorly understood, for which several competing mechanisms have been proposed to describe their formation. Mass measurements are generally difficult to carry out for isolated objects as well as for brown dwarfs orbiting low-mass stars, which are often too faint for a spectroscopic follow-up. Aims. Microlensing provides an alternative tool for the discovery and investigation of such faint systems. Here, we present an analysis of the microlensing event OGLE-2019-BLG-0033/MOA-2019-BLG-035, which is caused by a binary system composed of a brown dwarf orbiting a red dwarf. Methods. Thanks to extensive ground observations and the availability of space observations from Spitzer, it has been possible to obtain accurate estimates of all microlensing parameters, including the parallax, source radius, and orbital motion of the binary lens. Results. Following an accurate modeling process, we found that the lens is composed of a red dwarf with a mass of M(1) = 0:149 ± 0.010 M⊙ and a brown dwarf with a mass of M(2) = 0:0463 ± 0:0031 M at a projected separation of a⊥ = 0:585 au. The system has a peculiar velocity that is typical of old metal-poor populations in the thick disk. A percent-level precision in the mass measurement of brown dwarfs has been achieved only in a few microlensing events up to now, but will likely become more common in the future thanks to the Roman space telescope.
The microgravity ethanol droplet combustion experiments were performed aboard the STS-94/MSL-1 Shuttle mission within the Fiber-Supported Droplet Combustion-2 (FSDC-2) program. The burning histories and flame standoffs for pure ethanol and ethanol/water droplets were obtained from the images recorded with two 8 mm videocameras. The obtained results show that average gasification rate is related to the initial droplet size in a manner similar to n-alkanes and methanol and consistent with the results of Hara and Kumagai and the data taken recently in the NASA-Lewis 2.2 s droptower. A transient, moving finite-element chemically reacting flow model applied previously to sphero-symmetric combustion of methanol, methanol/water, n-alkane, and n-alkane binary mixture droplets was adopted for the problem of ethanol droplet combustion. The model includes detailed description of gas-phase reaction chemistry and transport, a simplified description of liquid phase transport, and non-luminous radiative heat transfer. Gas-phase chemistry was described with the detailed reaction mechanism of Norton and Dryer, which consists of 142 reversible elementary reactions of 33 species. Another recently published reaction mechanism of high-temperature ethanol oxidation was also considered. The model predictions were found to compare favorably with the experimental data. The model analysis also indicates that water condensation in the case of ethanol has smaller effect on average droplet gasification rate as compared with previously studied methanol cases. This effect is explained by non-ideal (azeotropic) behavior of binary ethanol-water mixtures. Further analysis of computational results and ethanol droplet radiative extinction behavior will be discussed.
The optical spectrum of the chemically peculiar HgMn type binary star chi Lupi has been analyzed to determine atmospheric parameters and elemental abundances. Echelle spectra were obtained with the 3.9 m Anglo-Australian telescope to exploit the extreme shape-lined nature of the spectrum. This study was undertaken in support of ultraviolet analyses currently underway that utilize echell spectra obtained with the Hubble Space Telescope. For the B9.5 V primary star we obtain T(sub eff) = 10650 K, log g = 3.9, and xi = 0 km/s, while for the A2 V secondary, T(sub eff) = 9200 K, log g = 4.0, and xi = 2 km/s. Most of the elemental abundances are typical of HgMn stars with similar T(sub eff) showing an overall iron-peak elemental abundance distribution that is basically solar in nature with enhancement of the light elements Si, P, and S, as well as all detected elements heavier than the iron group. Abundances for several elements have been determined for the first time in this star, including several of the rare-earths. The secondary star spectrum shows Am star characteristics. We also discuss the relative merits of the equivalent width and synthetic spectrum techniques in determining the elemental abundences, concluding that the synthetic spectrum technique is necessary for obtaining abundances with the utmost accuracy.
The detection of coherent X-ray pulsations at ∼314 Hz (3.2 ms) classifies MAXI J1957+032 as a fast-rotating, accreting neutron star. We present the temporal and spectral analysis performed using NICER observations collected during the latest outburst of the source. Doppler modulation of the X-ray pulsation revealed the ultra-compact nature of the binary system characterized by an orbital period of ∼1 h and a projected semimajor axis of 14 lt-ms. The neutron star binary mass function suggests a minimum donor mass of 1.7 × 10 −2 M ⊙ , assuming a neutron star mass of 1.4 M ⊙ and a binary inclination angle lower than 60 deg. This assumption is supported by the lack of eclipses or dips in the X-ray light curve of the source. We characterized the 0.5–10 keV energy spectrum of the source in outburst as the superposition of a relatively cold black-body-like thermal emission compatible with the emission from the neutron star surface and a Comptonization component with photon index consistent with a typical hard state. We did not find evidence for iron K α lines or reflection components.
We consider the reliability analysis of phased-mission systems with common-cause failures in this paper. Phased-mission systems (PMS) are systems supporting missions characterized by multiple, consecutive, and nonoverlapping phases of operation. System components may be subject to different stresses as well as different reliability requirements throughout the course of the mission. As a result, component behavior and relationships may need to be modeled differently from phase to phase when performing a system-level reliability analysis. This consideration poses unique challenges to existing analysis methods. The challenges increase when common-cause failures (CCF) are incorporated in the model. CCF are multiple dependent component failures within a system that are a direct result of a shared root cause, such as sabotage, flood, earthquake, power outage, or human errors. It has been shown by many reliability studies that CCF tend to increase a system's joint failure probabilities and thus contribute significantly to the overall unreliability of systems subject to CCF.We propose a separable phase-modular approach to the reliability analysis of phased-mission systems with dependent common-cause failures as one way to meet the above challenges in an efficient and elegant manner. Our methodology is twofold: first, we separate the effects of CCF from the PMS analysis using the total probability theorem and the common-cause event space developed based on the elementary common-causes; next, we apply an efficient phase-modular approach to analyze the reliability of the PMS. The phase-modular approach employs both combinatorial binary decision diagram and Markov-chain solution methods as appropriate. We provide an example of a reliability analysis of a PMS with both static and dynamic phases as well as CCF as an illustration of our proposed approach. The example is based on information extracted from a Mars orbiter project. The reliability model for this orbiter considers the various phases of Launch, Cruise, Mars Orbit Insertion, and Orbit. Some of the CCF for the orbiter in this mission include environmental effects, such as micrometeoroids, human operator errors, and software errors.