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At least 1,747 records · Page 97

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NASA NTRS2001

High-Pressure Synthesis of Metal-Ceramic Nano-Composites

The major problems in fabrication of nano-crystal line materials form nano-powders are: (1), coarsening of the initial nano-size grains, (2), insufficient densification (high concentration of pores), and, (3), conversion of diamond into graphite (for diamond-based ceramics). We have developed a novel technique of the synthesis of nano-composite materials applying very high (up to about 10 GPa) pressures. In this technique, one component is pre-compacted and placed next to another having a lower melting point temperature. The whole sample is pressed and the temperature raised above the melting point of the second component, what results in the melt getting pressed into the (nano-size) pores of the compact. Upon subsequent crystallization the melt forms the second nanophase. The process is fast, on the order of seconds, and the temperatures are relatively low what prevents, or at least significantly reduces coarsening of the starting nanophase grains. Also, conversion of diamond into graphite can be prevented. The technique allows for control of the final product properties through a proper selection of (1) the initial compact density and grain size, (2) chemical composition of the source, and (3) the temperature and pressure of the process. The application of the technique to the synthesis of SiC and diamond with Si, Ge, and different metals. Results of the in-situ investigation of the synthesis process by synchrotron X-ray diffraction technique will be presented.

Gierlotka, S.↗

NASA NTRS1997

A Chemical and Structural Study of the A1N-Si Interface

Samples of A1N grown on silicon [111] subtrates were examined using electron enery loss spectroscopy (EELS) and selected area diffraction (SAD) with high-resolution transmission electron microscopy (TEM) to determine the source of out-of-place tilts and in-plane rotations of the A1N crystallites at the Si interface.

silicon out-of-plane tilts in-plane rotations sili↗

NASA NTRS2009

Medical Challenges of the First Canadian Long-Duration Space Mission: Lessons Learned

In 2008, Dr. Thirsk was assigned to the crew of Expedition 20/21. This Expedition represented a milestone for the Canadian Space Program since it was the first time that a Canadian would take part in a long-duration mission. Robert Thirsk had the privilege of expanding the boundaries of space exploration by living and working on board the International Space Station for six months. The launch took place on May 27, 2009 aboard a Soyuz rocket from the Cosmodrome in Baikonur, Kazakhstan. This abstract was written before Dr. Thirsk returned to Kazakhstan. Objective: To gather all medically relevant data needed to support the first Canadian long-duration mission in space, and process it to derive lessons learned for presentation and for public disclosure. Methods: Sources of data used for analysis for Expedition 20 on International Space Station included flight selection data, maintenance annual physicals, Flight Medicine Clinic visits, parabolic flight experiments, preflight exams and baseline data collections, daily in-flight exercise countermeasure and science payloads, weekly periodic fitness, nutrition, radiation and payload assessments, postflight medical exams, rehabilitation, and science activities.

Hamilton, Douglas R.↗

NASA NTRS2016

Simulation-Based Airframe Noise Prediction of a Full-Scale, Full Aircraft

A previously validated computational approach applied to an 18%-scale, semi-span Gulfstream aircraft model was extended to the full-scale, full-span aircraft in the present investigation. The full-scale flap and main landing gear geometries used in the simulations are nearly identical to those flown on the actual aircraft. The lattice Boltzmann solver PowerFLOW® was used to perform time-accurate predictions of the flow field associated with this aircraft. The simulations were performed at a Mach number of 0.2 with the flap deflected 39 deg. and main landing gear deployed (landing configuration). Special attention was paid to the accurate prediction of major sources of flap tip and main landing gear noise. Computed farfield noise spectra for three selected baseline configurations (flap deflected 39 deg. with and without main gear extended, and flap deflected 0 deg. with gear deployed) are presented. The flap brackets are shown to be important contributors to the farfield noise spectra in the mid- to high-frequency range. Simulated farfield noise spectra for the baseline configurations, obtained using a Ffowcs Williams and Hawkings acoustic analogy approach, were found to be in close agreement with acoustic measurements acquired during the 2006 NASA-Gulfstream joint flight test of the same aircraft.

Khorrami, Mehdi R.↗

NASA NTRS2021

All-Sky Search for Short Gravitational-Wave Bursts in the Third Advanced LIGO and Advanced Virgo Run

This paper presents the results of a search for generic short-duration gravitational-wave transients in datafrom the third observing run of Advanced LIGO and Advanced Virgo. Transients with durations ofmilliseconds to a few seconds in the 24–4096 Hz frequency band are targeted by the search, with noassumptions made regarding the incoming signal direction, polarization, or morphology. Gravitationalwaves from compact binary coalescences that have been identified by other targeted analyses are detected,but no statistically significant evidence for other gravitational wave bursts is found. Sensitivities to a varietyof signals are presented. These include updated upper limits on the source rate density as a function of thecharacteristic frequency of the signal, which are roughly an order of magnitude better than previous upperlimits. This search is sensitive to sources radiating as little as∼10−10M⊙c2in gravitational waves at∼70Hz from a distance of 10 kpc, with 50% detection efficiency at a false alarm rate of one per century.The sensitivity of this search to two plausible astrophysical sources is estimated: neutron starfmodes,which may be excited by pulsar glitches, as well as selected core-collapse supernova models.

R Abbott↗

NASA NTRSDate not supplied

Conceptual Integration Studies of Localized Active Flow Control on the Wing of a Commercial Aircraft

A study of conceptual integration and performance of localized active flow control technology onto wings of short-to-medium-range project passenger airplanes is summarized. Using predicted aerodynamic performance improvement opportunities on a computational fluid dynamics reference aircraft, this paper presents the estimated performance opportunities for conceptual implementation of studied wing localized active flow control technology for low-speed (takeoff and landing) application on a Project Research Aircraft configuration. Using conceptual active flow control systems and structural integration weight penalties for studied concepts, potential relevant net performance benefits can be obtained with reliable active flow control in takeoff and landing. The conceptual integration study identifies potential localized wing active flow control application opportunities for high-lift conditions using energy sources available on modern aircraft. Material benefits are estimated for takeoff and landing configurations for selected localized wing active flow control applications. The study concluded that substantial low-speed Maximum Lift and Lift/Drag related performance improvements may be possible with localized wing high-lift active flow control systems powered by auxiliary power unit, engine bleed, or electrical compressors - with due consideration of integration and weight impacts as well as availability requirements of such systems.

drag reduction↗

NASA NTRS2022

Space Induced Discharge Model to Be Used on Interface Circuit Vulnerability Assessment

Charging can occur in space due to plasma and high energy particles. Charging is especially severe in certain earth orbits such as geostationary orbit, medium earth orbit and highly inclined orbit. A spacecraft that travels to other planets such as Jupiter also encounters high level of charging due to Jupiter’s radiation belt. The major concern for spacecraft operation due to charging is the survival of sensitive electrical circuits. Dielectrics and floating metal can charge up and discharge onto interface circuits. The electrical circuits need to be evaluated for survival from the electrostatic-discharge (ESD) threat. Both ESD induced upset and damage need to be assessed. The interface circuits are often located inside a shielded unit in the spacecraft structure or a shielded vault with sufficient radiation shielding to avoid surface and internal charging. The materials external to the highly shielded area can charge up and discharge onto wires that can directly dissipate the ESD onto the interface circuits. Figure 1 shows a possible discharge mechanism onto the interfacing circuits. If the wire has an external shield or a coaxial line, some or most of the discharge can flow on the shield to chassis ground. There is always coupling from external discharge. If the wire has no shield, the discharge flows onto the interface circuit. Fig. 1 Possible discharge paths onto the interface circuits. The purpose of this article is to address how to model the ESD threat to be used as the discharge source onto the interface circuit based on the electron beam test data. Different models are needed for different impedances associated with the interface circuits. Once those models are derived, one needs to analyze the interface circuit with the corresponding model using an electrical simulation tool. Then, the circuit’s front-end components can be assessed for damage and upset. Upset is highly dependent on the circuit operation and system requirements, and thus it is not addressed any further. Damage of electrical parts is often rated under Human-Body-Model (HBM) ESD. One can utilize this industry-wide available information to assess the damage vulnerability due to space discharges. However, the HBM waveform does not always match the discharge waveform. To estimate the damage vulnerability of the circuit and set margin, one needs to compare the equivalent energy delivered to the victim between a HBM discharge and the results from an ESD source model based on actual discharges. This paper presents such a comparison for a few select cases.

Xie, Julie↗

DOE OSTI2014

Generator powered electrically heated diesel particulate filter

A control circuit for a vehicle powertrain includes a switch that selectivity interrupts current flow between a first terminal and a second terminal. A first power source provides power to the first terminal and a second power source provides power to the second terminal and to a heater of a heated diesel particulate filter (DPF). The switch is opened during a DPF regeneration cycle to prevent the first power source from being loaded by the heater while the heater is energized.

42 ENGINEERING↗

DOE OSTI2021

Supply voltage decoupling circuits for voltage droop mitigation

Circuits and methods are provided for utilizing decoupling capacitors to mitigate voltage droop on power supply lines of a power distribution network. A power supply line is capacitively decoupled using a first decoupling capacitor connected to the power supply line and charged to a first voltage level of the power supply line. A second decoupling capacitor is pre-charged to a second voltage level greater than the first voltage level and held in standby. A control circuit determines or predicts an occurrence of a droop event in which the first voltage decreases to a level which is at or below a droop threshold voltage level, and selectively connects the pre-charged second decoupling capacitor to the power supply line to source additional boosting current through discharging of the second decoupling capacitor and thereby capacitively decouple the power supply line using the higher second voltage and additional boosting current.

Zhang, Xin↗

DOE OSTI2017

Facile Separation of Sr-90, Fe-55, Nb-94, Ni-59,63 with Large Amount of Ca by Controlled pH Precipitation - 17190

it is important to manage low-and intermediate-level radioactive wastes from nuclear power plants due to a permanent disposal. According to the Nuclear Safety and Security Commission (NSSC), among all the regulatory radionuclides, a few radionuclides from the fission products and corrosion products such as Sr-90, Fe-55, Nb-94, Ni-59,63 which emit low-energy x-ray and beta radiation. Thus, it is necessary to separate beta-emitting nuclides individually. For that reason, KAERI has established analytical procedures which can separate Sr-90, Fe-55, Nb-94, Ni-59,63 from radioactive waste samples. However, when radioactive wastes contain large amount of Ca (above 300 mg), it is not easy to recover the target radionuclides because high concentration of Ca has a strong influence on the effective analyses. In order to combat this problem, there was an attempt to make the precipitate as CaF{sub 2} by using hydrofluoric acid. However, this way had a limitation; Fe-55, Nb-94 were precipitated as fluoride compounds as well as Ca. In this study, we have focused on developing a separation procedure stage by stage in the radioactive wastes with Sr-90, Fe-55, Nb-94, Ni-59,63 and large amount of Ca (1500 mg). The detailed steps are described below; (1) Separation of Fe-55, Nb-94, Ni-59,63 as metal hydroxide precipitates: low solubility product constant (Ksp) between pH 6 and pH 10. (2) Selective elimination of Ca-oxalate complex under strong acidic conditions. Consequently, all the metal sources were sequentially separated and quantitatively recovered by inductively coupled plasma atomic emission spectrometric (ICP-AES) analysis, the recovery is as follows; Sr-90 (3 mg): 89.47±5.48%, Fe-55 (20 mg): 99.80±3.19%, Nb-94 (20 mg): 97.45±2.42%, Ni-59,63 (2 mg): 83.59±15.31%, Ca (1500 mg): 85.32±6.38%, respectively. This methodology will help us separation of radioactive wastes efficiently if apply properly. (authors)

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2013

WATER MASER SURVEY ON AKARI AND IRAS SOURCES: A SEARCH FOR ''LOW-VELOCITY'' WATER FOUNTAINS

We present the results of a 22 GHz H{sub 2}O maser survey toward a new sample of asymptotic giant branch (AGB) and post-AGB star candidates. Most of the objects are selected for the first time based on the AKARI data, which have high flux sensitivity in the mid-infrared ranges. We aim at finding H{sub 2}O maser sources in the transient phase between the AGB and post-AGB stages of evolution, where the envelopes start to develop large deviations from spherical symmetry. The observations were carried out with the Effelsberg 100 m radio telescope. Among 204 observed objects, 63 detections (36 new) were obtained. We found four objects that may be ''water fountain'' sources (IRAS 15193+3132, IRAS 18056-1514, OH 16.3-3.0, and IRAS 18455+0448). They possess an H{sub 2}O maser velocity coverage much smaller than those in other known water fountains. However, the coverage is still larger than that of the 1612 MHz OH maser. It implies that there is an outflow with a higher velocity than the envelope expansion velocity (typically {<=}25 km s{sup -1}), meeting the criterion of the water fountain class. We suggest that these candidates are possibly oxygen-rich late AGB or early post-AGB stars in a stage of evolution immediately after the spherically symmetric AGB mass loss has ceased.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

NuSTAR unveils a Compton-thick type 2 quasar in MrK 34

We present Nuclear Spectroscopic Telescope Array (NuSTAR) 3-40 keV observations of the optically selected Type 2 quasar (QSO2) SDSS J1034+6001 or Mrk 34. The high-quality hard X-ray spectrum and archival XMM-Newton data can be fitted self-consistently with a reflection-dominated continuum and a strong Fe Kα fluorescence line with equivalent width >1 keV. Prior X-ray spectral fitting below 10 keV showed the source to be consistent with being obscured by Compton-thin column densities of gas along the line of sight, despite evidence for much higher columns from multiwavelength data. NuSTAR now enables a direct measurement of this column and shows that N {sub H} lies in the Compton-thick (CT) regime. The new data also show a high intrinsic 2-10 keV luminosity of L {sub 2-10} ∼ 10{sup 44} erg s{sup –1}, in contrast to previous low-energy X-ray measurements where L {sub 2-10} ≲ 10{sup 43} erg s{sup –1} (i.e., X-ray selection below 10 keV does not pick up this source as an intrinsically luminous obscured quasar). Both the obscuring column and the intrinsic power are about an order of magnitude (or more) larger than inferred from pre-NuSTAR X-ray spectral fitting. Mrk 34 is thus a 'gold standard' CT QSO2 and is the nearest non-merging system in this class, in contrast to the other local CT quasar NGC 6240, which is currently undergoing a major merger coupled with strong star formation. For typical X-ray bolometric correction factors, the accretion luminosity of Mrk 34 is high enough to potentially power the total infrared luminosity. X-ray spectral fitting also shows that thermal emission related to star formation is unlikely to drive the observed bright soft component below ∼3 keV, favoring photoionization instead.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

UNVEILING THE NATURE OF THE UNIDENTIFIED GAMMA-RAY SOURCES. V. ANALYSIS OF THE RADIO CANDIDATES WITH THE KERNEL DENSITY ESTIMATION

Nearly one-third of the γ-ray sources detected by Fermi are still unidentified, despite significant recent progress in this area. However, all of the γ-ray extragalactic sources associated in the second Fermi-LAT catalog have a radio counterpart. Motivated by this observational evidence, we investigate all the radio sources of the major radio surveys that lie within the positional uncertainty region of the unidentified γ-ray sources (UGSs) at a 95% level of confidence. First, we search for their infrared counterparts in the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) and then we analyze their IR colors in comparison with those of the known γ-ray blazars. We propose a new approach, on the basis of a two-dimensional kernel density estimation technique in the single [3.4] – [4.6] – [12] μm WISE color-color plot, replacing the constraint imposed in our previous investigations on the detection at 22 μm of each potential IR counterpart of the UGSs with associated radio emission. The main goal of this analysis is to find distant γ-ray blazar candidates that, being too faint at 22 μm, are not detected by WISE and thus are not selected by our purely IR-based methods. We find 55 UGSs that likely correspond to radio sources with blazar-like IR signatures. An additional 11 UGSs that have blazar-like IR colors have been found within the sample of sources found with deep recent Australia Telescope Compact Array observations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Exploratory Spectroscopy of Magnetic Cataclysmic Variables Candidates and Other Variable Objects

The increasing number of synoptic surveys made by small robotic telescopes, such as the photometric Catalina Real-Time Transient Survey (CRTS), provides a unique opportunity to discover variable sources and improves the statistical samples of such classes of objects. Our goal is the discovery of magnetic Cataclysmic Variables (mCVs). These are rare objects that probe interesting accretion scenarios controlled by the white-dwarf magnetic field. In particular, improved statistics of mCVs would help to address open questions on their formation and evolution. We performed an optical spectroscopy survey to search for signatures of magnetic accretion in 45 variable objects selected mostly from the CRTS. In this sample, we found 32 CVs, 22 being mCV candidates, 13 of which were previously unreported as such. If the proposed classifications are confirmed, it would represent an increase of 4% in the number of known polars and 12% in the number of known IPs. A fraction of our initial sample was classified as extragalactic sources or other types of variable stars by the inspection of the identification spectra. Despite the inherent complexity in identifying a source as an mCV, variability-based selection, followed by spectroscopic snapshot observations, has proved to be an efficient strategy for their discoveries, being a relatively inexpensive approach in terms of telescope time.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Material Selection and Sizing of a Thermoelectric Generator (TEG) for Power Generation in a Self-Powered Heating System

By employing the high temperature heat source to directly generate the electricity needed to power auxiliary systems in a natural gas furnace, boiler or hot water heater, a “self-powered” heating system can provide several benefits. Compared with a traditional furnace, boiler or hot water heater, when overall fuel utilization is kept constant, the self-powered system will have a higher primary energy efficiency, lower operating costs, and dramatically improved building safety and resilience during electric grid outages. Furthermore, a self-powered heating system only has a single utility connection – natural gas, without an electric connection – thus simplifying installation. A thermoelectric generator can be used for direct energy conversion of thermal energy to electricity with no moving parts, which offers a very simple means to provide power for the self-powered heating system, and the operation is without noise or vibration and can thus provide a very long system life. This paper provides an analysis focused on materials selection and the thermal power requirements for a thermoelectric generator (TEG) for use in a self-powered heating system. The dimensionless figure of merit for thermoelectric materials, zT, is used to estimate the optimal efficiency that can be achieved with a TEG to produce the electric power required in such an application. Comparisons of the predicted efficiency, the required heat transfer rate to the TEG and the heat transfer area needed for sustained operation under thermal conditions relevant to the self-powered heating application are made for several potential thermoelectric materials. This analysis was used to develop system requirements for a self-powered hot water heater using a TEG for electric power generation.

Laclair, Tim↗

DOE OSTI2017

OBSERVATIONAL SELECTION EFFECTS WITH GROUND-BASED GRAVITATIONAL WAVE DETECTORS

Ground-based interferometers are not perfect all-sky instruments, and it is important to account for their behavior when considering the distribution of detected events. In particular, the LIGO detectors are most sensitive to sources above North America and the Indian Ocean, and as the Earth rotates, the sensitive regions are swept across the sky. However, because the detectors do not acquire data uniformly over time, there is a net bias on detectable sources’ right ascensions. Both LIGO detectors preferentially collect data during their local night; it is more than twice as likely to be local midnight than noon when both detectors are operating. We discuss these selection effects and how they impact LIGO’s observations and electromagnetic (EM) follow-up. Beyond galactic foregrounds associated with seasonal variations, we find that equatorial observatories can access over 80% of the localization probability, while mid-latitudes will access closer to 70%. Facilities located near the two LIGO sites can observe sources closer to their zenith than their analogs in the south, but the average observation will still be no closer than 44° from zenith. We also find that observatories in Africa or the South Atlantic will wait systematically longer before they can begin observing compared to the rest of the world; though, there is a preference for longitudes near the LIGOs. These effects, along with knowledge of the LIGO antenna pattern, can inform EM follow-up activities and optimization, including the possibility of directing observations even before gravitational-wave events occur.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2001

Aerodynamic Performance of Scale-Model Turbofan Outlet Guide Vanes Designed for Low Noise

The design of effective new technologies to reduce aircraft propulsion noise is dependent on an understanding of the noise sources and noise generation mechanisms in the modern turbofan engine. In order to more fully understand the physics of noise in a turbofan engine, a comprehensive aeroacoustic wind tunnel test programs was conducted called the 'Source Diagnostic Test.' The text was cooperative effort between NASA and General Electric Aircraft Engines, as part of the NASA Advanced Subsonic Technology Noise Reduction Program. A 1/5-scale model simulator representing the bypass stage of a current technology high bypass ratio turbofan engine was used in the test. The test article consisted of the bypass fan and outlet guide vanes in a flight-type nacelle. The fan used was a medium pressure ratio design with 22 individual, wide chord blades. Three outlet guide vane design configurations were investigated, representing a 54-vane radial Baseline configuration, a 26-vane radial, wide chord Low Count configuration and a 26-vane, wide chord Low Noise configuration with 30 deg of aft sweep. The test was conducted in the NASA Glenn Research Center 9 by 15-Foot Low Speed Wind Tunnel at velocities simulating the takeoff and approach phases of the aircraft flight envelope. The Source Diagnostic Test had several acoustic and aerodynamic technical objectives: (1) establish the performance of a scale model fan selected to represent the current technology turbofan product; (2) assess the performance of the fan stage with each of the three distinct outlet guide vane designs; (3) determine the effect of the outlet guide vane configuration on the fan baseline performance; and (4) conduct detailed flowfield diagnostic surveys, both acoustic and aerodynamic, to characterize and understand the noise generation mechanisms in a turbofan engine. This paper addresses the fan and stage aerodynamic performance results from the Source Diagnostic Test.

Hughes, Christopher E.↗

NASA NTRS1972

A modular Space Station/Base electrical power system - Requirements and design study.

The requirements and procedures necessary for definition and specification of an electrical power system (EPS) for the future space station are discussed herein. The considered space station EPS consists of a replaceable main power module with self-contained auxiliary power, guidance, control, and communication subsystems. This independent power source may 'plug into' a space station module which has its own electrical distribution, control, power conditioning, and auxiliary power subsystems. Integration problems are discussed, and a transmission system selected with local floor-by-floor power conditioning and distribution in the station module. This technique eliminates the need for an immediate long range decision on the ultimate space base power sources by providing capability for almost any currently considered option.

Eliason, J. T.↗