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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Near-source and Remote Observations of Kilometric Continuum Radiation from Multispacecraft Observations

[I] Kilometric continuum (KC) radiation was first identified from Geotail plasma wave observations. Past authors have shown that this emission has a frequency range that overlaps that of the auroral kilometric radiation (AKR) but is characterized by a fine structure of narrow-bandwidth, linear features that have nearly constant or drifting frequency. This fine structure is distinct from that of AKR. KC also apparently has a distinct source region probably associated with the low-latitude inner magnetosphere, consistent with direction-finding and ray-tracing results. We present new high-resolution electric and magnetic field observations of KC obtained by the Polar plasma wave instrument in the near-source region. These observations show intense electrostatic and less intense electromagnetic emissions near the magnetic equator at the plasmapause. Simultaneously, Geotail, located at 20 to 30 RE in radial distance, observes KC in the same frequency range. These data support a possible mode-conversion source mechanism near a region of high-density gradient. High-resolution data obtained from wideband receivers on board both Polar and Cluster show closely spaced bands of emission near the magnetic equator that may be due to many nearby independent sources of EM emission perhaps associated with density fluctuations or cavities in the plasmasphere.

Menietti, J. D.↗
NASA NTRS2007

High SBS-Threshold, Narrowband Pulses Frequency-Doubled to 770.3 nm

We present results of pulsed, narrowband amplification at 1540.6nm using a polarization maintaining, large mode area gain fiber co-doped with erbium and ytterbium. At a repetition rate of 55 kHz, 2.9 W of average 1540.6nm power were generated with a pulse duration of 136 ns, correspondiig to an stimulated Brillouin scattering (SBS) free peak power of 360 W. The amplified signal was frequency doubled in peridically poled potassium titanyl phosphate and conversion efficiencies of up to 56% were generated. When varying the repetition rate between 55- 150 kHz the conversion efficiency changed from 56% to 35% due to the limited pump power.

Dilley, C. E.↗
DOE OSTI2025

Ultrasonic deterrents provide no additional benefit over curtailment in reducing bat fatalities at an Ohio wind energy facility

Wind energy is important for achieving net-zero greenhouse gas emissions but also contributes to global bat mortality. Current strategies to minimize bat mortality due to collision with wind-turbine blades fall broadly into two categories: curtailment (limiting turbine operation during high-risk periods) and deterrence (discouraging bat activity near turbines). Recently, there has been interest in combining these strategies to achieve greater reductions in bat fatalities than either strategy might achieve in isolation. To investigate the effectiveness of combining curtailment with ultrasonic deterrent minimization strategies, we deployed six ultrasonic deterrents at nacelle height on 16 experimental turbines at Avangrid Renewables’ Blue Creek Wind Energy Facility. We rotated between four conditions (normal operations, curtailment only, deterrent only, curtailment and deterrent) randomly assigned to four wind turbines each night between 15 June and 3 October 2017. We found that bat mortality at wind turbines was independent of wind speed. The effectiveness of ultrasonic acoustic deterrents varied between high-frequency-calling species (eastern red bats) and low-frequency-calling species (hoary bats, silver-haired bats, and big brown bats). When deterrents were active, mortality was twice as high for eastern red bats compared to the control. Conversely, deterrents had a weak dampening effect on bat mortality for low-frequency species. We found no additive effects on mortality reduction for turbines operating both curtailment and deterrents compared to either approach in isolation. Our findings suggest that ultrasonic acoustic deterrents may not be effective for both high and low frequency echolocating bats. The increase in fatalities of eastern red bats is alarming and underscores the importance of considering site- and species-specific effects of minimization solutions.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1976

IR pumped third-harmonic generation and sum-frequency generation in diatomic molecules

The potential efficiency of using nonlinear up-conversion techniques for the high efficiency type lasers (CO,CO2, and chemical) is assessed. Results indicate that: the small pump photon energy necessitates the use of molecular media for conversion if resonance enhancement is to be used and that molecular systems present several problems. These difficulties include: their levels are complex; their transition probabilities are often unknown; and the oscillator strengths among vibrational levels in the ground electronic state of a molecule are much smaller than those among electronic states of an atom, thus limiting the magnitude of nonlinear interactions. It is shown that this problem can be eliminated by making use of vibronic transitions which, being primarily electronic transitions have much larger matrix elements and efficient conversion can be achieved with molecular systems.

She, C. Y.↗
NASA NTRS1977

Microcraters on lunar samples

The lunar microcrater phenomenology is described. The morphology of the lunar craters is in almost all aspects simulated in laboratory experiments in the diameter range from less than 1 nu to several millimeters and up to 60 km/s impact velocity. An empirically derived formula is given for the conversion of crater diameters into projectile diameters and masses for given impact velocities and projectile and target densities. The production size frequency distribution for lunar craters in the crater size range from approximately 1 nu to several millimeters in diameter is derived from various microcrater measurements within a factor of up to 5. Particle track exposure age measurements for a variety of lunar samples have been performed. They allow the conversion of the lunar crater size frequency production distributions into particle fluxes. The development of crater populations on lunar rocks under self-destruction by subsequent meteoroid impacts and crater overlap is discussed and theoretically described. Erosion rates on lunar rocks on the order of several millimeters per 10 yr are calculated. Chemical investigations of the glass linings of lunar craters yield clear evidence of admixture of projectile material only in one case, where the remnants of an iron-nickel micrometeorite have been identified.

Fechtig, H.↗
DOE OSTI2021

Atomic Layer Deposition with TiO2 for Enhanced Reactivity and Stability of Aromatic Hydrogenation Catalysts

Hydrogenation of aromatic molecules in fossil- and bio-derived fuels is essential for decreasing emissions of harmful combustion products and addressing growing concerns around urban air pollution. In this work, we used atomic layer deposition to significantly enhance the hydrogenation performance of a conventional supported Pd catalyst by applying an ultrathin coating of TiO2 in a scalable powder coating process. The TiO2-coated catalyst showed substantial gains in the conversion of multiple aromatic molecules, including a 5-fold improvement in turnover frequency versus the uncoated catalyst in the hydrogenation of naphthalene. This activity enhancement was maintained upon scaling the coating synthesis process from 3 to 100 g. Based on the results from Xray photoelectron spectroscopy, X-ray absorption spectroscopy, and computational modeling, the activity enhancement was attributed to ensemble effects resulting from partial TiO2 coverage of the Pd surface rather than fundamental changes to the Pd electronic structure. Additional durability testing confirmed that the TiO2 coating improved the thermal and hydrothermal stability of the catalyst as well as tolerance toward sulfur impurities in the reactant stream. Using an economic model of an industrial deep hydrogenation process, we found that an increase in catalyst activity or lifetime of 2× would justify even a relatively high estimate for the cost of TiO2 atomic layer deposition coatings at scale

atomic layer↗
NASA NTRS1995

Integrated back to back barrier-N-N(+) varactor diode tripler using a split-waveguide block

The back-to-back barrier-N-N(+) (bbBNN) varactor is a nonlinear device being developed for frequency multiplier applications above 100 GHz. Its symmetrical C-V characteristic, low series resistance, freedom from external bias and suitability to planarization make it an ideal choice for high frequency, low power, odd harmonic generation. In this paper, the performance of a 220-GHz waveguide tripler using, for the first time, a planar GaAs bbBNN device integrated on a quartz microstrip circuit is presented. A new split-waveguide block design has been employed to provide the proper embedding impedances to the device at the input and third harmonic output frequencies. A flange-to-flange tripling efficiency of 7% has been obtained at 220 GHz with an output power in excess of 700 mu W. This is believed to be the highest conversion efficiency yet reported for a tripler with an integrated device at this frequency. Theoretical calculations indicate that substantial improvement is possible with modest changes to the device and circuit parameters.

QUARTZ MICROSTRIP CIRCUITS↗
NASA NTRS2000

Characterization of Molybdate Conversion Coatings for Aluminum Alloys by Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion inhibiting properties of newly developed proprietary molybdate conversion coatings on aluminum alloy 2024-T3 under immersion in aerated 5% (w/w) NaCl. Corrosion potential and EIS measurements were gathered for six formulations of the coating at several immersion times for two weeks. Nyquist as well as Bode plots of the data were obtained. The conversion-coated alloy panels showed an increase in the corrosion potential during the first 24 hours of immersion that later subsided and approached a steady value. Corrosion potential measurements indicated that formulations A, D, and F exhibit a protective effect on aluminum 2024-T3. The EIS spectra of the conversion-coated alloy were characterized by an impedance that is higher than the impedance of the bare alloy at all the immersion times. The low frequency impedance, Z(sub lf) (determined from the value at 0.05 Hz) for the conversion-coated alloy was higher at all the immersion times than that of the bare panel. This indicates improvement of corrosion resistance with addition of the molybdate conversion coating. Scanning electron microscopy (SEM) revealed the presence of cracks in the coating and the presence of cubic crystals believed to be calcium carbonate. Energy dispersive spectroscopy (EDS) of the test panels revealed the presence of high levels of aluminum, oxygen, and calcium but did not detect the presence of molybdenum on the test panels. X-ray photoelectron spectroscopy (XPS) indicated the presence of less than 0.01 atomic percent molybdenum on the surface of the coating.

Calle, Luz Marina↗
NASA NTRS1969

Linear voltage-to-frequency converter

Voltage-to-frequency converter, with ultra-high input impedance and linear response, is used in analog to digital data conversion systems. Voltage-to-current converter, using MOSFET devices and a multivibrator, has ultra-linear voltage-to-frequency characteristics. It replaces voltage sensitive magnetic-core oscillators.

Lokerson, D. C.↗
NASA NTRS1998

Frequency-Domain Analysis of Diffusion-Cooled Hot-Electron Bolometer Mixers

A new theoretical model is introduced to describe heterodyne mixer conversion efficiency and noise (from thermal fluctuation effects) in diffusion-cooled superconducting hot-electron bolometers. The model takes into account the non-uniform internal electron temperature distribution generated by Wiedemann-Franz heat conduction, and accepts for input an arbitrary (analytical or experimental) superconducting resistance-versus- temperature curve. A non-linear large-signal solution is solved iteratively to calculate the temperature distribution, and a linear frequency-domain small-signal formulation is used to calculate conversion efficiency and noise. In the small-signal solution the device is discretized into segments, and matrix algebra is used to relate the heating modulation in the segments to temperature and resistance modulations. Matrix expressions are derived that allow single-sideband mixer conversion efficiency and coupled noise power to be directly calculated. The model accounts for self-heating and electrothermal feedback from the surrounding bias circuit.

Skalare, A.↗
DOE OSTI2023

Raman Wavelength Conversion in Ionic Liquids

Here, we explore the use of room-temperature ionic liquids (ILs) as Raman wavelength converters. ILs provide an engineerable framework to design suitable liquids for wavelength conversion over a broad spectral range, through careful selection of the molecular structures of the IL anions and cations so that specific characteristics can be obtained, such as a desirable Raman shift, low Brillouin scattering, and good optical transmission in the pump and Stokes wavelengths. Applying such criteria, we demonstrate that 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA) is an effective medium for conversion of 532-nm pulses from a Q-switched Nd :YAG laser to 603 nm. This corresponds to an approximate 2200 cm –1 shift, which can be used to generate mid-infrared radiation through subsequent difference frequency generation for optical pumping of CO 2 lasers. Threefold-higher Raman conversion efficiency is obtained in EMIM DCA compared with water under identical conditions in a proof-of-principle single-pass conversion setup, resulting in an efficient generation of multimillijoule, <6 ns duration, high-quality orange laser pulses in a wavelength region that is difficult to access at high energies. Consequently, we examine ILs representing two other classes of Raman-active functional groups and obtain conversion up to the fifth-order Stokes shift and first anti-Stokes shift. Through the tunable selection of their components and their useful dynamical properties, ILs provide a platform for efficient, simple, and alignment-tolerant high-energy Raman shifting with numerous industrial and technological applications.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1993

Generation of 369.4 nm Radiation by Efficient Doubling of a Diode Laser

The trapped ytterbium ion frequency standard under development at JPL is designed to supply ultra-stable reference signals to be used in spacecraft tests of general relativity and other science experiments. Only diode lasers meet the requirements of low power comsumption and small size for use aboard spacecraft, but diode lasers are not currently available at 369.4 nm wavelength. It is therefore necessary to employ frequency doubling methods to reach this frequency with diode lasers. Here we present the characteristics of the resonant cavity doubling system we have designed and preliminary UV conversion results.

ultra-stable↗
NASA NTRS2013

Efficient 1.6 Micron Laser Source for Methane DIAL

Methane is a potent greenhouse gas and on a per molecule basis has a warming influence 72 times that of carbon dioxide over a 20 year horizon. Therefore, it is important to look at near term radiative effects due to methane to develop mitigation strategies to counteract global warming trends via ground and airborne based measurements systems. These systems require the development of a time-resolved DIAL capability using a narrow-line laser source allowing observation of atmospheric methane on local, regional and global scales. In this work, a demonstrated and efficient nonlinear conversion scheme meeting the performance requirements of a deployable methane DIAL system is presented. By combining a single frequency 1064 nm pump source and a seeded KTP OPO more than 5 mJ of 1.6 μm pulse energy is generated with conversion efficiencies in excess of 20%. Even without active cavity control instrument limited linewidths (50 pm) were achieved with an estimated spectral purity of ~95%. Tunable operation over 400 pm (limited by the tuning range of the seed laser) was also demonstrated. This source demonstrated the critical needs for a methane DIAL system motivating additional development of the technology.

Shuman, Timothy↗
DOE OSTI2022

Gallium Nitride Superjunction Transistor (Continued Funding Report)

The initial goal of this project is to develop the gallium vacancy assisted diffusion (GAID) method in GaN and apply it to demonstrate 2-terminal, 3-terminal, and large area Superjunction-enhanced modules. These devices will find use in high efficiency power conversion applications with the capability of operating at higher voltages, higher frequency, and less loss than comparable stat-ofthe-art devices. The approach of this project has been to utilize simulation tools to drive diffusion experiments and inform semiconductor device fabrication processes. VASP has been relied upon to simulate first principles diffusion mechanisms while SILVACO TCAD has been utilized to understand tradeoffs of the the critical dimensions in GaN devices.

42 ENGINEERING↗
DOE OSTI2023

Real Space and Time Imaging of Collective Headgroup Dipole Motions in Zwitterionic Lipid Bilayers

Lipid bilayers are supramolecular structures responsible for a range of processes, such as transmembrane transport of ions and solutes, and sorting and replication of genetic materials, to name just a few. Some of these processes are transient and currently, cannot be visualized in real space and time. Here, we developed an approach using 1D, 2D, and 3D Van Hove correlation functions to image collective headgroup dipole motions in zwitterionic phospholipid bilayers. We show that both 2D and 3D spatiotemporal images of headgroup dipoles are consistent with commonly understood dynamic features of fluids. However, analysis of the 1D Van Hove function reveals lateral transient and re-emergent collective dynamics of the headgroup dipoles—occurring at picosecond time scales—that transmit and dissipate heat at longer times, due to relaxation processes. At the same time, the headgroup dipoles also generate membrane surface undulations due a collective tilting of the headgroup dipoles. A continuous intensity band of headgroup dipole spatiotemporal correlations—at nanometer length and nanosecond time scales—indicates that dipoles undergo stretching and squeezing elastic deformations. Importantly, the above mentioned intrinsic headgroup dipole motions can be externally stimulated at GHz-frequency scale, enhancing their flexoelectric and piezoelectric capabilities (i.e., increased conversion efficiency of mechanical energy into electric energy). In conclusion, we discuss how lipid membranes can provide molecular-level insights about biological learning and memory, and as platforms for the development of the next generation of neuromorphic computers.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1980

Bulk submillimeter-wave mixers: Strain and superlattices

Strained germanium crystals, doped with gallium, were used as heterodyne mixers at THz frequencies, with infrared bandwidths approaching a GHz. The mixer performance (conversion loss and mixer noise) was analyzed in terms of nonlinearities associated with acceptor levels and with relaxation rates of free holes. Comparison was made with similar mixers employing low lying donor levels in high purity GaAs and with hot electron InSb mixers.

Litvak, M. M.↗
NASA NTRS1993

Superconducting terahertz mixer using a transition-edge microbolometer

We present a new device concept for a mixer element for THz frequencies. This uses a superconducting transition-edge microbridge biased at the center of its superconducting transition near 4.2 K. It is fed from an antenna or waveguide structure. Power from a local oscillator and an RF signal produce a temperature and resulting resistance variation at the difference frequency. The new aspect is the use of a very short bridge in which rapid (less than 0.1 ns) outdiffusion of hot electrons occurs. This gives large intermediate frequency (IF) response. The mixer offers about 4 GHz IF bandwidth, about 80 ohm RF resistive impedance, good match to the IF amplifier, and requires only 1-20 nW of local oscillator power. The upper RF frequency is determined by antenna or waveguide properties. Predicted mixer conversion efficiency is 1/8, and predicted double-sideband receiver noise temperatures are 260 and 90 K for transition widths of 0.1 and 0.5 Tc, respectively.

Prober, D. E.↗