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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Recent progress in microscale modeling of RF sheaths

The microscale properties of RF sheaths in the ion cyclotron range of frequencies (ICRF) are investigated by means of analytical theory, nonlinear fluid and particle-in-cell (PIC) code modeling. Previous work that parametrized RF sheath properties, specifically the RF sheath impedance and the rectified (DC) sheath potential, is generalized to include the effect of net DC current flow through the sheath. Analytical results are presented in the low frequency limit where the displacement current is negligible, and tested against results from a fluid numerical model. Here, it is shown that when the sheath draws DC electron current, the voltage rectification is reduced from the zero current case, and the electron admittance is increased. In separate but related work on the microscale model, selected cases have been simulated with PIC codes to validate, further illuminate and extend fluid model results and their parametrizations. Quantitative agreement in trends for voltage rectification and sheath admittance vs. RF driving voltage is found.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Schottky contacts to N-polar GaN with SiN interlayer for elevated temperature operation

In this Letter, we unveil the high-temperature limits of N-polar GaN Schottky contacts enhanced by a low-pressure chemical vapor deposited (LPCVD) SiN interlayer. Compared to conventional Schottky diodes, the insertion of a 5 nm SiN lossy dielectric interlayer in-between Ni and N-polar GaN increases the turn-on voltage (V ON ) from 0.4 to 0.9 V and the barrier height ($\phi_B$) from 0.4 to 0.8 eV. This modification also reduces the leakage current at zero bias significantly: at room temperature, the leakage current in the conventional Schottky diode is >103 larger than that observed in the device with the SiN interlayer, while at 200 °C, this ratio increases to 105. Thus, the rectification ratio (ION/IOFF) at ±1.5 V reduces to less than one at 250 °C for the conventional Schottky diode, whereas for SiN-coated diodes, rectification continues until 500 °C. The I–V characteristics of the diode with an SiN interlayer can be recovered after exposure to 400 °C or lower. Contact degradation occurs at 500 °C, although devices are not destroyed yet. Here, we report N-polar GaN Schottky contact operation up to 500 °C using an LPCVD SiN interlayer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Frictional drag between superconducting LaAlO 3 /SrTiO 3 nanowires

Here we report frictional drag measurements between two superconducting LaAlO 3 /SrTiO 3 nanowires. In these experiments, current passing through one nanowire induces a voltage across a nearby electrically isolated nanowire. The frictional drag signal contains both symmetric and anti-symmetric components. The anti-symmetric component arises from the rectification of quantum shot noise in the drive nanowire by the broken symmetry in the drag nanowire. The symmetric component in the drag resistance is ascribed to rectification of thermal noise in the drive nanowire during superconducting-normal transition. The suppression of the symmetric component is observed when a normal nanowire is used as either a drag or drive nanowire with the other nanowire superconducting. The absence of symmetric drag resistance between a normal drag nanowire and a superconducting drive nanowire suggests a higher electron-hole asymmetry in the superconducting LaAlO 3 /SrTiO 3 nanowire arising from the 1D nature of superconductivity at LaAlO 3 /SrTiO 3 interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Magneto-opto-phononic inverse Faraday effect

Nonlinear frequency conversion processes, such as optical rectification, difference-frequency generation, and sum-frequency generation, are fundamental for producing electromagnetic radiation at diverse frequencies. In this work, we demonstrate that coherently excited infrared-active phonons can act as transducers for generating nonlinear magnetizations through phonon-magnon interactions, analogous to nonlinear optical frequency conversion. We derive analytical solutions for the time-dependent magnetizations arising from the second-order response to the electric field component of an ultrashort laser pulse. These solutions enable us to define second-order nonlinear magneto-electric susceptibilities, which describe rectification, impulsive excitation, and sum-frequency excitation of coherent magnons. Our theoretical framework naturally incorporates the conventional magneto-optic and phonon inverse Faraday effects and predicts a hybrid magneto-opto-phononic inverse Faraday effect involving photon-phonon-magnon scattering. This work highlights nonlinear phononics as a pathway for controlling magnetization in solids.

Landau-Lifschitz-Gilbert equation↗
DOE OSTI2022

Ionic transport in electrostatic Janus Membranes. An explicit solvent molecular dynamic simulation.

Janus –or two-sided, charged membranes offer promise as ionic current rectifiers. In such systems, pores consisting of two regions of opposite charge can be used to generate a current from a gradient in salinity. The efficiency of nanoscale Janus pores increases dramatically as their diameter becomes smaller. However, little is known about the underlying transport processes, particularly under experimentally accessible conditions. In this work, we examine the molecular basis for rectification in Janus nanopores using an applied electric field. Molecular simulations with explicit water and ions are used to examine the structure and dynamics of all molecular species in aqueous electrolyte solutions. For several macroscopic observables, the results of such simulations are consistent with experimental observations on asymmetric membranes. Our analysis reveals a number of previously unknown features, including a pronounced local re-orientation of water molecules in the pores, and a segregation of ionic species that has not been anticipated by previously reported continuum analyses of Janus pores. Using these insights, a model is proposed for ionic current rectification in which electric leakage at pore entrance controls net transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1976

Experimental study of digital image processing techniques for LANDSAT data

The author has identified the following significant results. Results are reported for: (1) subscene registration, (2) full scene rectification and registration, (3) resampling techniques, (4) and ground control point (GCP) extraction. Subscenes (354 pixels x 234 lines) were registered to approximately 1/4 pixel accuracy and evaluated by change detection imagery for three cases: (1) bulk data registration, (2) precision correction of a reference subscene using GCP data, and (3) independently precision processed subscenes. Full scene rectification and registration results were evaluated by using a correlation technique to measure registration errors of 0.3 pixel rms thoughout the full scene. Resampling evaluations of nearest neighbor and TRW cubic convolution processed data included change detection imagery and feature classification. Resampled data were also evaluated for an MSS scene containing specular solar reflections.

Rifman, S. S.↗
NASA NTRS1977

Nonlinear optical response of metal-barrier-metal junctions

The optical response of metal-barrier-metal (MBM) junctions is discussed, with emphasis on the nonlinearity of response associated with reversal of polarity as optical intensity is increased. This nonlinear behavior can be used to measure correlation functions of optical pulses or to generate ultrashort electrical pulses. Expressions for the current flowing through the insulating barrier (junction), and for the rectification current, are given. Pulse signal and polarity of the electrical pulse evolves as the junction bias is varied about the null-signal bias. The apparatus used to obtain rectification pulse signals is described; the calculated evolution of the rectified pulse shape is found to correspond to that of pulse signals obtained experimentally. The generation of pulses six orders of magnitude smaller than a previously-obtained instrument-limited 1.6 nanosecond pulse has been observed.

Fan, B.↗
NASA NTRS1976

Stereo mapping with the Viking Lander camera imagery

Stereomapping techniques applicable to the processing of imagery from facsimile cameras on board the Viking Mars landing vehicles are discussed. Two methods of stereomapping are considered: use of a gnomonic projection to transform the digital imagery to an equivalent of a perspective projection by computerized rectification through image processing; and interfacing a high-speed digital computer to an analytical plotter so that rectification and corrections proceed in real time. Contour maps produced during tests of the Viking Lander cameras, as well as maps of the area surrounding the Viking Lander on the Martian surface, are presented.

Wu, S. S. C.↗
NASA NTRS1981

Analogue implementation of analytic signal processing for pulse-echo systems

An alternative to rectification is proposed for detection of an ultrasonic signal. This method is especially useful in medical and non-destructive evaluation (nde) applications. With this method, the magnitude of the complex analytic signal is used to define the envelope of the ultrasonic waveform. The square of this quantity has been shown elsewhere to be equal to the true rate-of-arrival of energy. An earlier study, using digital data processing, has already demonstrated the superior resolvability of closely spaced interfaces obtained with the analytic signal magnitude, as compared to conventional rectification. Here, an analogue implementation is presented which utilizes single-sideband techniques to obtain both quadrature components of the analytic signal and its magnitude. A conventional transducer, pulser, and receiver are used.

Gammell, P. M.↗
NASA NTRS1984

Cartographic accuracy of Landsat-4 MSS and TM image data

Investigations of the cartographic quality of Landsat-4 MSS and TM image data in CCT-p formats have produced rectification accuracies (rmse/xy/ values) of + or - 2/3 to + or - 1 data pixel for both whole and subscene areas using polynomials of the first through third degree. In order to achieve these accuracies with MSS data, 15 or more Ground Control Points (GCPs) are required, whereas with the TM data sets as few as 5-10 GCPs will suffice. Factors which limit the cartographic rectification accuracies of the Landsat-4 data include: (1) spatial resolution of the data; (2) map and digitizing errors; and (3) terrain relief. Of these factors, data resolution is the most significant, limiting the location of GCPs to about + or - 0.5 pixel. Horizontal displacements due to terrain relief can be minimized by selecting GCPs at or near midrange elevations. Overall, the representative rmse(xy) values of + or - 25 and + or - 55 m for TM and MSS data sets are within U.S. National Map Accuracy Standards for cartographic products of 1:100,000 and 1:200,000 scale, respectively.

Welch, R.↗
NASA NTRS1987

Behavior of ion-implanted junction diodes in 3C SiC

p-n junction diodes have been formed by ion implantation of B or Al in 3C SiC and annealing at 1365 C. The current-voltage characteristics of the Al-implanted structures show little rectification. The B-implanted diodes show rectification, with ideality factors of 2.2 and higher, breakdown voltages between 5 and 10 V, and a series resistance of the order of 20 kohm. The current-voltage characteristics were measured between room temperature and 270 C. The extracted ideality factors increase with temperature.

Avila, R. E.↗
NASA NTRS1990

Ensemble Monte Carlo characterization of graded Al(x)Ga(1-x)As heterojunction barriers

The current-voltage characteristics of graded Al(x)Ga(1-x)As heterojunction barriers were investigated using a self-consistent ensemble Monte Carlo method. Results are presented for barriers with two doping levels (10 to the 15th/cu cm and 10 to the 17th/cu cm) and two barrier heights (100 and 265 meV). It was found that the lower barrier structure exhibited little rectification at room temperature at both doping levels, while the higher barrier exhibited considerable rectification. The structures with the lower doping value exhibited a smaller current in both forward and reverse regions, due to space-charge effect. The results of studies of the energy and momentum distribution functions along the barrier indicate that the assumption of drifted Maxwellian distribution used in energy-momentum models is not justified for Gamma valley electrons.

Kamoua, R.↗
NASA NTRS2004

Simulation and Analysis of Three-Phase Rectifiers for Aerospace Power Applications

Due to the nature of planned planetary missions, fairly large advanced power systems are required for the spacecraft. These future high power spacecrafts are expected to use dynamic power conversion systems incorporating high speed alternators as three-phase AC electrical power source. One of the early design considerations in such systems is the type of rectification to be used with the AC source for DC user loads. This paper address the issues involved with two different rectification methods, namely the conventional six and twelve pulses. Two circuit configurations which involved parallel combinations of the six and twelve-pulse rectifiers were selected for the simulation. The rectifier s input and output power waveforms will be thoroughly examined through simulations. The effects of the parasitic load for power balancing and filter components for reducing the ripple voltage at the DC loads are also included in the analysis. Details of the simulation circuits, simulation results, and design examples for reducing risk from damaging of spacecraft engines will be presented and discussed.

Truong, Long V.↗
DOE OSTI2024

Control-inspired design and power optimization of an active mechanical motion rectifier based power takeoff for wave energy converters

Ocean waves have high energy density and are persistent and predictable. Yet, converting wave energy to a useable form remains challenging. A significant hurdle is the oscillatory nature of waves resulting in the alternating loads, which necessitate the use of rectification at some stage of the energy conversion. This research effort presents a novel design of active mechanical motion rectifier (AMMR) for the power takeoff (PTO), which provides enhanced controllability and better power performance when compared to passive mechanical motion rectifiers (MMR). Inspired by transistors used in synchronous electrical rectifiers, the proposed design uses controllable electromagnetic clutches in the mechanical transmission to allow active engagement-disengagement control; thus, rectifying the oscillatory motion into a unidirectional rotation for high energy conversion efficiency and allowing the generator in unidirectional rotation to control the bidirectional wave capture structure for maximizing the power output. A semi-analytical computational approach is developed to efficiently evaluate the optimal power achieved using the proposed AMMR-based PTO and active control. It is found that the AMMR-based PTO design yields a higher optimal power than the previous passive MMR design across the wave spectrum. The influences of generator inertia and reactive power are discussed. Furthermore, the effects of control parameters on the power output and the optimal trajectories are analyzed. Wave tank tests with the AMMR prototype demonstrated the effectiveness of AMMR based PTO design and validated the numerical analysis.

16 TIDAL AND WAVE POWER↗
DOE OSTI2025

Light-Matter Interaction in Ultrastable Tunneling Nanogaps

Light emission and detection through tunnel junctions have emerged as a promising platform for studying nanoscale light–matter interactions, including electroluminescence and photoassisted transport. However, controlling these interactions in the tunneling regime has been challenging due to complex underlying mechanisms that remain poorly understood. A major obstacle is the difficulty in forming stable junctions that can function reliably over extended periods. In this study, we fabricate ultrastable tunneling junctions consisting of epitaxial indium–tin-oxide, epitaxial lutetium oxide, and gold. With their stable and consistent tunneling currents, we investigate photon-assisted transport phenomena using simple direct-current detection. Our results demonstrate that optical rectification is the primary contributor to the laser-induced current, alongside thermal effects and hot-electron currents. Furthermore, owing to their epitaxial nature and high breakdown threshold, this ultrastable platform holds promise for future real-world applications, including nanoscale light sources and multifunctional photodetectors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Electrical Validation Testing for ORPC MHK Generator, Modification 6: ORPC SBV for MHK Generator System (CRADA Final Report)

For the U.S. Department of Energy’s (DOE) 2016 Small Business Voucher for Marine and Hydrokinetic (MHK) System, Second Round 2016, ORPC intends to work with the National Renewable Energy Laboratory (NREL) to perform dynamometer testing of the MHK generator systems and its associated controls and inverters. ORPC will provide the generator, variable frequency drives (VFD), controls, and inverter for this testing. NREL will utilize the NREL Energy Systems Integration Facility (ESIF) and dynamometer facilities at the National Wind Technology Center (NWTC) for this work. Modification 6: Additionally, NREL will conduct a feasibility study for implementing passive DC rectification at the turbine.

17 WIND ENERGY↗