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Results for “phasing”

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

Phase Shift Control of a Three-Phase Inverter for Balanced Secondary Currents in Misaligned Three-Phase Inductive Power Transfer Systems

This paper presents a strategy for generating fundamental reference voltage commands for a double-sided LCC tuned three-phase wireless power transfer (WPT) system to achieve balanced output currents when the receiver and transmitter are not perfectly aligned. Formulas for translating the normalized fundamental current commands into phase-shift commands for two of the phase legs in a two-level three-phase inverter are derived. The methodology is validated through circuit simulations performed using coupler models derived from finite-element simulations. Simulation results for a 1.5 k W system design are included, which indicate near perfect correction of imbalance in the secondary currents for a typical misalignment case.

Pries, Jason↗
NASA NTRS1993

Temporal averaging of phase measurements in the presence of spurious phase drift - Application to phase-stepped real-time holographic interferometry

A technique that compensates for low spatial frequency spurious phase changes during an interference experiment is developed; it permits temporal averaging of multiple-phase measurements, made before and after object displacement. The method is tested with phase-stepped real-time holographic interferometry applied to cantilever bending of a piezoelectric bimorph ceramic. Results indicate that temporal averaging of the corrected data significantly reduces the white noise in a phase measurement without incurring systematic errors or sacrificing spatial resolution. White noise is reduced from 3 deg to less than 1 deg using these methods.

Ovryn, B.↗
DOE OSTI2013

Phase transitions in heated Sr{sub 2}MgTeO{sub 6} double perovskite oxide probed by X-ray diffraction and Raman spectroscopy

Double-perovskite oxide Sr{sub 2}MgTeO{sub 6} has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550 °C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100 °C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300 °C, changes in the slopes of temperature dependencies of external and O–Te–O bending modes are detected and interpreted as a second phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Asymmetric “melting” and “freezing” kinetics of the magnetostructural phase transition in B2-ordered FeRh epilayers

Synchrotron X-ray diffraction was used to study the phase transformation processes during the magnetostructural transition in a B2-ordered FeRh (001)-oriented epilayer grown on MgO by sputtering. Out-of-plane lattice constant measurements within the hysteretic regime of the transition reveal a microstructure consistent with the coexistence of lattice-expanded and contracted phases in spatially distinct regions. It was found that the phase separation is more pronounced during cooling than heating. Furthermore, whilst lattice-expanded domains that span the height of the film can be undercooled by several kelvins, there is no equivalent superheating. This asymmetry between the cooling and heating processes in FeRh is consistent with the difference in the kinetics of generic freezing and melting transitions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Initial phase zone for phase locking to the resonance, using “main condition” of phase stability in DC-biased single-sided multipactor

In the present work, the concept of accurate phase stability is employed to study a DC-biased single-sided multipactor. A “main condition” of phase stability was introduced in our previous studies of two-sided multipactors [M. Mostajeran, J. Instrum. 8, P04024 (2013); M. Mostajeran and M. Lamehi Rachti, Nucl. Instrum. Methods Phys. Res. A 615, 1–5 (2010)]. Using the same condition and assuming zero initial velocity for the secondary electrons, a regime of multipactors outside the resonance zones is found. The theoretical results are then verified by numerical simulation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Electrochemical and Raman spectroscopy identification of morphological and phase transformations in nanostructured TiO 2 (B)

TiO 2 (B) exhibits unique electrochemical lithiation behavior where two closely spaced reduction and oxidation peaks, referred to as “double peaks,” are observed for 3-D forms of bulk and nanostructured TiO 2 (B) while a single broad redox peak is observed for 2-D nanosheet architectures. Here, we have used a combination of transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Raman spectroscopy and cyclic voltammetry on TiO 2 (B) nanosheets as well as a series of thermally annealed nanosheets to map the morphological and phase transformation pathways that help clarify the structure-dependent lithiation behavior. We found that the double peak redox behavior only arises once a three dimensional nanocrystalline structure of TiO 2 (B) exists by observing nanoparticle growth on the TiO 2 (B) nanosheet surface via TEM at temperatures above 150 °C. This morphological transformation was also verified by Raman spectroscopy. The appearance of low-energy torsional modes at temperatures above 150 °C which are not observed in 2-D morphologies of TiO 2 (B) agrees well with TEM evidence of 3-D nanoparticle formation. Using scan rate dependent cyclic voltammetry we also verified that all lithiation behavior associated with TiO 2 (B) (either nanosheet or nanoparticle) is due primarily to a surface redox (pseudocapacitive) mechanism. The thermal annealing study also shows the phase transformation of surface nucleated TiO 2 (B) nanoparticles to anatase nanoparticles at temperatures above 200 °C. These studies clearly show how nano-morphological control can influence electrochemical lithiation behavior and help identify a possible mechanism to explain the double peak phenomenon observed for TiO 2 (B).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Band gap of epitaxial in-plane-dimerized single-phase NbO{sub 2} films

We demonstrate the epitaxial growth of high quality crystalline phase-pure NbO{sub 2} films on various oxide substrates using molecular beam epitaxy. Using a combination of reflection high-energy electron diffraction and x-ray diffraction we show that the films grow with the pseudo-rutile (100) orientation out of plane. The band gap of the NbO{sub 2} films is determined to be at least 1.0 eV using a combination of x-ray photoelectron spectroscopy and inverse photoelectron spectroscopy, in conjunction with hybrid density functional calculations of the density of states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Phase-field simulations of GaN growth by selective area epitaxy from complex mask geometries

Three-dimensional phase-field simulations of GaN growth by selective area epitaxy were performed. The model includes a crystallographic-orientation-dependent deposition rate and arbitrarily complex mask geometries. The orientation-dependent deposition rate can be determined from experimental measurements of the relative growth rates of low-index crystallographic facets. Growth on various complex mask geometries was simulated on both c-plane and a-plane template layers. Agreement was observed between simulations and experiment, including complex phenomena occurring at the intersections between facets. The sources of the discrepancies between simulated and experimental morphologies were also investigated. The model provides a route to optimize masks and processing conditions during materials synthesis for solar cells, light-emitting diodes, and other electronic and opto-electronic applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Structural phase transitions in SrTiO 3 nanoparticles

We present that pressure dependent structural measurements on monodispersed nanoscale SrTiO 3 samples with average diameters of 10 to ~80 nm were conducted to enhance the understanding of the structural phase diagram of nanoscale SrTiO 3 . A robust pressure independent polar structure was found in the 10 nm sample for pressures up to 13 GPa, while a size dependent cubic to tetragonal transition occurs (at P = P c ) for larger particle sizes. In conclusion, the results suggest that the growth of ~10 nm STO particles on substrates with significant lattice mismatch may maintain a polar state for a large range of strain values, possibly enabling device use.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Interplay of Gas-phase Reactions and Multi-phase Processes on Phase State and Growth Dynamics of Secondary Organic Aerosols

The formation, growth and evolution of secondary organic aerosols (SOA) are complex multiphase chemical processes, which represent one of the most challenging and demanding problems in research on atmospheric aerosol processes. The research goal of this project was to advance the fundamental understanding of the interplay between gas-phase chemistry and multiphase processes on phase state and growth dynamics of SOA for better predictivity of aerosol effects on climate and air quality.

54 ENVIRONMENTAL SCIENCES↗