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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Development of nano-Y2O3 dispersed Zr alloys synthesized by mechanical alloying and consolidated by pulse plasma sintering

Highlights: • Zr-Fe-Cr-Cu-Ti-1.0wt% nano-Y{sub 2}O{sub 3} dispersed alloys are fabricated by mechanical alloying and pulse plasma sintering. • These alloys record extremely high compressive strength, Young’s modulus, and hardness. • These mechanical properties are superior as compared to other commercially available Zr based alloys. • Dispersion of nanometric FeZr{sub 2}, Y{sub 2}Ti{sub 2}O{sub 7}, Fe{sub 2}Ti, ZrCu, Cr{sub 2}Zr, Y{sub 2}O{sub 3} leads to grain boundary pinning at elevated temperature. - Abstract: In this paper, Zr alloys are synthesized with nominal compositions: 50Zr-30Fe-10Cr-5Cu-5Ti (alloy A), and 49Zr-30Fe-10Cr-5Cu-5Ti-1Y{sub 2}O{sub 3} (alloy B), 45Zr-30Fe-10Cr-10Cu-5Ti (alloy C), 44Zr-30Fe-10Cr-10Cu-5Ti-1Y{sub 2}O{sub 3} (alloy D) (all in wt%) by mechanical alloying and consolidated by pulse plasma sintering at 1173 K (900 °C), 1223 K (950 °C) and 1273 K (1000 °C) using 75 MPa uniaxial pressure applied for 5 min and 70 kA pulsed current at 3 Hz pulse frequency. The microstructure and phase evolution during mechanical alloying and sintering has been characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM & TEM) and energy dispersive spectroscopy (EDS). Mechanical properties i.e. hardness and compressive strength were determined by using nano-indentation unit and universal testing machine. The produced alloys recorded very high levels of compressive strength (1359–2456 MPa), and hardness (7.05–10.05 GPa) which measures 1.5–2.0 times more than that of other Zr alloys (2 O{sub 3}) particles which can contribute to grain boundary pinning, and improved creep and oxidation resistance at elevated temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Low-Cost, Efficient and Durable High Temperature Wireless Sensors by Direct Write Additive Manufacturing for Application in Fossil Energy Systems

In-situ monitoring of physical parameters in fossil energy (FE) systems is challenging because of their high operating temperatures and oxidizing environments. This research aims utilize Aerosol Jet (AJ) nanoparticle printing, an advanced additive manufacturing method, to fabricate high temperature sensors for FE applications. Sensor films were fabricated by the AJ printing method with an excellent control over film microstructure and properties, in addition to creating less waste. Printing of six different materials, namely, silver (Ag), nickel (Ni), nickel-chromium (NiCr) alloy, copper (Cu), copper-nickel (CuNi), and carbon nanotubes (CNTs) was carried out for their evaluation of as sensor films. The films were then characterized using impedance spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). Film microstructure was correlated with the sensor electrical and mechanical behavior at different temperatures (24-500 °C) and frequencies (0.02 - 300 kHz). This knowledge was then used to fabricate, test, and characterize strain and temperature sensors for high temperature applications. The strain sensors were shown to have a very low thermal strain up to 500 °C and a 57% higher gauge factor compared to the commercially available counterparts. This enhance performance was attributed to the inherent porosity in the sensor films that allowed the films to exhibit a metamaterial-like behavior when deformed. The AJ printed temperature sensors were shown to have the highest Seebeck coefficient amongst all the film-based temperature sensors. In addition, fundamental aspects of crystal structure and phase transformations in Ba(Fe0.7Ta0.3)O3-δ (BFTO), a high temperature sensor material, was investigated along with 3D printed antennas that can transmit sensor signals at high temperatures. Two PhD students, one from first generation college-going underrepresented minority community (URM), two postdoctoral fellows, and several masters and undergraduate students were supported by this award. This work opens up the possibility of realizing low-cost high-performance sensor devices using advanced manufacturing techniques for high temperature FE applications.

20 FOSSIL-FUELED POWER PLANTS↗
NASA NTRS1988

In situ fatigue loading stage inside scanning electron microscope

A fatigue loading stage inside a scanning electron microscopy (SEM) was developed. The stage allows dynamic and static high-magnification and high-resolution viewing of the fatigue crack initiation and crack propagation processes. The loading stage is controlled by a closed-loop servohydraulic system. Maximum load is 1000 lb (4450 N) with test frequencies ranging up to 30 Hz. The stage accommodates specimens up to 2 inches (50 mm) in length and tolerates substantial specimen translation to view the propagating crack. At room temperature, acceptable working resolution is obtainable for magnifications ranging up to 10,000X. The system is equipped with a high-temperature setup designed for temperatures up to 2000 F (1100 C). The signal can be videotaped for further analysis of the pertinent fatigue damage mechanisms. The design allows for quick and easy interchange and conversion of the SEM from a loading stage configuration to its normal operational configuration and vice versa. Tests are performed entirely in the in-situ mode. In contrast to other designs, the NASA design has greatly extended the life of the loading stage by not exposing the bellows to cyclic loading. The loading stage was used to investigate the fatigue crack growth mechanisms in the (100)-oriented PWA 1480 single-crystal, nickel-based supperalloy. The high-magnification observations revealed the details of the crack growth processes.

Telesman, Jack↗
NASA NTRS1991

Spectrally resolved Rayleigh scattering diagnostic for hydrogen-oxygen rocket plume studies

A Rayleigh scattering diagnostic has been developed to measure gas density, temperature, and velocity in the exhaust plume of 100 N thrust class hydrogen-oxygen rockets. The spectrum of argon-ion laser light scattered by the gas molecules in the plume (predominantly water vapor) is measured with a scanning Fabry-Perot interferometer. The gas density is determined from the total scattered power, the gas temperature from the spectral width, and the velocity from the shift in the peak of the spectrum from the frequency of the incident laser light. The diagnostic has been demonstrated in a rocket test cell and a discussion of results is given.

Seasholtz, R. G.↗
NASA NTRS1992

An evaluation of corrosion protection by two epoxy primers on 2219-T87 and 7075-T73 aluminum

A comparison of the corrosion protection provided by two amine epoxy primers was made using salt fog, alternate immersion, and total immersion as exposure media. The study is the result of a request to use an unqualified low volatile organic carbon (VOC) primer (AKZO 463-6-78) in place of the current primer (AKZO 463-6-3) because environmental regulations have eliminated use of the current primer in many states. Primed, scribed samples of 2219-T87 and 7075-T73 aluminum were exposed to 5-percent NaCl salt fog and 3.5-percent NaCl alternate immersion for a period of 90 days. In addition, electrode samples immersed in 3.5-percent NaCl were tested using electrochemical impedance spectroscopy (EIS). The EG&G model 368 ac impedance measurement system was used to monitor changing properties of AKZO 463-6-78 and AKZO 463-6-3 primed 2219-T87 aluminum for a period of 30 days. The response of the corroding system of a frequency scan can be modeled in terms of an equivalent circuit consisting of resistors and capacitors in a specific arrangement. Each resistor/capacitor combination represents physical processes taking place within the electrolyte, at the electrolyte/primer surface, within the coating, and at the coating/substrate surface. Values for the resistors and capacitors are assigned following a nonlinear least squares fit of the data to the equivalent circuit. Changes in the values of equivalent circuit parameters during the 30-day exposure allow assessment of the time to and mechanism of coating breakdown.

Mendrek, M. J.↗
DOE OSTI2015

Efficient scatter distribution estimation and correction in CBCT using concurrent Monte Carlo fitting

Purpose: X-ray scatter is a significant impediment to image quality improvements in cone-beam CT (CBCT). The authors present and demonstrate a novel scatter correction algorithm using a scatter estimation method that simultaneously combines multiple Monte Carlo (MC) CBCT simulations through the use of a concurrently evaluated fitting function, referred to as concurrent MC fitting (CMCF). Methods: The CMCF method uses concurrently run MC CBCT scatter projection simulations that are a subset of the projection angles used in the projection set, P, to be corrected. The scattered photons reaching the detector in each MC simulation are simultaneously aggregated by an algorithm which computes the scatter detector response, S{sub MC}. S{sub MC} is fit to a function, S{sub F}, and if the fit of S{sub F} is within a specified goodness of fit (GOF), the simulations are terminated. The fit, S{sub F}, is then used to interpolate the scatter distribution over all pixel locations for every projection angle in the set P. The CMCF algorithm was tested using a frequency limited sum of sines and cosines as the fitting function on both simulated and measured data. The simulated data consisted of an anthropomorphic head and a pelvis phantom created from CT data, simulated with and without the use of a compensator. The measured data were a pelvis scan of a phantom and patient taken on an Elekta Synergy platform. The simulated data were used to evaluate various GOF metrics as well as determine a suitable fitness value. The simulated data were also used to quantitatively evaluate the image quality improvements provided by the CMCF method. A qualitative analysis was performed on the measured data by comparing the CMCF scatter corrected reconstruction to the original uncorrected and corrected by a constant scatter correction reconstruction, as well as a reconstruction created using a set of projections taken with a small cone angle. Results: Pearson’s correlation, r, proved to be a suitable GOF metric with strong correlation with the actual error of the scatter fit, S{sub F}. Fitting the scatter distribution to a limited sum of sine and cosine functions using a low-pass filtered fast Fourier transform provided a computationally efficient and accurate fit. The CMCF algorithm reduces the number of photon histories required by over four orders of magnitude. The simulated experiments showed that using a compensator reduced the computational time by a factor between 1.5 and 1.75. The scatter estimates for the simulated and measured data were computed between 35–93 s and 114–122 s, respectively, using 16 Intel Xeon cores (3.0 GHz). The CMCF scatter correction improved the contrast-to-noise ratio by 10%–50% and reduced the reconstruction error to under 3% for the simulated phantoms. Conclusions: The novel CMCF algorithm significantly reduces the computation time required to estimate the scatter distribution by reducing the statistical noise in the MC scatter estimate and limiting the number of projection angles that must be simulated. Using the scatter estimate provided by the CMCF algorithm to correct both simulated and real projection data showed improved reconstruction image quality.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1975

Laser Doppler velocimeter system simulation for sensing aircraft wake vortices. Part 2: Processing and analysis of LDV data (for runs 1023 and 2023)

A data analysis program constructed to assess LDV system performance, to validate the simulation model, and to test various vortex location algorithms is presented. Real or simulated Doppler spectra versus range and elevation is used and the spatial distributions of various spectral moments or other spectral characteristics are calculated and displayed. Each of the real or simulated scans can be processed by one of three different procedures: simple frequency or wavenumber filtering, matched filtering, and deconvolution filtering. The final output is displayed as contour plots in an x-y coordinate system, as well as in the form of vortex tracks deduced from the maxima of the processed data. A detailed analysis of run number 1023 and run number 2023 is presented to demonstrate the data analysis procedure. Vortex tracks and system range resolutions are compared with theoretical predictions.

Meng, J. C. S.↗
NASA NTRS1975

Hot corrosion evaluation of aluminide coated superalloys in support of an ASTM Round Robin program

Commercial aluminized coatings on substrates were hot corroded at 900 C in a 0.3 Mach burner rig with 5 ppm synthetic sea salt and at two cycling frequencies. Extensive post-exposure examinations were conducted on the corroded specimens such as metallography, X-ray diffraction, scanning electron microscopy, microprobe raster scans, and spectrographic analyses. Thermodynamic calculations were made of the equilibrium burner flame composition and the calculations were compared to the experimental findings. It was found that localized spalling of the coatings preceded coating failure. It is suggested that the spalling of the coatings is due to the formation of localized stresses caused by the depletion of chromium and aluminum in the coating or the enrichment of the coating with sulfur. For the materials and test conditions investigated, it was found that coating life is dependent only upon the initial coating thickness and not on the type of aluminized coating, the substrate, or the cycle frequency.

Santoro, G.↗
DOE OSTI2017

Design and implementation of wire tension measurement system for MWPCs used in the STAR iTPC upgrade

The STAR experiment at RHIC is planning to upgrade the Time Projection Chamber which lies at the heart of the detector. We have designed an instrument to measure the tension of the wires in the multi-wire proportional chambers (MWPCs) which will be used in the TPC upgrade. The wire tension measurement system causes the wires to vibrate and then it measures the fundamental frequency of the oscillation via a laser based optical platform. The platform can scan the entire wire plane, automatically, in a single run and obtain the wire tension on each wire with high precision. In this paper, the details about the measurement method and the system setup will be described. In addition, the test results for a prototype MWPC to be used in the STAR-iTPC upgrade will be presented.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Sustainable Shape Memory Elastomers with Reduced Melt Viscosity and Enhanced Stiffness

Melt reactive processing of lignin with nitrile rubber is a promising approach to synthesizing shape memory materials. The strong intramolecular interactions in lignin macromolecular structures, caused by π–π stacking in aromatic rings and hydrogen bonding, often result in large phase separation or low miscibility with rubbers. In this study, we investigated the chemical and molecular characteristics, as well as the stiffness and complex viscosity, of modified kraft lignin melt-reacted with an acrylonitrile/butadiene copolymer containing 41% acrylonitrile (NBR41). To enhance the macromolecular compatibility of kraft lignin with NBR41, kraft lignin was cross-linked with poly(propylene glycol) diglycidyl ether (PPDE) and trimethylolpropane triglycidyl ether (TTE), both rich in epoxy reactive groups capable of forming chemical bonds with hydroxyl and carboxyl groups. Here, our findings demonstrate that the modification of kraft lignin with PPDE and TTE resulted in significantly increased stiffness of the composites. The elastic modulus of NBR41-Kraft lignin-PPDE and NBR41-Kraft lignin-TTE increased by 82 and 162%, respectively. Both the yield strength and Young’s modulus of these two samples showed dramatic improvements. Specifically, the yield strength and Young’s modulus of NBR41-Kraft lignin-TTE increased nearly 4 and 3-fold, respectively, compared to the control sample. Interestingly, despite significant improvements in mechanical properties, the viscosity of NBR41-Kraft lignin-PPDE was substantially lower than that of the control sample. At 210 °C and an angular frequency of 1 rad/s, the complex viscosity of NBR41-Kraft lignin was approximately 100.25 ± 4.77 kPa·s, while that of NBR41-Kraft lignin-PPDE was significantly lower at 56 ± 0.93 kPa·s. These findings were validated through Fourier transform infrared spectroscopy, scanning electron microscopy, dynamic mechanical analysis, thermal characterization, rheological tests, and quasi-elastic neutron scattering techniques.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2019

Airborne Radar for sUAS Sense and Avoid

A primary challenge for the safe integration of small UAS operations into the National Airspace System (NAS) is traffic deconfliction, both from manned and unmanned aircraft. The UAS Traffic Management (UTM) project being conducted at the National Aeronautics and Space Administration (NASA) considers a layered approach to separation provision, ranging from segregation of operations through airspace volumes (geofences) to autonomous sense and avoid (SAA) technologies for higher risk, densely occupied airspace. Cooperative SAA systems, such as Automatic Dependent Surveillance-Broadcast (ADS-B) and/or vehicle-to-vehicle communication systems provide significant additional risk mitigation but they fail to adequately mitigate collision risks for non-cooperative (non-transponder equipped) airborne aircraft. The RAAVIN (Radar on Autonomous Aircraft to Verify ICAROUS Navigation) flight test being conducted by NASA and the Mid-Atlantic Aviation Partnership (MAAP) was designed to investigate the applicability and performance of a prototype, commercially available sUAS radar to detect and track non-cooperative airborne traffic, both manned and unmanned. The radar selected for this research was a Frequency Modulated Continuous Wave (FMCW) radar with 120 degree azimuth and 80 degree elevation field of view operating at 24.55GHz center frequency with a 200 MHz bandwidth. The radar transmits 2 watts of power thru a Metamaterial Electronically Scanning Array antenna in horizontal polarization. When the radar is transmitting, personnel must be at least 1 meter away from the active array to limit nonionizing radiation exposure. The radar physical dimensions are 18.7cm by 12.1cm by 4.1cm and it weighs less than 820 grams making it well suited for installation on small UASs. The onboard, SAA capability, known as ICAROUS, (Independent Configurable Architecture for Reliable Operations of Unmanned Systems), developed by NASA to support sUAS operations, will provide autonomous guidance using the traffic radar tracks from the onboard radar. The RAAVIN set of studies will be conducted in three phases. The first phase included outdoor, ground-based radar evaluations performed at the Virginia Tech’s Kentland Farm testing range in Blacksburg, VA. The test was designed to measure how well the radar could detect and track a small UAS flying in the radar’s field of view. The radar was used to monitor 5 test flights consisting of outbound, inbound and crossing routes at different ranges and altitudes. The UAS flown during the ground test was the Inspire 2, a quad copter weighing less than 4250 grams (10 pounds) at maximum payload. The radar was set up to scan and track targets over its full azimuthal field of view from 0 to 40 degrees in elevation. The radar was configured to eliminate tracks generated from any targets located beyond 2000 meters from the radar and moving at velocities under 1.45 meters per second. For subsequent phases of the study the radar will be integrated with a sUAS platform to evaluate its performance in flight for SAA applications ranging from sUAS to manned GA aircraft detections and tracking. Preliminary data analysis from the first outdoor ground tests showed the radar performed well at tracking the vehicle as it flew outbound and repeatedly maintained a track out to 1000 meters (maximum 1387 meters) until the vehicle slowed to a stop to reverse direction to fly inbound. As the Inspire flew inbound tracks from beyond 800 meters, a reacquisition time delay was consistently observed between when the Inspire exceeds a speed of 1.45 meters per second and when the radar indicated an inbound target was present and maintained its track. The time delay varied between 6 seconds to over 37 seconds for the inbound flights examined, and typically resulted in about a 200 meter closure distance before the Inspire track was maintained. The radar performed well at both acquiring and tracking the vehicle as it flew crossing routes out past 400 meters across the azimuthal field of view. The radar and ICAROUS software will be integrated and flown on a BFD-1400-SE8-E UAS during the next phase of the RAAVIN project. The main goal at the conclusion of this effort is to determine if this radar technology can reliably support minimum requirements for SAA applications of sUAS. In particular, the study will measure the range of vehicle detections, lateral and vertical angular errors, false and missed/late detections, and estimated distance at closest point of approach after an avoidance maneuver is executed. This last metric is directly impacted by sensor performance and indicates its suitability for the task.

Szatkowski, George N.↗
NASA NTRS2001

Vibration Sensitivity of a Wide-Temperature Electronically Scanned Pressure Measurement (ESP) Module

A vibration sensitivity test was conducted on a Wide-Temperature ESP module. The test object was Module "M4," a 16-channel, 4 psi unit scheduled for installation in the Arc Sector of NTF. The module was installed on a vibration exciter and loaded to positive then negative full-scale pressures (+/-2.5 psid). Test variables were the following: Vibration frequencies: 20, 55, 75 Hz. Vibration level: 1 g. Vibration axes: X, Y, Z. The pressure response was measured on each channel, first without and then with the vibration turned on, and the difference analyzed by means of the statistical t-test. The results show that the vibration sensitivity does not exceed 0.01% Full Scale Output per g (with the exception of one channel on one axis) to a 95 percent confidence level. This specification, limited by the resolution of the pressure source, lies well below the total uncertainty specification of 0.1 percent Full Scale Output.

Zuckerwar, Allan J.↗
DOE OSTI2018

Optimal strategy for polarization modulation in the LSPE-SWIPE experiment

Context. Cosmic microwave background (CMB) B-mode experiments are required to control systematic effects with an unprecedented level of accuracy. Polarization modulation by a half wave plate (HWP) is a powerful technique able to mitigate a large number of the instrumental systematics. Aims. Our goal is to optimize the polarization modulation strategy of the upcoming LSPE-SWIPE balloon-borne experiment, devoted to the accurate measurement of CMB polarization at large angular scales. Methods. We departed from the nominal LSPE-SWIPE modulation strategy (HWP stepped every 60 s with a telescope scanning at around 12 deg/s) and performed a thorough investigation of a wide range of possible HWP schemes (either in stepped or continuously spinning mode and at different azimuth telescope scan-speeds) in the frequency, map and angular power spectrum domain. In addition, we probed the effect of high-pass and band-pass filters of the data stream and explored the HWP response in the minimal case of one detector for one operation day (critical for the single-detector calibration process). We finally tested the modulation performance against typical HWP-induced systematics. Results. Our analysis shows that some stepped HWP schemes, either slowly rotating or combined with slow telescope modulations, represent poor choices. Moreover, our results point out that the nominal configuration may not be the most convenient choice. While a large class of spinning designs provides comparable results in terms of pixel angle coverage, map-making residuals and BB power spectrum standard deviations with respect to the nominal strategy, we find that some specific configurations (e.g., a rapidly spinning HWP with a slow gondola modulation) allow a more efficient polarization recovery in more general real-case situations. Conclusions. Although our simulations are specific to the LSPE-SWIPE mission, the general outcomes of our analysis can be easily generalized to other CMB polarization experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Atomic-resolution scanning transmission electron microscopy through 50-nm-thick silicon nitride membranes

Silicon nitride membranes can be used for windows of environmental chambers for in situ electron microscopy. We report that aberration corrected scanning transmission electron microscopy (STEM) achieved atomic resolution on gold nanoparticles placed on both sides of a 50-nm-thick silicon nitride membrane at 200 keV electron beam energy. Spatial frequencies of 1/1.2 A were visible for a beam semi-angle of 26.5 mrad. Imaging though a 100-nm-thick membrane was also tested. The achieved imaging contrast was evaluated using Monte Carlo simulations of the STEM imaging of a sample of with a representative geometry and composition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Novel covariance-based neutrality test of time-series data reveals asymmetries in ecological and economic systems

Systems as diverse as the interacting species in a community, alleles at a genetic locus, and companies in a market are characterized by competition (over resources, space, capital, etc) and adaptation. Neutral theory, built around the hypothesis that individual performance is independent of group membership, has found utility across the disciplines of ecology, population genetics, and economics, both because of the success of the neutral hypothesis in predicting system properties and because deviations from these predictions provide information about the underlying dynamics. However, most tests of neutrality are weak, based on static system properties such as species-abundance distributions or the number of singletons in a sample. Time-series data provide a window onto a system’s dynamics, and should furnish tests of the neutral hypothesis that are more powerful to detect deviations from neutrality and more informative about to the type of competitive asymmetry that drives the deviation. Here, we present a neutrality test for time-series data. We apply this test to several microbial time-series and financial time-series and find that most of these systems are not neutral. Our test isolates the covariance structure of neutral competition, thus facilitating further exploration of the nature of asymmetry in the covariance structure of competitive systems. Much like neutrality tests from population genetics that use relative abundance distributions have enabled researchers to scan entire genomes for genes under selection, we anticipate our time-series test will be useful for quick significance tests of neutrality across a range of ecological, economic, and sociological systems for which time-series data are available. Here, future work can use our test to categorize and compare the dynamic fingerprints of particular competitive asymmetries (frequency dependence, volatility smiles, etc) to improve forecasting and management of complex adaptive systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

In situ corrosion analysis of Al-Zn-In-Mg-Ti-Ce sacrificial anode alloy

The corrosion behaviour of Al-5Zn-0.02In-1Mg-0.05Ti-0.5Ce (wt.%) alloy has been investigated by immersion test, scanning electron microscopy, energy dispersive X-ray detector, electrochemical impedance spectroscopy and electrochemical noise. The results show that there exist different corrosion types of the alloy in 3.5% NaCl solution with the immersion time. At the initial stage of immersion, pitting due to the precipitates predominates the corrosion with a typical inductive loop at low frequencies in electrochemical impedance spectroscopy. The major precipitates of the alloy are MgZn{sub 2} and Al{sub 2}CeZn{sub 2} particles. The corrosion potentials of the bulk MgZn{sub 2} and Al{sub 2}CeZn{sub 2} alloys are negative with respect to that of {alpha}-Al, so the MgZn{sub 2} and Al{sub 2}CeZn{sub 2} precipitates can act as activation centre and cause the pitting. In the late corrosion, a relative uniform corrosion predominates the corrosion process controlled by the dissolution/precipitation of the In ions and characterized by a capacitive loop at medium-high frequencies in electrochemical impedance spectroscopy. The potential noise of the pitting shows larger amplitude fluctuation and lower frequency, but the potential noise of the uniform corrosion occurs with smaller amplitude fluctuation and higher frequency.

36 MATERIALS SCIENCE↗
DOE OSTI2011

THREE-DIMENSIONAL STRUCTURE OF MICROWAVE SOURCES FROM SOLAR ROTATION STEREOSCOPY VERSUS MAGNETIC EXTRAPOLATIONS

We use rotation stereoscopy to estimate the height of a steady-state solar feature relative to the photosphere, based on its apparent motion in the image plane recorded over several days of observation. The stereoscopy algorithm is adapted to work with either one- or two-dimensional data (i.e., from images or from observations that record the projected position of the source along an arbitrary axis). The accuracy of the algorithm is tested on simulated data, and then the algorithm is used to estimate the coronal radio source heights associated with the active region NOAA 10956, based on multifrequency imaging data over seven days from the Siberian Solar Radio Telescope near 5.7 GHz, the Nobeyama Radio Heliograph at 17 GHz, as well as one-dimensional scans at multiple frequencies spanning the 5.98-15.95 GHz frequency range from the RATAN-600 instrument. The gyroresonance emission mechanism, which is sensitive to the coronal magnetic field strength, is applied to convert the estimated radio source heights at various frequencies, h(f), to information about magnetic field versus height B(h), and the results are compared to a magnetic field extrapolation derived from photospheric magnetic field observations obtained by Hinode and Michelson Doppler Imager. We found that the gyroresonant emission comes from heights exceeding the location of the third gyrolayer irrespective of the magnetic extrapolation method; implications of this finding for coronal magnetography and coronal plasma physics are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Cooperative Adsorption of Trehalose to DPPC Monolayers at the Water-Air Interface Studied with Vibrational Sum Frequency Generation

A combination of surface tension, surface-specific vibrational spectroscopy, and differential scanning calorimetry experiments were performed to examine the ability of lipid films to enrich interfacial organic content by attracting soluble, neutral saccharides from bulk aqueous solution. This “cooperative adsorption” hypothesis has been proposed as a possible source of the high organic fractions found in sea spray aerosols and is believed to be responsible for cryoprotection in some organisms. Experiments described in this work show that the neutral disaccharide trehalose (Tre) is drawn to lipid films comprised of dipalmitoylphosphatidylcholine (DPPC), a saturated lipid that is a major component of most eukaryotic cells. The effects of Tre on DPPC monolayer structure and organization were tested with tightly packed monolayers in the two-dimensional solid phase (40 Å2/molecule) and more expanded monolayers in the two dimensional liquid condensed phase (55 Å2/molecule). Surface tension data show that DPPC monolayer behaviour remains largely unchanged until Tre bulk concentrations are sufficiently high (= 50 mM). In contrast, surface specific vibrational sum frequency spectra show that when Tre bulk concentrations are = 10 mM, DPPC monolayers in their liquid condensed state (55 Å2/molecule) became more ordered, implying relatively strong noncovalent interactions between the two species. Tre also induces changes in DPPC bilayer behaviour as evidenced by a gel to liquid crystalline phase transition temperature that increases with increasing Tre concentration. This result suggests that Tre associates with the DPPC headgroups in very specific ways leading to partial dehydration. Together, these results support the cooperative adsorption mechanism under some circumstances, namely that there is a minimum aqueous phase Tre concentration required to induce observable structural changes in a lipid monolayer, and that these effects are most pronounced with DPPC monolayers in their liquid condensed state compared to a tightly packed 2-dimensional solid.

Link, Katie A.↗