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DOE OSTI2022

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure 129 Xe NMR Techniques

Microsized pore parameters, such as pore size and distance between pores in a series of model EPDM rubbers, were determined in situ under the pressure of 500 psi using 129 Xe nuclear magnetic resonance (NMR) techniques: spin–lattice (T 1 ) and spin–spin (T 2 ) relaxation measurements, pulsed-field gradient (PFG) NMR, and two-dimensional exchange spectroscopy (2D EXSY). The T 1 /T 2 (>>1) ratio for the xenon confined in the pores is larger than that for nonconfined free xenon. This suggests that almost the entire pore surface interacts with xenon atoms like a closed pore. While these pores still connect each other through very narrow diffusion/exchange channels, it is possible to observe the echo decay in PFG-NMR and cross-peaks in 2D EXSY. The results show that both diffusion (D pore ≈ 2.1 × 10 –10 m 2 /s) and exchange (exchange rate, τ exch = a few tens of milliseconds) of xenon between a pore within the material and outer surface are prolonged. The exchange distances (l), which correspond to the xenon gas penetration depth, were estimated to be 70–100 μm based on the measured diffusion coefficients and exchange rate (1/τ exch ). NMR diffraction analysis reveals that pore size (a) and pore distance (b) are on the order of magnitude of micrometers and tens of micrometers, while the diffusion coefficients of xenon gas in the diffusion channels (D eff ) are about 10 –8 m 2 /s. Overall, this study suggests that the pores with a few micrometers connected through very narrow flowing channels with the length of several tens of micrometers are developed 70 to 100 μm below the rubber surface. Furthermore, the overall steady-state diffusion of xenon is slower, approximately 2 orders of magnitudes, than the diffusion in the channel between the pores. Finally, the pore and exchange distances correlated with the composition of rubbers showed that the properties of EPDM rubber as a high-pressure gas barrier could be improved by reducing the size of cracks and the depth of gas penetration by the addition of both carbon black and silica fillers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1977

Estimation of the geophysical properties of the ocean surface using aircraft microwave measurements

An improved model of the effects of sea state on microwave signature has been developed which incorporates the different effects of whitecaps and streaks to define the response of microwave channels to wind speed. This model has been demonstrated to agree with recent measurements. An approximation model has also been incorporated to describe the effects of precipitation on microwave radiation through a computationally rapid routine. The use of these models and a new technique to allow the selection of the most climatologically appropriate D-matrix is demonstrated in the inversion of data collected over the bering Sea. Surface wind speed agrees very well with observations while good results are obtained for integrated water vapor, and liquid water.

Fowler, M. G.↗

NASA NTRS1985

Estimation of atmospheric moisture content from microwave radiometric measurements during CCOPE

A multiple linear regression technique has been applied to retrieve continuous sequences of atmospheric moisture profiles from a set of measured data. In this method the selection of an optimal subset of sensor channels plays a crucial role, in order to reduce the impact of data noise and redundancy. The data were obtained with a 4-channel remote-sensing microwave instrument carried aboard an aircraft. In contrast, most previously reported moisture profile retrievals from microwave radiometry have been used on simulated, discontinuous data. Although the data were obtained over a land surface with only a limited amount of correlative data, the retrievals were quite successful.

Lambrigtsen, B. H.↗

DOE OSTI2024

Reducing the Barrier Height in Organic Transistors

Abstract Reducing the Schottky barrier height and Fermi level de‐pinning in metal‐organic semiconductor contacts are crucial for enhancing the performance of organic transistors. The reduction of the Schottky barrier height in bottom‐contact top‐gate organic transistors is demonstrated by adding 1 nm thick atomic layer deposited Al 2 O 3 on the source and drain contacts. By using two different donor‐acceptor copolymers, both p‐ and n‐ type transistors are investigated. Temperature‐dependent current–voltage measurements from non‐treated, self‐assembled monolayer treated, and Al 2 O 3 treated Au source‐drain contact field‐effect transistors with varying channel lengths are carried out. The drain current versus drain voltage near zero gate voltage, which may be described by the thermionic emission model at temperatures above 150 K, allows the estimation of the Schottky barrier height ( φ B ). The Al 2 O 3 contact‐treated transistors show more than 40% lower φ B compared with the non‐treated contacts in the p ‐type transistor. Similarly, an isoindigo‐based transistor, with n ‐type transport, shows a reduction in φ B with Al 2 O 3 treated contacts suggesting that such ultrathin oxide layers provide a universal method for reducing the barrier height.

Ghobadi, Arash↗

NASA NTRS1975

Spectral response of the Viking lander camera: Preliminary evaluation

One of the objectives of the Viking lander imaging investigation is to obtain color and near-infrared multispectral panoramas of the Martian surface using six spectral channels in the 0.4 to 1.1 microns wavelength range. This data can be compared with data obtained by imaging a reference test chart to construct approximate spectral reflectance curves that can then be matched to laboratory standards to aid in identifying surface materials. Some channels exhibit appreciable out-of-band spectral responses, making data reduction and interpretation difficult. A preliminary evaluation of predicted multispectral data for eight geological materials reveals that fairly good reflectance estimates can be made for those materials which have monotonically increasing or decreasing reflectances. Reflectance estimates for materials with more complex reflectances often do not reveal important spectral features and sometimes provide misleading results.

Kelly, W. L., IV↗

NASA NTRS1985

Comparison of mesospheric ozone measurements using the LRIR and UVMCS satellite instruments

A comparison between mesospheric ozone profiles determined by two radically different satellite-borne instruments is presented for the period of July to November, 1975. The Limb Radiance Inversion Radiometer measured 9.6-micron O3 emission, while the Ultraviolet Multiple Channel Spectrometer measured the atmospheric attenuation of solar ultraviolet radiation during passage of the OSO-8 satellite across the terminator. Only nine near coincident measurements were found. The individual instruments have estimated precision errors of + or - 10 to 15 percent. Agreement between ozone values as measured by the two techniques for specific cases varies between 10 and 20 percent. The statistical correlation is positive and significant at all altitudes where both instruments had reasonable signal-to-noise ratio. A maximum correlation of 0.76 occurred at 0.3 mb (about 59 km).

Millier, F.↗

NASA NTRS1985

Interpretation of F-106B in-flight lightning signatures

Various characteristics of the electromagnetic data obtained on a NASA F-106B aircraft during direct lightning strikes are presented. Time scales of interest range from 10 ns to 400 microsecond. The following topics are discussed: (1) Lightning current, I, measured directly versus I obtained from computer integration of measured I-dot; (2) A method of compensation for the low frequency cutoff of the current transformer used to measure I; (3) Properties of fast pulses observed in the lightning time-derivative waveforms; (4) The characteristic D-dot signature of the F-106B aircraft; (5) An RC-discharge interpretation for some lightning waveforms; (6) A method for inferring the locations of lightning channel attachment points on the aircraft by using B-dot data; (7) Simple, approximate relationships between D-dot and I-dot and between B and I; and (8) Estimates of energy, charge, voltage, and resistance for a particular lightning event.

Trost, T. F.↗

NASA NTRS1990

Streak camera receiver definition study

Detailed streak camera definition studies were made as a first step toward full flight qualification of a dual channel picosecond resolution streak camera receiver for the Geoscience Laser Altimeter and Ranging System (GLRS). The streak camera receiver requirements are discussed as they pertain specifically to the GLRS system, and estimates of the characteristics of the streak camera are given, based upon existing and near-term technological capabilities. Important problem areas are highlighted, and possible corresponding solutions are discussed.

Johnson, C. B.↗

NASA NTRS1992

Pattern recognition analysis of polar clouds during summer and winter

A pattern recognition algorithm is demonstrated which classifies eighteen surface and cloud types in high-latitude AVHRR imagery based on several spectral and textural features, then estimates the cloud properties (fractional coverage, albedo, and brightness temperature) using a hybrid histogram and spatial coherence technique. The summertime version of the algorithm uses both visible and infrared data (AVHRR channels 1-4), while the wintertime version uses only infrared data (AVHRR channels 3-5). Three days of low-resolution AVHRR imagery from the Arctic and Antarctic during January and July 1984 were analyzed for cloud type and fractional coverage. The analysis showed significant amounts of high cloudiness in the Arctic during one day in winter. The Antarctic summer scene was characterized by heavy cloud cover in the southern ocean and relatively clear conditions in the continental interior. A large region of extremely low brightness temperatures in East Antarctica during winter suggests the presence of polar stratospheric cloud.

Ebert, Elizabeth E.↗

NASA NTRS1991

Calculations of hadronic dissociation of 28Si projectiles at 14.6A GeV by nucleon emission

An optical potential abrasion-ablation collision model is used to calculate hadronic dissociation cross sections for one, two, and three nucleon removal for the first time for a 14.6A GeV 28Si beam fragmenting in aluminum, tin, and lead targets. These estimates are compared with recent semi-inclusive measurements. Significant differences between some calculated and measured semi-inclusive cross sections exist which cannot be resolved without measurements of the exclusive channel hadronic cross sections. Calculations for each exclusive reaction channel contributing to the semi-inclusive cross sections are presented and discussed.

NASA Program Radiation Health↗

NASA NTRS2024

Designing Lightweight Neutron Absorbing Composites Using a Comprehensive Absorber Areal Density Metric

Efforts to lightweight neutron absorbing composites are limited by incomplete understandings of the interaction between absorbing particles and their matrices. In this study, analytical models and a more physically representative simulation evaluated the penalty to neutron absorbing performance due to neutron channeling between large absorbing particles. Models and simulation agreed that B 4 C particles smaller than 100μm and especially those smaller than 10μm did not cause excessive neutron channeling. A more comprehensive neutron absorbing composite design metric – boron-10 equivalent areal density, which considers the particle size penalty and the matrix contribution to absorptivity – was introduced and used to estimate lightweighting via matrix substitution. Calculations using this new metric showed that a non-absorbing Mg matrix reduced mass by up to 35% over Al, constrained by the difference in mass density, while an absorbing Mg–Li matrix reduced mass by up to 60%, exceeding the difference in mass densities alone. Measurement of apparent absorber areal density through two experimental techniques – foil activation and direct counting – validated estimated absorber areal density as a neutron absorbing composite design metric. This updated understanding of the particle size penalty, newly introduced design metric, and experimental validation demonstrate a path to lightweight neutron absorbing composites.

Radiation shielding↗

NASA NTRS1994

Passive microwave remote sensing of rainfall with SSM/I: Algorithm development and implementation

A physically based algorithm sensitive to emission and scattering is used to estimate rainfall using the Special Sensor Microwave/Imager (SSM/I). The algorithm is derived from radiative transfer calculations through an atmospheric cloud model specifying vertical distributions of ice and liquid hydrometeors as a function of rain rate. The algorithm is structured in two parts: SSM/I brightness temperatures are screened to detect rainfall and are then used in rain-rate calculation. The screening process distinguishes between nonraining background conditions and emission and scattering associated with hydrometeors. Thermometric temperature and polarization thresholds determined from the radiative transfer calculations are used to detect rain, whereas the rain-rate calculation is based on a linear function fit to a linear combination of channels. Separate calculations for ocean and land account for different background conditions. The rain-rate calculation is constructed to respond to both emission and scattering, reduce extraneous atmospheric and surface effects, and to correct for beam filling. The resulting SSM/I rain-rate estimates are compared to three precipitation radars as well as to a dynamically simulated rainfall event. Global estimates from the SSM/I algorithm are also compared to continental and shipboard measurements over a 4-month period. The algorithm is found to accurately describe both localized instantaneous rainfall events and global monthly patterns over both land and ovean. Over land the 4-month mean difference between SSM/I and the Global Precipitation Climatology Center continental rain gauge database is less than 10%. Over the ocean, the mean difference between SSM/I and the Legates and Willmott global shipboard rain gauge climatology is less than 20%.

Ferriday, James G.↗

NASA NTRS1986

Error control techniques for satellite and space communications

High rate concatenated coding systems with trellis inner codes and Reed-Solomon (RS) outer codes for application in satellite communication systems are considered. Two types of inner codes are studied: high rate punctured binary convolutional codes which result in overall effective information rates between 1/2 and 1 bit per channel use; and bandwidth efficient signal space trellis codes which can achieve overall effective information rates greater than 1 bit per channel use. Channel capacity calculations with and without side information performed for the concatenated coding system. Concatenated coding schemes are investigated. In Scheme 1, the inner code is decoded with the Viterbi algorithm and the outer RS code performs error-correction only (decoding without side information). In scheme 2, the inner code is decoded with a modified Viterbi algorithm which produces reliability information along with the decoded output. In this algorithm, path metrics are used to estimate the entire information sequence, while branch metrics are used to provide the reliability information on the decoded sequence. This information is used to erase unreliable bits in the decoded output. An errors-and-erasures RS decoder is then used for the outer code. These two schemes are proposed for use on NASA satellite channels. Results indicate that high system reliability can be achieved with little or no bandwidth expansion.

Costello, D. J., Jr.↗

DOE OSTI2021

OGLE-2018-BLG-0567Lb and OGLE-2018-BLG-0962Lb: Two Microlensing Planets through the Planetary-caustic Channel

We present the analyses of two microlensing events, OGLE-2018-BLG-0567 and OGLE-2018-BLG-0962. In both events, the short-lasting anomalies were densely and continuously covered by two high-cadence surveys. The light-curve modeling indicates that the anomalies are generated by source crossings over the planetary caustics induced by planetary companions to the hosts. The estimated planet/host separation (scaled to the angular Einstein radius θ {sub E}) and mass ratio are (s, q × 10{sup 3}) = (1.81 ± 0.02, 1.24 ± 0.07) and (s, q × 10{sup 3}) = (1.25 ± 0.03, 2.38 ± 0.08), respectively. From Bayesian analyses, we estimate the host and planet masses as (M{sub h},M{sub p})=(0.25{sub −0.13}{sup +0.27} M{sub ⊙},0.32{sub −0.17}{sup +0.34} M{sub J}) and (M{sub h},M{sub p})=(0.54{sub −0.28}{sup +0.33} M{sub ⊙},1.34{sub −0.70}{sup +0.82} M{sub J}), respectively. These planetary systems are located at a distance of 7.06{sub −1.15}{sup +0.93} kpc for OGLE-2018-BLG-0567 and 6.50{sub −1.75}{sup +1.06} kpc for OGLE-2018-BLG-0962, suggesting that they are likely to be near the Galactic bulge. The two events prove the capability of current high-cadence surveys for finding planets through the planetary-caustic channel. We find that most published planetary-caustic planets are found in Hollywood events in which the source size strongly contributes to the anomaly cross-section relative to the size of the caustic.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Theoretical investigation of decoherence channels in athermal phonon sensors

The creation and evolution of nonequilibrium phonons is central in applications ranging from cosmological particle searches to decoherence processes in qubits. However, the fundamental understanding of decoherence pathways for athermal phonon distributions in solid-state systems remains an open question. Using first-principles calculations, we investigate the primary decay channels of athermal phonons in two technologically relevant semiconductors—Si and GaAs. We quantify the contributions of anharmonic, isotopic, and interfacial scattering in these materials. From this, we construct a model to estimate the thermal power in a readout scheme as a function of time. We discuss the implication of our results on noise limitations in current phonon sensor designs and strategies for improving coherence in next-generation phonon sensors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Parametrization of Generalized Parton Distributions from 𝑡-Channel String Exchange in AdS Spaces

We introduce a string-based parametrization for nucleon quark and gluon generalized parton distributions (GPDs) that is valid for all skewness. Our approach leverages conformal moments, representing them as the sum of spin-𝑗 nucleon 𝐴-form factor and skewness-dependent spin-𝑗 nucleon 𝐷-form factor, derived from 𝑡-channel string exchange in AdS spaces consistent with Lorentz invariance and unitarity. This model-independent framework, satisfying the polynomiality condition due to Lorentz invariance, uses Mellin moments from empirical data to estimate these form factors. With just five Regge slope parameters, our method accurately produces various nucleon quark GPD types and symmetric nucleon gluon GPDs through pertinent Mellin-Barnes integrals. Our isovector nucleon quark GPD is in agreement with existing lattice data, promising to improve the empirical extraction and global analysis of nucleon GPDs in exclusive processes, by avoiding the deconvolution problem at any skewness, for the first time.

QCD phenomenology↗

NASA NTRS1975

Skylab investigation of the upwelling off the Northwest coast of Africa

The upwelling off the NW coast of Africa in the vicinity of Cape Blanc was studied in February - March 1974 from aircraft and in September 1973 from Skylab. The aircraft study was designed to determine the effectiveness of a differential radiometer in quantifying surface chlorophyll concentrations. Photographic images of the S190A Multispectral Camera and the S190B Earth Terrain Camera from Skylab were used to study distributional patterns of suspended material and to locate ocean color boundaries. The thermal channel of the S192 Multispectral Scanner was used to map sea-surface temperature distributions offshore of Cape Blanc. Correlating ocean color changes with temperature gradients is an effective method of qualitatively estimating biological productivity in the upwelling region off Africa.

Szekielda, K. H.↗

NASA NTRS1977

Flash photolysis resonance fluorescence investigation of the reaction of Cl/2P/ atoms with ClONO2

Rate constants for the removal of Cl(2P) atoms by homogeneous gas phase reaction with ClONO2 were measured using the flash photolysis resonance fluorescence technique at 224, 250, and 273 K. The values obtained have been used to derive the above Arrhenius equation. The uncertainties expressed are 95% confidence limits obtained using the statistical standard deviation of the individual rate constants plus a 15% additional estimated uncertainty attributed to difficulties in chlorine nitrate concentration measurements. The results indicate that destruction of chlorine nitrate by reaction with chlorine atoms is perhaps the least important of the atmospheric reactive channels, and is at least three orders of magnitude slower than calculated photodissociation rates at all stratospheric altitudes.

Kurylo, M. J.↗