Construction and Study of Instrument Response Functions for Analysis of the National Ignition Facility ( NIF) Neutron Time-of-Flight Detectors
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Physics - Plasma physics↗
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One-Step Ahead Prediction of Thermal Mixing Tee Sensors with Long Short Term Memory (LSTM) Neural Networks
High-temperature advanced reactors under development, such as sodium fast reactors (SFR) and molten salt cooled reactors (MSCR), are expected to offer lower levelized cost of energy (LCOE) compared to existing light water reactor (LWR’s). In the existing light water reactors (LWR’s), operation and maintenance (O&M) expenses constitute the largest fraction of the total operating cost. Some of the O&M costs are related maintenance of sensors which can fail due to exposure to harsh environment in a reactor. The O&M costs of Advanced Reactor (AR)’s are expected to constitute a significant fraction of the total cost as well, because of high temperature and radiation level in AR are likely to cause material fatigue and premature failure of sensors and components. The O&M costs in AR’s could be reduced through integration of advanced informatics of performance-related sensors into a digital twin designed for reactor monitoring. For example, machine learning (ML) could be employed for real-time validation and correction of performance-related sensors, and reducing the number of performance-related physical sensor units through virtual sensing. As part of the effort, we investigate real-time validation of thermal hydraulic sensors through one-step ahead forecasting of sensor values using long short-term memory (LSTM) recurrent neural networks (RNN). The sensors are installed in a flow loop containing a thermal mixing tee, which is a common experimental model to study thermal fatigue in a thermal hydraulic loop. In addition, nonlinear transients generated in a thermal mixing tee constitute a good challenge data set for training and validation of ML algorithms. Sensors in this study include thermocouples, flow meters, and optical fibers for distributed temperature sensing. In one experiment, measurement data sets were obtained for a loop was filled with water, and in another experiment, measurements were performed on a loop filled with liquid metal Galinstan. We have also conducted preliminary investigation of one-step ahead prediction of fiber optics-based distributed temperature sensing with LSTM networks. In predicting fiber-based temperature measurements, we treated each gauge pitch of the fiber as an independent sensor. Accuracy of one-step ahead forecasting was estimated by calculating root mean square error (RMSE) for the test segment of time series of each sensor. RMSE’s for temperature sensors in water loop were, for the most part, lower than for the same sensors in Galinstan loop. The RMSE’s for flow meters were similar for both loops. The RMSE’s for distributed temperature measured with the fiber optic sensor were similar to those of the point sensors. Results of this study demonstrated the capability of LSTM one-step ahead forecasting with RMSE comparable to uncertainty in sensor measurements.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
Influence of Coupled Radiation and Ablation on the Aerothermodynamic Environment of Planetary Entry Vehicles
A review of recently published coupled radiation and ablation capabilities involving the simulation of hypersonic flowfields relevant to Earth, Mars, or Venus entry is presented. The three fundamental mechanisms of radiation coupling are identified as radiative cooling, precursor photochemistry, and ablation-radiation interaction. The impact of these mechanisms are shown to be significant for a 3 m radius sphere entering Earth at hypothetical Mars return conditions (approximately 15 km/s). To estimate the influence precursor absorption on the radiative flux for a wide range of conditions, a simplified approach is developed that requires only the non-precursor solution. Details of a developed coupled ablation approach, which is capable of treating both massively ablating flowfields in the sublimation regime and weakly ablating diffusion Climited oxidation cases, are presented. A review of the two primary uncoupled ablation approximations, identified as the blowing correction and film coefficient approximations, is made and their impact for Earth and Mars entries is shown to be significant for recession and convective heating predictions. Fully coupled ablation and radiation simulations are presented for the Mars return sphere throughout its entire trajectory. Applying to the Mars return sphere the Pioneer- Venus heritage carbon phenolic heatshield, which has properties available in the open literature, the differences between steady state ablation and coupling to a material response code are shown to be significant.
Johnston, Christopher O.↗
Spectrally reconfigurable quantum emitters enabled by optimized fast modulation
The ability to shape photon emission facilitates strong photon-mediated interactions between disparate physical systems, thereby enabling applications in quantum information processing, simulation and communication. Spectral control in solid state platforms such as color centers, rare earth ions, and quantum dots is particularly attractive for realizing such applications on-chip. Here we propose the use of frequency-modulated optical transitions for spectral engineering of single photon emission. Using a scattering-matrix formalism, we find that a two-level system, when modulated faster than its optical lifetime, can be treated as a single-photon source with a widely reconfigurable photon spectrum that is amenable to standard numerical optimization techniques. To enable the experimental demonstration of this spectral control scheme, we investigate the Stark tuning properties of the silicon vacancy in silicon carbide, a color center with promise for optical quantum information processing technologies. We find that the silicon vacancy possesses excellent spectral stability and tuning characteristics, allowing us to probe its fast modulation regime, observe the theoretically-predicted two-photon correlations, and demonstrate spectral engineering. Our results suggest that frequency modulation is a powerful technique for the generation of new light states with unprecedented control over the spectral and temporal properties of single photons.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
A forward speed effects study on jet noise from several suppressor nozzles in the NASA/Ames 40- by 80-foot wind tunnel
A test program was conducted in a 40 by 80 foot wind tunnel to evaluate the effect of relative velocity on the jet noise signature of a conical ejector, auxiliary inlet ejector, 32 spokes and 104 tube nozzle with and without an acoustically treated shroud. The freestream velocities in the wind tunnel were varied from 0 to 103.6 m/sec (300 ft/sec) for exhaust jet velocities of 259.1 m/sec (850 ft/sec) to 609.6 m/sec (2000 ft/sec). Reverberation corrections for the wind tunnel were developed and the procedure is explained. In conjunction with wind tunnel testing the nozzles were also evaluated on an outdoor test stand. The wind tunnel microphone arrays were duplicated during the outdoor testing. The data were then extrapolated for comparisons with data measured using a microphone array placed on a 30.5 meter (100 ft) arc. Using these data as a basis, farfield to nearfield arguments are presented with regards to the data measured in the wind tunnel. Finally, comparisons are presented between predictions made using existing methods and the measured data.
Beulke, M. R.↗
DESI Data Release 2 ELGs: Property-dependent subsamples, imaging systematics, and clustering
Using emission-line galaxies (ELGs) from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2, we evaluate a property-dependent correction to imaging systematics. We derive systematic weights following the same linear regression method used for other DESI tracers, but do so separately on ELG subsamples to provide a physically-informed alternative to the fiducial, neural-network-based approach. In doing so, we show that the deeper imaging in the Dark Energy Survey (DES) footprint leads to a higher overall number density but a lack of targets with extreme $g-r$ and $r-z$ colors. ELGs in the DES region also show a distinct redshift distribution when subsampled by position in the $g-r$ vs. $r-z$ plane. To address these effects, we implement a separate treatment of the DES footprint within the DESI catalog production pipeline, which is generally well-motivated and, in some cases, imperative for accurate clustering measurements. With DES treated separately, we find that property-dependent systematic weights further mitigate spurious clustering signal in $\sim$10% of subsamples, while the fiducial scheme remains optimal for the full sample.
Hagen, T. [Utah U.]↗
Substrate-Dependent Exciton Diffusion and Annihilation in Chemically Treated MoS 2 and WS 2
Atomically thin semiconductors such as monolayer MoS 2 and WS 2 exhibit nonlinear exciton–exciton annihilation at notably low excitation densities (below ~10 excitons/μm 2 in exfoliated MoS 2 ). In this work, we show that the density threshold at which annihilation occurs can be tuned by changing the underlying substrate. When the supporting substrate is changed from SiO 2 to Al 2 O 3 or SrTiO 3 , the rate constant for second-order exciton–exciton annihilation, k XX [cm 2 /s], is reduced by 1 or 2 orders of magnitude, respectively. Using transient photoluminescence microscopy, we measure the effective room-temperature exciton diffusion coefficient in bis(trifluoromethane)sulfonimide-treated MoS 2 to be in the range D = 0.03–0.06 cm 2 /s, corresponding to a diffusion length of L D = 350 nm for an exciton lifetime of τ = 18 ns, which does not depend strongly on the substrate. We discuss possible mechanisms for the observed behavior, including substrate permittivity, long-range exciton–exciton or exciton–charge interactions, defect-mediated Auger recombination, and spatially inhomogeneous exciton populations arising from substrate-induced disorder. Exciton annihilation limits the overall efficiency of 2D semiconductor devices operating at high exciton densities; the ability to tune these interactions via the underlying substrate is an important step toward more efficient optoelectronic technologies featuring atomically thin materials.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
The production and separation of 161 Tb with high specific activity at the University of Utah
Targeted radiotherapy (TRT) is an increasingly prominent area of research in nuclear medicine, particularly in the context of treating cancerous tumors. One radionuclide of considerable interest for TRT is terbium-161 (t 1/2 = 6.95 days), which undergoes beta emission and shares similar decay properties as 177 Lu (FDA-approved as LUTATHERA® and PLUVICTO®). Besides beta emission, 161 Tb also emits a significant number of conversion and Auger electrons further enhancing its therapeutic potential. Terbium-161 can be produced using nuclear reactors through an indirect neutron capture reaction, $^{160}_{64}$Gd(n,γ) $^{161}_{64}$Gd → (3.7 min, β – ) $^{161}_{65}$Tb, from 160 Gd targets. However, a key challenge in utilizing 161 Tb for TRT lies in effectively separating target and product materials to attain high specific activity for radiolabeling. Here, we detail the production of no-carrier added 161 Tb using low flux research reactors (mean thermal (< 0.625 eV) neutron flux: 1.356 ×10 12 n • cm –2 • s –1 ) like the University of Utah TRIGA Reactor, using enriched 160 Gd 2 O 3 targets (1.5 ± 0.3 µCi of 161 Tb per mg of 160 Gd target per hour of irradiation). We also developed a separation technique based on cation exchange and extraction chromatography, suitable for mCi level irradiations with targets exceeding 200 milligrams. In a simulated full-scale irradiation, 161 Tb was successfully isolated from large mass targets using cation exchange (AG 50W-X8, with 2-hydroxyisobutyric acid at 70 mM, pH 4.75) and extraction chromatography (LN Resin, 0.5 – 0.75 M HNO 3 ) methods. Here, this resulted in high apparent molar activities of [ 161 Tb]Tb-DOTA (113 ± 3 MBq/nmol), demonstrating high purity 161 Tb relevant for potential future preclinical applications.
161Tb↗
The DEHVILS in the details: Type Ia supernova Hubble residual comparisons and mass step analysis in the near-infrared
Measurements of type Ia supernovae (SNe Ia) in the near-infrared (NIR) have been used both as an alternate path to cosmology compared to optical measurements and as a method of constraining key systematics for the larger optical studies. With the DEHVILS sample, the largest published NIR sample with consistent NIR coverage of maximum light across three NIR bands ( Y, J , and H ), we check three key systematics: (i) the reduction in Hubble residual scatter as compared to the optical, (ii) the measurement of a “mass step” or lack thereof and its implications, and (iii) the ability to distinguish between various dust models by analyzing slopes and correlations between Hubble residuals in the NIR and optical. We produce SN Ia simulations of the DEHVILS sample and find that it is harder to differentiate between various dust models than previously understood. Additionally, we find that fitting with the current SALT3-NIR model does not yield accurate wavelength-dependent stretch-luminosity correlations, and we propose a limited solution for this problem. From the data, we see that (i) the standard deviation of Hubble residual values from NIR bands treated as standard candles are 0.007–0.042 mag smaller than those in the optical, (ii) the NIR mass step is not constrainable with the current sample size of 47 SNe Ia from DEHVILS, and (iii) Hubble residuals in the NIR and optical are correlated in the data. We test a few variations on the number and combinations of filters and data samples, and we observe that none of our findings or conclusions are significantly impacted by these modifications.
Astronomy & Astrophysics↗
A -type antiferromagnetic order in the Zintl-phase insulator EuZn 2 P 2
Zintl phases, containing strongly covalently bonded frameworks with separate ionically bonded ions, have emerged as a critical materials family in which to couple magnetism and strong spin-orbit coupling to drive diverse topological phases of matter. Here we report the single-crystal synthesis, magnetic, thermodynamic, transport, and theoretical properties of the Zintl compound EuZn 2 P 2 that crystallizes in the anti-La 2 O 3 (CaAl 2 Si 2 ) P-3m1 structure, containing triangular layers of Eu 2+ ions. In-plane resistivity measurements reveal insulating behavior with an estimated activation energy of E g = 0.11eV. Specific heat and magnetization measurements indicate antiferromagnetic ordering at T N = 23K. Curie-Weiss analysis of in-plane and out of plane magnetic susceptibility from T = 150 to 300 K yields p eff = 8.61 for μ 0 H⊥c and p eff = 7.74 for μ 0 H//c, close to the expected values for the 4f 7 J = S = 7/2 Eu 2+ ion and indicative of weak anisotropy. Below T N , a significant anisotropy of χ ⊥ /χ // ≈ 2.3 develops, consistent with A-type magnetic order as observed in isostructural analogs and as predicted by the density functional theory calculations reported herein. The positive Weiss temperatures of θ W =19.2K for μ 0 H⊥c and θ W =41.9K for μ 0 H//c show a similar anisotropy and suggest competing ferromagnetic and antiferromagnetic interactions. Comparing Eu magnetic ordering temperatures across trigonal EuM 2 X 2 (M= divalent metal, X= pnictide) shows that EuZn 2 P 2 exhibits the highest ordering temperature, with variations in T N correlating with changes in expected dipolar interaction strengths within and between layers and independent of the magnitude of electrical conductivity. These results provide experimental validation of the crystochemical intuition that the cation Eu 2+ layers and the anionic (M 2 X 2 ) 2– framework can be treated as electronically distinct subunits, enabling further predictive materials design.
36 MATERIALS SCIENCE↗
Helium escape from the Earth's atmosphere - The charge exchange mechanism revisited
We have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.
Lie-Svendsen, O.↗
Electron Stark Broadening Database for Atomic N, O, and C Lines
A database for efficiently computing the electron Stark broadening line widths for atomic N, O, and C lines is constructed. The line width is expressed in terms of the electron number density and electronatom scattering cross sections based on the Baranger impact theory. The state-to-state cross sections are computed using the semiclassical approximation, in which the atom is treated quantum mechanically whereas the motion of the free electron follows a classical trajectory. These state-to-state cross sections are calculated based on newly compiled line lists. Each atomic line list consists of a careful merger of NIST, Vanderbilt, and TOPbase line datasets from wavelength 50 nm to 50 micrometers covering the VUV to IR spectral regions. There are over 10,000 lines in each atomic line list. The widths for each line are computed at 13 electron temperatures between 1,000 K 50,000 K. A linear least squares method using a four-term fractional power series is then employed to obtain an analytical fit for each line-width variation as a function of the electron temperature. The maximum L2 error of the analytic fits for all lines in our line lists is about 5%.
Liu, Yen↗
A Semi-Empirical Density Law for Ternary, Homogeneous PuCl 3 /HCl/H 2 O Solutions
Nuclear material operations pose unique hazards that are not encountered in other chemical, energy, or manufacturing industries. One of these hazards is the potential for a nuclear criticality accident when handling fissile isotopes such as 235 U and 239 Pu. These hazards are particularly high when fissile material is dissolved in solution as the neutron behaviors of the system can change rapidly with the physical and chemical changes accessible in solution. Current estimates of solution density used for criticality safety are outdated and hinder fissile material handling. Developing new estimates for these safety calculations requires experimental characterization and the derivation of empirical density models. We have derived a density law describing PuCl 3 /HCl/H 2 O solutions from experimental data characterizing solution density. Density data was treated using a Pitzer-derived eight-parameter equation, defining density as a function of analyte concentrations, temperature, and interactions between these variables. The model is predictive across the concentration and temperature ranges from which it was derived. The potential effects of varying oxidation states of plutonium, which are easily accessible in aqueous media, on the bulk solution density of the ternary system were also investigated. The resulting Pitzer-derived density law was applied to a nuclear criticality safety model, and the impact of the experimental characterization of solution density relative to previous estimates was demonstrated to be significant and suggest that the current approach to estimating density in nuclear criticality safety calculations may lead to overly conservative controls.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
The role of drop velocity in statistical spray description
The justification for describing a spray by treating drop velocity as a random variable on an equal statistical basis with drop size was studied experimentally. A double-exposure technique using fluorescent drop photography was used to make size and velocity measurements at selected locations in a steady ethanol spray formed by a swirl atomizer. The size-velocity data were categorized to construct bivariate spray density functions to describe the spray immediately after formation and during downstream propagation. It was found that a statistical treatment of drop velocity was supported by the data. Spray density function shapes and modal characteristics depended strongly on position and the amount of droplet-gas interaction that had occurred. Bimodal density functions were formed by environmental interaction during downstream propagation. Large differences were also found between spatial mass density and mass flux size distributions at the same location.
Groeneweg, J. F.↗
Correlation of critical current density to quasi-biaxial texture and grain boundary cleanliness in fully dense Bi-2212 wires
The distinctive quasi-biaxial texture of Bi 2 Sr 2 CaCu 2 O x (Bi-2212) plays an important role in enabling high critical current density ($J_c$) in Bi-2212 round wires (RWs). Here we studied three over pressure heat treated wires with $J_c$ varying by a factor of ~10, all being fully dense. Using electron backscatter diffraction, we observed the differences in biaxial texture in these three wires. Transmission electron microscopy also revealed differences in grain boundary (GB) cleanliness and connectivity. These analyses showed that high $J_c$ is unambiguously correlated to the best biaxial texture, which is in turn correlated to slow cooling from the liquid melt into solid Bi-2212. However, at 4.2 K, there is a negligible difference in intragrain pinning in the three wires, suggesting that the $J_c$ variation by a factor of ~10 is primarily due to variable filament and intergrain connectivity. In this work, the principal determinants of intergrain connectivity is the quasi-biaxial texture and GB cleanliness. Overall, $J_c$ optimization of the Bi-2212 RW is a complex multi-variable process, but this study shows that maximizing the biaxial texture quality is an important first step in such an optimization process.
36 MATERIALS SCIENCE↗
Comprehensive proteomics analysis of stressed human islets identifies GDF15 as a target for type 1 diabetes intervention
Type 1 diabetes results from the progressive loss of beta cells, a process propagated by pro-inflammatory cytokine signaling that disrupts the balance between the expression of pro- and anti-apoptotic proteins. To identify such proteins, we performed comprehensive proteomics of human pancreatic islets treated with interleukin-1ß and interferon-?, leading to the identification of 11,325 proteins, of which 387 were significantly regulated by treatment. We then tested the function of growth/differentiation factor 15 (GDF15), which was repressed by the cytokine treatment. We found that GDF15 translation was blocked during inflammation, while the addition of exogenous GDF15 inhibited interleukin-1ß/interferon-?-induced apoptosis of human islets and a human beta-cell line. Furthermore, administration of GDF15 significantly decreased insulitis in NOD mice. Our approach provides a unique resource for the identification of the human islet proteins regulated by cytokines and was effective in discovering a potential target for type 1 diabetes therapy.
Nakayasu, Ernesto S.↗
Supported Electrophilic Organoruthenium Catalyst for the Hydrosilylation of Olefins
A series of supported electrophilic organoruthenium complexes has been synthesized via surface organometallic chemistry (SOMC) techniques and applied to the selective hydrosilylation of olefins. The air-sensitive 16e - complex Cp*RuMes(PCy 3 ) (1) (Cp* = pentamethylcyclopentadienyl, Mes = mesityl) was synthesized by the treatment of Cp*RuCl(PCy 3 ) with mesityl Grignard MesMgBr. This species was chemisorbed onto sulfated zirconia SO 4 /ZrO 2 , but the resulting material was inactive toward cyclohexene hydrosilylation with phenylsilane. Instead, Cp*RuMes(PCy 3 ) was treated with phenylsilane (PhSiH 3 ) to provide a ruthenium disilyl hydride complex Cp*RuH(SiH 2 Ph) 2 (PCy 3 ) (3), which was fully characterized by NMR spectroscopy and single-crystal X-ray diffraction. Grafting this species onto SO 4 /ZrO 2 resulted in the formation of phenylsilane along with the surface electrophilic species [Cp*RuH(R)(X-SiHPh)(PCy 3 )] (R = H, O 3 S-O or O 3 Zr-O; 4a, 4b, X = O 3 S-O, and O 3 Zr-O, respectively) as the major species. Material 4 was characterized via a combination of spectroscopic techniques including dynamic nuclear polarization (DNP)-enhanced solid-state NMR spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray absorption spectroscopy (XAS), and density function theory (DFT) calculations. Further, capping the remaining acid sites on 4 with Me 3 Si-SiMe 3 provides 5, which significantly reduces side reactions, such as olefin isomerization and silane redistribution. Catalyst 5 is a highly robust and selective hydrosilylation catalyst and can be recycled up to 5 times without significant diminishment of activity. Exclusive anti-Markovnikov regiochemistry, cis-addition selectivity, and the inactivity of secondary and tertiary silanes provide support for the proposed Glaser-Tilley mechanism involving cationic ruthenium silylene species analogous to homogeneous systems.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Two-stream modeling of plasmaspheric refilling
Plasmaspheric refilling on an L = 4 flux tube was studied by using a time-dependent, hydrodynamic plasmaspheric flow model in which the ion streams from the two hemispheres are treated as distinct fluids. In the model the continuity, momentum, and energy equations of a two-ion (O(+) and H(+)), quasi-neutral, currentless plasma are solved along a closed geomagnetic field line; diffusive equilibrium is not assumed. collisions between all stream pairs and with neutral species are included. The model includes a corotating, tilted dipole magnetic field and neutral winds. Ionospheric sources and sinks are accounted for in a self-consistent manner. Electrons are assumed to be heated by photoelectrons. The model flux tube extends from a 200-km altitude in one hemisphere to a 200-km altitude in the other hemisphere. Initially, the upwelling streams pass through each other practically unimpeded. When the streams approach the boundary in the conjugate ionosphere, a shock develops there, which moves upward and dissipates slowly; at about the same time a reverse shock develops in the hemisphere of origin, which moves upward. After about 1 hour, large shocks develop in each stream near the equator; these shocks move toward the equator and downward after crossing the equator. However, these shocks are probably artificial, because counterstreaming flows occur in each H(+) fluid, which the model can only handle by creating shocks.
Guiter, S. M.↗