Symmetric achromatic low-beta collider interaction region design concept
Not Available
Morozov, V. S.↗
SEARCH · Engineering Papers
Results for “Low”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Toward Understanding the Effect of Low-Activity Waste Glass Composition on Sulfur Solubility
The concentration of sulfur in nuclear waste glass melter feed must be maintained below the point where salt accumulates on the melt surface. The allowable concentrations may range from 0.37 to over 2.05 weight percent (of SO3 on a calcined oxide basis). If the amount of sulfur exceeds its tolerance level a molten salt will accumulate and upset melter operations and potentially shorten melter useful life. Therefore relatively conservative limits have been placed on sulfur loading in melter feed which in-turn significantly impacts the amount of glass that will be produced, in particular at the Hanford site. Crucible-scale sulfur solubility data and scaled melter sulfur tolerance data have been collected on simulated Hanford waste glasses over the last 15 years. These data were compiled and analyzed. A model was developed to predict the solubility of SO3 in glass based on 312 individual glass compositions. This model was shown to well represent the data, accounting for over 80% of the variation in data and was well validated. The model was also found to accurately predict the tolerance for sulfur in melter feed based on 19 scaled melter tests. The model is appropriate for control of waste glass processing which includes uncertainty quantification. The model also gives quantitative estimates of component concentration effects on sulfur solubility. The components that most increase sulfur solubility are Li2O > V2O5 ≈ TiO2 < CaO < P2O5 ≈ ZnO. The components that most decrease sulfur solubility are Cl > Cr2O3 > SiO2 ≈ ZrO2 > Al2O3.
Borosilicate↗
Low damage etching method of low-k material with a neutral beam for interlayer dielectric of semiconductor device
To reduce the cross-talk between nanoscale devices, low-k materials such as methyl silsesquioxane (MSQ), which is damaged easily during plasma etching, are introduced as an intermetallic dielectric material in addition to the use of copper as the conducting material for the reduction of parasitic resistance and capacitance. In this study, beam techniques such as neutral/ion beams were used in the etching of MSQ and the effect of these beam techniques on the reduction of the degradation of the MSQ were investigated. When MSQ was etched using the same CF{sub 4} etch gas at the similar etch rate as that used for conventional MSQ etching using inductively coupled plasmas (ICPs), the neutral/ion beam etching showed lower F contents and lower penetration depth of F, indicating decreased degradation by fluorination of MSQ during etching using the beam techniques. Especially, the neutral beam etching technique showed the lowest F contamination and the lower penetration depth of F among the etch methods. When the dielectric constant was measured after the etching of the same depth, the MSQ etched with the neutral beam showed the lowest change of the dielectric constant, while that etched using the ICP showed the highest change of dielectric constant. The lower degradation, that is, the lower chemical modification of MSQ material with the beam technique is believed to be related to the decreased concentration of radical species in the processing chamber reacting with the MSQ surface, while the lowest degradation using the neutral beam is believed to be due to the lower reaction rate of the reactive neutral compared to reactive ions.
36 MATERIALS SCIENCE↗
Optimization of a chlorine-based deep vertical etch of GaN demonstrating low damage and low roughness
The dry etching of GaN to form deep vertical structures is a critical step in many power device processes. To accomplish this, a chlorine and argon etch is investigated in detail to satisfy several criteria simultaneously such as surface roughness, crystal damage, and etch angle. Etch depths from 2 to 3.4 μm are shown in this paper. The authors investigate the formation of etch pits and its contributing factors. In addition, a nickel hard mask process is presented, with an investigation into the causes of micromasking and a pre-etch to prevent it. The authors show the results of optimized etch conditions resulting in a 2 μm deep, 0.831 nm rms roughness etch, with a 7.6° angle from vertical and low surface damage as measured by photoluminescence.
Tahhan, Maher↗
Enhanced MEA Performance for PEMFCs under Low Relative Humidity and Low Oxygen Content Conditions via Catalyst Functionalization
This work demonstrates that functionalizing annealed-Pt/Ketjen black EC300j (a-Pt/KB) and dealloyed-PtNi/Ketjen black EC300j (d-PtNi/KB) catalysts using p-phenyl sulfonic acid can effectively enhance performance in the membrane electrode assemblies (MEAs) of proton exchange membrane fuel cells (PEMFCs). The functionalization increased the size of both Pt and PtNi catalyst particles and resulted in the further leaching of Ni from the PtNi catalyst while promoting the formation of nanoporous PtNi nanoparticles. The size of the SO3H-Pt/KB and SO3H-PtNi/KB carbon-based aggregates decreased dramatically, leading to the formation of catalyst layers with narrower pore size distributions.MEA tests highlighted the benefits of the surface functionalization, in which the cells with SO3H-Pt/KB and SO3H-PtNi/KB cathode catalysts showed superior high current density performance under reduced RH conditions, in comparison with cells containing annealed Pt/KB (a-Pt/KB) and de-alloyed PtNi/KB (d-PtNi/KB) catalysts. The performance improvement was particularly evident when using reactant gases with low relative humidity, indicating that the hydrophilic functional groups on the carbon improved the water retention in the cathode catalyst layer. These results show a new avenue for enhancing catalyst performance for the next generation of catalytic materials for PEMFCs.
Xin, Le↗
Measurement of Ionic Conductivity and Electrode Polarization at Low Temperatures on 8YSZ by a DC Technique
Measurement of ionic conductivity and electrode polarization resistance on a 8YSZ sample with platinum paste electrodes was conducted using a DC method with high input impedance meters over a temperature range from 119°C to 589°C. Over the entire temperature range, the meter resistance was much larger than the sample resistance including the polarization resistance. At lower temperatures, a faraday cage was used to minimize noise. The measured polarization resistance was also verified using electrochemical impedance spectroscopy. Ionic conductivity of 8YSZ exhibited Arrhenius behavior with an activation energy of ~1.1 eV, in good agreement with the literature. In the low current regime, electrode kinetics could be described by the linearized form of the Butler-Volmer equation. At higher current densities, electrode kinetics exhibited Tafel behavior. The polarization resistance exhibited Arrhenius behavior with the activation energy ranging between 1.05 and 1.27 eV. The present work shows that electrode polarizations can be investigated using a DC method. The approach may allow study of different electrodes in various atmospheres using one sample.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Multigroup Radiation-Hydrodynamics with a High-Order, Low-Order Method
Recent efforts at Los Alamos National Laboratory to develop a moment-based, scale-bridging [or high-order (HO)–low-order (LO)] algorithm for solving large varieties of the transport (kinetic) systems have shown promising results. A part of our ongoing effort is incorporating this methodology into the framework of the Eulerian Applications Project to achieve algorithmic acceleration of radiationhydrodynamics simulations in production software. By starting from the thermal radiative transfer equations with a simple material-motion correction, we derive a discretely consistent energy balance equation (LO equation). We demonstrate that the corresponding LO system for the Monte Carlo HO solver is closely related to the original LO system without material-motion corrections. We test the implementation on a radiative shock problem and show consistency between the energy densities and temperatures in the HO and LO solutions as well as agreement with the semianalytic solution. We also test the approach on a more challenging two-dimensional problem and demonstrate accuracy enhancements and algorithmic speedups. This paper extends a recent conference paper by including multigroup effects.
42 ENGINEERING↗
Low-threshold supercontinuum generation in polycrystalline media
Until recently, the generation of super-octave continua in bulk materials at full repetition rates of femtosecond (fs) oscillators has been limited to a few special cases of Kerr lens mode-locked Ti:sapphire lasers. In 2019, we described a 3.4-octave fs source with 50 nJ pulse energy at the repetition rate of 78 MHz based on polycrystalline Cr:ZnS [Vasilyev et al. , Optica 6 , 126 ( 2019 ) OPTIC8 2334-2536 10.1364/OPTICA.6.000126 ]. Here we explain the mechanism of fs supercontinuum generation in transition-metal doped polycrystalline II-VI semiconductors at relatively low (nJ-level) pulse energy. We demonstrate that this new supercontinuum regime is enabled by a complex, yet well-reproducible, interplay between the effects arising from the third-order nonlinearity, the quadratic nonlinearities, and thermal optical effects in the medium. We also demonstrate the control of fs pulse propagation in disordered χ <#comment/> ( 2 ) media via the control of the material microstructure.
Vasilyev, Sergey (ORCID:0000000225203547)↗
Low thermal conductivity oxides
Oxides hold great promise as new and improved materials for thermal-barrier coating applications. The rich variety of structures and compositions of the materials in this class, and the ease with which they can be doped, allow the exploration of various mechanisms for lowering thermal conductivity. In this article, we review recent progress in identifying specific oxides with low thermal conductivity from both theoretical and experimental perspectives. We explore the mechanisms of lowering thermal conductivity, such as introducing structural/chemical disorder, increasing material density, increasing the number of atoms in the primitive cell, and exploiting the structural anisotropy. We conclude that further systematic exploration of oxide crystal structures and chemistries are likely to result in even further improved thermal-barrier coatings.
36 MATERIALS SCIENCE↗
Fermentation of low-cost sustainable feedstocks to produce low-greenhouse gas generating food proteins
Rapidly scaling and producing more protein from low-cost sustainable sugar sources allowed Perfect Day to meet short-term goals for regulatory testing and provided samples for industrial partners. LBNL and Perfect Day were able to identify ideal process chain to better demonstrate the far-reaching benefits of Perfect Day’s technology. Finally, the data generated from these scale-up experiments were used to further strengthen Perfect Day’s techno-economic and life-cycle analyses.
59 BASIC BIOLOGICAL SCIENCES↗
EAM-HLR: Enhancing the low-resolution E3SM Atmosphere Model with an ML model of high-low-resolution residual in convective processes
Focal Area(s). (2) Augment the low-resolution (LR) E3SM Atmosphere Model (EAM) with a machine learning (ML) column model of the residual in convective processes with respect to high-resolution (HR) and ultra-HR (UHR) simulation and observational data. Science Challenge. Substantially improve LR EAM climatology to increase multidecadal water cycle (WC) predictability.
54 ENVIRONMENTAL SCIENCES↗
OGLE-2018-BLG-1185b: A Low-mass Microlensing Planet Orbiting a Low-mass Dwarf
We report an analysis of the planetary microlensing event OGLE-2018-BLG-1185, which was observed by a large number of ground-based telescopes and by the Spitzer Space Telescope. The ground-based light curve indicates a low planet–host star mass ratio of q = (6.9 ± 0.2) × 10{sup −5}, which is near the peak of the wide-orbit exoplanet mass-ratio distribution. We estimate the host star and planet masses with a Bayesian analysis using the measured angular Einstein radius under the assumption that stars of all masses have an equal probability of hosting the planet. The flux variation observed by Spitzer is marginal, but still places a constraint on the microlens parallax. Imposing a conservative constraint that this flux variation should be Δf {sub Spz} < 4 instrumental flux units yields a host mass of M{sub host}=0.37{sub −0.21}{sup +0.35} M{sub ⊙} and a planet mass of m{sub p}=8.4{sub −4.7}{sup +7.9} M{sub ⊕}. A Bayesian analysis including the full parallax constraint from Spitzer suggests smaller host star and planet masses of M{sub host}=0.091{sub −0.018}{sup +0.064} M{sub ⊙} and m{sub p}=2.1{sub −0.4}{sup +1.5} M{sub ⊕}, respectively. Future high-resolution imaging observations with the Hubble Space Telescope or Extremely Large Telescope could distinguish between these two scenarios and help reveal the planetary system properties in more detail.
47 OTHER INSTRUMENTATION↗
Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. I. Classifying Low-mass Host Stars Observed during Campaigns 1–7
We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1–7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our Infrared Telescope Facility/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3–M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13 R{sub ⊙} (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.
79 ASTRONOMY AND ASTROPHYSICS↗
No Evidence for Feedback: Unexceptional Low-ionization Winds in Host Galaxies of Low Luminosity Active Galactic Nuclei at Redshift z ∼ 1
We study winds in 12 X-ray AGN host galaxies at z∼1. We find, using the low-ionization Fe ii λ2586 absorption in the stacked spectra, that the probability distribution function (PDF) of the centroid-velocity shift in AGNs has 50th (median), 16th, and 84th percentiles of (−87, −251, +86) km s{sup −1} respectively. The PDF of the velocity dispersion in AGNs has 50th (median), 84th, and 16th percentiles of (139, 253, 52) km s{sup −1} respectively. The centroid velocity and the velocity dispersions are obtained from a two-component (ISM+wind) absorption-line model. The equivalent width PDF of the outflow in AGNs has 50th (median), 84th, and 16th percentiles of (0.4, 0.8, 0.1) Å. There is a strong ISM component in Fe ii λ2586 absorption (with (1.2, 1.5, 0.8) Å, implying the presence of a substantial amount cold gas in the host galaxies. For comparison, star-forming and X-ray undetected galaxies at a similar redshift, matched roughly in stellar mass and galaxy inclination, have a centroid-velocity PDF with percentiles of (−74, −258, +90) km s{sup −1}, and a velocity-dispersion PDF with percentiles of (150, 259, 57) km s{sup −1}. Thus, winds in the AGN are similar to star formation-driven winds, and are too weak to escape and expel substantial cool gas from galaxies. Our sample doubles the previous sample of AGNs studied at z∼0.5 and extends the analysis to z∼1. A joint reanalysis of the z∼0.5 AGN sample and our sample yields consistent results to the measurements above.
79 ASTRONOMY AND ASTROPHYSICS↗
CO2 and CH4 Production in Low-Temperature Soil Incubations from Low and High Centered Polygons, Utqiagvik (Barrow), Alaska, 2012-2013
The dataset consists of respiration and methane production rates obtained from soil microcosm studies carried out under controlled temperature and incubation conditions. Soils represent the low- and high-centered polygon active layers and permafrost (when present) from the NGEE-Arctic Intensive Study Site 1. This dataset includes 1 .csv file, 1 .xlsx file, and 1 .pdf file. The Next-Generation Ecosystem Experiments: Arctic (NGEE Arctic), was a research effort to reduce uncertainty in Earth System Models by developing a predictive understanding of carbon-rich Arctic ecosystems and feedbacks to climate. NGEE Arctic was supported by the Department of Energy's Office of Biological and Environmental Research. The NGEE Arctic project had two field research sites: 1) located within the Arctic polygonal tundra coastal region on the Barrow Environmental Observatory (BEO) and the North Slope near Utqiagvik (Barrow), Alaska and 2) multiple areas on the discontinuous permafrost region of the Seward Peninsula north of Nome, Alaska. Through observations, experiments, and synthesis with existing datasets, NGEE Arctic provided an enhanced knowledge base for multi-scale modeling and contributed to improved process representation at global pan-Arctic scales within the Department of Energy's Earth system Model (the Energy Exascale Earth System Model, or E3SM), and specifically within the E3SM Land Model component (ELM).
54 ENVIRONMENTAL SCIENCES↗
Analysis for oxygen by gas-phase polarography at low temperatures and low pressures - a prototype assembly.
Oxygen analysis at low temperatures and pressures by gas phase polarography
OXYGEN APPARATUS↗
A low-torque support for low thrust measurement and attitude control testing
Gas bearing used as low-torque support system to study spacecraft attitude control systems in simulated space environment
ATTITUDE CONTROL↗