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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

hiss, a new tool for H i stacking: application to NIBLES spectra

Abstract H i stacking has proven to be a highly effective tool to statistically analyse average H i properties for samples of galaxies which may or may not be directly detected. With the plethora of H i data expected from the various upcoming H i surveys with the SKA Precursor and Pathfinder telescopes, it will be helpful to standardize the way in which stacking analyses are conducted. In this work we present a new python-based package, hiss, designed to stack H i (emission and absorption) spectra in a consistent and reliable manner. As an example, we use hiss to study the H i content in various galaxy sub-samples from the NIBLES survey of SDSS galaxies which were selected to represent their entire range in total stellar mass without a prior colour selection. This allowed us to compare the galaxy colour to average H i content in both detected and non-detected galaxies. Our sample, with a stellar mass range of $10^8 \lt {{ M}}_\star \, (\text{M}_\odot) \lt 10^{12}$, has enabled us to probe the H i-to-stellar mass gas fraction relationship more than half an order of magnitude lower than in previous stacking studies.

Healy, J.↗
DOE OSTI2016

Structural and optical studies of hydrothermally synthesized MoS{sub 2} nanostructures

Transition-metal dichalcogenides like molybdenum disulphide have intrigued intensive interest as two-dimensional (2D) materials beyond extensively studied graphene due to their unique electronic and optical properties. Here we report the hydrothermal synthesis of MoS{sub 2} nanostructures without the addition of any surfactants. The structural and optical properties of the synthesized samples were characterized by various techniques, including X-ray diffraction (XRD), UV-Vis absorption, photoluminescence (PL), and Raman analysis. XRD and Raman spectroscopic studies confirm the formation of hexagonal phase and well ordered stacking of S-Mo-S layers. The increased lattice parameters of MoS{sub 2} samples are due to the stress or strain induced bending and folding of the layers. The synthesized MoS{sub 2} nanostructures shows a large optical absorption in 300-700 nm region and strong luminescence at 640 nm. In addition, the optical results demonstrates the quantum confinement in layered d-electron material MoS{sub 2} that can lead to engineer its various properties for electronic and optoelectronic applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Pacific Northwest National Laboratory Facility Radionuclide Emissions Units and Sampling Systems

Battelle–Pacific Northwest Division operates numerous research and development (R&D) laboratories in Richland, WA, including those associated with Pacific Northwest National Laboratory (PNNL) on the U.S. Department of Energy (DOE)’s Hanford Site and PNNL Site that have the potential for radionuclide air emissions. The National Emission Standard for Hazardous Air Pollutants (NESHAP 40 CFR 61, Subparts H and I) requires an assessment of all emission units that have the potential for radionuclide air emissions. Potential emissions are assessed annually by PNNL staff members. Sampling, monitoring, and other regulatory compliance requirements are designated based upon the potential-to-emit dose criteria found in the regulations. The purpose of this document is to describe the facility radionuclide air emission sampling program and provide current and historical facility emission unit system performance, operation, and design information. For sampled systems, a description of the buildings, exhaust units, control technologies, and sample extraction details is provided for each registered emission unit. Additionally, applicable stack sampler configuration drawings, figures, and photographs are provided. Deregistered emission unit details are provided as necessary for up to 5 years post closure.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRSDate not supplied

The Scientific Significance of Potential Samples From the Jezero Crater Rim

The Mars 2020 Perseverance rover has been exploring Jezero crater, Mars to characterize the geology,assess the potential for rocks to represent ancient habitable environments and/or preserve biosignatures, and collect a suite of scientifically compelling samples for return to Earth (Farleyet al.,2020).Thus far, Perseverance has collected samples that represent the diversity of igneous materials encountered on the crater floor and a suite of aqueously deposited sedimentary rocks from the fanand margin units(Simon et al., 2023; Bosak et al., 2024). When the rover ascendsthe crater rimit will encounter rocktypesthat are not included in the current sample cache. These include rocks fromthe Noachian whose mineralogical, geochemical, and geochronological recordswould greatly expand our understanding of early Mars. Some of the exposures are understood to come from subsurface aquifers that may represent the most ancient potentially habitablesubsurfaceenvironmentson Mars(Ehlmann et al., 2024). Samples ofthese rocks will add uniquescientific value tothe sample cache and to the Mars sample returnprogramby addressing outstanding questions in Mars science including potential habitability and how the climate and the interior of the planet evolved through time.

Mars 2020↗
NASA NTRS1985

Diffusion welding of Cassegrainian concentrator cell stack assemblies

Development of a procedure to join the components of the Cassegrainian concentrator photovoltaic cell stack assembly was studied. Diffusion welding was selected as the most promising process, and was concentrated on exclusively. All faying surfaces were coated with silver to promote welding. The first phase of the study consisted of developing the relationship between process parameters and joint strength using silver plated steel samples and an isostatic pressure system. In the second phase, mockups of the cell stack assembly were welded in a hot isostatic press. Excellent joint strength was achieved with parameters of 350 C and 10 ksi, but the delicate GaAs component could not survive the welding cycle without cracking. The tendency towards cracking was found to be affected by both temperature and pressure. Further work will be required in the future to solve this problem.

Gangl, K. J.↗
DOE OSTI2016

UV light induced insulator-metal transition in ultra-thin ZnO/TiO{sub x} stacked layer grown by atomic layer deposition

In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1–7) of ZnO/TiO{sub x} layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O{sub 2} and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ∼ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent conducting oxides.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Rapid determination of 226 Ra in emergency urine samples

A new method has been developed at the Savannah River National Laboratory (SRNL) that can be used for the rapid determination of 226 Ra in emergency urine samples following a radiological incident. If a radiological dispersive device event or a nuclear accident occurs, there will be an urgent need for rapid analyses of radionuclides in urine samples to ensure the safety of the public. Large numbers of urine samples will have to be analyzed very quickly. This new SRNL method was applied to 100 mL urine aliquots, however this method can be applied to smaller or larger sample aliquots as needed. The method was optimized for rapid turnaround times; urine samples may be prepared for counting in <3 h. A rapid calcium phosphate precipitation method was used to pre-concentrate 226 Ra from the urine sample matrix, followed by removal of calcium by cation exchange separation. A stacked elution method using DGA Resin was used to purify the 226 Ra during the cation exchange elution step. This approach combines the cation resin elution step with the simultaneous purification of 226 Ra with DGA Resin, saving time. 133 Ba was used instead of 225 Ra as tracer to allow immediate counting; however, 225 Ra can still be used as an option. The rapid purification of 226 Ra to remove interferences using DGA Resin was compared with a slightly longer Ln Resin approach. A final barium sulfate micro-precipitation step was used with isopropanol present to reduce solubility; producing alpha spectrometry sources with peaks typically <40 keV FWHM (full width half max). This new rapid method is fast, has very high tracer yield (>90 %), and removes interferences effectively. The sample preparation method can also be adapted to ICP-MS measurement of 226 Ra, with rapid removal of isobaric interferences.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2020

Spin-Dependent Thermoelectric Power of Nanoislands

The Seebeck effect explains the generation of electric voltage as a result of a temperature gradient. Its efficiency, defined as the ratio of the generated electric voltage to the temperature difference, is sensitive to local inhomogeneities that alter the scattering rate and the density of the conduction electrons. Spin-polarized Seebeck tunneling generates a distinct thermovoltage in spin-up and spin-down charge transport channels, which, as a key to spin caloritronics, focuses on transport phenomena related to spin and heat. Here, we report spatially resolved measurement of the spin-dependent thermovoltage in a tunneling junction formed by ferromagnetic Co nanoislands and a Ni tip using spin-dependent scanning tunneling thermovoltage microscopy (SP-STVthM). We resolve the nanoscale thermoelectric powers with respect to spin polarization, nanoisland size, stacking order of Co layers on a Cu substrate, and local sample heterogeneities. The observed thermally generated spin voltages are supported by first-principles and model calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Manganese-rich high entropy oxides for lithium-ion batteries:materials design approaches to address voltage fade

Lithium- and manganese-rich oxides are of interest as lithium-ion battery cathode materials as Mn is earth abundant, low cost, and can deliver high capacity. Herein, a high entropy strategy was used to prepare Mn rich high entropy oxide (HEO) materials by including four additional metals (Ni, Co, Fe and Al) in the compositions using a mild co-precipitation method. Two HEOs (Li x Ni 0.1 Mn 0.6 Co 0.1 Al 0.1 Fe 0.1 O y , where x = 1.5 for HEO-L and x = 0.5 for HEO-H) with layered and spinel-layered hybrid structures were investigated where the morphology, elemental composition, structure, atomic level phase distribution, and electrochemistry were determined. The HEO-L samples involve a Li 2 TMO 3 layered structure with ~39% stacking faults. HEO-H is a hybrid structure comprised of 80 wt% spinel and 20 wt% LiMO 2 layered structure. The high entropy manganese-rich HEO-L showed higher capacity and 93% retention of the average voltage after 100 cycles while HEO-H showed higher capacity retention and near 100% average voltage retention. Finally, operando X-ray absorption spectroscopy revealed that the Ni, Co, and Mn are redox active in both materials while the Fe center remains at the Fe 3+ oxidation state throughout cycling, where the changes in the oxidation states for both materials during discharge were consistent with the delivered electrochemical capacity rationalizing the observed electrochemistry.

25 ENERGY STORAGE↗
DOE OSTI2014

Influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures and lattice defects accumulation

The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Masses of Sunyaev-Zel’dovich galaxy clusters detected by the Atacama Cosmology Telescope: Stacked lensing measurements with Subaru HSC year 3 data

We present a stacked lensing analysis of 96 galaxy clusters selected by the thermal Sunyaev-Zel’dovich (SZ) effect in maps of the cosmic microwave background (CMB). We select foreground galaxy clusters with a 5 σ -level SZ threshold in CMB observations from the Atacama Cosmology Telescope, while we define background source galaxies for the lensing analysis with secure photometric redshift cuts in Year 3 data of the Subaru Hyper Suprime Cam survey. We detect the stacked lensing signal in the range of 0.1 < R [ h - 1 Mpc ] < 100 in each of three cluster redshift bins, 0.092 < z ≤ 0.445 , 0.445 < z ≤ 0.695 , and 0.695 < z ≤ 1.180 , with 32 galaxy clusters in each bin. The cumulative signal-to-noise ratios of the lensing signal are 14.6, 12.0, and 6.6, respectively. Using a halo-based forward model, we then constrain statistical relationships between the mass inferred from the SZ observation (i.e. SZ mass) and the total mass derived from our stacked lensing measurements. At the average SZ mass in the cluster sample ( 2.1 - 2.4 × 10 14 h - 1 M ⊙ ), our likelihood analysis shows that the average total mass differs from the SZ counterpart by a factor of 1.3 ± 0.2 , 1.6 ± 0.2 , and 1.6 ± 0.3 (68%) in the aforementioned redshift ranges, respectively. Our limits are consistent with previous lensing measurements, and we find that the cluster modeling choices can introduce a 1 σ -level difference in our parameter inferences.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Crack Identification and Characterization in Deformed Nb3Sn Rutherford Cable Stacks Using Machine Learning

An investigation of instance segmentation of cracks in Nb3Sn 4-stack 40-strand Rutherford cables using machine learning is presented. Three samples were uniaxially and biaxially loaded before metallographic inspections were performed. The Mask R-CNN model was used in the Detectron2 framework with pre-trained weights but fine-tuned to detect and segment cracks. The model detected cracks with bounding box and mask average precisions (AP) of 42.8 and 27.9, respectively, and was used for instance segmentation of all cracks in the three samples. More cracks were found in the sample pre-loaded along the z-axis (i.e., along the cable length). Pre-loading along the x-axis (i.e., on the cables edges) reduced the number of cracks and changed the crack orientation distribution, away from being highly aligned with the y-axis (i.e., normal to the cables broad faces), i.e., the direction with the highest applied load. Fine-tuning of the Segment Anything Model (SAM) was also studied but performed poorly without human-provided prompts. However, the zero-shot capability of SAM showed high promises to accelerate the image annotation process for applications beyond this study.

Croteau, Jean-Francois↗
DOE OSTI2016

TH-AB-209-04: 3D Light Sheet Luminescence Imaging with Cherenkov Radiation

Purpose: To recover a three-dimensional density distribution of luminescent molecular probes located several centimeters deep within a highly scattering tissue. Methods: We developed a novel sheet beam Cherenkov-excited luminescence scanned imaging (CELSI) methodology. The sample was irradiated by a horizontally oriented, vertically scanned 6 MV X-ray sheet beam (200mm × 5mm, 0.2mm vertical step) from a radiotherapy linear accelerator. The resulting Cherenkov light emission – and thus luminescent probe excitation – occurred exclusively along the irradiation plane due to a short diffusion path of secondary particles and Cherenkov photons. Cherenkov-excited luminescence was detected orthogonally to the sheet beam by gated, intensified charge coupled device camera. Analogously to light sheet microscopy, a series of luminescence images was taken for varied axial positions (depths) of the Cherenkov light sheet in sample. Knowledge of the excitation plane position allowed a 3D image stack deconvolution and depth-variant attenuation correction. The 3D image post-processing yielded a true spatial density distribution of luminescent molecules in highly scattering tissue. Results: We recovered a three-dimensional shape and position of 400 µL lesion-mimicking phantom tubes containing 25 µM solution of PtG4 molecular probe from 3 centimeter deep tissue-like media. The high sensitivity of CELSI also allowed resolving 100 micron capillaries of test solution. Functional information of partial oxygen pressure at the site of PtG4 molecular probe was recovered from luminescence lifetime CELSI. Finally, in-vivo sheet beam CELSI localized milimeter-sized PtG4-labelled tumor phantoms in multiple biological objects (hairless mice) from single scan. Conclusion: Presented sheet beam CELSI technique greatly extended the useful depth range of luminescence molecular imaging. More importantly, the light sheet microscopy approach was successfully adapted to CELSI, providing means to recover a completely attenuation-corrected 3D image of luminescent probe distribution. Gated CELSI acquisition yielded functional information of a spatially resolved oxygen concentration map of deep lying targets. This work was supported by NIH research grant R01CA109558 and R21EB017559, as well as by Pilot Grant Funds from the Norris Cotton Cancer Center.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Rest-frame optical emission lines in z ∼ 3.5 Lyman-break-selected galaxies: The ubiquity of unusually high [O III]/Hβ ratios at 2 Gyr

We present K-band spectra of rest-frame optical emission lines for 24 star-forming galaxies at z ∼ 3.2–3.7 using MOSFIRE on the Keck I telescope. Strong rest-frame optical [O iii] and Hβ emission lines were detected in 18 Lyman break galaxies (LBGs). The median flux ratio of [O iii]λ5007 to Hβ is 5.1{sub −0.5}{sup +0.5}. This is a factor of 5–10 times higher than in local galaxies with similar stellar masses. None of our sources are detected in deep X-ray stacks, ruling out significant contamination by active galactic nuclei. Combining our sample with a variety of LBGs from the literature, including 49 galaxies selected in a very similar manner, we find a high median ratio of [O iii]/Hβ = 4.8{sub −1.7}{sup +0.8}. This high ratio seems to be a ubiquitous feature of z ∼ 3–4 LBGs, very different from typical local star-forming galaxies at similar stellar masses. The only comparable systems at z ∼ 0 are those with similarly high specific star formation rates (SSFRs), though ∼5 times lower stellar masses. High SSFRs may result in a higher ionization parameter, higher electron density, or harder ionizing radiation, which, combined different elemental abundances, result in a much higher [O iii]/Hβ line ratio. This implies a strong relation between a global property of a galaxy, the SSFR, and the local conditions of ISM in star-forming regions.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2024

Masses of Sunyaev-Zel’dovich Galaxy Clusters Detected by the Atacama Cosmology Telescope: Stacked Lensing Measurements with Subaru HSC Year 3 Data

We present a stacked lensing analysis of 96 galaxy clusters selected by the thermal Sunyaev-Zel’dovich (SZ) effect in maps of the cosmic microwave background (CMB). We select foreground galaxy clusters with a 5σ-level SZ threshold in CMB observations from the Atacama Cosmology Telescope, while we define background source galaxies for the lensing analysis with secure photometric redshift cuts in Year 3 data of the Subaru Hyper Suprime Cam survey. We detect the stacked lensing signal in the range of 0.1 < R[h −1 Mpc] < 100 in each of three cluster redshift bins, 0.092 < z ≤ 0.445, 0.445 < z ≤ 0.695, and 0.695 < z ≤ 1.180, with 32 galaxy clusters in each bin. The cumulative signal-to-noise ratios of the lensing signal are 14.6, 12.0, and 6.6, respectively. Using a halo-based forward model, we then constrain statistical relationships between the mass inferred from the SZ observation (i.e. SZ mass) and the total mass derived from our stacked lensing measurements. At the average SZ mass in the cluster sample (2.1 − 2.4 × 10 14 h −1 M⊙), our likelihood analysis shows that the average total mass differs from the SZ counterpart by a factor of 1.3 ± 0.2, 1.6 ± 0.2, and 1.6 ± 0.3 (68%) in the aforementioned redshift ranges, respectively. Our limits are consistent with previous lensing measurements, and we find that the cluster modeling choices can introduce a 1σ-level difference in our parameter inferences.

Masato Shirasaki↗
DOE OSTI2015

Relationship between star formation rate and black hole accretion at z=3: the different contributions in quiescent, normal, and starburst galaxies

We investigate the co-evolution of the black hole accretion rate (BHAR) and the star formation rate (SFR) in 1.5<z<2.5 galaxies displaying a greater diversity of star-forming properties compared to previous studies. We combine X-ray stacking and far-IR photometry of stellar mass-limited samples of normal star-forming, starburst, and quiescent/quenched galaxies in the COSMOS field. We corroborate the existence of a strong correlation between BHAR (i.e., the X-ray luminosity, L{sub X}) and stellar mass (M{sub *}) for normal star-forming galaxies, though we find a steeper relation than previously reported. We find that starbursts show a factor of three enhancement in BHAR compared to normal SF galaxies (against a factor of six excess in SFR), while quiescents show a deficit of a factor times 5.5 at a given mass. One possible interpretation of this is that the starburst phase does not coincide with cosmologically relevant BH growth, or that starburst-inducing mergers are more efficient at boosting SFR than BHAR. Contrary to studies based on smaller samples, we find that the BHAR/SFR ratio of main-sequence (MS) galaxies is not mass invariant, but scales weakly as M{sub ∗}{sup 0.43±0.09}, implying faster BH growth in more massive galaxies at z∼2. Furthermore, BHAR/SFR during the starburst is a factor of two lower than in MS galaxies, at odds with the predictions of hydrodynamical simulations of merger galaxies that foresee a sudden enhancement of L{sub X}/SFR during the merger. Finally, we estimate that the bulk of the accretion density of the universe at z∼2 is associated with normal star-forming systems, with only ∼6(±1)% and ∼11(±1)% associated with starburst and quiescent galaxies, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Investigation of long-term light stability of negative charge injected into oxide-nitride-oxide passivation stack of crystalline silicon solar cells

A negatively charged oxide-nitride-oxide stack for field-effect passivation of crystalline silicon solar cells is discussed. The negative charge was injected into the stack by a plasma charge injection technology. Charge stability was studied by exposing samples to AM1.5 simulation visible light and full-spectrum light at temperatures ranging from 55 to 78 °C for up to 300 h. Charge injection and loss were quantified based on shifts in the flatband voltage of capacitance–voltage curves measured with a mercury probe. The most probable mechanism of charge loss was found to be diffusion of negative charged hydrogen atoms through nitride and bottom oxide. The optimum recipe for each layer of the stack was investigated to minimize the loss of injected charge. The flatband voltage decay of the optimized stack was found to fit a power-law trend, suggesting the dispersive transport of hydrogen atoms with a dispersion parameter of ~0.06–0.07. The optimized stack is projected to maintain a negative charge density of about 3.6 × 10 12 cm –2 or more after 25 years of field operation in an environment such as Arizona, which would be sufficient for field-effect passivation under one-sun illumination. Furthermore, the high stability of the negative injected charge makes the plasma charging technology a safer and lower cost alternative to Al 2 O 3 -passivation technology commonly used to passivate p-type surfaces.

14 SOLAR ENERGY↗