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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Temperature-dependent oxygen isotope fractionation in otoliths of juvenile Chinook salmon ( Oncorhynchus tshawytscha )

Oxygen thermometry has become a widely used technique for reconstructing thermal history in calcifying organisms but interpretation can be subject to predictive error from vital effects. To better understand these processes in Chinook salmon (Oncorhynchus tshawytscha) we experimentally constructed a temperature-dependent, otolith–water fractionation relationship for oxygen isotopes (δ 18 O) by rearing post-yolk absorptive juvenile fish at nominal temperatures from 6 to 21 °C. Temperature and otolith precipitation rate had significant effects on the otolith–water δ 18 O fractionation, but somatic growth rate did not. The slope of the δ 18 O fractionation equation also differed significantly from that of synthetic aragonite. Furthermore, our results suggest the expression of kinetic effects on δ 18 O fractionation in otoliths of Chinook salmon that are increasingly constrained at higher temperatures by other physical and physiological processes involved in mineral formation. Species-specific δ 18 O fractionation equations have considerable utility to reconstruct temperature history in Pacific salmon, but applications should recognize the potential for inferential uncertainty arising from interacting vital effects.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2021

Coral Oxygen Isotopic Records Capture the 2015/2016 El Niño Event in the Central Equatorial Pacific

Coral oxygen isotopes (δ^(18)O) from the central equatorial Pacific provide monthly resolved records of El Niño-Southern Oscillation activity over past centuries to millennia. However, calibration studies using in situ data to assess the relative contributions of warming and freshening to coral δ^(18)O records are exceedingly rare. Furthermore, the fidelity of coral δ^(18)O records under the most severe thermal stress events is difficult to assess. Here, we present six coral δ^(18)O records and in situ temperature, salinity, and seawater δ^(18)O data from Kiritimati Island (2°N, 157°W) spanning the very strong 2015/16 El Niño event. Local sea surface temperature (SST) anomalies of +2.4 ± 0.4°C and seawater δ^(18)O anomalies of −0.19 ± 0.02‰ contribute to the observed coral δ^(18)O anomalies of −0.58 ± 0.05‰, consistent with a ∼70% contribution from SST and ∼30% from seawater δ^(18)O. Our results demonstrate that Kiritimati coral δ^(18)O records can provide reliable reconstructions even during the largest class of El Niño events.

Oxygen isotope anomalies↗
DOE OSTI2020

Influence of Tabula Rasa on Process- and Light-Induced Degradation of Solar Cells Fabricated From Czochralski Silicon

Monocrystalline Si solar cells are fabricated from Czochralski (Cz) Si, which contains 10 17 –10 18 cm -3 oxygen atoms. Cz Si undergoes degradation during high-temperature thermal processing steps, such as dopant diffusion to form the p - n junction. This degradation in the bulk minority carrier lifetime can be related to the formation of oxygen precipitates. We found that a high-temperature annealing process known as tabula rasa (TR) not only mitigates process-induced degradation via oxygen precipitate nuclei dissolution, but also modifies subsequent light-induced degradation. We report on the bulk carrier lifetime of n - and p -type Cz Si after TR, which homogenizes the interstitial oxygen in the bulk Si to its monoatomic form in either an N 2 or O 2 environment. A control sample, which was not subjected to a TR processing step, experienced severe process-induced degradation during a boron emitter thermal budget as oxygen precipitates were formed in the Si bulk. These precipitates could be imaged using photoluminescence. Additionally, samples that underwent a TR processing step prior to the boron emitter thermal budget show efficient gettering of metallic impurities compared to the control sample, which showed a decline in the implied open-circuit voltage after the gettering step. Furthermore, modification of the interstitial oxygen bonding by TR had a strong effect on the light-induced degradation kinetics. Instead of a typically observed monotonic decrease, minority carrier lifetime increases first, followed by a nonmonotonic decrease over a ~20 h period. Finally, we conclude that by modifying the interstitial oxygen bonding via TR pretreatment, p -type Cz Si wafers become substantially resistant to harsh solar cell processes and strongly modified light-induced degradation, which would open alternative ways to mitigate this degradation mechanism.

14 SOLAR ENERGY↗
DOE OSTI2023

Sustainable and Green Production of Nanostructured Cellulose by a 2-Step Mechano-Enzymatic Process

Nanostructured cellulose (NC) represents an emerging sustainable biomaterial for diverse biotechnological applications; however, its production requires hazardous chemicals that render the process ecologically unfriendly. Using commercial plant-derived cellulose, an innovative strategy for NC production based on the combination of mechanical and enzymatic approaches was proposed as a sustainable alternative to conventional chemical procedures. After ball milling, the average length of the fibers was reduced by one order of magnitude (down to 10–20 μm) and the crystallinity index decreased from 0.54 to 0.07–0.18. Moreover, a 60 min ball milling pre-treatment followed by 3 h Cellic Ctec2 enzymatic hydrolysis led to NC production (15% yield). Analysis of the structural features of NC obtained by the mechano-enzymatic process revealed that the diameters of the obtained cellulose fibrils and particles were in the range of 200–500 nm and approximately 50 nm, respectively. Interestingly, the film-forming property on polyethylene (coating ≅ 2 μm thickness) was successfully demonstrated and a significant reduction (18%) of the oxygen transmission rate was obtained. Altogether, these findings demonstrated that nanostructured cellulose could be successfully produced using a novel, cheap, and rapid 2-step physico-enzymatic process that provides a potential green and sustainable route that could be exploitable in future biorefineries.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2008

Estimated Environmental Exposures for MISSE-3 and MISSE-4

Both modeling techniques and a variety of measurements and observations were used to characterize the environmental conditions experienced by the specimens flown on the MISSE-3 (Materials International Space Station Experiment) and MISSE-4 space flight experiments. On August 3, 2006, astronauts Jeff Williams and Thomas Reiter attached MISSE-3 and -4 to the Quest airlock on ISS, where these experiments were exposed to atomic oxygen (AO), ultraviolet (UV) radiation, particulate radiation, thermal cycling, meteoroid/space debris impact, and the induced environment of an active space station. They had been flown to ISS during the July 2006 STS-121 mission. The two suitcases were oriented so that one side faced the ram direction and one side remained shielded from the atomic oxygen. On August 18,2007, astronauts Clay Anderson and Dave Williams retrieved MISSE-3 and-4 and returned them to Earth at the end of the STS-118 mission. Quantitative values are provided when possible for selected environmental factors. A meteoroid/debris impact survey was performed prior to de-integration at Langley Research Center. AO fluences were calculated based on mass loss and thickness loss of thin polymeric films of known AO reactivity. Radiation was measured with thermoluminescent detectors. Visual inspections under ambient and "black-light" at NASA LaRC, together with optical measurements on selected specimens, were the basis for the initial contamination level assessment.

Pippin, Gary↗
NASA NTRS1984

Impact of lunar and planetary missions on the space station

The impacts upon the growth space station of several advanced planetary missions and a populated lunar base are examined. Planetary missions examined include sample returns from Mars, the Comet Kopff, the main belt asteroid Ceres, a Mercury orbiter, and a saturn orbiter with multiple Titan probes. A manned lunar base build-up scenario is defined, encompassing preliminary lunar surveys, ten years of construction, and establishment of a permanent 18 person facility with the capability to produce oxygen propellant. The spacecraft mass departing from the space station, mission Delta V requirements, and scheduled departure date for each payload outbound from low Earth orbit are determined for both the planetary missions and for the lunar base build-up. Large aerobraked orbital transfer vehicles (OTV's) are used. Two 42 metric ton propellant capacity OTV's are required for each the the 68 lunar sorties of the base build-up scenario. The two most difficult planetary missions (Kopff and Ceres) also require two of these OTV's. An expendable lunar lander and ascent stage and a reusable lunar lander which uses lunar produced oxygen are sized to deliver 18 metric tons to the lunar surface. For the lunar base, the Space Station must hangar at least two non-pressurized OTV's, store 100 metric tons of cryogens, and support an average of 14 OTV launch, return, and refurbishment cycles per year. Planetary sample return missions require a dedicated quarantine module.

Source record↗
DOE OSTI2020

Factors controlling the oxygen isotopic composition of lacustrine authigenic carbonates in Western China: implications for paleoclimate reconstructions

Abstract In the carbonate-water system, at equilibrium, the oxygen isotopic composition of carbonate is dependent not only on the temperature but also on the isotopic composition of host water in which the carbonate is formed. In this study, lake surface sediment and water samples were collected from 33 terminal lakes in Western China to evaluate controls on the oxygen isotopic composition of lacustrine authigenic carbonates (δ 18 O carb ) and its spatial distribution. Our results show that water oxygen isotopic composition (δ 18 O water ) rather than lake summer water temperature (T water ), is the main determinant of δ 18 O carb , irrespective of whether oxygen isotope equilibrium is achieved. There are significant linear correlations between δ 18 O carb and elevation, as well as that between δ 18 O carb and latitude for lakes located on the Tibetan Plateau. In Western China, the spatial distribution of δ 18 O carb is consistent with that of δ 18 O water , and is ultimately controlled by the isotopic composition of local precipitation (δ 18 O precipitation ) that depends on the source of water vapor. Therefore, changes in δ 18 O carb can be predominantly interpreted as variations of δ 18 O water , which in turn represent changes in δ 18 O precipitation for paleoclimate reconstructions in this region, and may be relevant to studies of other areas.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Triple oxygen isotope compositions of globally distributed soil carbonates record widespread evaporation of soil waters

The stable isotopic composition of pedogenic carbonates is central to many studies of past climate and topography, providing a basis for our understanding of Earth's terrestrial history. A core assumption of many applications of oxygen isotope values (δ 18 O) of pedogenic carbonate is that they reflect the δ 18 O value of precipitation (rain/snow). Here, this assumption is violated if soil carbonates form in evaporated soil waters. In this work, we develop a means to identify evaporation in ancient soils using the triple oxygen isotope composition ( 16 O- 17 O- 18 O) of pedogenic carbonates.

58 GEOSCIENCES↗
NASA NTRS1984

Interstellar O2. I - Abundance, excitation, and prospects for detection of O-16O-18 at radio frequencies

Molecular oxygen, O2, is predicted to be an important constituent of the interstellar gas, but it has not yet been detected in interstellar clouds. In this paper, the gas phase production and destruction of O2 are reconsidered, a non-LTE calculation of level populations at cloud temperatures is presented, and O2 column densities in diffuse and dark clouds are predicted. Ground-based detection of the 234 GHz line of O-16O-18 is shown to be feasible; if CO and O2 are comparable in abundance in clouds similar to the Taurus molecular cloud or in giant molecular clouds, the brightness temperature is predicted to be 0.1 K.

Black, J. H.↗
NASA NTRS2011

Hot, Massive Stars in I Zw 18

I Zw 18 is one of the most primitive blue, compact dwarf galaxies. The ionized gas in I Zw 18 has a low oxygen abundance (O approx.1/30 Osun) and nitrogen abundance (N-1/100 Nsun) (Pequignot 2008). We have obtained a far-UV spectrum of the northwest massive star cluster of I Zw 18 using Hubble's Cosmic Origins Spectrograph (COS). The spectrum is compatible with continuous star-formation over the past approx.10 Myr, and a very low metallicity, log Z/Zsun 1.7, although the stellar surface may be enhanced in carbon. Stellar wind lines are very weak, and the edge velocity of wind lines is very low (approx.250 km/s).

Heap, Sara R.↗
DOE OSTI2022

The effect of oxygen concentration on the speciation of laser ablated uranium

Abstract In order to model the fate and transport of particles following a nuclear explosion, there must first be an understanding of individual physical and chemical processes that affect particle formation. One interaction pertinent to fireball chemistry and resultant debris formation is that between uranium and oxygen. In this study, we use laser ablation of uranium metal in different concentrations of oxygen gas, either 16 O 2 or 18 O 2 , to determine the influence of oxygen on rapidly cooling uranium. Analysis of recovered particulates using infrared absorption and Raman spectroscopies indicate that the micrometer-sized particulates are predominantly amorphous UO x (am-UO x , where 3 ≤ x ≤ 4) and UO 2 after ablation in 1 atm of pure O 2 and a 1% O 2 /Ar mixture, respectively. Energy dispersive X-ray spectroscopy (EDS) of particulates formed in pure O 2 suggest an O/U ratio of ~ 3.7, consistent with the vibrational spectroscopy analysis. Both am-UO x and UO 2 particulates convert to α-U 3 O 8 when heated. Lastly, experiments performed in 18 O 2 environments show the formation of 18 O-substituted uranium oxides; vibrational frequencies for am-U 18 O x are reported for the first time. When compared to literature, this work shows that cooling timescales can affect the structural composition of uranium oxides (i.e., crystalline vs. amorphous). This indicator can be used in current models of nuclear explosions to improve our predicative capabilities of chemical speciation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1989

Isotopic study of oxygen diffusion in oxide coatings

Diffusion of oxygen in thin films of silicon dioxide was studied using oxygen isotopically enriched in oxygen of atomic mass 18 (O-18). This subject is of interest because thin films of dielectrics such as SiO2 are proposed for use as a protective coatings for solar mirrors in low Earth orbit, which is a strongly oxidizing environment. Films of this material were prepared with a direct current magnetron using reactive sputtering techniques. To produce (O-18)- enriched SiO2, a standard 3.5-in.-diameter silicon wafer was reactively sputtered using (O-18)-enriched (95 percent) oxygen as the plasma feed gas. The films were characterized using Rutherford backscattering and Secondary Ion Mass Spectrometer (SIMS) to establish stoichiometry and purity. Subsequently, the films were exposed to an air-derived oxygen plasma in a standard laboratory plasma reactor for durations of up to 10 hr. The concentration ratio of O-16 as a function of depth was determined using SIMS profiling and compared to a baseline, nonplasma exposed sample. A value for the diffusivity of oxygen near the surface of these films was obtained and found to be about 10(-15)sq cm/sec.

Gulino, Daniel A.↗
DOE OSTI2023

The Zonal Patterns in Late Quaternary Tropical South American Precipitation

Speleothem oxygen isotope records (δ 18 O) of tropical South American rainfall in the late Quaternary show a zonal “South American Precipitation Dipole” (SAPD). The dipole is characterized by opposing east-west precipitation anomalies compared to the present—wetter in the east and drier in the west at the mid-Holocene (~7 ka), and drier in the east and wetter in the west at the Last Glacial Maximum (~21 ka). However, the SAPD remains enigmatic because it is expressed differently in western versus eastern δ18O records and isotope-enabled climate model simulations usually misrepresent the magnitude and/or spatial pattern of δ 18 O change. Here, we address the SAPD enigma in two parts. First, we re-interpret the δ 18 O data to account for upwind rainout effects that are known to be pervasive in tropical South America, but are not always considered in Quaternary paleoclimate studies. Our revised interpretation reconciles the δ 18 O data with cave infiltration and other proxy records, and indicates that the centroid of tropical South American rainfall has migrated zonally over time. Second, using an energy balance model of tropical atmospheric circulation, we hypothesize that zonal migration of the precipitation centroid can be explained by regional energy budget shifts, such as changing Saharan albedo associated with the African Humid Period, that have not been modeled in previous SAPD studies. This hypothesis of a migrating precipitation centroid presents a new framework for interpreting δ18O records from tropical South America and may help explain the zonal rainfall anomalies that predate the late Quaternary.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

A stable isotope record of late Quaternary hydrologic change in the northwestern Brooks Range, Alaska (eastern Beringia)

A submillennial-resolution record of lake water oxygen isotope composition (δ 18 O) from chironomid head capsules is presented from Burial Lake, northwest Alaska. The record spans the Last Glacial Maximum (LGM; ~20–16k cal a bp) to the present and shows a series of large lake δ 18 O shifts (~5‰). Relatively low δ 18 O values occurred during a period covering the LGM, when the lake was a shallow, closed-basin pond. Higher values characterize deglaciation (~16–11.5k cal a Bp) when the lake was still closed but lake levels were higher. A rapid decline between ~11 and 10.5k cal a Bp indicates that lake levels rose to overflowing. Lake δ 18 O values are interpreted to reflect the combined effects of changes in lake hydrology, growing season temperature and meteoric source water as well as large-scale environmental changes impacting this site, including opening of the Bering Strait and shifts in atmospheric circulation patterns related to ice-sheet dynamics. The results indicate significant shifts in precipitation minus evaporation across the late Pleistocene to early Holocene transition, which are consistent with temporal patterns of vegetation change and paludification. This study provides new perspectives on the paleohydrology of eastern Beringia concomitant with human migration and major turnover in megafaunal assemblages.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1992

Intensified array camera imaging of solid surface combustion aboard the NASA Learjet

An intensified array camera was used to image weakly luminous flames spreading over thermally thin paper samples in a low gravity environment aboard the NASA-Lewis Learjet. The aircraft offers 10 to 20 sec of reduced gravity during execution of a Keplerian trajectory and allows the use of instrumentation that is delicate or requires higher electrical power than is available in drop towers. The intensified array camera is a charge intensified device type that responds to light between 400 and 900 nm and has a minimum sensitivity of 10(exp 6) footcandles. The paper sample, either ashless filter paper or a lab wiper, burns inside a sealed chamber which is filled with 21, 18, or 15 pct. oxygen in nitrogen at one atmosphere. The camera views the edge of the paper and its output is recorded on videotape. Flame positions are measured every 0.1 sec to calculate flame spread rates. Comparisons with drop tower data indicate that the flame shapes and spread rates are affected by the residual g level in the aircraft.

Weiland, Karen J.↗