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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Creating molecular macrocycles for anion recognition

The creation and functionality of new classes of macrocycles that are shape persistent and can bind anions is described. The genesis of triazolophane macrocycles emerges out of activity surrounding 1,2,3-triazoles made using click chemistry; and the same triazoles are responsible for anion capture. Mistakes made and lessons learnt in anion recognition provide deeper understanding that, together with theory, now provides for computer-aided receptor design. The lessons are acted upon in the creation of two new macrocycles. First, cyanostars are larger and like to capture large anions. Second is tricarb, which also favors large anions but shows a propensity to self-assemble in an orderly and stable manner, laying a foundation for future designs of hierarchical nanostructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The Sixth Data Release of the Radial Velocity Experiment (RAVE). I. Survey Description, Spectra, and Radial Velocities

The Radial Velocity Experiment (Rave) is a magnitude-limited (9 < I < 12) spectroscopic survey of Galactic stars randomly selected in Earth’s southern hemisphere. The Rave medium-resolution spectra (R ~ 7500) cover the Ca-triplet region (8410–8795 Å). The sixth and final data release (DR6) is based on 518,387 observations of 451,783 unique stars. Rave observations were taken between 2003 April 12 and 2013 April 4. Here we present the genesis, setup, and data reduction of Rave as well as wavelength-calibrated and flux-normalized spectra and error spectra for all observations in Rave DR6. Furthermore, we present derived spectral classification and radial velocities for the Rave targets, complemented by cross-matches with Gaia DR2 and other relevant catalogs. A comparison between internal error estimates, variances derived from stars with more than one observing epoch, and a comparison with radial velocities of Gaia DR2 reveals consistently that 68% of the objects have a velocity accuracy better than 1.4 km s{sup –1}, while 95% of the objects have radial velocities better than 4.0 km s{sup –1}. Stellar atmospheric parameters, abundances and distances are presented in a subsequent publication. The data can be accessed via the Rave website (http://rave-survey.org) or the Vizier database.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Dynamical Avenues for Mercury’s Origin. I. The Lone Survivor of a Primordial Generation of Short-period Protoplanets

The absence of planets interior to Mercury continues to puzzle terrestrial-planet formation models, particularly when contrasted with the relatively high derived occurrence rates of short-period planets around Sun-like stars. Recent work proposed that the majority of systems hosting hot super-Earths attain their orbital architectures through an epoch of dynamical instability after forming in quasi-stable, tightly packed configurations. Isotopic evidence seems to suggest that the formation of objects in the super-Earth-mass regime is unlikely to have occurred in the solar system as the terrestrial-forming disk is thought to have been significantly mass deprived starting around 2 Myr after the formation of calcium-aluminum-rich inclusions—a consequence of either Jupiter’s growth or an intrinsic disk feature. Nevertheless, terrestrial-planet formation models and high-resolution investigations of planetesimal dynamics in the gas-disk phase occasionally find that quasi-stable protoplanets with mass comparable to that of Mars emerge in the vicinity of Mercury’s modern orbit. In this paper, we investigate whether it is possible for a primordial configuration of such objects to be cataclysmically destroyed in a manner that leaves Mercury behind as the sole survivor without disturbing the other terrestrial worlds. We use numerical simulations to show that this scenario is plausible. In many cases, the surviving Mercury analog experiences a series of erosive impacts, thereby boosting its Fe/Si ratio. A caveat of our proposed genesis scenario for Mercury is that Venus typically experiences at least one late giant impact.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

BAWLD-CH 4 : a comprehensive dataset of methane fluxes from boreal and arctic ecosystems

Methane (CH 4 ) emissions from the boreal and arctic region are globally significant and highly sensitive to climate change. There is currently a wide range in estimates of high-latitude annual CH 4 fluxes, where estimates based on land cover inventories and empirical CH 4 flux data or process models (bottom-up approaches) generally are greater than atmospheric inversions (top-down approaches). A limitation of bottom-up approaches has been the lack of harmonization between inventories of site-level CH 4 flux data and the land cover classes present in high-latitude spatial datasets. Here we present a comprehensive dataset of small-scale, surface CH 4 flux data from 540 terrestrial sites (wetland and non-wetland) and 1247 aquatic sites (lakes and ponds), compiled from 189 studies. The Boreal–Arctic Wetland and Lake Methane Dataset (BAWLD-CH 4 ) was constructed in parallel with a compatible land cover dataset, sharing the same land cover classes to enable refined bottom-up assessments. BAWLD-CH 4 includes information on site-level CH 4 fluxes but also on study design (measurement method, timing, and frequency) and site characteristics (vegetation, climate, hydrology, soil, and sediment types, permafrost conditions, lake size and depth, and our determination of land cover class). The different land cover classes had distinct CH 4 fluxes, resulting from definitions that were either based on or co-varied with key environmental controls. Fluxes of CH 4 from terrestrial ecosystems were primarily influenced by water table position, soil temperature, and vegetation composition, while CH 4 fluxes from aquatic ecosystems were primarily influenced by water temperature, lake size, and lake genesis. Models could explain more of the between-site variability in CH 4 fluxes for terrestrial than aquatic ecosystems, likely due to both less precise assessments of lake CH 4 fluxes and fewer consistently reported lake site characteristics. Analysis of BAWLD-CH 4 identified both land cover classes and regions within the boreal and arctic domain, where future studies should be focused, alongside methodological approaches. Overall, BAWLD-CH 4 provides a comprehensive dataset of CH 4 emissions from high-latitude ecosystems that are useful for identifying research opportunities, for comparison against new field data, and model parameterization or validation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Artifacts from manganese reduction in rock samples prepared by focused ion beam (FIB) slicing for X-ray microspectroscopy

The spatial distribution oftransition metal valence states is of broad interest in the microanalysis ofgeological and environmental samples. An example is rock varnish, a naturalmanganese (Mn)-rich rock coating, whose genesis mechanism remains a subjectof scientific debate. We conducted scanning transmission X-ray microscopywith near-edge X-ray absorption fine-structure spectroscopy (STXM-NEXAFS)measurements of the abundance and spatial distribution of different Mnoxidation states within the nano- to micrometer thick varnish crusts. Suchmicroanalytical measurements of thin and hard rock crusts require samplepreparation with minimal contamination risk. Focused ion beam (FIB) slicingwas used to obtain ~100–1000 nm thin wedge-shaped slices of thesamples for STXM, using standard parameters. Yet, while this preparationis suitable for investigating element distributions and structures in rocksamples, we observed artifactual modifications of the Mn oxidation states atthe surfaces of the FIB slices. Our results imply that the preparationcauses a reduction of Mn 4+ to Mn 2+ . We draw attention tothis issue, since FIB slicing, scanning electron microscopy (SEM) imaging,and other preparation and visualization techniques operating in thekilo-electron-volt range are well-established in geosciences, but researchersare often unaware of the potential for the reduction of Mn and possibly otherelements in the samples.

58 GEOSCIENCES↗
DOE OSTI2022

Grand Challenges: wind energy research needs for a global energy transition

Wind energy is anticipated to play a central role in enabling a rapid transition from fossil fuels to a system based largely on renewable power. For wind power to fulfill its expected role as the backbone – providing nearly half of the electrical energy – of a renewable-based, carbon-neutral energy system, critical challenges around design, manufacture, and deployment of land and offshore technologies must be addressed. During the past 3 years, the wind research community has invested significant effort toward understanding the nature and implications of these challenges and identifying associated gaps. The outcomes of these efforts are summarized in a series of 10 articles, some under review by Wind Energy Science (WES) and others planned for submission during the coming months. This letter explains the genesis, significance, and impacts of these efforts.

17 WIND ENERGY↗
DOE OSTI2022

Diversification of multipotential postmitotic mouse retinal ganglion cell precursors into discrete types

The genesis of broad neuronal classes from multipotential neural progenitor cells has been extensively studied, but less is known about the diversification of a single neuronal class into multiple types. We used single-cell RNA-seq to study how newly born (postmitotic) mouse retinal ganglion cell (RGC) precursors diversify into ~45 discrete types. Computational analysis provides evidence that RGC transcriptomic type identity is not specified at mitotic exit, but acquired by gradual, asynchronous restriction of postmitotic multipotential precursors. Some types are not identifiable until a week after they are generated. Immature RGCs may be specified to project ipsilaterally or contralaterally to the rest of the brain before their type identity emerges. Optimal transport inference identifies groups of RGC precursors with largely nonoverlapping fates, distinguished by selectively expressed transcription factors that could act as fate determinants. Our study provides a framework for investigating the molecular diversification of discrete types within a neuronal class.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1967

Organic geochemical studies. I.

Organic geochemical criteria for differentiating molecules originating from biological and nonbiological processes, noting isoprenoid hydrocarbons genesis problems

Calvin, M.↗
NASA NTRS1968

On the origin of the heavy nuclei.

Heavy nuclei origin based on empirical abundance distribution, discussing stellar, galactic and cosmic events for nuclear genesis

Amiet, J. P.↗
NASA NTRS1971

Lunar-Surface Closeup Stereoscopic Photography on the Sea of Tranquility (Apollo 11 Landing Site)

Analysis of returned lunar samples provides limited information about lunar geology. To obtain information about in-place lunar material, a closeup stereoscopic camera capable of photographing small-scale surface features was built and was used at the Apollo 11 landing site. Stereoscopic photographs were taken of surface areas relative to the lunar module, and the surfaces photographed were analyzed. The photographs are classified into five groups: soil disturbed by astronaut activities, generally undisturbed soil, loose aggregate surface material, crater bottoms with prominent glass deposits, and hard rock deposits. Glass deposits in the returned samples are described for comparison with the features observed in the photographs. The stereoscopic photographs were of outstanding quality and show the nature of lunar-surface material in detail. Lunar topography was reconstructed from the photographs with an analytical plotter. The photography results indicate that the closeup composition and genesis of lunar soil at the Apollo 11 landing site.

Greenwood, W. R.↗
NASA NTRS1971

Lunar Surface Closeup Stereoscopic Photography on the Ocean of Storms (Apollo 12 Landing Site)

To obtain information about in-place lunar rocks and soil, a closeup stereoscopic camera capable of photographing small scale surface features was used at the Apollo 12 landing site on the Ocean of Storms. Fifteen stereoscopic photograph pairs were obtained. The stereoscopic pairs were of excellent quality and showed the in-place lunar material in detail. The photographs were analyzed and the results compared with the results of the Apollo 12 core sample analysis and other investigations. Significant information about the physical composition and genesis of the lunar soil at the Apollo 12 landing site was obtained. The cohesive soil on the Ocean of Storms probably results from repetitive bombardment of basalt flows by meteorites over long periods of time.

Heiken, G.↗
NASA NTRS1972

Origin of quaternary basalts from the Black Rock Desert Region, Utah.

An evaluation has been made of the relative roles of fractional crystallization and crustal contamination in the genesis of basaltic magmas from the Black Rock Desert region in Utah. As a result, geochemical variations of these basalts have been defined as a function of their ages of eruption.

Condie, K. C.↗
NASA NTRS1971

Genetic implications of the shapes of Martian and lunar craters.

Discussion of the problem of lunar crater genesis in the light of some considerations prompted by lunar and Martian crater similarities. By analogy with the moon, Martian craters seem both to vary in initial shape according to the energy of the impact that formed them and to have been modified subsequently by endogenic and surface processes. A proposed model for the geologic development of large Martian and lunar craters outlines a time-dependent sequence of events. Craters which have undergone rapid isostatic adjustment on the moon have distinctive morphologies and occur preferentially along mare basin-upland margins.

Pike, R. J.↗
NASA NTRS1972

Geometric similitude of lunar and terrestrial craters.

Application of an elementary technique of dimensional analysis, that of testing for geometric similitude, suggests an impact genesis for most lunar craters. Geometrically similar phenomena fulfill four requirements: (1) log-log plots of paired descriptive variables are linear, (2) slopes of these plots equal ratios of the dimensions of the two variables, (3) intercepts of the plots are the same and (4) phenomena belong to the same general taxonomic group. Five topographic criteria are used to test lunar and terrestrial craters for geometric similitude: the variation of rim diameter with (1) interior depth, (2) exterior rim height, (3) exterior rim width and (4) rim crest circularity, and (5) variation of exterior rim height with crater depth. By all criteria, fresh bowl-shaped lunar craters between 10 m and 20 km in diameter are geometrically similar to fresh terrestrial meteorite craters and craters produced by chemical and nuclear explosives at shallow depths of burial. Most lunar craters exceeding 10-20 km in diameter fulfill only the last three criteria of similitude.

Pike, R. J.↗
NASA NTRS1971

The Mariner 6 and 7 pictures of Mars

A comprehensive set of high quality reproductions of the final, computer-processed television pictures of Mars is presented. The genesis and unique characteristics of the pictures are explained, interesting features are pointed out, and some indication of their significance in the history of Mars investigations is provided.

Collins, S. A., Jr.↗
NASA NTRS1972

The ages of lunar material from Fra Mauro, Hadley Rille, and Spur Crater.

Ar-40/Ar-39 dating techniques were applied to estimate the age of twelve crystalline and fragmented Fra Mauro rock samples and six Hadley Rille and Spur Crater rock samples provided by the Apollo 14 and 15 missions. Genesis histories of some associated lunar surface features are traced back on the basis of obtained rock age values.

Husain, L.↗