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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Variations in the Peak Position of the 6.2 micron Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population

This paper presents the results of an investigation of the molecular characteristics that underlie the observed peak position and profile of the nominal 6.2 micron interstellar emission band generally attributed to the CC stretching vibrations of polycyclic aromatic hydrocarbons (PAHs). It begins with a summary of recent experimental and theoretical studies ofthe spectroscopic properties of large (>30 carbon atoms) PAH cations as they relate to this aspect of the astrophysical problem. It then continues with an examination of the spectroscopic properties of a number of PAH variants within the context of the interstellar 6.2 micron emission, beginning with a class of compounds known as polycyclic aromatic nitrogen heterocycles (PANHs; PAHs with one or more nitrogen atoms substituted into their carbon skeleton). In this regard, we summarize the results of recent relevant experimental studies involving a limited set of small PANHs and their cations and then report the results of a comprehensive computational study that extends that work to larger PANH cations including many nitrogen-substituted variants of coronene(+) (C24H12(+)), ovalene(+) (C32H14(+)), circumcoronene(+) (C54H18(+)), and circum-circumcoronene(+) (C96H24(+)). Finally, we report the results of more focused computational studies of selected representatives from a number of other classes of PAH variants that share one or more of the key attributes of the PANH species studied. These alternative classes of PAH variants include (1) oxygen- and silicon-substituted PAH cations; (2) PAH-metal ion complexes (metallocenes) involving the cosmically abundant elements magnesium and iron; and (3) large, asymmetric PAH cations. Overall, the studies reported here demonstrate that increasing PAH size alone is insuEcient to account for the position of the shortest wavelength interstellar 6.2 micron emission bands, as had been suggested by earlier studies. On the other hand, this work reveals that substitution of one or more nitrogen atoms within the interior of the carbon skeleton of a PAH cation induces a significant blueshift in the position of the dominant CC stretching feature of these compounds that is suf6cient to account for the position of the interstellar bands. Subsequent studies of the effects of substitution by other heteroatoms (O and Si), metal ion complexation (Fe(+), Mg(+), and Mg(2+)), and molecular symmetry variation-all of which fail to reproduce the blueshift observed in the PANH cations-indicate that N appears to be unique in its ability to accommodate the position of the interstellar 6.2 micron bands while simultaneously satisfying the other constraints of the astrophysical problem. This result implies that the peak position of the interstellar feature near 6.2 micron traces the degree of nitrogen substitution in the population, that most of the PAHs responsible for the interstellar IR emission features incorporate nitrogen within their aromatic networks, and that a lower limit of 1%-2% of the cosmic nitrogen is sequestered within the interstellar PAH population. Finally, in view of the ubiquity and abundance of interstellar PAHs and the permanent dipoles and distinctive electronic structures of these nitrogen-substituted variants, this work impacts a wide range of observational phenomena outside of the infrared region of the spectrum including the forest of unidentified molecular rotational features and the anomalous Galactic foreground emission in the microwave, and the diffuse interstellar bands (DIBs) and other structure in the interstellar extinction curve in the ulhviolet/visible. These astrophysical ramifications are discussed, and the dipole moments and rotational constants are tabulated to facilitate further investigations of the astrophysical role of nitrogen-substituted aromatic compounds.

Hudgins, Douglas M.↗
NASA NTRS2014

Focal Gray Matter Plasticity as a Function of Long Duration Bedrest: Preliminary Results

Long duration spaceflight (i.e., 22 days or longer) has been associated with changes in sensorimotor systems, resulting in difficulties that astronauts experience with posture control, locomotion, and manual control. It is unknown whether and how spaceflight impacts sensorimotor brain structure and function, and whether such changes may potentially underlie behavioral effects. Long duration head down tilt bed rest has been used repeatedly as an exclusionary analog to study microgravity effects on the sensorimotor system [1]. Bed rest mimics microgravity in body unloading and bodily fluid shifts. We are currently testing sensorimotor function, brain structure, and brain function pre and post a 70‐day bed rest period. We will acquire the same measures on NASA crewmembers starting in 2014. Here we present the results of the first eight bed rest subjects. Subjects were assessed at 12 and 7 days before‐, at 7, 30, and ~70 days in‐, and at 8 and 12 days post 70 days of bed rest at the NASA bed rest facility, UTMB, Galveston, TX, USA. At each time point structural MRI scans (i.e., high resolution T1‐weighted imaging and Diffusion Tensor Imaging (DTI)) were obtained using a 3T Siemens scanner. Focal changes over time in gray matter density were assessed using the voxel based morphometry 8 (VBM8) toolbox under SPM. Focal changes in white matter microstructural integrity were assessed using tract based spatial statistics (TBSS) as part of the FMRIB software library (FSL). TBSS registers all DTI scans to standard space. It subsequently creates a study specific white matter skeleton of the major white matter tracts. Non‐parametric permutation based t‐tests and ANOVA's were used for voxel‐wise comparison of the skeletons. For both VBM and TBSS, comparison of the two pre bed rest measurements did not show significant differences. VBM analysis revealed decreased gray matter density in bilateral areas including the frontal medial cortex, the insular cortex and the caudate nucleus from pre to in bed rest. Over the same time period, there was an increase in gray matter density in the cerebellum, occipital, and parietal cortices. The majority of these changes did not recover from during to post bed rest. TBSS analyses will also be presented. Extended bed rest, which is an analog for microgravity, can result in gray matter changes and potentially in microstructural white matter changes in areas that are important for neuromotor behavior and cognition. These changes did not recover at two weeks post bed rest. These results have significant public health implications, and will also aid in interpretation of our future data obtained pre and post spaceflight. Whether the effects of bed rest wear off at longer times post bed rest, and if they are associated with behavior are important questions that warrant further research.

Koppelmans, V.↗
DOE OSTI2023

8. Open-Loop Toolpath Generation

Open-loop paths, as opposed to closed-loop paths, have start and end points that are at different locations. Open-loop paths, commonly called “skeletons,” can be generated through multiple approaches. Most approaches utilize a shape's medial axis transform and build appropriate pathing around this representation. In this chapter, a specific implementation consisting of three major steps will be discussed. These steps are Voronoi diagram generation, skeleton pruning, and path consolidation. With the major components of the implementation covered, two additional optimizations will also be described. These two optimizations, chamfering and smoothing, will be highlighted as ways to improve overall pathing quality.

Borish, Michael↗
DOE OSTI2021

Seawater Desalination Derived Entirely from Ocean Biomass

Solar-driven interfacial evaporation shows great prospects for seawater desalination with its rapid fast evaporation rate and high photothermal conversion efficiency. Here, a sustainable, biodegradable, non-toxic, and highly efficient full ocean biomass-based solar-driven evaporator is reported, which is composed of chitosan (CS) hydrogel as the hydratable skeleton and cuttlefish ink (CI) as the photothermal material. Under solar irradiation, the cuttlefish ink powder harvests solar energy and heats the surrounding water. Simultaneously, the water in the three-dimensional network of chitosan hydrogel is rapidly replenished by the interconnected porous structure and the hydrophilic functional groups attached to the polymer chains. With its enlarged evaporation surface, high solar absorptance, adequate water transportation, good salt drainage, and heat localization, the CI/CS-based evaporator achieves a remarkable evaporation rate of 4.1 kg m-2 h-1 under one sun irradiance (1 kW m-2) with high-quality freshwater yields. This full ocean biomass-based evaporator with abundant raw material availability provides new possibilities for an efficient, stable, sustainable, and environmentally friendly solar evaporator with guaranteed water quality.

BIOMASS FUELS,INORGANIC, ORGANIC, PHYSICAL, AND AN↗
DOE OSTI2021

Stochastic parametric skeletal dosimetry model for humans: General approach and application to active marrow exposure from bone-seeking beta-particle emitters

The objective of this study is to develop a skeleton model for assessing active marrow dose from bone-seeking beta-emitting radionuclides. This article explains the modeling methodology which accounts for individual variability of the macro- and microstructure of bone tissue. Bone sites with active hematopoiesis are assessed by dividing them into small segments described by simple geometric shapes. Spongiosa, which fills the segments, is modeled as an isotropic three-dimensional grid (framework) of rod-like trabeculae that “run through” the bone marrow. Randomized multiple framework deformations are simulated by changing the positions of the grid nodes and the thickness of the rods. Model grid parameters are selected in accordance with the parameters of spongiosa microstructures taken from the published papers. Stochastic modeling of radiation transport in heterogeneous media simulating the distribution of bone tissue and marrow in each of the segments is performed by Monte Carlo methods. Model output for the human femur at different ages is provided as an example. The uncertainty of dosimetric characteristics associated with individual variability of bone structure was evaluated. An advantage of this methodology for the calculation of doses absorbed in the marrow from bone-seeking radionuclides is that it does not require additional studies of autopsy material. The biokinetic model results will be used in the future to calculate individual doses to members of a cohort exposed to 89,90 Sr from liquid radioactive waste discharged to the Techa River by the Mayak Production Association in 1949–1956. Further study of these unique cohorts provides an opportunity to gain more in-depth knowledge about the effects of chronic radiation on the hematopoietic system. In addition, the proposed model can be used to assess the doses to active marrow under any other scenarios of 90 Sr and 89 Sr intake to humans.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Plutonium in Manhattan Project workers: Using autopsy data to evaluate organ content and dose estimates based on urine bioassay with implications for radiation epidemiology

Purpose Radiation dose estimates in epidemiology typically rely on intake predictions based on urine bioassay measurements. The purpose of this article is to compare the conventional dosimetric estimates for radiation epidemiology with the estimates based on additional post-mortem tissue radiochemical analysis results. Methods The comparison was performed on a unique group of 11 former Manhattan Project nuclear workers, who worked with plutonium in the 1940s, and voluntarily donated their bodies to the United States Transuranium and Uranium Registries. Results Post-mortem organ activities were predicted using different sets of urine data and compared to measured activities. Use of urinalysis data collected during the exposure periods overestimated the systemic (liver+skeleton) deposition of 239 Pu by 155±134%, while the average bias from using post-exposure urinalyses was –4±50%. Committed effective doses estimated using early urine data differed from the best estimate by, on average, 196±193%; inclusion of follow-up urine measurements in analyses decreased the mean bias to 0.6±36.3%. Cumulative absorbed doses for the liver, red marrow, bone surface, and brain were calculated for the actual commitment period. Conclusion On average, post-exposure urine bioassay results were in good agreement with post-mortem tissue analyses and were more reliable than results of urine bioassays collected during the exposure.

60 APPLIED LIFE SCIENCES↗
NASA NTRS2015

Augmented Virtual Reality Laboratory

Real time motion tracking hardware has for the most part been cost prohibitive for research to regularly take place until recently. With the release of the Microsoft Kinect in November 2010, researchers now have access to a device that for a few hundred dollars is capable of providing redgreenblue (RGB), depth, and skeleton data. It is also capable of tracking multiple people in real time. For its original intended purposes, i.e. gaming, being used with the Xbox 360 and eventually Xbox One, it performs quite well. However, researchers soon found that although the sensor is versatile, it has limitations in real world applications. I was brought aboard this summer by William Little in the Augmented Virtual Reality (AVR) Lab at Kennedy Space Center to find solutions to these limitations.

Resolved Skeleton↗
DOE OSTI2020

Anatomical Fraction segmentation in the biomass bales

The U.S. Department of Energy Bioenergy Technologies Office (BETO) is committed to the development of sustainable, nationwide, commercial biofuel production to displace petroleum-derived fuels, increase domestic energy production, and encourage the creation of a domestic bioenergy and bioproducts industry. Operating a commercial-scale bioenergy operation requires significant technological advancements for determining biomass feedstock quality during the preprocessing stage. Usage of non-food feedstocks- e.g., corn-stover, pine residue, and forest residue - at the biorefineries reduces strain on the food supply chain. But the non-food feedstock heterogeneity- physical size, shape, and chemical composition-poses a significant challenge during milling, conveyance, feeding, and biofuel conversion processes. 3D X-Ray imaging (CT) is capable of distinguishing material features by detecting density and compositional differences. But the inherent complexity introduced during harvesting and bailing makes the reconstruction and interpretation of baled biomass materials from x-ray data time consuming, laborious, and expensive. Feedstocks are low-density materials that produce small contrast differences in the x-ray images. This paper focuses on using the shape and texture properties, using 3D image processing techniques like 3D skeletonization, directional statistics to characterize and extract volumetric content of the different tissue samples in the biomass bales.

09 BIOMASS FUELS↗
DOE OSTI2023

Comprehensively Strengthened Metal‐Oxygen Bonds for Reversible Anionic Redox Reaction

Introducing anionic redox in layered oxides is an effective approach to breaking the capacity limit of conventional cationic redox. However, the anionic redox reaction generally suffers from excessive oxidation of lattice oxygen to O 2 and O 2 release, resulting in local structural deterioration and rapid capacity/voltage decay. Here, a Na 0.71 Li 0.22 Al 0.05 Mn 0.73 O 2 (NLAM) cathode material is developed by introducing Al 3+ into the transition metal (TM) sites. Thanks to the strong Al–O bonding strength and small Al 3+ radius, the TMO 2 skeleton and the holistic TM–O bonds in NLAM are comprehensively strengthened, which inhibits the excessive lattice oxygen oxidation. The obtained NLAM exhibits a high reversible capacity of 194.4 mAh g —1 at 20 mA g —1 and decent cyclability with 98.6% capacity retention over 200 cycles at 200 mA g —1 . In situ characterizations reveal that the NLAM experiences phase transitions with an intermediate OP4 phase during the charge–discharge. Theoretical calculations further confirm that the Al substitution strategy is beneficial for improving the overlap between Mn 3d and O 2p orbitals. Importantly, this finding sheds light on the design of layered oxide cathodes with highly reversible anionic redox for sodium storage.

25 ENERGY STORAGE↗
DOE OSTI2026

A Holistic Stabilization of the Anode in Lithium‐Sulfur Batteries Through a Ternary Alloy Fusion

The anode in lithium–sulfur batteries (LSBs) is plagued by not only inhomogeneous lithium (Li) deposition, but also by parasitic side-reactions. Often, a thick anode (∼400 µm) is used to compensate for these drawbacks, lowering gravimetric and volumetric energy densities. In this work, we demonstrate a ternary alloy anode fabricated via scalable thermal fusion of Li with aluminum (Al) and tellurium (Te) to cohesively address these issues. The Al–Li skeleton serves to homogenize Li deposition as well as reinforce the anode, allowing it to be rolled down to low thicknesses. Te incorporation suppresses the reaction of Li with polysulfides (Li 2 Sn) to form lithium sulfide (Li 2 S) and electrolyte degradation. It can also facilitate the formation of polytellurosulfides (Li 2 Te x Sy), which are far more conducive to Li + -ion diffusion. Even under a lean electrolyte/sulfur (E/S) ratio of 8 µL mg −1 and a low negative/positive (N/P) ratio of 3, capacities over 900 mA h g −1 at a C/5 rate are obtained in cells with Li–Te–Al anodes with a capacity retention of 80% after 70 cycles. In comparison, the baseline lithium-metal anode retains only 35% after 50 cycles. Furthermore, the Li–Te–Al anodes confer a 24% boost to gravimetric energy density at the pouch cell level.

25 ENERGY STORAGE↗
DOE OSTI2021

A Sodium–Antimony–Telluride Intermetallic Allows Sodium-Metal Cycling at 100% Depth of Discharge and as an Anode-Free Metal Battery

In this work, repeated cold rolling and folding is employed to fabricate a metallurgical composite of sodium–antimony–telluride Na 2 (Sb 2/6 Te 3/6 Vac 1/6 ) dispersed in electrochemically active sodium metal, termed “NST-Na.” This new intermetallic has a vacancy-rich thermodynamically stable face-centered-cubic structure and enables state-of-the-art electrochemical performance in widely employed carbonate and ether electrolytes. NST-Na achieves 100% depth-of-discharge (DOD) in 1 m NaPF 6 in G2, with 15 mAh cm –2 at 1 mA cm –2 and Coulombic efficiency (CE) of 99.4%, for 1000 h of plating/stripping. Sodium-metal batteries (SMBs) with NST-Na and Na 3 V 2 (PO 4 ) 3 (NVP) or sulfur cathodes give significantly improved energy, cycling, and CE (>99%). An anode-free battery with NST collector and NVP obtains 0.23% capacity decay per cycle. Imaging and tomography using conventional and cryogenic microscopy (Cryo-EM) indicate that the sodium metal fills the open space inside the self-supporting sodiophilic NST skeleton, resulting in dense (pore-free and solid electrolyte interphase (SEI)-free) metal deposits with flat surfaces. The baseline Na deposit consists of filament-like dendrites and “dead metal”, intermixed with pores and SEI. Density functional theory calculations show that the uniqueness of NST lies in the thermodynamic stability of the Na atoms (rather than clusters) on its surface that leads to planar wetting, and in its own stability that prevents decomposition during cycling.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Porous FeCo Glassy Alloy as Bifunctional Support for High-Performance Zn-Air Battery

Zn-air battery (ZAB) is attracting increasing attention due to its high safety and performance. However, the practical application of ZAB relies heavily on developing durable support materials to replace conventional carbon supports which have unrecoverable corrosion issues, severely jeopardizing ZAB performance. Herein, a novel porous FeCo glassy alloy was developed as bifunctional catalytic support for ZAB. Specifically, the conducting skeleton of the porous glassy alloy was used to stabilize oxygen reduction cocatalysts, and more importantly, the FeCo served as the primary phase for oxygen evolution. To prove the concept of catalytic glassy alloy support, ultra-small Pd nanoparticles were anchored, as oxygen reduction active sites, on the porous FeCo (noted as Pd/FeCo) for ZAB. The Pd/FeCo exhibited a significantly improved electrocatalytic activity for oxygen reduction (a half-wave potential of 0.85 V) and oxygen evolution (a potential of 1.55 V to reach 10 mA cm –2 ) in the alkaline media. When used in the ZAB, the Pd/FeCo delivered an output power density of 117 mW cm –2 and outstanding cycling stability for over 200 h (400 cycles), surpassing the conventional carbon-supported Pt/C+IrO 2 catalysts. Such an integrated design of combining highly active components with porous architecture provides a new strategy to develop novel nanostructured electrocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High‐Performance Ternary Organic Solar Cells with Enhanced Luminescence Efficiency and Miscibility Enabled by Two Compatible Acceptors

Abstract The ternary strategy has proven to be an effective method for improving the efficiency of organic solar cells (OSCs). However, designing and selecting the third component still pose challenges. In this study, this issue is addressed by focusing on the PBDB‐T:Y18‐F binary system and introducing a new, strong luminescent, asymmetric small‐molecule acceptor (SMA) called L8‐CBIC‐Cl, which shares a similar skeleton with Y18‐F. The similarity in molecular framework facilitates good compatibility between the two acceptors, resulting in the formation of an alloy‐like acceptor phase. Furthermore, the norbornenyl‐modified end group in L8‐CBIC‐Cl contributes to its strong luminescent properties, which in turn leads to a low non‐radiative energy loss and a high open‐circuit voltage. Consequently, the PBDB‐T:L8‐CBIC‐Cl:Y18‐F based ternary devices realize a high power conversion efficiency (PCE) up to 17.01%, which is higher than PBDB‐T:Y18‐F device (14.49%). Importantly, L8‐CBIC‐Cl exhibits a good universality as a guest acceptor in other three binary systems (D18:Y6, D18:BTP‐eC9‐4F, and D18:L8‐BO). The D18:L8‐BO:L8‐CBIC‐Cl device shows an impressive efficiency of 19%. The work demonstrates that employing SMA with a high PLQY and better miscibility with host acceptor as the third component has a great potential for developing high‐efficiency ternary OSCs.

Chemistry↗
DOE OSTI2021

Accurate Determination of the Quantity and Spatial Distribution of Counterions around a Spherical Macroion

Abstract The accurate distribution of countercations (Rb + and Sr 2+ ) around a rigid, spherical, 2.9‐nm size polyoxometalate cluster, {Mo 132 } 42− , is determined by anomalous small‐angle X‐ray scattering. Both Rb + and Sr 2+ ions lead to shorter diffuse lengths for {Mo 132 } than prediction. Most Rb + ions are closely associated with {Mo 132 } by staying near the skeleton of {Mo 132 } or in the Stern layer, whereas more Sr 2+ ions loosely associate with {Mo 132 } in the diffuse layer. The stronger affinity of Rb + ions towards {Mo 132 } than that of Sr 2+ ions explains the anomalous lower critical coagulation concentration of {Mo 132 } with Rb + compared to Sr 2+ . The anomalous behavior of {Mo 132 } can be attributed to majority of negative charges being located at the inner surface of its cavity. The longer anion–cation distance weakens the Coulomb interaction, making the enthalpy change owing to the breakage of hydration layers of cations more important in regulating the counterion–{Mo 132 } interaction.

Chen, Jiahui↗
DOE OSTI2023

Separating Xylene Isomers with a Calcium Metal‐Organic Framework

Abstract The purification of p‐xylene (pX) from its xylene isomers represents a challenging but important industrial process. Herein, we report the efficient separation of pX from its ortho‐ and meta‐ isomers by a microporous calcium‐based metal–organic framework material (HIAM‐203) with a flexible skeleton. At 30 °C, all three isomers are accommodated but the adsorption kinetics of o‐xylene (oX) and m‐xylene (mX) are substantially slower than that of pX, and at an elevated temperature of 120 °C, oX and mX are fully excluded while pX can be adsorbed. Multicomponent column breakthrough measurements and vapor‐phase/liquid‐phase adsorption experiments have demonstrated the capability of HIAM‐203 for efficient separation of xylene isomers. Ab initio calculations have provided useful information for understanding the adsorption mechanism.

Yu, Liang↗
DOE OSTI2022

Fully Conjugated Poly(phthalocyanine) Scaffolds Derived from a Mechanochemical Approach Towards Enhanced Energy Storage

Phthalocyanines (Pc)-derived materials represent an attractive category of porous organic scaffolds featured by extensive π-conjugated networks, but their construction is still limited to the solution-based pathways, producing materials with inferior conductivity and porosity. Herein, a mechanochemistry-driven approach was developed leveraging the on-surface polymerization of aromatic nitrile monomers with ortho-positioned dicyano groups in the presence of metal catalysts (magnesium, zinc, or aluminum) under neat and ambient conditions. Diverse Pc-functionalized conjugated porous networks (Pc-CPNs) were obtained featured by extensively and fully π-conjugated skeletons, high surface areas, and hierarchical porosities. The monomers in this mechanochemical approach could be extended to those difficult to be handled in solution-based procedures. In this work, the Pc-CPNs displayed attractive electrochemical performance as supercapacitor and anodes in batteries, together with superb long-term stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Separating Xylene Isomers with a Calcium Metal–Organic Framework

Here, the purification of p-xylene (pX) from its xylene isomers represents a challenging but important industrial process. Herein, we report the efficient separation of pX from its ortho- and meta- isomers by a microporous calcium-based metal–organic framework material (HIAM-203) with a flexible skeleton. At 30 °C, all three isomers are accommodated but the adsorption kinetics of o-xylene (oX) and m-xylene (mX) are substantially slower than that of pX, and at an elevated temperature of 120 °C, oX and mX are fully excluded while pX can be adsorbed. Multicomponent column breakthrough measurements and vapor-phase/liquid-phase adsorption experiments have demonstrated the capability of HIAM-203 for efficient separation of xylene isomers. Ab initio calculations have provided useful information for understanding the adsorption mechanism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗