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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

The Cognition Battery: Developing a Normative Database for Spaceflight and Examining the Impact of Prolonged Isolation and Confinement on Cognitive Performance

INTRODUCTION: Astronauts on future long duration space exploration will be required to execute complex tasks in which even minor errors could have devastating consequences. Intact cognition is critical to maintain exceptional performance standards and it is possible that variability even at the highest ends of the performance spectrum will impact operational tasks. Exposure to spaceflight hazards could compromise cognitive performance, and decrements have been documented under conditions of altered gravity and radiation exposure. The cognitive impacts of prolonged isolation and confinement remain relatively unknown. Traditional neuropsychological assessments cannot support earth independent monitoring, do not have normative comparisons for high functioning individuals, and most are not sensitive enough to detect small performance decrements. The Cognition Battery was developed to address these limitations but currently lacks comprehensive normative data. In this project, we aimed to 1) develop a preliminary normative database for astronauts and astronaut surrogates using the Cognition Battery, and 2) characterize differences in cognitive performance after short and long duration analog missions. PARTICIPANTS & METHODS: We assessed baseline cognitive performance by administering the Cognition Battery to 97 astronaut and astronaut surrogates recruited to approximate astronaut demographics (mean age: 39.38, SD=7.62; 35.1% female; 91.7% advanced degrees). For aim 1, we calculated speed and accuracy outcomes for each subtest and summarized the data with descriptive statistics. We examined the relationship between age and performance with Pearsons’s correlations and the relationship between gender and performance with independent samples t-tests. A subset of individuals on short duration (n=48; mean age: 38.18, SD=7.14; 37.5% female; 91.7% advanced degrees) missions of 45 days and long duration (n=34; mean age: 42.12, SD=8.39; 38.2% female; 94.1% advanced degrees) missions ranging from 4-8 months were administered the Cognition Battery during and after their respective missions. For aim 2, we accounted for practice effects using published corrections, and z-transformed post-mission scores using the full sample’s baseline scores. One-way analysis of covariance tests determined the main effect of analog duration on post-mission performance, after accounting for age and gender. The False Discovery Rate method was applied to adjust for multiple comparisons. RESULTS: In the full normative sample, older age was associated with slower reaction times on a processing speed task (r=.39, p=.02), and men were more accurate on processing speed (t=-2.19, p=.03) and faster on sustained attention (t=2.02, p=.049) and risk-taking tasks (t=2.49, p=.02). We observed a main effect of duration on performance on tasks of visual memory (f(1)=5.62, p=.04), processing speed (f(1)=5.48, p=.03), and sensorimotor functioning (f(1)=39.52, p < .001), such that slower performance was observed after long duration missions relative to short. Only sensorimotor functioning was significant after adjustments for multiple comparisons (adjusted p<.001). DISCUSSION: The full sample represents the largest dataset of cognitive performance assessed by the Cognition Battery available and can be used for further research in spaceflight and high-performance populations. Relationships between performance and key demographic variables suggest future research that include age and gender stratification is needed. Our results also show minimal changes in cognitive performance between longer and shorter periods of isolation and confinement.

S I Dev↗
DOE OSTI2013

Platform Technology Development for the Radiosynthesis of Targeted Molecular Probes (Final Scientific/Technical Report)

The report contains a summary of the objectives, approaches taken and results obtained during this funding period. The overall objective of this proposal was to develop and optimize a generic labeling approach for peptide based targeted molecular imaging agents. The hypothesis of the project was based on the solid-phase-peptide synthesis approach that is a flexible, generic and reproducible approach, which can result in high specific activity radiolabeled peptides but had previously suffered from low yields and lengthy reaction times that were not suitable for fluorine-18 chemistry. We proposed to investigate/optimize each step of peptide synthesis and radiolabeling to reduce the overall synthesis time and develop a technology that was widely applicable to many peptide ligands. Conditions investigated for optimization included the resin type, the solvent system, the coupling conditions and the cleavage conditions. After optimization of each condition on the model peptide VQAAIDYING with 4-[ 18 F]fluorobenzoic acid ([ 18 F]FBA) the approach was applied to numerous clinically relevant peptides. Overall this approach has significantly improved the radiolabeling yields, radiochemical purity and decreased the overall synthesis time of these peptides. We have developed a robust generic platform for labeling peptides that can be used as molecular probes not only for PET but for other modalities such as SPECT, MRI and optical imaging.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2014

Method of increasing anhydrosugars, pyroligneous fractions and esterified bio-oil

The device and method are provided to increase anhydrosugars yield during pyrolysis of biomass. This increase is achieved by injection of a liquid or gas into the vapor stream of any pyrolysis reactor prior to the reactor condensers. A second feature of our technology is the utilization of sonication, microwave excitation, or shear mixing of the biomass to increase the acid catalyst rate for demineralization or removal of hemicellulose prior to pyrolysis. The increased reactivity of these treatments reduces reaction time as well as the required amount of catalyst to less than half of that otherwise required. A fractional condensation system employed by our pyrolysis reactor is another feature of our technology. This system condenses bio-oil pyrolysis vapors to various desired fractions by differential temperature manipulation of individual condensers comprising a condenser chain.

09 BIOMASS FUELS↗
DOE OSTI2022

Self-healing barrier films for vacuum insulation panels

A self-healing vacuum insulation panel and a method of manufacture are provided. The vacuum insulation panel includes a self-healing, multi-layer barrier film including a separator between a curing agent and a curable resin. Upon damage to the separator, the curing agent penetrates the separator due to a pressure differential across the barrier film and reacts with the curable resin to seal any cuts or punctures. The curing agent and the curable resin can be selected to have long term stability and a short reaction time with no need for external stimuli. As a result, the multi-layer barrier film can retain the internal vacuum and maintain a desirably low thermal conductivity using low-cost, commercially available epoxies and curing agents.

Biswas, Kaushik↗
DOE OSTI2016

TREAT reactor LEU fuel-clad chemical interaction empirical modeling analysis

DOE is converting TREAT (Transient Reactor Test) facility from its existing highly enriched uranium (HEU) core to a low-enriched uranium (LEU) core. In order to assess the magnitude of chemical interaction between fuel and cladding materials during physical contact under expected TREAT operational limits, planned transients tests, and reactivity accident scenarios, a combination of experimental testing and thermodynamic modeling was performed to predict the expected chemical interactions among fuel and cladding chemical constituents. Thermodynamic calculations were then validated with empirical data from experiments that emulate TREAT's expected upper operational limits. Pellet samples composed of LEU oxide powder dispersed in a graphite matrix had intimate contact with zirconium-based alloy cladding. The samples were subjected to long-term isothermal heating under high vacuum. Specimen characterization consisted of scanning electron microscopy, x-ray diffraction analysis, and x-ray tomography. ThermoCalc software and Ellingham's diagrams were used for thermodynamic calculations. The X-ray tomography and SEM analysis of the pellets showed a homogeneous distribution of UO{sub 2} particles within the graphite matrix with isolated larger UO{sub 2} agglomerates. The SEM analysis showed the formation of a lamellar structure between the large UO{sub 2} agglomerate and the graphite matrix. This is an indication that diffusion is taking place at a rather moderate temperature and reaction time during the pellet fabrication. Secondary phases, with high Al and Mg content, were detected inside a UO{sub 2} agglomerate using SEM in SE/EBSD mode and chemical analysis with EDS. LEU feedstock impurities, as Al and Mg, seem to promote the chemical reactivity between UO{sub 2} particles and graphite matrix. XRD analysis of a pellet sample showed the presence of UO{sub 2} and graphite, but no other crystalline phases were detected with this technique. Thermodynamic analysis through the use of Ellingham diagrams showed that within TREAT's operational to reactivity accident temperature (278-820 Celsius degrees), UO{sub 2} can be reduced to U metal by Zr due to a more favorable ΔG for the oxidation of Zr.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Understanding Nitrate Chemistry - The Key to Safer and More Efficient TRU Waste Acceptance - 19618

Investigations into the Waste Isolation Pilot Plant (WIPP) radiological release from a transuranic (TRU) waste drum concluded that the event was initiated by a thermal runaway, principally involving interactions between the polysaccharide-based kitty litter and nitric acid, which released radiological material along with hot gases and combustible materials from the drum. In this paper, the hazards of polysaccharides present as either starch based kitty litter or cellulose rags in a TRU waste drum exposed to nitric acid (and by extension metal nitrate salts) have been evaluated, based on considerations of how complex nitrogen redox cycles carry out the aqueous phase oxidation of alcohols and related organic functional groups. These exothermic reactions, coupled with a positive feedback loop inherent to nitrogen redox chemistry, can initiate an autocatalytic thermal runaway and explosive gas generation, which poses the most significant risk under ambient conditions where acidic solution may be present (in small quantities as free liquid or sorbed within a solid matrix). Nitric acid is an extremely potent oxidant but is itself remarkably inert, rarely interacting directly with oxidizable substrates and instead exerting its vast potential energy through lower oxidation state reactants such as nitrogen dioxide and nitrous acid that are generated from its slow self-decomposition. Nitrous acid is the reactant that carries out substrate oxidation, and systems that are not pre-loaded with nitrous acid will experience an induction period before significant reactivity commences. Under oxidizing fuel-lean conditions, nitrogen dioxide may induce autocatalytic nitrous acid formation, which may supplement additional side-reactions, potentially leading to thermal runaway. Therefore, the system is most vulnerable at the end of an induction period. Metal nitrate salts promote this ambient temperature solution chemistry (cf. traditional oxidizer properties of metal nitrate salts, which operate in the solid state at elevated temperatures) by releasing nitric acid into the system via hydrolysis. Unlike simple alcohols with a single hydroxyl functional group, the chemistry of polymeric carbohydrates (polysaccharides) such as starches and cellulose is more diverse. Therefore, the oxidation of the simple monomeric carbohydrate glucose is first examined to provide insight into the analogous reactivity with polysaccharides. Although less reactive than alcohols by virtue of extensive hydrogen bonding, carbohydrates are oxidized by nitric acid through the same fundamental mechanisms, complicated by a variety of competing side reactions including acid-catalyzed hydrolytic depolymerization to more reactive (ultimately monomeric) units, as well as other degradation reactions promoted by radical mechanisms. For this reason, polysaccharides such as starches that are more susceptible to hydrolysis are more reactive than cellulose, with the attendant microbial population in starch based kitty litter adding a special aspect of reactivity. From this safety evaluation, a bounding latency period has been developed beyond which a stored TRU waste drum that contains polysaccharides (starch based kitty litter excluded) commingled with nitric acid and/or metal nitrate salts may no longer present a hazard under ambient conditions, based on a compilation of induction periods and reaction times involving nitric acid with various oxidizable substrates under a variety of conditions from synthetic procedures, tests, and adverse incident scenarios. By obviating the need for costly treatment options or characterization, a better understanding of nitrate redox chemistry and the hazards it presents with polysaccharide oxidation thus provides a more efficient means to safely dispose of TRU waste generated within the Department of Energy (DOE) complex. (author)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Free energy difference to create the M-OH* intermediate of the oxygen evolution reaction by time-resolved optical spectroscopy

Theoretical descriptors differentiate the catalytic activity of materials for the oxygen evolution reaction by the strength of oxygen binding in the reactive intermediate created upon electron transfer. Recently, time-resolved spectroscopy of a photo-electrochemically driven oxygen evolution reaction followed the vibrational and optical spectra of this intermediate, denoted M-OH*. However, these inherently kinetic experiments have not been connected to the relevant thermodynamic quantities. Here we discover that picosecond optical spectra of the Ti-OH* population on lightly doped SrTiO 3 are ordered by the surface hydroxylation. A Langmuir isotherm as a function of pH extracts an effective equilibrium constant relatable to the free energy difference of the first oxygen evolution reaction step. Thus, time-resolved spectroscopy of the catalytic surface reveals both kinetic and energetic information of elementary reaction steps, which provides a critical new connection between theory and experiment by which to tailor the pathway of water oxidation and other surface reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1999

In Site Analysis of a High Temperature Cure Reaction in Real Time Using Modulated Fiber-Optic FT-Raman Spectroscopy

The vibrational spectrum of a high temperature (330 C) polymerization reaction was successfully monitored in real time using a modulated fiber-optic FT-Raman spectrometer. A phenylethynyl terminated monomer was cured, and spectral evidence for two different reaction products was acquired. The products are a conjugated polyene chain and a cyclized trimer. This is the first report describing the use of FT-Raman spectroscopy to monitor a high temperature (greater than 250 C) reaction in real time.

Cooper, John↗
NASA NTRS1999

In Situ Analysis of a High-Temperature Cure Reaction in Real Time Using Modulated Fiber-Optic FT-Raman Spectroscopy

The vibrational spectrum of a high-temperature (330 C) polymerization reaction was successfully monitored in real time with the use of a modulated fiber-optic Fourier transform (FT)-Raman spectrometer. A phenylethynyl-terminated monomer was cured, and spectral evidence for two different reaction products was acquired. The products are a conjugated polyene chain and a cyclized trimer. This is the first report describing the use of FT-Raman spectroscopy to monitor a high temperature (greater than 250 C) reaction in real time.

Aust, Jeffrey F.↗
DOE OSTI2015

Description of nucleon-transfer and fusion reactions within time-dependent approaches and coupled-channel method

The time-dependent Schrödinger equation and the method of perturbed stationary states that is based on the expansion of the total wave function for the system of two nuclear cores and a nucleon in a set of nucleon two-center functions are used to describe nucleon transfers and fusion in low-energy nuclear reactions. A set of multichannel equations that couple the relative motion of nuclei to the motion of the nucleon is obtained. The kinetic-energy coupling matrix is similar to the coupling matrix for collective excitations of nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time

Abstract Electrocyclic reactions are characterized by the concerted formation and cleavage of both σ and π bonds through a cyclic structure. This structure is known as a pericyclic transition state for thermal reactions and a pericyclic minimum in the excited state for photochemical reactions. However, the structure of the pericyclic geometry has yet to be observed experimentally. We use a combination of ultrafast electron diffraction and excited state wavepacket simulations to image structural dynamics through the pericyclic minimum of a photochemical electrocyclic ring-opening reaction in the molecule α-terpinene. The structural motion into the pericyclic minimum is dominated by rehybridization of two carbon atoms, which is required for the transformation from two to three conjugated π bonds. The σ bond dissociation largely happens after internal conversion from the pericyclic minimum to the electronic ground state. These findings may be transferrable to electrocyclic reactions in general.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Transient cycling of nitrogen, organic carbon and oxygen within the free-flowing Columbia River corridor: Linking exposure time dependent biogeochemical reactions to river stage fluctuations (Final project report)

The objective of this project was to develop next-generation techniques for representing the transformations of complex reaction networks like those impacting transient river-corridors, then apply them to develop upscaling tools. The project contributed significantly to the development of Lagrangian “mass transfer particle tracking” (MTPT) tools that are the first numerical framework that explicitly separates mixing and spreading processes; a crucial distinction for accurate representations of reaction rates across scales. The MTPT approach uses an operator splitting scheme where physical transport processes are simulated using classical random walk methods and each particle is treated as a “container” that carries with it any number of chemical species. Mixing between particles is simulated using a colocation-probability based mass transfer kernel and reactions are evaluated on each particle after mixing. The method is stable, accurate, and also allows the explicit modeling of residence time distributions of the individual containers of mass. The MTPT scheme allowed us to explore several research questions related to reactive transport in river corridors and complex reaction networks. We found that it is possible to quantify the exposure time distributions (ETDs) of reactants and that this does suggest some pathways to upscaling. However, comparable approximations can be obtained using simplified (reduced dimensionality) MTPT simulations in less time with similar uncertainty, so development of extensive ETD-based methods was not productive. The major findings are that i) the MTPT schemes are robust and highly accurate across a range of arbitrarily complex reactions, ii) the methods can be efficiently parallelized and the parallel performance characteristics of MTPT are predictable, and iii) the MTPT tools allow simultaneous tracking of residence time. The development of these research tools into efficient software packages continues. The methods are already available to the community because open-source, working examples have been included with all publications.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Characterizing acid diffusion lengths in chemically amplified resists from measurements of deprotection kinetics

The acid-catalyzed deprotection of glassy poly(4-hydroxystyrene-co-tertbutyl acrylate) films was studied with infrared absorbance spectroscopy and stochastic simulations. Experimental data were interpreted with a simple description of subdiffusive acid transport coupled to second-order acid loss. This model predicts key attributes of observed deprotection rates, such as fast reaction at short times, slow reaction at long times, and a nonlinear dependence on acid loading. Fickian diffusion is approached by increasing the post-exposure bake temperature or adding plasticizing agents to the polymer resin. These findings demonstrate that acid mobility and overall deprotection kinetics are coupled to glassy matrix dynamics. To complement the analysis of bulk kinetics, acid diffusion lengths were calculated from the anomalous transport model and compared with nanopattern line widths. The consistent scaling between experiments and simulations suggests that the anomalous diffusion model could be further developed into a predictive lithography tool.

Patil, Abhijit A.↗
DOE OSTI2015

Analysis of the HindIII-catalyzed reaction by time-resolved crystallography

A time-resolved study using the freeze-trap method elucidates the mechanism of the DNA-cleaving reaction of HindIII. In order to investigate the mechanism of the reaction catalyzed by HindIII, structures of HindIII–DNA complexes with varying durations of soaking time in cryoprotectant buffer containing manganese ions were determined by the freeze-trap method. In the crystal structures of the complexes obtained after soaking for a longer duration, two manganese ions, indicated by relatively higher electron density, are clearly observed at the two metal ion-binding sites in the active site of HindIII. The increase in the electron density of the two metal-ion peaks followed distinct pathways with increasing soaking times, suggesting variation in the binding rate constant for the two metal sites. DNA cleavage is observed when the second manganese ion appears, suggesting that HindIII uses the two-metal-ion mechanism, or alternatively that its reactivity is enhanced by the binding of the second metal ion. In addition, conformational change in a loop near the active site accompanies the catalytic reaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Competitive autocatalytic reactions in chaotic flows with diffusion: Prediction using finite-time Lyapunov exponents

We investigate chaotic advection and diffusion in autocatalytic reactions for time-periodic sine flow computationally using a mapping method with operator splitting. We specifically consider three different autocatalytic reaction schemes: a single autocatalytic reaction, competitive autocatalytic reactions, which can provide insight into problems of chiral symmetry breaking and homochirality, and competitive autocatalytic reactions with recycling. In competitive autocatalytic reactions, species B and C both undergo an autocatalytic reaction with species A such that A+B→2B and A+C→2C. Small amounts of initially spatially localized B and C and a large amount of spatially homogeneous A are advected by the velocity field, diffuse, and react until A is completely consumed and only B and C remain. We find that local finite-time Lyapunov exponents (FTLEs) can accurately predict the final average concentrations of B and C after the reaction completes. The species that starts in the region with the larger FTLE has, with high probability, the larger average concentration at the end of the reaction. If B and C start in regions with similar FTLEs, their average concentrations at the end of the reaction will also be similar. When a recycling reaction is added, the system evolves towards a single species state, with the FTLE often being useful in predicting which species fills the entire domain and which is depleted. The FTLE approach is also demonstrated for competitive autocatalytic reactions in journal bearing flow, an experimentally realizable flow that generates chaotic dynamics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

An exact and efficient first passage time algorithm for reaction–diffusion processes on a 2D-lattice

We present an exact and efficient algorithm for reaction–diffusion–nucleation processes on a 2D-lattice. The algorithm makes use of first passage time (FPT) to replace the computationally intensive simulation of diffusion hops in KMC by larger jumps when particles are far away from step-edges or other particles. Our approach computes exact probability distributions of jump times and target locations in a closed-form formula, based on the eigenvectors and eigenvalues of the corresponding 1D transition matrix, maintaining atomic-scale resolution of resulting shapes of deposit islands. We have applied our method to three different test cases of electrodeposition: pure diffusional aggregation for large ranges of diffusivity rates and for simulation domain sizes of up to 4096×4096 sites, the effect of diffusivity on island shapes and sizes in combination with a KMC edge diffusion, and the calculation of an exclusion zone in front of a step-edge, confirming statistical equivalence to standard KMC simulations. The algorithm achieves significant speedup compared to standard KMC for cases where particles diffuse over long distances before nucleating with other particles or being captured by larger islands.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Time-resolved x-ray crystallography capture of a slow reaction tetrahydrofolate intermediate

Time-resolved crystallography is a powerful technique to elucidate molecular mechanisms at both spatial (angstroms) and temporal (picoseconds to seconds) resolutions. We recently discovered an unusually slow reaction at room temperature that occurs on the order of days: the in crystalline reverse oxidative decay of the chemically labile (6S)-5,6,7,8-tetrahydrofolate in complex with its producing enzyme Escherichia coli dihydrofolate reductase. Here, we report the critical analysis of a representative dataset at an intermediate reaction time point. A quinonoid-like intermediate state lying between tetrahydrofolate and dihydrofolate features a near coplanar geometry of the bicyclic pterin moiety, and a tetrahedral sp 3 C6 geometry is proposed based on the apparent mFo-DFc omit electron densities of the ligand. The presence of this intermediate is strongly supported by Bayesian difference refinement. Isomorphous Fo-Fo difference map and multi-state refinement analyses suggest the presence of end-state ligand populations as well, although the putative intermediate state is likely the most populated. A similar quinonoid intermediate previously proposed to transiently exist during the oxidation of tetrahydrofolate was confirmed by polarography and UV-vis spectroscopy to be relatively stable in the oxidation of its close analog tetrahydropterin. We postulate that the constraints on the ligand imposed by the interactions with the protein environment might be the origin of the slow reaction observed by time-resolved crystallography.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Time-Resolved, NIR Two-Tone Frequency Modulation Spectroscopy for Quantitative Measurement of HO 2 Radical in Fuel Oxidation Reactions

Time-resolved two-tone frequency modulation (TTFM) absorption spectroscopy has been used to measure, in situ and quantitatively, hydroperoxy (HO 2 ) radical in fuel oxidation reactions at the first overtone transitions (2v 1 ) of HO 2 near 1509nm. Typical HO 2 detection limit is on the order of 10 11 molecule cm -3 , which corresponds to a relative absorption of 10 -5 . TTFM method successfully removes low frequency thermal lensing noise in measured HO 2 kinetic time traces, which is a general noise source in fuel oxidation absorption experiments. Compared with previous works, we have upgraded the TTFM experiment with a NIR distributed feedback (DFB) diode laser, a fiber-coupled broadband phase modulator, and a two-channel wave generator, which have improve the performance of our experiment substantially.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗