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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Dual-Stimuli Responsive Single-Chain Polymer Folding via Intrachain Complexation of Tetramethoxyazobenzene and β-Cyclodextrin

We synthesize and characterize a triblock polymer with asymmetric tetramethoxyazobenzene (TMAB) and β-cyclodextrin functionalization, taking advantage of the well-characterized azobenzene derivative-cyclodextrin inclusion complex to promote photoresponsive, self-contained folding of the polymer in an aqueous system. We use 1 H NMR to show the reversibility of (E)-to-(Z) and (Z)-to-(E) TMAB photoisomerization, and evaluate the thermal stability of (Z)-TMAB and the comparatively rapid acid-catalyzed thermal (Z)-to-(E) isomerization. Important for its potential use as a functional material, we show the photoisomerization cyclability of the polymeric TMAB chromophore and calculate isomerization quantum yields by extinction spectroscopy. To verify self-inclusion of the polymeric TMAB and cyclodextrin, we use two-dimensional 1 H NOESY NMR data to show proximity of TMAB and cyclodextrin in the (E)-state only; however, (Z)-TMAB is not locally correlated with cyclodextrin. Lastly, the observed decrease in photoisomerization quantum yield for the dual-functionalized polymer compared to the isolated chromophore in an aqueous solution confirms TMAB and β-cyclodextrin not only are in proximity to one another, but also form the inclusion complex.

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

Strain rate effects on the mechanical behavior of porous titanium with different pore sizes

High strain-rate (up to 6600 s –1 ) and quasi-static compression tests are conducted on a powder-sintered porous titanium with different pore sizes (mean: 30 μm and 120 μm). In situ X-ray imaging is implemented to characterize the pores-scale deformation dynamics. The yield strength as a function of strain rate exhibits two stages of rate sensitivity, and the transition occurs at 1600 s –1 . X-ray images show that pore compaction and strain localizations occur preferentially at pores oriented perpendicular to the loading direction under quasi-static loading, but become more random under high strain-rate loading as a result of higher driving force and plastic deformation nucleation rate. Here, the more homogeneous nucleation of plastic deformation contributes to the increased rate sensitivity beyond 1600 s –1 . At the same strain rate, the yield strength of porous Ti as well as strain field homogeneity decreases significantly with increasing pore size. The small pore spacing in fine-pored Ti reduces the degree of stress concentrations around pores. Therefore, the higher stress concentrations in coarse-pored Ti lead to an earlier yield of matrix around pores and thus a lower bulk yield strength.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Functional Expansion Tallies Using MCNP6 PTRAC Files [Slides]

Accuracy is vital for many radiation transport applications. Monte Carlo (MC) codes are the most accurate, but they are expensive for fine meshes. Functional Expansion Tallies (FETs) yield smoother, lower-variance results with far fewer degrees of freedom.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

A crop yield change emulator for use in GCAM and similar models: Persephone v1.0

Abstract. Future changes in Earth system state will impact agricultural yields and, through these changed yields, can have profound impacts on the global economy. Global gridded crop models estimate the influence of these Earth system changes on future crop yields but are often too computationally intensive to dynamically couple into global multi-sector economic models, such as the Global Change Assessment Model (GCAM) and other similar-in-scale models. Yet, generalizing a faster site-specific crop model's results to be used globally will introduce inaccuracies, and the question of which model to use is unclear given the wide variation in yield response across crop models. To examine the feedback loop among socioeconomics, Earth system changes, and crop yield changes, rapidly generated yield responses with some quantification of crop response uncertainty are desirable. The Persephone v1.0 response functions presented in this work are based on the Agricultural Model Intercomparison and Improvement Project (AgMIP) Coordinated Climate-Crop Modeling Project (C3MP) sensitivity test data set and are focused on providing GCAM and similar models with a tractable number of rapid to evaluate dynamic yield response functions corresponding to a range of the yield response sensitivities seen in the C3MP data set. With the Persephone response functions, a new variety of agricultural impact experiments will be open to GCAM and other economic models: for example, examining the economic impacts of a multi-year drought in a key agricultural region and how economic changes in response to the drought can, in turn, impact the drought.

58 GEOSCIENCES↗
DOE OSTI2024

Embedding Thiols into Choline Phosphate Polymer Zwitterions

Abstract The compositional scope of polymer zwitterions has grown significantly in recent years and now offers designer synthetic materials that are broadly applicable across numerous areas, including supracolloidal structures, electronic materials interfaces, and macromolecular therapeutics. Among recent developments in polymer zwitterion syntheses are those that allow insertion of reactive functionality directly into the zwitterionic moiety, yielding new monomer and polymer structures that hold potential for maximizing the impact of zwitterions on the macromolecular materials chemistry field. This manuscript describes the preparation of zwitterionic choline phosphate (CP) methacrylates containing either aromatic or aliphatic thiols embedded directly into the zwitterionic moiety. The polymerization of these functional CP methacrylates by reversible addition‐fragmentation chain‐transfer methodology yields polymeric zwitterionic thiols containing protected thiol functionality in the zwitterionic units. After polymerization, the protected thiols are liberated to yield thiol‐rich polymer zwitterions which serve as precursors to subsequent reactions that produce polymer networks as well as polymer‐protein bioconjugates.

Polymer Science↗
DOE OSTI2024

Formation and transformation of iron oxy-hydroxide precursor clusters to ferrihydrite

Iron (Fe) oxy-hydroxide minerals such as ferrihydrite (Fh) are ubiquitous in Earth-surface environments and important in biogeochemical element cycling. Recent research has suggested that their formation is preceded by the precipitation of ultrasmall (~1 nm) Keggin-like Fe oxy-hydroxide clusters. However, relatively little is understood about the structure of the precursor clusters and the impacts of pH and time on their growth and transformation to more stable phases. Here, we used a new method that involves mixed flow reactors (MFR) to synthesize these Fe oxy-hydroxide precursor clusters at pH 1.0, 1.5, 2.5, and 4.5. In situ and ex situ synchrotron scattering measurements and laboratory small-angle X-ray scattering (SAXS) were used to study the structure and size of Fe oxy-hydroxide clusters and their transformation products, respectively. Results show that with increasing pH, the particle size and structural order of samples increase, forming solids that resemble 2-line Fh at pH 4.5. The experimental data were compared with X-ray pair distribution functions (PDF) calculated for a range of Fe(III) oxyhydroxide clusters, including Fe 13 Keggin isomers computed previously using density functional theory (DFT), which yielded at best only partial agreement at short range (<5 Å). Aging of the clusters synthesized at pH 1.5 and 2.5 results in growth and transformation via Ostwald ripening to mixtures of goethite (Gt) and lepidocrocite (Lp). This process was inhibited by immediately reacting the early-formed clusters with phosphate (PO 4 3– ), suggesting that oxyanion surface complexes can stabilize the initial clusters by preventing growth and crystallization to more stable phases.

58 GEOSCIENCES↗
DOE OSTI2024

A reactive molecular dynamics model for uranium/hydrogen containing systems

Uranium-based materials are valuable assets in the energy, medical, and military industries. However, understanding their sensitivity to hydrogen embrittlement is particularly challenging due to the toxicity of uranium and the computationally expensive nature of quantum-based methods generally required to study such processes. In this regard, we have developed a Chebyshev Interaction Model for Efficient Simulation (ChIMES) that can be employed to compute energies and forces of U and UH3 bulk structures with vacancies and hydrogen interstitials with accuracy similar to that of Density Functional Theory (DFT) while yielding linear scaling and orders of magnitude improvement in computational efficiency. Here, we show that the bulk structural parameters, uranium and hydrogen vacancy formation energies, and diffusion barriers predicted by the ChIMES potential are in strong agreement with the reference DFT data. We then use ChIMES to conduct molecular dynamics simulations of the temperature-dependent diffusion of a hydrogen interstitial and determine the corresponding diffusion activation energy. Our model has particular significance in studies of actinides and other high-Z materials, where there is a strong need for computationally efficient methods to bridge length and time scales between experiments and quantum theory.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Functional but not taxonomic diversity increases productivity of Populus in the southeastern United States

Plant interactions like competition and facilitation impact ecosystem function and resilience. Improving our understanding of the relationships between these interactions and community productivity has important implications for managers of production systems in forestry and agriculture as well as conservation science. Populus spp. are an excellent model system for exploring how inter‐ and intraspecific interactions impact ecosystem functions, such as productivity, in forest plantations. In this study, we compared aboveground productivity of six Populus clones from three different taxa grown in monoclonal and mixed‐clonal plots. The different mixture treatments were intended to experimentally test aboveground biomass response to contrasting levels of taxonomic diversity and functional diversity based on nitrogen use characteristics of Populus clones. We hypothesize that functional diversity would be more important than taxonomic diversity in increasing aboveground productivity of mixed‐clonal plantings compared to monocultures. In addition, a subset of treatments was carried out on additional sites representing a productivity gradient in order to determine if the relationship between biodiversity and productivity in these systems diminished at more productive sites as suggested by the stress‐gradient hypothesis. We found that functionally diverse mixtures of clones had greater yield of aboveground biomass than the average of their constituent monocultures, while more taxonomically diverse mixes of clones did not differ from the average of their constituent monocultures. However, when reestablished on sites with extremely high or low productivity, the best performing clone mixture also did not differ from the average of its constituent monocultures. Our results suggest that intimate clone mixtures of Populus have the potential to significantly increase productivity, but results vary by mixture and by site. To capitalize on positive biodiversity effects on yield in production systems, targeted mixtures based on divergent functional traits linked to different use and acquisition strategies for site‐specific limiting resources are most likely to be successful.

BEF↗
DOE OSTI2019

Measurement of prompt D 0 , D + , D *+ , and DS+$ {\mathrm{D}}_{\mathrm{S}}^{+} $ production in p–Pb collisions at sNN$ \sqrt{{\mathrm{s}}_{\mathrm{NN}}} $ = 5.02 TeV

The measurement of the production of prompt D 0 , D + , D *+, and $D_S^+$ mesons in proton–lead (p–Pb) collisions at the centre-of-mass energy per nucleon pair of \mathrm{\sqrt{s_{NN}}}$ = 5.02 TeV, with an integrated luminosity of 292 ± 11 μb -1 , are reported. Differential production cross sections are measured at mid-rapidity (-96 < y cms < 0.04) as a function of transverse momentum (p T ) in the intervals 0 < p T < 36 GeV/c for D 0 , 1 < p T < 36 GeV/c for D + and D *+ , and 2 < p T < 24 GeV/c for D + mesons. For each species, the nuclear modification factor R pPb is calculated as a function of p T using a proton-proton (pp) reference measured at the same collision energy. The results are compatible with unity in the whole p T range. The average of the non-strange D mesons R pPb is compared with theoretical model predictions that include initial-state effects and parton transport model predictions. The p T dependence of the D 0 , D + , and D *+ nuclear modification factors is also reported in the interval 1 < p T < 36 GeV/c as a function of the collision centrality, and the central-to-peripheral ratios are computed from the D-meson yields measured in different centrality classes. The results are further compared with charged-particle measurements and a similar trend is observed in all the centrality classes. The ratios of the p T -differential cross sections of D 0 , D + , D *+ , and $D_S^+$ mesons are also reported. The $D_S^+$ and D + yields are compared as a function of the charged-particle multiplicity for several p T intervals. No modification in the relative abundances of the four species is observed with respect to pp collisions within the statistical and systematic uncertainties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Study of charged particle production at high p T using event topology in pp, p–Pb and Pb–Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV

This letter reports measurements which characterize the underlying event associated with hard scatterings at mid-pseudorapidity (|$η$| < 0.8) in pp, p–Pb and Pb–Pb collisions at centre-of-mass energy per nucleon pair, $\sqrt{s_{NN}}=5.02$ TeV. The measurements are performed with ALICE at the LHC. Different multiplicity classes are defined based on the event activity measured at forward rapidities. The hard scatterings are identified by the leading particle defined as the charged particle with the largest transverse momentum ($p_{T}$) in the collision and having 8 < $p_{T}$ < 15 GeV/c. The $p_{T}$ spectra of associated particles (0.5 < $p_{T}$ < 6 GeV/c) are measured in different azimuthal regions defined with respect to the leading particle direction: toward, transverse, and away. The associated charged particle yields in the transverse region are subtracted from those of the away and toward regions. The remaining jet-like yields are reported as a function of the multiplicity measured in the transverse region. The measurements show a suppression of the jet-like yield in the away region and an enhancement of high-$p_{T}$ associated particles in the toward region in central Pb–Pb collisions, as compared to minimum-bias pp collisions. These observations are consistent with previous measurements that used two-particle correlations, and with an interpretation in terms of parton energy loss in a high-density quark gluon plasma. These yield modifications vanish in peripheral Pb–Pb collisions and are not observed in either high-multiplicity pp or p–Pb collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Scale sensitivity of ethanol production via consolidated bioprocessing with consideration of feedstock cost

We examine feedstock cost and minimum selling price for ethanol production from corn stover as a function of scale, stover yield, participation rate, and price incentives for two conversion technologies: a conventional base case featuring thermochemical pretreatment with added cellulase, and an advanced case featuring consolidated bioprocessing with cotreatment (C-CBP). Delivered feedstock cost ranged from $\$85$ Mg −1 at small (10 million gallons year −1 or ~38 million L year −1 ) scale with high yield and participation rates to $\$124$ Mg −1 at large scale (60 million gallons year −1 or 227 million L year −1 ) and low yield and participation rates. The minimum ethanol selling price (MESP) was approximately twofold lower for the advanced case compared with the base case. The payback period was several times lower for the advanced case compared with the base case, with increasing disparity at smaller scales, and was highly sensitive to ethanol price supports. For both C-CBP and the conventional processing paradigm, MESP decreased with increasing scale, indicating that the cost penalty due to higher feedstock transport distances was more than outweighed by lower capital costs. However, the cost penalty for operation at small scale, expressed in $ gallon −1 ethanol, is lower for C-CBP than for the conventional paradigm by roughly twofold. Particularly for initial applications of C-CBP, we speculate that this cost penalty will likely be modest compared with the anticipated benefits of small-scale operation such as increased opportunity to use existing infrastructure, easier plant siting and supply chain establishment, and lower total investment required.

biorefinery scale↗
DOE OSTI2021

Solvothermal Synthesis of [Cr 7 S 8 (en) 8 Cl 2 ]Cl 3 ⋅ 2H 2 O with Magnetically Frustrated [Cr 7 S 8 ] 5+ Double‐Cubes**

Abstract A novel transition metal chalcohalide [Cr 7 S 8 (en) 8 Cl 2 ]Cl 3 ⋅ 2H 2 O, with [Cr 7 S 8 ] 5+ dicubane cationic clusters, has been synthesized by a low temperature solvothermal method, using dimethyl sulfoxide (DMSO) and ethylenediamine ( en ) solvents. Ethylenediamine ligand exhibits bi‐ and monodentate coordination modes; in the latter case ethylenediamine coordinates to Cr atoms of adjacent clusters, giving rise to a 2D polymeric structure. Although magnetic susceptibility shows no magnetic ordering down to 1.8 K, a highly negative Weiss constant, θ =−224(2) K, obtained from Curie‐Weiss fit of inverse susceptibility, suggests strong antiferromagnetic (AFM) interactions between S =3/2 Cr(III) centers. Due to the complexity of the system with (2 S +1) 7 =16384 microstates from seven Cr 3+ centers, a simplified model with only two exchange constants was used for simulations. Density‐functional theory (DFT) calculations yielded the two exchange constants to be J 1 =−21.4 cm −1 and J 2 =−30.2 cm −1 , confirming competing AFM coupling between the shared Cr 3+ center and the peripheral Cr 3+ ions of the dicubane cluster. The best simulation of the experimental data was obtained with J 1 =−20.0 cm −1 and J 2 =−21.0 cm −1 , in agreement with the slightly stronger AFM exchange within the triangles of the peripheral Cr 3+ ions as compared to the AFM exchange between the central and peripheral Cr 3+ ions. This compound is proposed as a synthon towards magnetically frustrated systems assembled by linking dicubane transition metal‐chalcogenide clusters into polymeric networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Development of a Novel Equilibrium Passive Sampling Device for Methylmercury in Sediment and Soil Porewaters

In this work, we explored the concept of equilibrium passive sampling for methylmercury (MeHg) using the strategy developed for hydrophobic organic chemicals. Passive sampling should allow prediction of the concentration of the chemically labile fraction of MeHg in sediment porewaters based on equilibrium partitioning into the sampler, without modeling diffusion rates through the sampler material. Our goals were to identify sampler materials with the potential to mimic MeHg partitioning into animals and sediments and provide reversible sorption in a time frame appropriate for in situ samplers. Candidate materials tested included a range of polymers embedded with suitable sorbents for MeHg. The most promising were activated carbon (AC) embedded in agarose, thiol–self-assembled monolayers on mesoporous supports embedded in agarose, and cysteine-functionalized polyethylene terephthalate, which yielded log sampler–water partition coefficients of 2.8 to 5 for MeHgOH and MeHg complexed with dissolved organic matter (Suwannee River humic acid). Sampler equilibration time in sediments was approximately 1 to 2 wk. Investigation of the MeHg accumulation mechanism by AC embedded in agarose suggested that sampling was kinetically influenced by MeHg interactions with AC particles and not limited by diffusion through the gel for this material. Also, AC exhibited relatively rapid desorption of Hg and MeHg, indicating that this sorbent is capable of reversible, equilibrium measurements. In sediment:water microcosms, porewater concentrations made with isotherm-calibrated passive samplers agreed within a factor of 2 (unamended sediment) or 4 (AC-amended sediment) with directly measured concentrations. The present study demonstrates a potential new approach to passive sampling of MeHg.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Charged-particle nuclear modification factors in XeXe collisions at $ \sqrt{s_{\mathrm{NN}}} = 5.44 $ TeV

Here, the differential yields of charged particles having pseudorapidity within |η| < 1 are measured using xenon-xenon (XeXe) collisions at $ \sqrt{s_{\mathrm{NN}}} = 5.44 $ TeV. The data, corresponding to an integrated luminosity of 3.42 μb –1 , were collected in 2017 by the CMS experiment at the LHC. The yields are reported as functions of collision centrality and transverse momentum, p T , from 0.5 to 100 GeV. A previously reported p T spectrum from proton-proton collisions at √s = 5.02 TeV is used for comparison after correcting for the difference in center-of-mass energy. The nuclear modification factors using this reference, R AA * , are constructed and compared to previous measurements and theoretical predictions. In head-on collisions, the R AA * has a value of 0.17 in the p T range of 6–8 GeV, but increases to approximately 0.7 at 100 GeV. Above ≈6 GeV, the XeXe data show a notably smaller suppression than previous results for lead-lead (PbPb) collisions at $ \sqrt{s_{\mathrm{NN}}} = 5.02 $ TeV when compared at the same centrality (i.e., the same fraction of total cross section). However, the XeXe suppression is slightly greater than that for PbPb in events having a similar number of participating nucleons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

The effect of pore structure in ethane-selective metal-organic frameworks for ethylene purification

Separation of ethylene from ethane is of great importance in petrochemical industry. Adsorptive separation making use of porous materials such as metal-organic frameworks (MOFs) is an energy efficient technology compared to the conventional cryogenic distillation. However, preferential adsorption of ethylene over ethane represents the major current challenge. Here we demonstrate how pore structure can significantly alter the adsorption selectivity in two isoreticular Zr-MOFs. A simple ligand functionalization in UiO-66 yields smaller/better matching pore for ethane, and weaker interaction with ethylene, greatly enhancing ethane/ethylene selectivity in MOF-801. Ab initio calculations combined with in situ infrared spectroscopic analysis unveil the nature of host-guest interactions and differences in the overall binding energies. Polymer-grade ethylene (99.9%) can be produced directly from ethane/ethylene mixture in a single step. Having well-balanced adsorption capacity and selectivity, low-cost synthesis and easy scalability MOF-801 stands out as a promising ethane-selective adsorbent for one-step ethylene purification under ambient conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tailoring grain growth and solid solution strengthening of single-phase CrCoNi medium-entropy alloys by solute selection

In the present study, we selected solutes to be added to the CrCoNi medium-entropy alloy (MEA) based on the mismatch of self-diffusion activation energy (SDQ) between the alloying elements and constituent elements of the matrix, and then investigated their grain growth behavior and mechanical properties. Mo and Al were selected as the solutes for investigation primarily because they have higher and lower SDQ, respectively, than those of the matrix elements; a secondary factor was their higher and lower shear modulus. Their concentrations were fixed at 3 at.% each because previous work had shown these compositions to be single-phase solid solutions with the face-centered cubic structure. Three alloys were produced by arc melting, casting, homogenizing, cold rolling and annealing at various temperatures and times to produce samples with different grain sizes. They were (a) the base alloy CrCoNi, (b) the base alloy plus 3 at.% Mo, and (c) the base alloy plus 3 at.% Al. The activation energies for grain growth of the CrCoNi, CrCoNi-3Mo and CrCoNi-3Al MEAs were found to be ~251, ~368 and ~219 kJ/mol, respectively, consistent with the notion that elements with higher SDQ (in this study Mo) retard grain growth (likely by a solute-drag effect), whereas those with lower values (Al) accelerate grain growth. The room-temperature tensile properties show that Mo increases the yield strength by ~40% but Al addition has a smaller strengthening effect consistent with their relative shear moduli. The yield strength as a function of grain size for the three singlephase MEAs follows the classical Hall-Petch relationship with much higher slopes (> 600 MPa μm -0.5 ) than traditional solid solutions. Furthermore, this work shows that the grain growth kinetics and solid solution strengthening of the CrCoNi MEA can be tuned by selecting solute elements that have appropriate diffusion and physical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Temperature-dependent formation of gradient structures with anomalous hardening in an Al–Si alloy

The temperature effect on forming gradient structure in an Al-Si alloy during surface severe deformation is studied in this report. The intermediate temperature (473 K) produces the steepest gradient structure by an anomalous hardening on the top layer compared to lower (300 K) and higher temperature (673 K) counterparts. Our analysis shows profuse aluminum oxide particles in the top layer of the gradient structure under 473 K and thus lead to anomalous hardening by oxide-dispersion strengthening. Here, the counterintuitive enhancement of strengthening at the intermediate temperature is explained by the dynamic interplay between thermal-driven, mechanical-aided oxidation and the wear-induced loss of surface materials as a function of temperature, which yields a critical processing temperature to achieve the steepest gradient structure.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A fitting algorithm for optimizing ion implantation energies and fluences

In this work we describe a method to automatically generate an ion implantation recipe, a set of energies and fluences, to produce a desired defect density profile in a solid using the fewest required energies. We simulate defect density profiles for a range of ion energies, fit them with an appropriate function, and interpolate to yield defect density profiles at arbitrary ion energies. Given Ν energies, we then optimize a set of Ν energy-fluence pairs to match a given target defect density profile. Finally, we find the minimum Ν such that the error between the target defect density profile and the defect density profile generated by the Ν energy-fluence pairs is less than a given threshold. Inspired by quantum sensing applications with nitrogen-vacancy centers in diamond, we apply our technique to calculate optimal ion implantation recipes to create uniform-density 1 μm surface layers of 15 N or vacancies (using 4 He).

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗