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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Characterization of spent nuclear fuel canister surface roughness using surface replicating molds

In this study we present a replication method to determine surface roughness and to identify surface features when a sample cannot be directly analyzed by conventional techniques. As a demonstration, this method was applied to an unused spent nuclear fuel dry storage canister to determine variation across different surface features. In this study, an initial material down-selection was performed to determine the best molding agent and determined that non-modified Polytek PlatSil23-75 provided the most accurate representation of the surface while providing good usability. Other materials that were considered include Polygel Brush-On 35 polyurethane rubber (with and without Pol-ease 2300 release agent), Polytek PlatSil73-25 silicone rubber (with and without PlatThix thickening agent and Pol-ease 2300 release agent), and Express STD vinylpolysiloxane impression putty. The ability of PlatSil73-25 to create an accurate surface replica was evaluated by creating surface molds of several locations on surface roughness standards representing ISO grade surfaces N 3 , N 5 , N 7 , and N 8 . Overall, the molds were able to accurately reproduce the expected roughness average (R a ) values, but systematically over-estimated the peak-valley maximum roughness (R z ) values. Using a 3D printed sample cell, several locations across the stainless steel spent nuclear fuel canister were sampled to determine the surface roughness. These measurements provided information regarding variability in normal surface roughness across the canister as well as a detailed evaluation on specific surface features (e.g., welds, grind marks, etc.). The results of these measurements can support development of dry storage canister ageing management programs, as surface roughness is an important factor for surface dust deposition and accumulation. This method can be applied more broadly to different surfaces beyond stainless steel to provide rapid, accurate surface replications for analytical evaluation by profilometry.

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

Full structural ensembles of intrinsically disordered proteins from unbiased molecular dynamics simulations

Abstract Molecular dynamics (MD) simulation is widely used to complement ensemble-averaged experiments of intrinsically disordered proteins (IDPs). However, MD often suffers from limitations of inaccuracy. Here, we show that enhancing the sampling using Hamiltonian replica-exchange MD (HREMD) led to unbiased and accurate ensembles, reproducing small-angle scattering and NMR chemical shift experiments, for three IDPs of varying sequence properties using two recently optimized force fields, indicating the general applicability of HREMD for IDPs. We further demonstrate that, unlike HREMD, standard MD can reproduce experimental NMR chemical shifts, but not small-angle scattering data, suggesting chemical shifts are insufficient for testing the validity of IDP ensembles. Surprisingly, we reveal that despite differences in their sequence, the inter-chain statistics of all three IDPs are similar for short contour lengths (< 10 residues). The results suggest that the major hurdle of generating an accurate unbiased ensemble for IDPs has now been largely overcome.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Atomic imprinting into metallic glasses

Abstract Nanoimprinting by thermoplastic forming has attracted significant attention due to its promise of low-cost fabrication of functionalized surfaces and nanostructured devices, and metallic glasses have been identified as a material class ideally suited for nanoimprinting. In particular, their featureless atomic structure suggests that there may not be an intrinsic size limit to the material’s ability to replicate a mould. Here we demonstrate atomic-scale imprinting into a platinum-based metallic glass alloy under ambient conditions using atomic step edges of a strontium titanate single crystal as a mould. The moulded metallic glass replicates the ‘atomic smoothness’ of the strontium titanate, with identical roughness to the one measured on the mould even after multiple usages and with replicas exhibiting an exceptional long-term stability of years. By providing a practical, reusable, and potentially high-throughput approach for atomic imprinting, our findings may open novel applications in surface functionalization through topographical structuring.

Li, Rui↗
DOE OSTI2016

Enhanced sampling simulation analysis of the structure of lignin in the THF–water miscibility gap

Using temperature replica-exchange molecular dynamics, we characterize a globule-to-coil transition for a softwood-like lignin biopolymer in a tetrahydrofuran (THF)-water cosolvent system at temperatures at which the cosolvent undergoes a de-mixing transition. The lignin is found to be in a coil state, similar to that in the high-temperature miscible region. Analysis of the transition kinetics indicates that THF acts in a surfactant-like fashion. In conclusion, the present study thus suggests that THF-water based pretreatments may efficiently remove lignin from biomass even at relatively low (non-water boiling) temperatures.

09 BIOMASS FUELS↗
DOE OSTI2017

Induced polarization restricts the conformational distribution of a light-harvesting molecular triad in the ground state

The light-harvesting molecular triad consisting of carotenoid polyene (C), diaryl-porphyrin (P) and pyrrole-fullerene (C60) is a donor–acceptor molecule capable of absorbing incident light in the visible range. Its ability to convert solar energy to electrical excitation and charge separation energy suggests a great potential in real-world applications. The ensemble of its conformations under ambient conditions varies widely according to its electronic state. In previous work, we applied a non-polarizable model to study the conformational distribution of the molecular triad in the ground and charge separated states. However, due to the lack of polarization, which imparts subtle changes in the charge distribution on atoms, molecular simulations fail to produce accurate average dipole moments. We developed the first polarizable model for a molecular triad to investigate the structural and dynamic properties of a molecular triad in the ground state in an explicit organic solvent, tetrahydrofuran (THF). We performed first-principles electronic structure calculations of the individual components in the triad as well as THF and then fit the partial atomic charges to the electrostatic potential using the i-RESP methodology. We validated these force field parameters by comparing the thermodynamic and dynamic properties obtained from molecular dynamics simulations with those from experiments. We enhanced the sampling of the triad conformations with replica exchange molecular dynamics simulations. We characterized the effects of induced polarization on the structural stability of the triad by analyzing the free energy landscapes constructed with polarizable force fields. Furthermore, by using principal component analysis, we found that the molecular triad conformations adopted a small range of torsional angles with induced polarization. The triad conformation solvated in polar solvent with a polarizable force field qualitatively agrees with that obtained from nuclear magnetic resonance spectroscopy.

Starovoytov, Oleg N.↗
DOE OSTI2017

Fabrication and optical characterization of polystyrene opal templates for the synthesis of scalable, nanoporous (photo)electrocatalytic materials by electrodeposition

Finding solutions to improve the performance of semiconductor light absorbers and catalyst materials remains an outstanding issue that prevents the realization of solar fuel generators. Nanostructuring approaches of photoelectrocatalytic materials have the potential to reduce bulk recombination and improve electron-hole pair separation in semiconductor light absorbers, as well as to increase the active surface area and influence the activity in catalytic systems. Herein, we propose a versatile approach for the synthesis of reproducible, highly homogeneous, large scale nanoporous (photo)electrocatalytic materials for artificial photosynthesis. By identifying and carefully analyzing critical parameters for forming opal templates from solutions of colloidal polystyrene beads (PS), we are able to reproducibly fabricate large area ( > cm 2 ) PS films with high optical quality over a wide diameter range (170-600 nm). Using these PS bead opal films as templates, we demonstrate that electrodeposition is a suitable bottom-up infilling technique to produce scalable, homogeneous, and highly ordered nanoporous (photo)electrocatalytic materials, namely Cu 2 O, BiVO 4 , CuBi 2 O 4 , and Cu. Here, we provide morphological, structural, and optical characterization of the resulting opal replicas. Finally, we demonstrate preliminary integration of the Cu 2 O inverse opal film into a working photocathode under CO 2 reduction conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Localization of Zn 2+ ions affects the structural folding and mechanics of Nereis virens Nvjp-1

Several biological organisms utilize metal-coordination bonds to produce remarkable materials, such as the jaw of the marine worm Nereis virens, where metal-coordination bonds yield remarkable hardness without mineralization. Though the structure of a major component of the jaw, the Nvjp-1 protein, has recently been resolved, a detailed nanostructural understanding of the role of metal ions on the structural and mechanical properties of the protein is missing, especially with respect to the localization of metal ions. In this work, atomistic replica exchange molecular dynamics with explicit water and Zn 2+ ions and steered molecular dynamics simulations were used to explore how the initial localization of the Zn 2+ ions impacts the structural folding and mechanical properties of Nvjp-1. We found that the initial distribution of metal ions for Nvjp-1, and likely for other proteins with high amounts of metal-coordination, has important effects on the resulting structure, with larger metal ion quantity resulting in a more compact structure. These structural compactness trends, however, are independent from the mechanical tensile strength of the protein, which increases with greater hydrogen bond content and uniform distribution of metal ions. Our results indicate that different physical principles underlie the structure or mechanics of Nvjp-1, with broader implications in the development optimized hardened bioinspired materials and the modeling of proteins with significant metal ion content.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

SU(3) breaking and the pseudo-scalar spectrum in multi-taste QCD

Using the Sigma model to explore the lowest order pseudo-scalar spectrum with SU(3) breaking, this talk considers an additional exact "taste" symmetry to mimic species doubling. Rooting replicas of a valid approach such as Wilson fermions reproduces the desired physical spectrum. In contrast, extra symmetries of the rooted staggered approach leave spurious states and a flavor dependent taste multiplicity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Storage events: distributed users, federation and beyond

For federated storage to work well, some knowledge from each storage system must exist outside that system, regardless of the use case. This is needed to allow coordinated activity; e.g., executing analysis jobs on worker nodes with good accessibility to the data.Currently, this is achieved by clients notifying central services of activity; e.g., a client notifies a replica catalogue after an upload. Unfortunately, this forces end users to use bespoke clients. It also forces clients to wait for asynchronous activities to finish.dCache provides an alternative approach: storage events. In this approach the storage systems (rather than the clients) become the coordinating service, notifying interested parties of key events.At DESY, we are investigating storage events along with Apache OpenWhisk and Kubernetes to build a "serverless" cloud, similar to AWS Lambda or Google Cloud Functions, for photon science use cases.Storage events are more generally useful: catalogues are notified whenever data is uploaded or delete, tape becomes more efficient because analysis can start immediately after the data is on disk, caches can be "smart" fetching new datasets preemptively.In this paper we will present work within dCache to support a new event-based interface, with which these and other use cases become more efficient.

Millar, A.Paul↗
DOE OSTI2019

dCache - Joining the noWORM Storage Club

For over a decade, dCache.ORG has provided robust software, called dCache, that is used at more than 80 universities and research institutes around the world, allowing these sites to provide reliable storage services for the WLCG experiments and many other scientific communities. The flexible architecture of dCache allows running it in a wide variety of configurations and platforms - from all-in-one Raspberry-Pi up to hundreds of nodes in multi-petabyte infrastructures. The life cycle of scientific data is well defined - collected, processed, archived and finally deleted, when it’s not needed anymore. Moreover, during all those stages the data is never modified: either the original data is used, or new derived data is produced. With this knowledge, dCache was designed to handle immutable files as efficiently as possible. Data replication, HSM connectivity and data-server independent operations are only possible due to the immutable nature of stored data. Nowadays many commercial vendors provide such write-once-read-many or WORM storage systems, as they become more and more demanded with grown demand of audio, photo and video content in the web. On the other hand by providing standard NFSv4.1 interface dCache is often used as a general-purpose file-system, especially by new communities, like photon scientists or microbiologists. Although many users are aware of data immutability, some applications and use cases still require in-place updates of stored files. To satisfy new requirements some fundamental changes have to be applied to dCache’s core design. However, new developments must not compromise any aspect of existing functionality. In this presentation we will show new developments in dCache to turn it into a regular file system. We will discuss the challenges to build a distributed storage system, ‘life’ with POSIX compliance, handling of multiple replicas and backward compatibility by providing WORM and noWORM capabilities within the same storage system.

Mkrtchyan, Tigran↗
DOE OSTI2021

dCache: from Resilience to Quality of Service

A major goal of future dCache development will be to allow users to define file Quality of Service (QoS) in a more flexible way than currently available. This will mean implementing what might be called a QoS rule engine responsible for registering and managing time-bound QoS transitions for files or storage units. In anticipation of this extension to existing dCache capabilities, the Resilience service, which maintains on-disk replica state, needs to undergo both structural modification and generalization. This paper describes ongoing work to transform Resilience into the new architecture which will eventually support a more broadly defined file QoS.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Temperature dependence of the energy bandgap of two-dimensional hexagonal boron nitride probed by excitonic photoluminescence

Hexagonal boron nitride (hBN) is an emerging material for the exploration of new physics in two-dimensional (2D) systems that are complementary to graphene. Nanotubes with a diameter (∼60 nm) that is much larger than the exciton binding energy in hBN have been synthesized and utilized to probe the fundamental optical transitions and the temperature dependence of the energy bandgap of the corresponding 2D hBN sheets. An excitonic transition at 5.901 eV and its longitudinal optical phonon replica at 5.735 eV were observed. The excitonic emission line is blue shifted by about 130 meV with respect to that in hBN bulk crystals due to the effects of reduced dimensionality. The temperature evolution of the excitonic emission line measured from 300 to 800 K revealed that the temperature coefficient of the energy bandgap of hBN nanotubes with large diameters (or equivalently hBN sheets) is about 0.43 meV/{sup 0}K, which is a factor of about 5 times smaller than the theoretically predicted value for the transitions between the π and π* bands in hBN bulk crystals and 6 times smaller than the measured value in AlN epilayers with a comparable energy bandgap. The observed weaker temperature dependence of the bandgap than those in 3D hBN and AlN is a consequence of the effects of reduced dimensionality in layer-structured hBN.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A simple scanning spectrometer based on a stretchable elastomeric reflective grating

We report a scanning optical spectrometer based on the use of a stretchable elastomeric reflective grating. The grating is obtained by supersonic cluster beam implantation of silver nanoparticles on polydimethylsiloxane previously grooved by molding to create a replica of a commercial digital versatile disk grating. The use of a stretchable grating allows the spectrometer spanning the whole optical wavelength range by solely extending the diffraction element by more than 100% of its original dimensions. The stretchable reflective optical grating shows excellent performances and stability upon thousands of stretching cycles. The use of this elastomeric element makes the optical layout and the mechanics of the spectrometer extremely simple and advantageous for those applications where spectral resolution is not a major requirement. As a proof of principle, we present the absorption spectrum of Rhodamine B in solution obtained by our spectrometer and compared to commercial instruments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Simulation study of the effects of surface chemistry and temperature on the conformations of ssDNA oligomers near hydrophilic and hydrophobic surfaces

We study the effects of the presence of a hydrophilic and a hydrophobic surface on the conformations and interactions of a single-stranded DNA (ssDNA) oligomer using atomistic molecular dynamics, umbrella sampling, and temperature-replica exchange. Our simulations capture the expected interactions between the ssDNA and the two surfaces (e.g., hydrogen bonds, hydrophobic interactions), but we find that the surface chemistry does not strongly affect the exposure of the relatively hydrophobic nucleobases or the hydrophilic phosphate backbone in a 16-base ssDNA. Likewise, the surfaces do not strongly affect the preferred size of the ssDNA compared to bulk solution, although the hydrophilic surface does favor slightly more compact ssDNA conformations than the hydrophobic surface. In more compact conformations, the negative charge of the ssDNA is more concentrated, and the energetic interactions of the DNA and DNA-bound counterions with the hydrophilic surface are more favorable, which consequently favors smaller ssDNA sizes. Increasing temperature, regardless of the presence or chemistry of a surface, makes it less unfavorable for the ssDNA to assume both compact and extended conformations. With increasing temperature the free energy cost of assuming a compact conformation is reduced to a greater extent than the cost of assuming an extended conformation. The reason for this difference is the entropically favorable release of DNA-bound water molecules upon assuming a compact conformation. Increasing temperature decreases water-DNA interactions while surprisingly increasing counterion-DNA interactions, changes which are attributed to the relative balance of entropic and energetic contributions for water molecules and counterions bound to the ssDNA.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Study of nano imprinting using soft lithography on Krafty glue and PVDF polymer thin films

The present work reveals soft lithography strategy based on self assembly and replica molding for carrying out micro and nanofabrication. It provides a convenient, effective and very low cost method for the formation and manufacturing of micro and nano structures. Al-layer of compact disc (sony CD-R) used as a stamp with patterned relief structures to generate patterns and structures with pattern size of 100nm height, 1.7 μm wide. In literature, PDMS (Polydimethylsiloxane) solution is widely used to get negative copy of the Al-layer. In this work, we have used inexpensive white glue (Polyvinylacetate + water), 15gm (□5) and PVDF (Polyvinylidene difluoride) spin coated films and successfully transferred the nano patterns of Al layer on to white glue and PVDF films.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Optical properties of strain-free AlN nanowires grown by molecular beam epitaxy on Si substrates

The optical properties of catalyst-free AlN nanowires grown on Si substrates by molecular beam epitaxy were investigated. Such nanowires are nearly free of strain, with strong free exciton emission measured at room temperature. The photoluminescence intensity is significantly enhanced, compared to previously reported AlN epilayer. Moreover, the presence of phonon replicas with an energy separation of ∼100 meV was identified to be associated with the surface-optical phonon rather than the commonly reported longitudinal-optical phonon, which is further supported by the micro-Raman scattering experiments.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Optical density of states in ultradilute GaAsN alloy: Coexistence of free excitons and impurity band of localized and delocalized states

Optically active states in liquid phase epitaxy-grown ultra-dilute GaAsN are studied. The feature-rich low temperature photoluminescence spectrum has contributions from excitonic band states of the GaAsN alloy, and two types of defect states—localized and extended. The degree of delocalization for extended states both within the conduction and defect bands, characterized by the electron temperature, is found to be similar. The degree of localization in the defect band is analyzed by the strength of the phonon replicas. Stronger emission from these localized states is attributed to their giant oscillator strength.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Parallel continuous simulated tempering and its applications in large-scale molecular simulations

In this paper, we introduce a parallel continuous simulated tempering (PCST) method for enhanced sampling in studying large complex systems. It mainly inherits the continuous simulated tempering (CST) method in our previous studies [C. Zhang and J. Ma, J. Chem. Phys. 130, 194112 (2009); C. Zhang and J. Ma, J. Chem. Phys. 132, 244101 (2010)], while adopts the spirit of parallel tempering (PT), or replica exchange method, by employing multiple copies with different temperature distributions. Differing from conventional PT methods, despite the large stride of total temperature range, the PCST method requires very few copies of simulations, typically 2–3 copies, yet it is still capable of maintaining a high rate of exchange between neighboring copies. Furthermore, in PCST method, the size of the system does not dramatically affect the number of copy needed because the exchange rate is independent of total potential energy, thus providing an enormous advantage over conventional PT methods in studying very large systems. The sampling efficiency of PCST was tested in two-dimensional Ising model, Lennard-Jones liquid and all-atom folding simulation of a small globular protein trp-cage in explicit solvent. The results demonstrate that the PCST method significantly improves sampling efficiency compared with other methods and it is particularly effective in simulating systems with long relaxation time or correlation time. We expect the PCST method to be a good alternative to parallel tempering methods in simulating large systems such as phase transition and dynamics of macromolecules in explicit solvent.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗