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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Determination of the volume fraction of precipitates in a nitrided Fe-0.354 wt% C-2.93 wt% Cr model alloy by anomalous small angle X-ray scattering

Highlights: • Anomalous small-angle X-ray scattering (ASAXS) is used to study nitriding of Fe-Cr-C steels. • ASAXS gives access to chemical information of nanoscaled nitrides. • The volume fraction of nitrides is determined along the diffusion layer. - Abstract: Anomalous small angle scattering (ASAXS) is a powerful non-destructive technique that can provide characteristic features of nanoscale precipitates such as the volume fraction, and chemical composition. In this paper, the technique is used for the first time to explore nanoscale MN nitrides (M = Cr,Fe) after nitriding of a model iron alloy (Fe-0.354 wt% C-2.93 wt% Cr).

36 MATERIALS SCIENCE↗
DOE OSTI2016

Influence of multi-walled carbon nanotubes (MWCNTs) volume percentage on the magnetic and microwave absorbing properties of BaMg{sub 0.5}Co{sub 0.5}TiFe{sub 10}O{sub 19}/MWCNTs nanocomposites

Graphical abstract: Reflection losses of (a) doped barium hexaferrite, BaMg{sub 0.5}Co{sub 0.5}TiFe{sub 10}O{sub 19}, sample and their nanocomposites with (b) 4 vol. (c) 8 vol. and (d) 12 vol.% of MWCNTs are presented. - Highlights: • BaMg{sub 0.5}Co{sub 0.5}TiFe{sub 10}O{sub 19}/MWCNTs nanocomposites were synthesized. • The structural, magnetic and microwave absorption properties were investigated. • The microwave absorption is strongly influenced by volume percentage of MWCNTs. • The nanocomposite with 8 vol.% of MWCNTs can be proposed as a wideband absorber. - Abstract: In this study BaMg{sub 0.5}Co{sub 0.5}TiFe{sub 10}O{sub 19}/MWCNTs nanocomposites with different amount of MWCNTs (0, 4, 8 and 12 vol.%) were synthesized. Here, the X-ray diffraction (XRD), Fourier transform spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to demonstrate the structural and morphological characteristics of the prepared samples. XRD along with FTIR examinations exhibited that the nanocomposites were successfully synthesized. Vibrating sample magnetometer (VSM) showed the relatively strong dependence of saturation magnetization and coercivity on the volume percentage of MWCNTs. The microwave evaluation also confirmed that the complex permittivity of nanocomposites could be enhanced by adding MWCNTs. Finally, the nanocomposite with 8% vol. of MWCNTs exhibited the best microwave absorption performance among the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Decrease of the lumpectomy cavity volume after whole-breast irradiation affects small field boost planning

To determine whether small field boost (SFB) replanning is necessary when the lumpectomy cavity (LPC) decreases during whole-breast irradiation (WBI) and what parameters might predict a change in the SFB plan. Forty patients had computed tomography (CT) simulation (CT1) within 60 days of surgery and were resimulated (CT2) after 37.8-41.4 Gy for SFB planning. A 3-field photon plan and a single en face electron plan were created on both CTs and compared. In the 26 patients who had a {>=}5 cm{sup 3} and a {>=}25% decrease in lumpectomy cavity volume (LCV) between CT scans, the SFB plan using photons was different in terms of normal breast tissue volume irradiated (BTV) (p < 0.001), and field dimensions (p < 0.001). In 20/35 patients, the energy or field size changed for electron plans on CT2, but no tested characteristics predicted for a change. Less BTV was irradiated using electrons than photons in 29% (CT1) to 37% (CT2). SFB replanning needs to be individualized to each patient because of the variety of factors that can impact dosimetric planning. Replanning is recommended when using 3-field photons if the patient has experienced a {>=}5 cm{sup 3} and a {>=}25% decrease in LCV during WBI. Some patients may benefit from electron SFB replanning but no tested characteristics reliably predict those who may benefit the most. The amount of BTV irradiated is less with electrons than in photon plans and this has the potential to improve cosmesis, a clinically important outcome in breast-conserving therapy.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Whole-brain hippocampal sparing radiation therapy: Volume-modulated arc therapy vs intensity-modulated radiation therapy case study

The hippocampus is responsible for memory and cognitive function. An ongoing phase II clinical trial suggests that sparing dose to the hippocampus during whole-brain radiation therapy can help preserve a patient's neurocognitive function. Progressive research and advancements in treatment techniques have made treatment planning more sophisticated but beneficial for patients undergoing treatment. The aim of this study is to evaluate and compare hippocampal sparing whole-brain (HS-WB) radiation therapy treatment planning techniques using volume-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT). We randomly selected 3 patients to compare different treatment techniques that could be used for reducing dose to the hippocampal region. We created 2 treatment plans, a VMAT and an IMRT, from each patient's data set and planned on the Eclipse 11.0 treatment planning system (TPS). A total of 6 plans (3 IMRT and 3 VMAT) were created and evaluated for this case study. The physician contoured the hippocampus as per the Radiation Therapy Oncology Group (RTOG) 0933 protocol atlas. The organs at risk (OR) were contoured and evaluated for the plan comparison, which included the spinal cord, optic chiasm, the right and left eyes, lenses, and optic nerves. Both treatment plans produced adequate coverage on the planning target volume (PTV) while significantly reducing dose to the hippocampal region. The VMAT treatment plans produced a more homogenous dose distribution throughout the PTV while decreasing the maximum point dose to the target. However, both treatment techniques demonstrated hippocampal sparing when irradiating the whole brain.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2022

Machine learning prediction on the fractional free volume of polymer membranes

Fractional free volume (FFV) characterizes the microstructural level features of polymers and affects their properties including thermal, mechanical, and separation performance. Experimental measurements and theoretical analyses have been used to quantify the FFV of polymers, but challenges remain because of their limitations. Experimental measurements are laborious and based on semi empirical equations, while Bondi’s group contribution theory involves ambiguities like the determination of van der Waals volume and the choice of factor values in the theoretical equation. To efficiently evaluate the FFV of polymers, this study utilizes high-throughput molecular dynamics (MD) simulations to build a large dataset regarding polymer’s FFV. Based on this large dataset, we further build machine learning (ML) models to establish the composition-structure relation. Inspired by group contribution theory which correlates polymer’s functional groups to FFV, our ML models correlate polymer’s substructures or physico-chemical indexes to FFV. Here, our study first benchmarks the MD simulation protocol to obtain reliable FFV of polymers and then carries out high-throughput MD simulations for more than 6,500 homopolymers and 1,400 polyamides. Such a large and diverse dataset makes the well-trained ML models more generalizable, compared with the group contribution theory. The efficiency of a feed forward neural network model is further demonstrated by applying it to a hypothetical polyimide dataset of more than 8 million chemical structures. The predicted FFVs of hypothetical polyimides are further validated by MD simulations. The obtained FFVs of the 8 million polymers, plus their previously reported gas separation performances, demonstrate the promising capability of ML virtual screening for the discovery of polymer membranes with exceptional permeability/selectivity.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Measurement of G-phase volume fraction and number density in duplex stainless steels using transmission electron microscopy

Duplex stainless steels (DSS) have a high toughness and strength due the presence of both austenitic and ferritic phases. These alloys have had limited use in power production applications due to thermal embrittlement caused by spinodal decomposition and development of G-phase precipitates in the ferrite. Lean grade DSS alloys (e.g., 2101, 2003) may offer improved thermal stability due to the reduction of Cr- and Ni-equivalent elements when compared to standard grade compositions (e.g., 2205, 2209). The abundance of the G-phase was measured in five duplex stainless steels, three wrought alloys (2101, 2003, 2205) and their matching filler metals (2101-w, 2209-w), after aging at 427 °C for 1000 h and 10,000 h. The G-phase volume fraction, number density, size, and precipitate spacing were found using quantitative analysis of transmission electron microscopy dark field images and the composition of G-phase precipitates on other clusters were characterized with atom probe tomography (APT). In the welded alloys, the G-phase was found to develop rapidly, relative to the wrought material. A positive correlation was found between the nickel equivalent composition of the alloy and the G-phase volume fraction. The alloys 2205, 2209, and 2101-w, which are higher in Cr and Ni, all showed significant G-phase precipitation, further strengthening the hypothesis that lean grade DSS alloys are more thermally stable against precipitation in the ferrite. Electron diffraction showed a secondary phase present in the 2101 wrought alloy at 10,000 h, but it was not crystallographically consistent with the G-phase; APT showed the presence of nanoclusters rich in both nickel and copper for this alloy. In conclusion, no secondary phases or clusters were found in 2003 after 10,000 h of aging, so it may be a candidate alloy for applications that require long-life times at high operating temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2012

The Effect of Metallic Coatings and Crystallinity on the Volume Expansion of Silicon during Electrochemical Lithiation and Delithiation

Applying surface coatings to alloying anodes for Li-ion batteries can improve rate capability and cycle life, but it is unclear how this second phase affects mechanical deformation during electrochemical reaction. Here, in-situ transmission electron microscopy is employed to investigate the electrochemical lithiation and delithiation of silicon nanowires (NWs) with copper coatings. When copper is coated on one sidewall, the NW bilayer structure bends due to length changes in the silicon during delithiation. Tensile hoop stress causes conformal copper coatings to fracture during lithiation without undergoing bending deformation. In addition, in-situ and ex-situ observations indicate that a copper coating plays a role in suppressing volume expansion during lithiation. Finally, the deformation characteristics and dimensional changes of amorphous, polycrystalline, and single-crystalline silicon are compared and related to observed electrochemical behavior. This study reveals important aspects of the deformation process of silicon anodes, and the results suggest that metallic coatings can be used to improve rate behavior and to manage or direct volume expansion in optimized silicon anode frameworks.

Energy↗
DOE OSTI2010

Czochralski Silicon as a Detector Material for S-LHC Tracker Volumes

With an expected ten-fold increase in luminosity in S-LHC, the radiation environment in the tracker volumes will be considerably harsher for silicon-based detectors than the already harsh LHC environment. Since 2006, a group of CMS institutes, using a modified CMS DAQ system, has been exploring the use of Magnetic Czochralski silicon as a detector element for the strip tracker layers in S-LHC experiments. Both p+/n-/n+ and n+/p-/p+ sensors have been characterized, irradiated with proton and neutron sources, assembled into modules, and tested in a CERN beamline. There have been three beam studies to date and results from these suggest that both p+/n-/n+ and n+/p-/p+ Magnetic Czochralski silicon are sufficiently radiation hard for the $R>25$ cm regions of S-LHC tracker volumes. The group has also explored the use of forward biasing for heavily irradiated detectors, and although this mode requires sensor temperatures less than -50\,$^\circ$C, the charge collection efficiency appears to be promising.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

PET imaging of thin objects: measuring the effects of positron range and partial-volume averaging in the leag of Nicotiana Tabacum

PET imaging in plants is receiving increased interest as a new strategy to measure plant responses to environmental stimuli and as a tool for phenotyping genetically engineered plants. PET imaging in plants, however, poses new challenges. In particular, the leaves of most plants are so thin that a large fraction of positrons emitted from PET isotopes ({sup 18}F, {sup 11}C, {sup 13}N) escape while even state-of-the-art PET cameras have significant partial-volume errors for such thin objects. Although these limitations are acknowledged by researchers, little data have been published on them. Here we measured the magnitude and distribution of escaping positrons from the leaf of Nicotiana tabacum for the radionuclides {sup 18}F, {sup 11}C and {sup 13}N using a commercial small-animal PET scanner. Imaging results were compared to radionuclide concentrations measured from dissection and counting and to a Monte Carlo simulation using GATE (Geant4 Application for Tomographic Emission). Simulated and experimentally determined escape fractions were consistent. The fractions of positrons (mean {+-} S.D.) escaping the leaf parenchyma were measured to be 59 {+-} 1.1%, 64 {+-} 4.4% and 67 {+-} 1.9% for {sup 18}F, {sup 11}C and {sup 13}N, respectively. Escape fractions were lower in thicker leaf areas like the midrib. Partial-volume averaging underestimated activity concentrations in the leaf blade by a factor of 10 to 15. The foregoing effects combine to yield PET images whose contrast does not reflect the actual activity concentrations. These errors can be largely corrected by integrating activity along the PET axis perpendicular to the leaf surface, including detection of escaped positrons, and calculating concentration using a measured leaf thickness.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Finite-volume quantization condition from the N/D representation

We propose a new model-independent method for determining hadronic resonances from lattice QCD. The formalism is derived from the general principles of unitarity and analyticity, as encoded in the N/D representation of a partial-wave two-body amplitude. The associated quantization condition relates the finite-volume spectrum to the infinite-volume numerator $\mathscr{N}$, used to reconstruct the scattering amplitude from dispersive relations. Unlike the original Lüscher condition, this new formalism is valid for energies coinciding with the left-hand cuts from arbitrary one- and multiparticle exchanges.

Dawid, Sebastian M. [Univ. of Washington, Seattle,↗
DOE OSTI2016

Strength statistics of single crystals and metallic glasses under small stressed volumes

It has been well documented that plastic deformation of crystalline and amorphous metals/alloys shows a general trend of “smaller is stronger”. The majority of the experimental and modeling studies along this line have been focused on finding and reasoning the scaling slope or exponent in the logarithmic plot of strength versus size. In contrast to this view, here we show that the universal picture should be the thermally activated nucleation mechanisms in small stressed volume, the stochastic behavior as to find the weakest links in intermediate sizes of the stressed volume, and the convolution of these two mechanisms with respect to variables such as indenter radius in nanoindentation pop-in, crystallographic orientation, pre-strain level, sample length as in uniaxial tests, and others. Furthermore, experiments that cover the entire spectrum of length scales and a unified model that treats both thermal activation and spatial stochasticity have discovered new perspectives in understanding and correlating the strength statistics in a vast of observations in nanoindentation, micro-pillar compression, and fiber/whisker tension tests of single crystals and metallic glasses.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Arbitrarily High-Order-Accurate, Hermite WENO Limited, Boundary-Averaged Multi-Moment Constrained Finite-Volume (BA-MCV) Schemes for 1-D Transport

This study introduces the Boundary Averaged Multi-moment Constrained finite-Volume (BA- MCV) scheme for 1-D transport with Hermite Weighted Essentially Non-Oscillatory (HWENO) limiting using the ADER Differential Transform (ADER-DT) time discretization. The BA- MCV scheme evolves a cell average using a Finite-Volume (FV) scheme, and it adds further constraints as point wise derivatives of the state at cell boundaries, which are evolved in strong form using PDE derivatives. The resulting scheme maintains a Maximum Stable CFL (MSCFL) value of one no matter how high-order the scheme is. Also, parallel communication requirements are very low and will be described. h-refinement experiments demonstrate proper convergence order, and p-refinement experiments demonstrate expected exponential convergence. The over- all ADER-DT + BA-MCV + HWENO scheme is a scalable and larger time step alternative to Galerkin methods for multi-moment fluid simulation in climate and weather applications.

Norman, Matthew↗
DOE OSTI2022

Heat conduction in an irregular magnetic field. Part 2. Heat transport as a measure of the effective non-integrable volume

Given the large anisotropy of transport processes in magnetized plasmas, the magnetic field structure can strongly impact heat diffusion: magnetic surfaces and cantori form barriers to transport while chaotic layers and island structures can degrade confinement. When a small but non-zero amount of perpendicular diffusion is included, the structure of the magnetic field becomes less important, allowing pressure gradients to be supported across chaotic regions and island chains. We introduce a metric for the effective volume over which the local parallel diffusion dominates based on the solution to the anisotropic heat diffusion equation. To validate this metric, we consider model fields with a single island chain and a strongly chaotic layer for which analytic predictions of the relative parallel and perpendicular transport can be made. We also analyse critically chaotic fields produced from different sets of perturbations, highlighting the impact of the mode number spectrum on the heat transport. Our results indicate that this metric coincides with the effective volume of non-integrability in the limit $\kappa _{\perp } \rightarrow 0$ , where $\kappa_{\perp}$ is the perpendicular diffusion coefficient. We propose that this metric be used to assess the impact of non-integrability on the heat transport in stellarator equilibria.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Enzyme Reactions in Nanoporous, Picoliter Volume Containers

Advancements in nanoscale fabrication allow creation of small volume reaction containers that can facilitate the screening and characterization of enzymes. A porous, ~19 pL volume vessel has been used in this work to carry out enzyme reactions under varying substrate concentrations. Glucose oxidase and horseradish peroxidase can be contained in these structures and diffusively fed with a solution containing glucose and the fluorogenic substrate Amplex Red through the engineered nanoscale pore structure. Fluorescent microscopy was used to monitor the reaction, which was carried out under microfluidic control. Kinetic characteristics of the enzyme were evaluated and compared with results from conventional scale reactions. These picoliter, nanoporous containers can facilitate quick determination of enzyme kinetics in microfluidic systems without the requirement of surface tethering and can be used for applications in drug discovery, clinical diagnostics and high-throughput screening.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Native state volume fluctuations in proteins as a mechanism for dynamic allostery

Allostery enables tight regulation of protein function in the cellular environment. While existing models of allostery are firmly rooted in the current structure-function paradigm, the mechanistic basis for allostery in the absence of structural change remains unclear. In this study, we show that a typical globular protein is able to undergo significant changes in volume under native conditions while exhibiting no additional changes in protein structure. These native state volume fluctuations were found to correlate with changes in internal motions that were previously recognized as a source of allosteric entropy. This finding offers a novel mechanistic basis for allostery in the absence of canonical structural change. As a result, the unexpected observation that function can be derived from expanded, low density protein states has broad implications for our understanding of allostery and suggests that the general concept of the native state be expanded to allow for more variable physical dimensions with looser packing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Breakdown of Volume Scaling in Auger Recombination in CdSe/CdS Heteronanocrystals: The Role of the Core-Shell Interface

Spatial confinement of electronic excitations in semiconductor nanocrystals (NCs) results in a significant enhancement of nonradiative Auger recombination (AR), such that AR processes can easily dominate the decay of multiexcitons. AR is especially detrimental to lasing applications of NCs, as optical gain in these structures explicitly relies on emission from multiexciton states. In standard NCs, AR rates scale linearly with inverse NC volume. Here, we investigate multiexciton dynamics in hetero-NCs composed of CdSe cores and CdS shells of tunable thickness. We observe a dramatic decrease in the AR rates at the initial stage of shell growth, which cannot be explained by traditional volume scaling alone. Rather, fluorescence-line-narrowing studies indicate that the suppression of AR correlates with the formation of an alloy layer at the core-shell interface suggesting that this effect derives primarily from the “smoothing” of the confinement potential associated with interfacial alloying. These data highlight the importance of NC interfacial structure in the AR process and provide general guidelines for the development of new nanostructures with suppressed AR for future lasing applications.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Representative elementary volume estimation for porosity, moisture saturation, and air-water interfacial areas in unsaturated porous media: Data quality implications

Achieving a representative elementary volume (REV) has become a de facto criterion for demonstrating the quality of {mu}CT measurements in porous media systems. However, the data quality implications of an REV requirement have not been previously examined. In this work, deterministic REVs for porosity, moisture saturation (S{sub W}), and air-water interfacial area (A{sub I}) were estimated using a set of 49 {mu}CT images of eight unsaturated homogeneous porous media with heterogeneity in moisture distributions present in varying degrees. Estimated porosity REVs were <8 mm{sup 3} for all cases, smaller than typical CT image sizes ({approx}100 mm{sup 3}). Estimated S{sub W} and A{sub I} REVs were <55 mm{sup 3} for cases with homogeneous moisture distributions but could not be estimated for cases with heterogeneous moisture distributions, due to the absence of a distinct 'REV plateau' within the maximum imaged volume. Conventionally, S{sub W} and A{sub I} data from such non-REV cases would be excluded. The implications of excluding data on the basis of REV were examined by comparing A{sub I}-S{sub W} data measured on image windows of increasing size against the expected linear A{sub I}-S{sub W} relationship. At measurement scales exceeding porosity REV, random fluctuations in A{sub I}-S{sub W} data were excluded, even for cases containing heterogeneous moisture distributions. In contrast, requiring measurement scales to exceed S{sub W} and A{sub I} REV appeared overly restrictive and resulted in visible loss of reliable A{sub I}-S{sub W} data. We attribute these findings to overestimation of REVs due to inherently problematic estimation of deterministic REVs in real systems. Implications of these findings for ensuring CT data quality and the efficient use of CT data are discussed.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2016

Lithium-coated polymeric matrix as a minimum volume-change and dendrite-free lithium metal anode

Lithium metal is the ideal anode for the next generation of high-energy-density batteries. Nevertheless, dendrite growth, side reactions and infinite relative volume change have prevented it from practical applications. Here, we demonstrate a promising metallic lithium anode design by infusing molten lithium into a polymeric matrix. The electrospun polyimide employed is stable against highly reactive molten lithium and, via a conformal layer of zinc oxide coating to render the surface lithiophilic, molten lithium can be drawn into the matrix, affording a nano-porous lithium electrode. Importantly, the polymeric backbone enables uniform lithium stripping/plating, which successfully confines lithium within the matrix, realizing minimum volume change and effective dendrite suppression. The porous electrode reduces the effective current density; thus, flat voltage profiles and stable cycling of more than 100 cycles is achieved even at a high current density of 5 mA cm -2 in both carbonate and ether electrolyte. Furthermore, the advantages of the porous, polymeric matrix provide important insights into the design principles of lithium metal anodes.

36 MATERIALS SCIENCE↗