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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Communication: Accurate higher-order van der Waals coefficients between molecules from a model dynamic multipole polarizability

Due to the absence of the long-range van der Waals (vdW) interaction, conventional density functional theory (DFT) often fails in the description of molecular complexes and solids. In recent years, considerable progress has been made in the development of the vdW correction. However, the vdW correction based on the leading-order coefficient C{sub 6} alone can only achieve limited accuracy, while accurate modeling of higher-order coefficients remains a formidable task, due to the strong non-additivity effect. Here, we apply a model dynamic multipole polarizability within a modified single-frequency approximation to calculate C{sub 8} and C{sub 10} between small molecules. We find that the higher-order vdW coefficients from this model can achieve remarkable accuracy, with mean absolute relative deviations of 5% for C{sub 8} and 7% for C{sub 10}. Inclusion of accurate higher-order contributions in the vdW correction will effectively enhance the predictive power of DFT in condensed matter physics and quantum chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Muon-Neutrino Charged-Current Cross Sections from MicroBooNE: First Simultaneous Measurements of Final States with and without Protons for Muon-Neutrino Scattering on Argon

A detailed understanding of muon neutrino charged-current interactions on argon is crucial to the study of neutrino oscillations in current and future experiments using liquid argon time projection chambers. To help fill this need, MicroBooNE has produced a comprehensive set of cross section measurements which simultaneously probe the leptonic and hadronic systems by dividing the inclusive channel into final states with and without protons. Data-driven model validation utilizing the conditional constraint formalism is employed to detect mismodeling that may bias the nominal flux averaged cross section results, which are extracted with the Wiener-SVD unfolding method. The results are compared to widely used event generator predictions revealing significant mismodeling of final states without protons, possibly due to insufficient treatment of final state interactions. These are first differential muon neutrino-argon cross section measurements made simultaneously for final states with and without protons and provide novel information that will help stimulate the improvement of event generator modeling.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2014

A FIB/TEM/Nanosims Study of a Wark-Lovering Rim on an Allende CAI

Ca- Al-rich inclusions (CAIs) are commonly surrounded by Wark-Lovering (WL) rims - thin (approx. 50 micrometers) multilayered sequences - whose mineralogy is dominated by high temperature minerals similar to those that occur in the cores of CAIs [1]. The origins of these WL rims involved high temperature events in the early nebula such as condensation, flashheating or reaction with a nebular reservoir, or combinations of these processes. These rims formed after CAI formation but prior to accretion into their parent bodies. We have undertaken a coordinated mineralogical and isotopic study of WL rims to determine the formation conditions of the individual layers and to constrain the isotopic reservoirs they interacted with during their history. We focus here on the spinel layer, the first-formed highest- temperature layer in the WL rim sequence. Results and Discussion: We have performed mineralogical, chemical and isotopic analyses of an unusual ultrarefractory inclusion from the Allende CV3 chondrite (SHAL) consisting of an approx. 500 micrometers long single crystal of hibonite and co-existing coarsegrained perovskite. SHAL is partially surrounded by WL rim. We previously reported on the mineralogy, isotopic compositions and trace elements in SHAL [2-4]. The spinel layer in the WL rim is present only on the hibonite and terminates abruptly at the contact with the coarse perovskite. This simple observation shows that the spinel layer is not a condensate in this case (otherwise spinel would have condensed on the perovskite as well). The spinel layer appears to have formed by gas-phase corrosion of the hibonite by Mg-rich vapors such that the spinel layer grew at the expense of the hibonite. We also found that the spinel layer has the same 16Orich composition as the hibonite. The spinel layer is polycrystalline and individual crystals do not show a crystallographic relationship with the hibonite. An Al-diopside layer overlies the spinel layer, and is present on both the hibonite and perovskite. While the spinel is 16O-rich, WL-rim perovskite and pyroxene are 16O-poor. This isotopic heterogeneity likely reflects O isotopic equilibration of WL-rim perovskite and pyroxene with a planetary O isotopic reservoir after the WL rim formation. The hibonite is zoned and contains wt.% levels of Ti, Mg and Fe in contact with the Fe-bearing spinel (Sp60Hc40) in the WL rim. The Fe enrichment in spinel is likely related to the Na-Fe metasomatism that is ubiquitous in Allende. Conclusions: The petrography and microstructure of the spinel layer in a WL rim sequence shows that it formed by gas phase reactions at high temperature in the nebula. The oxygen isotopic composition of the spinel indicates that this WL rim layer formed in the same (or similar) nebular gas reservoir as the host CAI.

Keller, L. P.↗
DOE OSTI2014

Communication: Electron transfer mediated decay enabled by spin-orbit interaction in small krypton/xenon clusters

In this work we study the influence of relativistic effects, in particular spin-orbit coupling, on electronic decay processes in KrXe{sub 2} clusters of various geometries. For the first time it is shown that inclusion of spin-orbit coupling has decisive influence on the accessibility of a specific decay pathway in these clusters. The radiationless relaxation process is initiated by a Kr 4s ionization followed by an electron transfer from xenon to krypton and a final second ionization of the system. We demonstrate the existence of competing electronic decay pathways depending in a subtle way on the geometry and level of theory. For our calculations a fully relativistic framework was employed where omission of spin-orbit coupling leads to closing of two decay pathways. These findings stress the relevance of an adequate relativistic description for clusters with heavy elements and their fragmentation dynamics.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2013

Impact of Radiatively Interactive Dust Aerosols in the NASA GEOS-5 Climate Model: Sensitivity to Dust Particle Shape and Refractive Index

We investigate the radiative effects of dust aerosols in the NASA GEOS-5 atmospheric general circulation model. GEOS-5 is improved with the inclusion of a sectional aerosol and cloud microphysics module, the Community Aerosol and Radiation Model for Atmospheres (CARMA). Into CARMA we introduce treatment of the dust and sea salt aerosol lifecycle, including sources, transport evolution, and sinks. The aerosols are radiatively coupled to GEOS-5, and we perform a series of multi-decade AMIP-style simulations in which dust optical properties (spectral refractive index and particle shape distribution) are varied. Optical properties assuming spherical dust particles are from Mie theory, while those for non-spherical shape distributions are drawn from a recently available database for tri-axial ellipsoids. The climatologies of the various simulations generally compare well to data from the MODIS, MISR, and CALIOP space-based sensors, the ground-based AERONET, and surface measurements of dust deposition and concentration. Focusing on the summertime Saharan dust cycle we show significant variability in our simulations resulting from different choices of dust optical properties. Atmospheric heating due to dust enhances surface winds over important Saharan dust sources, and we find a positive feedback where increased dust absorption leads to increased dust emissions. We further find that increased dust absorption leads to a strengthening of the summertime Hadley cell circulation, increasing dust lofting to higher altitudes and strengthening the African Easterly Jet. This leads to a longer atmospheric residence time, higher altitude, and generally more northward transport of dust in simulations with the most absorbing dust optical properties. We find that particle shape, although important for radiance simulations, is a minor effect compared to choices of refractive index, although total atmospheric forcing is enhanced by greater than 10 percent for simulations incorporating a spheroidal shape distribution versus ellipsoidal or spherical shapes.

radiative forcing↗
DOE OSTI2015

Correlation between inter-spin interaction and molecular dynamics of organic radicals in organic 1D nanochannels

One-dimensional (1D) molecular chains of 4-substituted-2,2,6,6-tetramethyl-1-piperidinyloxyl (4-X-TEMPO) radicals were constructed in the crystalline 1D nanochannels of 2,4,6-tris(4-chlorophenoxy)-1,3,5-triazine (CLPOT) used as a template. The ESR spectra of CLPOT inclusion compounds (ICs) using 4-X-TEMPO were examined on the basis of spectral simulation using EasySpin program package for simulating and fitting ESR spectra. The ESR spectra of [(CLPOT){sub 2}-(TEMPO){sub 1.0}] IC were isotropic in the total range of temperatures. The peak-to-peak line width (ΔB{sub pp}) became monotonically narrower from 2.8 to 1.3 mT with increase in temperature in the range of 4.2–298 K. The effect of the rotational diffusion motion of TEMPO radicals in the CLPOT nanochannels for the inter-spin interaction of the [(CLPOT){sub 2}-(TEMPO){sub 1.0}] IC was found to be smaller than the case of [(TPP){sub 2}−(TEMPO){sub 1.0}] IC (TPP = tris(o-phenylenedioxy)cyclotriphosphazene) reported in our previous study. The ΔB{sub pp} of the [(CLPOT){sub 2}-(TEMPO){sub 1.0}] IC in the whole range of temperatures was much narrower than the estimation to be based on the Van Vleck’s formula for the second moment of the rigid lattice model where the electron spin can be considered as fixed; 11 mT of Gaussian line-width component. This suggests the possibility of exchange narrowing in the 1D organic-radical chains of the [(CLPOT){sub 2}-(TEMPO){sub 1.0}] IC. On the other hand, the ESR spectra of [(CLPOT){sub 2}-(MeO-TEMPO){sub 0.41}] IC (MeO-TEMPO = 4-methoxy-TEMPO) were reproduced by a superposition of major broad isotropic adsorption line and minor temperature-dependent modulated triplet component. This suggests that the IC has the part of 1D organic-radical chains and MeO-TEMPO molecules isolated in the CLPOT nanochannels.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Final Report on the Development of an Improved Cloud Microphysical Product for Model and Remote Sensing Evaluation using RACORO Observations

We proposed to analyze data collected during the Routine Aerial Facilities (AAF) Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) in order to develop an integrated product of cloud microphysical properties (number concentration of drops in different size bins, total liquid drop concentration integrated over all bin sizes, liquid water content LWC, extinction of liquid clouds bw, effective radius of water drops re, and radar reflectivity factor) that could be used to evaluate large-eddy simulations (LES), general circulation models (GCMs) and ground-based remote sensing retrievals, and to develop cloud parameterizations with the end goal of improving the modeling of cloud processes and properties and their impact on atmospheric radiation. We have completed the development of this microphysical database and have submitted it to ARM for consideration of its inclusion on the ARM database as a PI product. This report describes the development of this database, and also describes research that has been conducted on cloud-aerosol interactions using the data obtained during RACORO. A list of conference proceedings and publications is also included.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

First Experimental Test of the Ratio Method

The ratio is a new reaction observable suggested to extract accurately structure information on halo nuclei. It corresponds to the ratio of differential cross sections for scattering and breakup, which is predicted to remove the uncertainty related to the reaction dynamics. We present here the first experimental test of the method for the 11 Be + 12 C collision at E Lab = 20A MeV performed at Texas A&M University. Differential cross sections for scattering and inclusive one-neutron breakup have been measured with the new detector array BlueSTEAl. The ratio of cross sections is very smooth and independent of the projectile-target interaction, which demonstrates the validity of the ratio method. We extend our analysis to existing 11 Be + 208 Pb data, confirming that the method works well on any target.

11Be↗
DOE OSTI2026

Charged Pion Production Explorations Using the NOvA Near Detector

The~300T NOvA Near Detector (ND) utilizes segmented liquid scintillator to reconstruct interacting neutrinos arriving from the NuMI Beamline at Fermilab. Given NuMI’s intensity and the ND’s relatively short baseline, NOvA has recorded some of the world’s highest statistics for neutrino interactions around ~2GeV, in great similarity to the forthcoming DUNE experiment. This energy regime is replete with resonant interactions, which will form the plurality of final states in DUNE. NOvA seeks to empower the community with measurements of processes for both semi-exclusive and semi-inclusive charged pion production across muon kinematics and pion angle via single-and multidifferential neutrino scattering cross sections. This poster will review current progress across several related analyses, and look forward to future results.

Roy, Palash K. [Wichita State U.] (ORCID:000000022↗
NASA NTRS2002

Probabilistic Fatigue: Computational Simulation

Fatigue is a primary consideration in the design of aerospace structures for long term durability and reliability. There are several types of fatigue that must be considered in the design. These include low cycle, high cycle, combined for different cyclic loading conditions - for example, mechanical, thermal, erosion, etc. The traditional approach to evaluate fatigue has been to conduct many tests in the various service-environment conditions that the component will be subjected to in a specific design. This approach is reasonable and robust for that specific design. However, it is time consuming, costly and needs to be repeated for designs in different operating conditions in general. Recent research has demonstrated that fatigue of structural components/structures can be evaluated by computational simulation based on a novel paradigm. Main features in this novel paradigm are progressive telescoping scale mechanics, progressive scale substructuring and progressive structural fracture, encompassed with probabilistic simulation. These generic features of this approach are to probabilistically telescope scale local material point damage all the way up to the structural component and to probabilistically scale decompose structural loads and boundary conditions all the way down to material point. Additional features include a multifactor interaction model that probabilistically describes material properties evolution, any changes due to various cyclic load and other mutually interacting effects. The objective of the proposed paper is to describe this novel paradigm of computational simulation and present typical fatigue results for structural components. Additionally, advantages, versatility and inclusiveness of computational simulation versus testing are discussed. Guidelines for complementing simulated results with strategic testing are outlined. Typical results are shown for computational simulation of fatigue in metallic composite structures to demonstrate the versatility of this novel paradigm in predicting a priori fatigue life.

Chamis, Christos C.↗
NASA NTRS2009

Atlantic Tropical Cyclogenetic Processes during SOP-3 NAMMA in the GEOS-5 Global Data Assimilation and Forecast System

This article investigates the role of the Saharan Air Layer (SAL) in tropical cyclogenetic processes associated with a non-developing and a developing African easterly wave observed during the Special Observation Period (SOP-3) phase of the 2006 NASA African Monsoon Multidisciplinary Analyses (NAMMA). The two waves are chosen because both interact heavily with Saharan air. A global data assimilation and forecast system, the NASA GEOS-5, is being run to produce a set of high-quality global analyses, inclusive of all observations used operationally but with denser satellite information. In particular, following previous works by the same Authors, the quality-controlled data from the Atmospheric Infrared Sounder (AIRS) used to produce these analyses have a better coverage than the one adopted by operational centers. From these improved analyses, two sets of 31 5-day high resolution forecasts, at horizontal resolutions of both half and quarter degrees, are produced. Results show that very steep moisture gradients are associated with the SAL in forecasts and analyses even at great distance from the Sahara. In addition, a thermal dipole (warm above, cool below) is present in the non-developing case. Moderate Resolution Imaging Spectroradiometer (MODIS) show that aerosol optical thickness is higher in the non-developing case. Altogether, results suggest that radiative effect of dust may play some role in producing a thermal structure less favorable to cyclogenesis. Results also indicate that only global horizontal resolutions on the order of 20-30 kilometers can capture the large-scale transport and the fine thermal structure of the SAL, inclusive of the sharp moisture gradients, reproducing the effect of tropical cyclone suppression which has been hypothesized by previous authors from observational and regional modeling perspectives. These effects cannot be fully represented at lower resolutions. Global resolution of a quarter of a degree is a minimum critical threshold to investigate Atlantic tropical cyclogenesis from a global modeling perspective.

Reale, Oreste↗
DOE OSTI2019

First Measurements of Inclusive Muon Neutrino Charged Current Differential Cross Sections on Argon at 0.8 GeV Average Neutrino Energy with the MicroBooNE Detector

Current and next-generation precision neutrino oscillation experiments aim to determine the neutrino mass ordering, to measure the extent of CP violation in the lepton sector and to probe beyond Standard Model physics, such as sterile neutrinos. These experiments rely on models for neutrino interactions with matter that are complicated by nuclear effects and final state interactions. To date, these effects cannot be modelled precisely, especially for heavy target nuclei, typically used in modern neutrino experiments. Many future experiments will employ detectors based on the liquid argon time projection chamber technology. As a consequence, neutrino-argon cross-section measurements are of the outmost importance, especially given the relative scarcity of neutrino-argon data, due to the novelty of the technology. This thesis presents the first measurement of muon-neutrino charged-current inclusive cross section on argon at a mean neutrino energy of 0.8 GeV. Data were collected using the MicroBooNE liquid argon time projection chamber in the Fermilab Booster neutrino beam during a period of six months, corresponding to an exposure of $1.6 \times 10^{20}$ protons on target. The measured cross section is presented as a function of the outgoing muon momentum, using multiple Coulomb scattering as a measurement technique, as well as the muon angle with respect to the beam direction. A comparison of the measured cross section obtained with two different configurations of the \textsc{Genie} neutrino event generator is performed, and better agreement is found when using nuclear-effect modelling in the theoretical calculations. Additionally, the total flux integrated cross section is measured to be $0.693 \pm 0.010 \, (\text{stat.}) \pm 0.165 \, (\text{syst.}) \times 10^{-38} \, \text{cm}^{2}$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Initial demonstration of automated fuel performance modeling with 1977 EBR-II metallic fuel pins using BISON code with FIPD and IMIS databases

Using the BISON fuel performance code, simulations were conducted using an automated process to read initial and operating conditions from the Fuels Irradiation and Physics Database (FIPD) and Integral Fast Reactor materials information system (IMIS) database, which contains metallic fuel data from the Experimental Breeder Reactor-II (EBR-II). This work demonstrates use of an integrated framework to access the vast majority of EBR-II experimental fuel pin data to support rapid development of fuel performance models for next-generation metallic fuel systems. With this capability, validation for fuel qualification can be performed rapidly. Between IMIS and FIPD, there is enough information to conduct 1977 unique EBR-II metallic fuel pin histories from 24 different experiments, at varying levels of detail between the two databases. Each of these histories includes a high-resolution power history, flux history, coolant channel flow rates, and coolant channel temperatures. Fission gas release (FGR), cumulative damage fraction (CDF), fuel axial swelling, cladding profilometry, and burnup were all simulated in BISON. The results were compared to post-irradiation examination (PIE) results for the initial demonstration of automated BISON modeling. BISON simulations conducted with IMIS and FIPD were in rough agreement with PIE measurements and calculations. Cladding profilometry, FGR, and fuel axial swelling were found to be in rough agreement with PIE measurements, depending on the physics used within the BISON input files. Here, the mechanical contact solver chosen was found to significantly impact axial fuel swelling and cladding strain predictions. CDF values were assessed to see whether pin failure may have been predicted (CDF ≥ 1). This work suggests that continued development of an automated tool for BISON should focus on inclusion of the Fast Flux Test Facility (FFTF) experimental data for a larger database for metallic fuel, improved physical models to better capture fuel performance, such as fuel-cladding interactions, and a more detailed comparison with available PIE data to further the BISON model development.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Partonic transverse distributions of up and down quarks

The quark-gluon dynamics manifests itself in a set of non-perturbative functions describing all possible spin-spin and spin-orbit correlations. The Transverse Momentum Dependent parton distributions (TMDs) and Generalized Parton Distributions (GPDs) carry information not only on the longitudinal but also on the transverse momentum and position of partons, providing rich and direct information on the orbital motion of quarks. Single and Dihadron semi-inclusive and hard exclusive production, both in current and target fragmentation regions, provide a variety of spin and azimuthal angle dependent observables, sensitive to the dynamics of quark-gluon interactions. Studies of the 3D PDFs are currently driving the upgrades of several existing facilities (JLab, COMPASS and RHIC), and the design and construction of new facilities worldwide (EIC, FAIR, and JPARC). In this talk, we present an overview of the current status and some future measurements of the orbital structure of nucleons at Jefferson Lab.

Avagyan, Harutyun↗
DOE OSTI2026

Continuum contribution to charged-current absorption of low-energy $ν_e$ on $^{40}$Ar

Accurate modeling of the absorption of tens-of-MeV $ν_e$ on $^{40}$Ar is needed to enable measurements of astrophysical neutrinos using large liquid argon time projection chamber (LArTPC) detectors, such as those planned for the Deep Underground Neutrino Experiment (DUNE). We revisit the MARLEY neutrino interaction model used in present estimates of DUNE sensitivity to supernova and solar neutrino signals. Multiple theoretical refinements are pursued, especially in the unbound continuum region of nuclear excitation energy. Inclusive charged-current neutrino-argon cross sections are calculated using a hybrid strategy. Nuclear transitions to unbound states are treated using a Hartree-Fock Continuum Random Phase Approximation (HF-CRPA) model, including forbidden contributions. Allowed transitions to low-lying discrete levels are also included using indirect measurements and approximate corrections for the momentum transfer dependence. Exclusive predictions are obtained by coupling these calculations with a statistical nuclear de-excitation model. The impact on observables of interest for DUNE and similar experiments is examined in terms of both total and differential cross sections. Our refined calculations predict a lower allowed portion of the cross section relative to the prior MARLEY model. At neutrino energies appreciably below 100 MeV, the inclusion of forbidden transitions does not fully compensate for the loss of allowed strength. For a representative neutrino burst from a galactic core-collapse supernova, our results suggest that MARLEY 1.2.0 overestimates the event yield in a DUNE-like detector by approximately 20%. However, because this overestimation is more severe at backwards angles, use of the charged-current $ν_e$-$^{40}$Ar reaction for supernova pointing may be more feasible than previously expected.

Gardiner, Steven [Fermilab]↗
DOE OSTI2012

Control of calcium carbonate crystallization by using anionic polymethylsiloxanes as templates

Sulfonated (SO{sub 3}H-PMS) and carboxylated (CO{sub 2}H-PMS) polymethylsiloxanes were synthesized and their effects as anionic template modifier on the CaCO{sub 3} crystal morphologies were evaluated. In vitro crystallization assays of CaCO{sub 3} were performed at room temperature by using gas diffusion method at different concentration, pH and time. SEM images of CaCO{sub 3} showed well-defined short calcite piles (ca. 5 {mu}m) and elongated calcite (ca. 20 {mu}m) when SO{sub 3}H-PMS was used. When CO{sub 2}H-PMS was used, the morphology of CaCO{sub 3} crystals was single-truncated at pH 7-9 and aggregated-modified calcite at pH 10-11. However, at pH 12 the least stable donut-shaped vaterite crystals were formed. EDS and XRD confirmed the presence of Si from anionic PMS templates on the CaCO{sub 3} surfaces and its polymorphism, respectively. Results showed that the selective morphologies of CaCO{sub 3} reflect the electrostatic interaction of anionic groups of functionalized PMS with Ca{sup 2+} adsorbed on CaCO{sub 3} crystals. Rounded and truncated-modified fluorescent CaCO{sub 3} was also produced by the inclusion of functionalized PMS into the lattice of CaCO{sub 3} matrix. We demonstrated that the anionic PMS offer a good modifier for polymer-controlled crystallization and a convenient approach for understanding the biomineralization field. - Graphical abstract: Optical photographs of rounded and truncated-modified fluorescent CaCO{sub 3} produced by the inclusion of sulfonated (SO{sub 3}H-PMS) polymethylsiloxanes into the lattice of CaCO{sub 3} matrix. Insert represents the simulation of modified and fluorescent CaCO{sub 3} crystals using Software JCrystal, (2008). Highlights: Black-Right-Pointing-Pointer We prepared two anionic polymethylsiloxanes (PMS) as templates. Black-Right-Pointing-Pointer Their modifier capacity on the CaCO{sub 3} crystal morphologies was demonstrated. Black-Right-Pointing-Pointer At pH 12, the least stable donut-shaped vaterite, was formed. Black-Right-Pointing-Pointer EDS confirmed the presence of Si from anionic PMS templates on the CaCO{sub 3} surfaces. Black-Right-Pointing-Pointer Fluorescent CaCO{sub 3} was produced by the inclusion of PMS into the CaCO{sub 3} matrix.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Inclusive studies of two- and three-nucleon short-range correlations in 3 H and 3 He

Inclusive electron scattering at carefully chosen kinematics can isolate scattering from the high-momentum nucleons in short-range correlations (SRCs). SRCs are produced by the hard, short-distance interactions of nucleons in the nucleus, and because the two-nucleon (2N) SRCs arise from the same N-N interaction in all nuclei, the cross section in the SRC-dominated regime is identical up to an overall scaling factor. This scaling behavior has been used to identify SRC dominance and to measure the contribution of SRCs in a wide range of nuclei. We examine this scaling behavior over a range of momentum transfers using new data on 2 H, 3 H, and 3 He, and find an expanded scaling region compared to heavy nuclei. Motivated by this improved scaling, we examine the 3 H and 3 He data in kinematics where three-nucleon SRCs may play an important role. The data for the largest struck nucleon momenta are consistent with isolation of scattering from three-nucleon SRCs, and suggest that the very highest momentum nucleons in 3 He have a nearly isospin-independent momentum configuration.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Unraveling the multi-step crystallization mechanism of polytetrafluoroethylene, modified polytetrafluoroethylene, and their nanocomposites with boron nitride nanobarbs: Experimental insights and theoretical analysis

The non-isothermal crystallization behavior and kinetics of polytetrafluoroethylene (PTFE) composites with boron nitride nanobarb (BNNB), a new generation nanostructure with unique surface morphology and mechanical “barbs” have been analyzed, understanding these properties is essential for their high-end applications as thermal interface materials (TIM) for microwave, 5G and microelectronic devices. The analysis of the crystallization parameters includes crystallization onset, peak and end temperatures, crystallization half-life and overall crystallinity of PTFE, modified PTFE and their BNNB composites. The results were further analyzed using theoretical models such as the combined Avrami-Ozawa model. It was found that BNNB supports crystallization in the modified PTFE but shows minimal effect on the crystallization of PTFE. Due to the limitation of the classical theoretical models used above in fully characterizing the multi-step crystallization process of PTFE, an in-depth analysis using the model-free advanced isoconversional computation was used to characterize the PTFE crystallization based on the evolution of activation energy with fractional crystallinity and for the first time with temperature. Three kinetic regions were identified in the crystallization mechanism. Here, this study investigated the molecular organization and microstructural evolution of PTFE, modified PTFE and their composites during non-isothermal crystallization using advanced X-ray scattering measurements. An insight into the changes undergone by the material's microstructural units including crystallite size and morphology, lamellar thickness and lamellar interfacial layer thickness, and crystallographic phase dynamics during non-isothermal cooling from the melt, was provided here in this work. The effect of copolymer modification of PTFE and the inclusion of pristine and functionalized BNNB (a thermally conductive and electrically insulating ceramic) are both new investigations that provide valuable knowledge for the development of materials with strong matrix-nanofiller interaction and guidance for optimizing sintering and cooling cycles, two key steps in PTFE processing that largely affect the material microstructural features. Overall, the result of the three-part investigation demonstrates that BNNB supports crystallization in the modified PTFE up to 20 wt% concentration and at low and high cooling rates typically used in the industrial processing of PTFE.

36 MATERIALS SCIENCE↗