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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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DOE OSTI2021

Beyond optimization—supervised learning applications in relativistic laser-plasma experiments

We explore the applications of machine learning techniques in relativistic laser-plasma experiments beyond optimization purposes. We predict the beam charge of electrons produced in a laser wakefield accelerator given the laser wavefront change caused by a deformable mirror. Machine learning enables feature analysis beyond merely searching for an optimal beam charge, showing that specific aberrations in the laser wavefront are favored in generating higher beam charges. Supervised learning models allow characterizing the measured data quality as well as recognizing irreproducible data and potential outliers. Furthermore, we also include virtual measurement errors in the experimental data to examine the model robustness under these conditions. This work demonstrates how machine learning methods can benefit data analysis and physics interpretation in a highly nonlinear problem of relativistic laser-plasma interaction.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Electrostatic point charge fitting as an inverse problem: Revealing the underlying ill-conditioning

Atom-centered point charge (PC) model of the molecular electrostatics—a major workhorse of the atomistic biomolecular simulations—is usually parameterized by least-squares (LS) fitting of the point charge values to a reference electrostatic potential, a procedure that suffers from numerical instabilities due to the ill-conditioned nature of the LS problem. To reveal the origins of this ill-conditioning, we start with a general treatment of the point charge fitting problem as an inverse problem and construct an analytical model with the point charges spherically arranged according to Lebedev quadrature which is naturally suited for the inverse electrostatic problem. This analytical model is contrasted to the atom-centered point-charge model that can be viewed as an irregular quadrature poorly suited for the problem. This analysis shows that the numerical problems of the point charge fitting are due to the decay of the curvatures corresponding to the eigenvectors of LS sum Hessian matrix. In part, this ill-conditioning is intrinsic to the problem and is related to decreasing electrostatic contribution of the higher multipole moments, that are, in the case of Lebedev grid model, directly associated with the Hessian eigenvectors. For the atom-centered model, this association breaks down beyond the first few eigenvectors related to the high-curvature monopole and dipole terms; this leads to even wider spread-out of the Hessian curvature values. Using these insights, it is possible to alleviate the ill-conditioning of the LS point-charge fitting without introducing external restraints and/or constraints. Also, as the analytical Lebedev grid PC model proposed here can reproduce multipole moments up to a given rank, it may provide a promising alternative to including explicit multipole terms in a force field.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2015

Determination of transition metal ion distribution in cubic spinel Co{sub 1.5}Fe{sub 1.5}O{sub 4} using anomalous x-ray diffraction

We report anomalous x-ray diffraction studies on Co ferrite with composition Co{sub 1.5}Fe{sub 1.5}O{sub 4} to obtain the distribution of transition metal ions in tetrahedral and octahedral sites. We synthesize spinel oxide (Co{sub 1.5}Fe{sub 1.5}O{sub 4}) through co-precipitation and subsequent annealing route. The imaginary part (absorption) of the energy dependent anomalous form factor is measured and the real part is calculated theoretically through Kramers–Krönig transformation to analyze anomalous x-ray diffraction peak intensities. Fe and Co K-edge x-ray absorption near edge structure (XANES) spectra are used to estimate charge states of transition metals. Our analysis, within experimental errors, suggests 44% of the tetrahedral sites contain Co in +2 oxidation state and the rest 56% sites contain Fe in +2 and +3 oxidation states. Similarly, 47% of the octahedral sites contain Fe in +3 oxidation states, whereas, the rest of the sites contain Co in +2 and +3 oxidation states. While a distinct pre-edge feature in the Fe K-edge XANES is observed, Co pre-edge remains featureless. Implications of these results to magnetism are briefly discussed.

36 MATERIALS SCIENCE↗

DOE OSTI2013

The relevance of particle flux monitors in accelerator-based activation analysis

One of the most critical parameters in activation analysis is the flux density of the activating radiation, its spatial distribution in particular. The validity of the basic equation for calculating the activity induced to the exposed item depends upon the fulfilment of several conditions, the most relevant of them being equal doses of incident activating radiation received by the unknown sample, the calibration material and the reference material, respectively. This requirement is most problematic if accelerator-produced radiation is used for activation. Whilst nuclear research reactors usually are equipped with exposure positions that provide fairly homogenous activation fields for thermal neutron activation analysis accelerator-generated particle beams (neutrons, photons, charged particles) usually exhibit axial and, in particular, sharp radial flux gradients. Different experimental procedures have been developed to fulfil the condition mentioned above. In this paper, three variants of the application of flux monitors in photon activation analysis are discussed (external monitor, additive and inherent internal monitor). Experiments have indicated that the latter technique yields highest quality of the analytical results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2012

Metastable charged sparticles and the cosmological {sup 7}Li problem

We consider the effects of metastable charged sparticles on Big-Bang Nucleosynthesis (BBN), including bound-state reaction rates and chemical effects. We make a new analysis of the bound states of negatively-charged massive particles with the light nuclei most prominent in BBN, and present a new code to track their abundances, paying particular attention to that of {sup 7}Li. Assuming, as an example, that the gravitino is the lightest supersymmetric particle (LSP), and that the lighter stau slepton, τ-tilde {sub 1}, is the metastable next-to-lightest sparticle within the constrained minimal supersymmetric extension of the Standard Model (CMSSM), we analyze the possible effects on the standard BBN abundances of τ-tilde {sub 1} bound states and decays for representative values of the gravitino mass. Taking into account the constraint on the CMSSM parameter space imposed by the discovery of the Higgs boson at the LHC, we delineate regions in which the fit to the measured light-element abundances is as good as in standard BBN. We also identify regions of the CMSSM parameter space in which the bound state properties, chemistry and decays of metastable charged sparticles can solve the cosmological {sup 7}Li problem.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2007

The Effect of Variable End of Charge Battery Management on Small-Cell Batteries

Batteries are critical components for spacecraft, supplying power to all electrical systems during solar eclipse. These components must be lightweight due to launch vehicle limitations and the desire to fly heavier, more capable payloads, and must show excellent capacity retention with age to support the ever growing durations of space missions. ABSL's heritage Lithium Ion cell, the ABSL 18650HC, is an excellent low mass solution to this problem that has been proven capable of supporting long mission durations. The NASA Glenn Research Center recently proposed and initiated a test to study the effects of reduced end of charge voltage on aging of the ABSL 18650HC and other Lithium Ion cells. This paper presents the testing details, a method to analyze and compare capacity fade between the different cases, and a preliminary analysis of the to-date performance of ABSL s cells. This initial analysis indicates that employing reduced end of charge techniques could double the life capabilities of the ABSL 18650HC cell. Accordingly, continued investigation is recommended, particularly at higher depths of discharge to better assess the method s potential mass savings for short duration missions.

Neubauer, Jeremy S.↗

DOE OSTI2015

Impact of nonadiabatic charge transfer on the rate of redox chemistry of carbon oxides on rutile TiO2 (110) surface

We present the results of a density functional theory (DFT) within the LDA+U approximation on large models of partially reduced TiO2 (110) rutile surface to investigate the nature of charge transfer and the role of non-adiabatic effects on three prototypical redox reactions: (i) O2 adsorption (ii) CO oxidation and (iii) CO2 reduction. Charge-constrained DFT (cDFT) is used to estimate kinetic parameters for a Marcus theory rate law that accounts for adiabatic coupling effects on reaction rates. We find that for O2 adsorption, the coupling between adiabatic states is strong, leading to fast charge transfer rates. The lowest energy structures at high coverage consist of two chemisorbed O2-, one adsorbed at a VO site and the other adsorbed at an adjacent Ti5C site. For CO oxidation, however, all reactions are kinetically hindered on the ground state due to the weak adiabatic coupling at the state crossing, such that one has to overcome two kinetically unfavorable charge transfer events to drive the process (non-adiabatically) on the thermal ground state. The process can be driven by photochemical means but would result in an adsorbed radical [OCOO-] intermediate species. Similarly, CO2 reduction also proceeds via a non-adiabatic charge transfer to form an adsorbed CO2- species followed by a second non-adiabatic charge transfer to produce CO. Our analysis provides important computational guidelines for modeling these types of processes. We thank Z. Dohnalek, M. Hendersen, G. Kimmel, H. Metieu, and N. Petrik for invaluable discussions. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences and performed at the Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national laboratory operated for DOE by Battelle. Computational resources were provided at W. R. Wiley Environmental Molecular Science Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research located at PNNL and the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory.

charge transfer↗

DOE OSTI2019

Development of an Advanced Force Field for Water Using Variational Energy Decomposition Analysis

Given the piecewise approach to modeling intermolecular interactions for force fields, they can be difficult to parametrize since they are fit to data like total energies that only indirectly connect to their separable functional forms. Furthermore, by neglecting certain types of molecular interactions such as charge penetration and charge transfer, most classical force fields must rely on, but do not always demonstrate, how cancellation of errors occurs among the remaining molecular interactions accounted for such as exchange repulsion, electrostatics, and polarization. In this work we present the first generation of the (many-body) MB-UCB force field that explicitly accounts for the decomposed molecular interactions commensurate with a variational energy decomposition analysis, including charge transfer, with force field design choices that reduce the computational expense of the MB-UCB potential while remaining accurate. We optimize parameters using only a single water molecule and water cluster data up through pentamers, with no fitting to condensed phase data, and we demonstrate that high accuracy is maintained when the force field is subsequently validated against conformational energies of larger water cluster data sets, radial distribution functions of the liquid phase, and the temperature dependence of thermodynamic and transport water properties. Finally, we conclude that MB-UCB is comparable in performance to MB-Pol but is less expensive and more transferable by eliminating the need to represent short-ranged interactions through large parameter fits to high order polynomials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Temperature dependence of the electronic transitions in BiFeO{sub 3} thin film studied by spectroscopic ellipsometry

The temperature dependence of the electronic response of BiFeO{sub 3} thin film grown on a SrTiO{sub 3} substrate is investigated using spectroscopic ellipsometry. By analyzing the pseudodielectric function, we identify two d-d crystal field transitions of Fe{sup 3+} ions in the energy region between 1 and 2 eV. The d-d transitions show abnormal temperature dependence that cannot be attributed to conventional electron-phonon interactions. The origin of the abnormal temperature dependence is discussed in terms of spin-charge coupling. The temperature dependence of the charge transfer transitions located above 2.5 eV is characterized by standard critical point model analysis of the 2nd derivatives of the dielectric function. This analysis provides detailed information of the critical point parameters for charge transfer transitions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2023

Measurement of the Sensitivity of Two-Particle Correlations in $\mathcal{pp}$ Collisions to the Presence of Hard Scatterings

A key open question in the study of multiparticle production in high-energy pp collisions is the relationship between the “ridge”—i.e., the observed azimuthal correlations between particles in the underlying event that extend over all rapidities—and hard or semihard scattering processes. In particular, it is not known whether jets or their soft fragments are correlated with particles in the underlying event. To address this question, two-particle correlations are measured in pp collisions at $\sqrt{s}$=13 TeV using data collected by the ATLAS experiment at the LHC, with an integrated luminosity of 15.8 pb -1 , in two different configurations. In the first case, charged particles associated with jets are excluded from the correlation analysis, while in the second case, correlations are measured between particles within jets and charged particles from the underlying event. Second-order flow coefficients, v2, are presented as a function of event multiplicity and transverse momentum. These measurements show that excluding particles associated with jets does not affect the measured correlations. Moreover, particles associated with jets do not exhibit any significant azimuthal correlations with the underlying event, ruling out hard processes contributing to the ridge.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Optical Spectroscopy and Superconductivity of Cuprates (Review)

The optical properties of low-dimensional dielectric cuprates, including parent systems for high-temperature superconductors, such as La{sub 2}CuO{sub 4}, Sr{sub 2}CuO{sub 2}Cl{sub 2}, and YBa{sub 2}Cu{sub 3}O{sub 6} are briefly reviewed. The main focus is on the d–d and p–d charge transfer transitions, which determine the fundamental absorption band. The analysis of optical properties shows the instability of parent cuprates against the d–d charge transfer with the formation of metastable electron–hole (EH) dimers of the Cu{sup 1+}–Cu{sup 3+}-type pairs coupled by the two-particle transfer and characterized by the giant electric polarizability. The formation of a system of stable EH dimers upon nonisovalent substitution determines the unconventional properties of the pseudogap and superconducting phases of doped cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Nondestructive microstructural investigation of defects in 4H-SiC epilayers using a multiscale luminescence analysis approach

The development of metal oxide semiconductor field effect transistors (MOSFETs) utilizing epitaxially grown 4H-SiC has accelerated in recent years due to their favorable properties, including a high breakdown field, high saturated electron drift velocity, and good thermal conductivity. However, extended defects in epitaxial 4H-SiC can affect both device yields and operational lifetime. In this work, we demonstrate the importance of a multiscale luminescence characterization approach to studying nondestructively extended defects in epitaxial 4H-SiC semiconducting materials. Multiscale luminescence analysis reveals different aspects of excess charge carrier recombination behavior based on the scale of a particular measurement. Combining measurements of the same extended defect area at different scales tells us more about the essential nature of that defect and its microstructure. Here, we use photoluminescence imaging and cathodoluminescence spectrum imaging to investigate the recombination behavior of several different types of extended defects, including stacking faults, inclusions, and basal plane dislocations. A detailed understanding of the optoelectronic properties of extended defects in epitaxial SiC helps elucidate the microstructure of extended defects and can provide pathways to mitigate detrimental changes during device operation related to their evolution, such as the recombination enhanced dislocation glide effect that affects SiC-based MOSFETs.

3C-inclusion↗

DOE OSTI2023

First Observation of a Doubly Charged Tetraquark and Its Neutral Partner

A combined amplitude analysis is performed for the decays $B^0$ → $\overline{D}$ 0 $D_s^+$$π^–$ and $B^+$ → $D^–$$D_s^+$$π^+$, which are related by isospin symmetry. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV. The full data sample corresponds to an integrated luminosity of 9 fb –1 . Two new resonant states with masses of 2.908 ± 0.011 ± 0.020 GeV and widths of 0.136 ± 0.023 ± 0.013 GeV are observed, which decay to $D_s^+$$π^+$ and $D_s^+$$π^–$ respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content [c$\overline{s}$u$\overline{d}$], and the latter state is a neutral tetraquark composed of [c$\overline{s}$$\overline{u}$d] quarks. Both states are found to have spin-parity of 0 + , and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Study on Nanocellulose Properties Processed Using Different Methods and Their Aerogels

In this paper the effects of different mechanical methods including homogenization, ultrasonication and grinding on the properties of the nanocellulose materials and their aerogels, were investigated. The cellulose nanocrystal products, (CNC-H) and (CNC-U), were prepared by homogenization and ultrasonication of the acid hydrolyzed pulps, respectively. The aerogel products were produced by solvent exchanging of nanocellulose hydrogels with tertiary butyl alcohol and followed by freeze drying. The nanocellulose materials were studied using transmission electron microscopy, field emission scanning electron microscopy (FE-SEM), Fourier transformed infrared spectroscopy (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA). Size distribution and surface charges of the nanocellulose suspensions were measured by zetasizer. Also, the morphology, the porosity properties and surface area of the CNCs and CNF aerogels were investigated via FE-SEM and nitrogen adsorption–desorption isotherms. The results showed that CNC-H has higher surface charge, suspension stability (− 41.8 mV), crystallinity index (74.7%) and better size dispersion than CNC-U and CNF with an average particle size of 122 nm. CNC-H microstructures demonstrated homogeneous network structure with smaller nanometer dimensions (15–30 nm width and 60–400 nm length). However, the CNC-H showed lower thermal stability compared to CNC-U and CNF. Larger average pore size (16.32 nm), pore volume (0.42 cc/g) and high specific surface area (> 100 m{sup 2} g{sup −1}) in CNC-H aerogel were obtained. Graphical Abstract: Suspensions of nanocellulose (NC) were prepared by different mechanical methods: Homogenizing, Ultrasonic and grinding. The NC products were investigated and their differences in morphology and other characteristics were studied. The aerogels were prepared from the nanocellulose hydrogels. The nitrogen physisorption was used to study the pore characteristics of the aerogels. .

36 MATERIALS SCIENCE↗

DOE OSTI2019

Azimuthal asymmetries of back-to-back π ± - ( π 0 , η , π ± ) pairs in e + e - annihilation

This work reports the first observation of azimuthal asymmetries around the thrust axis in e + e – annihilation of pairs of back-to-back charged pions in one hemisphere, and π 0 and η mesons in the opposite hemisphere. These results are complemented by a new analysis of pairs of back-to-back charged pions. The π 0 and η asymmetries rise with the relative momentum z of the detected hadrons as well as with the transverse momentum with respect to the thrust axis. These asymmetries are sensitive to the Collins fragmentation function $H$ $^{1}_{⊥}$ and provide complementary information to previous measurements with charged pions and kaons in the final state. In particular, the η final states will provide additional information on the flavor structure of $H$ $^{1}_{⊥}$. This is the first measurement of the explicit transverse-momentum dependence of the Collins fragmentation function from Belle data. It uses a dataset of 980.4 fb –1 collected by the Belle experiment at or near a center- of-mass energy of 10.58 GeV.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2022

Atomic structure and Mott nature of the insulating charge density wave phase of 1T-TaS 2

Here, using x-ray pair distribution function (PDF) analysis and computer modeling, we explore structure models for the complex charge density wave (CDW) phases of layered 1T-TaS 2 that both well capture their atomic-level features and are amenable to electronic structure calculations. The models give the most probable position of constituent atoms in terms of 3D repetitive unit cells comprising a minimum number of Ta–S layers. Structure modeling results confirm the emergence of star-of-David (SD) like clusters of Ta atoms in the high-temperature incommensurate (IC) CDW phase and show that, contrary to the suggestions of recent studies, the low-temperature commensurate (C) CDW phase expands upon cooling thus reducing lattice strain. The C-CDW phase is also found to preserve the stacking sequence of Ta–S layers found in the room temperature, nearly commensurate (NC) CDW phase to a large extent. DFT based on the PDF refined model shows that bulk C-CDW 1T-TaS 2 also preserves the insulating state of individual layers of SD clusters, favoring the Mott physics description of the metal-to-insulator (NC-CDW to C-CDW) phase transition in 1T-TaS 2 . Our work highlights the importance of using precise crystal structure models in determining the nature of electronic phases in complex materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Linear instabilities in the hot-ion regime in a high-field spherical tokamak

Abstract The present operating high-field compact spherical tokamak ST40 is an important step toward an ST-based fusion reactor (Gryaznevich and Asunta 2017 Fusion Eng. Des. 123 177; McNamara 2023 Nucl. Fusion 63 054002). Temperature and density profiles and their uncertainties in recent hot ion ST40 plasmas with central ion temperatures exceeding 8.6 keV, have been inferred using an integrated analysis of several diagnostics including line-of-sight integration and volume average measurements, as well as limited profile information from a charge-exchange-recombination spectrometer. A linear gyrokinetic stability analysis has been carried out to identify the most unstable micro-instabilities in these hot ion plasmas. In one of these plasmas, it is found that linear growth rates of both ion- and electron-scale ( k θ ρ s ⩾ 0.2 where k θ is the poloidal wavenumber and ρ s is the ion gyro-radius with sound speed) modes decrease from the edge toward the core of the plasma (i.e. from ρ = 0.8 to 0.3 where ρ is the square root of the normalized magnetic flux), while the change of linear growth rates at k θ ρ s < 0.2 is non-monotonic. In particular, at ρ = 0.3 no unstable mode was found at k θ ρ s > 5 , and about an order of magnitude reduction in the maximum linear growth rate in the ion-scale wavenumber range of 0.2 ⩽ k θ ρ s < 1 is seen at ρ = 0.3 compared with the ρ = 0.8 location. It is found through parametric scans that while the ion temperature gradient (ITG) mode/trapped electron mode (TEM) and kinetic ballooning mode (KBM)/kinetic shear Alfvén (KSA) mode are more important in the plasma core, ubiquitous mode (UM) is found to be the important ion-scale instability at ρ ⩾ 0.6 . At ρ = 0.8, two instabilities are found at the electron scale, with one being the typical electrostatic electron temperature gradient (ETG) mode at ρ e scale and beyond and the other being an unidentified low-real-frequency instability (at the intermediate scale between electron and ion gyroradii) which can propagate in the ion direction and is driven by ETG. The existence of UM at the ion scale and the low-real-frequency instability and ETG mode at the electron scale at ρ = 0.8 is supported by an extensive linear gyrokinetic stability analysis of another ST40 hot ion plasma in a wider parametric range, taking into account the uncertainties in the experimental profiles.

ubiquitous mode↗

DOE OSTI2018

Nucleon Axial Radius and Muonic Hydrogen — A New Analysis and Review

Weak capture in muonic hydrogen (μH) as a probe of the chiral properties and nucleon structure predictions of quantum chromodynamics (QCD) is reviewed. A recent determination of the axial-vector charge radius squared, , from a model independent z expansion analysis of neutrino-nucleon scattering data is employed in conjunction with the MuCap measurement of the singlet muonic hydrogen capture rate, , to update the induced pseudoscalar nucleon coupling derived from experiment, and predicted by chiral perturbation theory. Accounting for correlated errors this implies , confirming theory at the 8% level. If instead, the predicted expression for is employed as input, then the capture rate alone determines , or together with the independent z expansion neutrino scattering result, a weighted average . Sources of theoretical uncertainty are critically examined and potential experimental improvements are described that can reduce the capture rate error by about a factor of 3. Muonic hydrogen can thus provide a precise and independent value which may be compared with other determinations, such as ongoing lattice gauge theory calculations. The importance of an improved determination for phenomenology is illustrated by considering the impact on critical neutrino-nucleus cross sections at neutrino oscillation experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗