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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

MO-FG-202-01: A Fast Yet Sensitive EPID-Based Real-Time Treatment Verification System

Purpose: To create a real-time EPID-based treatment verification system which robustly detects treatment delivery and patient attenuation variations. Methods: Treatment plan DICOM files sent to the record-and-verify system are captured and utilized to predict EPID images for each planned control point using a modified GPU-based digitally reconstructed radiograph algorithm which accounts for the patient attenuation, source energy fluence, source size effects, and MLC attenuation. The DICOM and predicted images are utilized by our C++ treatment verification software which compares EPID acquired 1024×768 resolution frames acquired at ∼8.5hz from Varian Truebeam™ system. To maximize detection sensitivity, image comparisons determine (1) if radiation exists outside of the desired treatment field; (2) if radiation is lacking inside the treatment field; (3) if translations, rotations, and magnifications of the image are within tolerance. Acquisition was tested with known test fields and prior patient fields. Error detection was tested in real-time and utilizing images acquired during treatment with another system. Results: The computational time of the prediction algorithms, for a patient plan with 350 control points and 60×60×42cm^3 CT volume, is 2–3minutes on CPU and <27 seconds on GPU for 1024×768 images. The verification software requires a maximum of ∼9ms and ∼19ms for 512×384 and 1024×768 resolution images, respectively, to perform image analysis and dosimetric validations. Typical variations in geometric parameters between reference and the measured images are 0.32°for gantry rotation, 1.006 for scaling factor, and 0.67mm for translation. For excess out-of-field/missing in-field fluence, with masks extending 1mm (at isocenter) from the detected aperture edge, the average total in-field area missing EPID fluence was 1.5mm2 the out-of-field excess EPID fluence was 8mm^2, both below error tolerances. Conclusion: A real-time verification software, with EPID images prediction algorithm, was developed. The system is capable of performing verifications between frames acquisitions and identifying source(s) of any out-of-tolerance variations. This work was supported in part by Varian Medical Systems.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Tetraquark operators in lattice QCD and exotic flavour states in the charm sector

We present a general class of operators resembling compact tetraquarks which have a range of colour-flavour-spin structures, transform irreducibly under the symmetries of the lattice and respect other relevant symmetries. These constructions are demonstrated in lattice QCD calculations with light quarks corresponding to m π = 391 MeV. Using the distillation framework, correlation functions involving large bases of meson-meson and tetraquark operators are computed in the isospin-1 hidden-charm and doubly-charmed sectors, and finite-volume spectra are extracted with the variational method. We find the spectra are insensitive to the addition of tetraquark operators to the bases of meson-meson operators. For the first time, through using diverse bases of meson-meson operators, the multiple energy levels associated with meson-meson levels which would be degenerate in the non-interacting limit are extracted reliably. The number of energy levels in each spectrum is found to be equal to the number of expected non-interacting meson-meson levels in the energy region considered and the majority of energies lie close to the non-interacting levels. Furthermore, there is no strong indication for any bound state or narrow resonance in the channels we study.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Sequential Image Recovery Using Joint Hierarchical Bayesian Learning

Abstract Recovering temporal image sequences (videos) based on indirect, noisy, or incomplete data is an essential yet challenging task. We specifically consider the case where each data set is missing vital information, which prevents the accurate recovery of the individual images. Although some recent (variational) methods have demonstrated high-resolution image recovery based on jointly recovering sequential images, there remain robustness issues due to parameter tuning and restrictions on the type of sequential images. Here, we present a method based on hierarchical Bayesian learning for the joint recovery of sequential images that incorporates prior intra- and inter-image information. Our method restores the missing information in each image by “borrowing” it from the other images. More precisely, we couple sequential images by penalizing their pixel-wise difference. The corresponding penalty terms (one for each pixel and pair of subsequent images) are treated as weakly-informative random variables that favor small pixel-wise differences but allow occasional outliers. As a result, all of the individual reconstructions yield improved accuracy. Our method can be used for various data acquisitions and allows for uncertainty quantification. Some preliminary results indicate its potential use for sequential deblurring and magnetic resonance imaging.

Xiao, Yao↗
DOE OSTI2019

Influences of the impurity and magnetic field on the probability density and the period of the asymmetric Gaussian potential qubit

The eigenenergies and eigenfunctions of the ground and first-excited states of an electron, which is coupled to an LO-phonon in a quantum dot with an asymmetric Gaussian (AG) potential, Coulomb bound potential and the magnetic field was studied by using Lee-Low-Pines transformation and Pekar variation method. A single qubit can be realized in this two-level quantum system. Numerical results show that the probability density of electrons in the qubit oscillates with changing the time, the well width and the well depth the AG potential. The probability density obviously fluctuates with changes in the magnetic-field cyclotron (MFC) frequency, the dielectric constant (DC) ratio and the electron–phonon coupling (EPC) strength, respectively, which is not conducive to constructing a suitable qubit. The oscillation period of the qubit decreases with increasing the DC ratio, EPC strength and the MFC frequency, respectively, which has an adverse effect on the survival time of qubit.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Spin–isospin effects on Isgur–Wise function for heavy-baryon transitions

In this paper, the baryonic wave function has been obtained with the Cornell potential, a combination of linear and Coulomb terms, using the hyper-radial Schrödinger equation and an improved variational method while on the other hand, hyperfine interactions are considered, including smeared standard hyperfine term, isospin dependent and spin–isospin dependent terms in order to improve the results. Then, the baryonic Isgur–Wise function in hyperspherical coordinates has been investigated employing both mentioned wave functions. Finally, in particular, the charged radius and the decay width of transition have been reported for both methods and compared with those obtained in experiments or theories.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Multiple stable states and Dicke phase transition for two atoms in an optical cavity

We study in the present paper the multiple stable states of two different atoms in a single-mode quantum cavity by means of variational method. Eigenenergies and eigenstates are obtained analytically in the optical coherent state of cavity field. The ground state displays the known Dicke phase transition from the normal to superradiant phases at the critical value of atom–field coupling. The rich phase diagrams including the stable excited states are presented respectively for two atoms with different level spaces and atom–field couplings. By adjusting the ratios of two-atom couplings or level spaces, one atom can be in the normally populated state, while the other is in the inversely populated state. We also observe the stimulated radiation from the inversely populated state. Particularly, the normal and stimulated radiations are interchangeable respectively for two atoms. Moreover, the maximally entangled state can be generated with two identical atoms.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Silencing Drp1 inhibits glioma cells proliferation and invasion by RHOA/ ROCK1 pathway

Backgrounds: Dynamin-related protein 1 (Drp1) is a newly discovered therapeutic target for tumor initiation, migration, proliferation, and chemosensitivity. In the present study, we aimed to examine the level of expression and distribution of DRP1 in glioma tissues and explore the concrete mechanism of DRP1 played in glioma. Methods: Expression of DRP1 in glioma tissues was determined by immunohistochemistry staining. The DRP1 gene was knocked down using small interfering RNA, and was overexpressed using plasmids in glioma cells. To assess changes in cell function, in vitro assays for invasion and growth were applied. Protein expression was tested by using Western-blot method. Variation of F-actin in cells was analyzed using immunofluorescence staining. Interactions between proteins were determined by co-immunoprecipitation. Results: The protein expression levels of DRP1 were significantly increased in glioma tissues compared to the normal brain tissues. Down-regulation of DRP1 decreased cell proliferation and invasion, and inhibited the formation of pseudopodias and microvillis. Moreover, a possible link between DRP1 and RHOA was confirmed when interactions between these two proteins were observed in the cells. Conclusions: Our results demonstrated that silencing DRP1 regulated the cytoskeleton remodeling through inhibiting RHOA/ROCK1 pathway, and thus decreased the proliferation and invasion of glioma cells. - Highlights: • DPR1 is significantly increased in glioma tissues. • Down-regulation of DRP1 in glioma cells inhibits cell proliferation. • Down-regulation of DRP1 in glioma cells inhibits cell invasion and induces F-actin remodeling. • Down-regulation of DRP1 inhibits RHOA/ROCK1 pathway in glioma cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Fast & accurate emulation of two-body scattering observables without wave functions

We combine Newton's variational method with ideas from eigenvector continuation to construct a fast & accurate emulator for two-body scattering observables. The emulator will facilitate the application of rigorous statistical methods for interactions that depend smoothly on a set of free parameters. Our approach begins with a trial K or T matrix constructed from a small number of exact solutions to the Lippmann–Schwinger equation. Subsequent emulation only requires operations on small matrices. We provide several applications to short-range potentials with and without the Coulomb interaction and partial-wave coupling. It is shown that the emulator can accurately extrapolate far from the support of the training data. When used to emulate the neutron-proton cross section with a modern chiral interaction as a function of 26 free parameters, it reproduces the exact calculation with negligible error and provides an over 300x improvement in CPU time.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Understanding the origin of Tabula Rasa-induced defects in n-type Cz c-Si: The case of nitrogen atmosphere

Phosphorus-doped Czochralski-grown silicon (Cz-Si) has been gaining market share in the large-scale manufacturing of high-efficiency silicon (Si)-based photovoltaic (PV) devices thanks to higher carrier lifetimes than their boron-doped counterpart. However, the fabrication of n-type Cz-Si based solar cells often requires process steps with much higher temperatures and longer times than p-type Silicon. Defect interaction with the high temperatures during such processes tend to be detrimental to the n-type Cz-Si carrier lifetime, therefore limiting the final device efficiency. Short thermal anneals before cell processing, known as Tabula Rasa (TR), have been proposed to mitigate the thermally induced lifetime degradation during n-type Cz-Si solar cell fabrication. This work thoroughly investigates the defects responsible for the lifetime degradation after TR in a N 2 atmosphere treatment. We use temperature-injection-dependent lifetime spectroscopy and the thickness variation method to decouple the effects of TR treatment in the bulk and the surface of the n-type Cz-Si wafers. Using the defect parameter contour mapping (DPCM), we identify the defect energy level (E t ) and the capture cross-section ratio (k) of the most likely process-induced defect, which aligns with previously proposed Si vacancy-associated defects. The DPCM reveals that these vacancy-associated defects have a shallow energy level E t - E v ~0.13 eV and very efficient electron capture cross section k~600. Unexpectedly, the bulk degradation due to vacancy defects in the volume of the wafer, is accompanied by a significant increase in the surface recombination as well. Through evaluating the surface recombination velocity temperature- and injection dependence, we show that after TR, at room temperature and for an injection level of 10 15 cm -3 , in a wafer passivated with a-Si:H(i) the surface recombination dominates the overall lifetime response. Here we hypothesize that the near surface vacancy-associated bulk defects play a role in lowering the electron diffusion current into the a-Si:H(i) from the c-Si(n) reducing the field-effect passivation.

14 SOLAR ENERGY↗
DOE OSTI2023

Revealing Variable Dependences in Hexagonal Boron Nitride Synthesis via Machine Learning

Wafer-scale monolayer two-dimensional (2D) materials have been realized by epitaxial chemical vapor deposition (CVD) in recent years. To scale up the synthesis of 2D materials, a systematic analysis of how the growth dynamics depend on the growth parameters is essential to unravel its mechanisms. However, the studies of CVD-grown 2D materials mostly adopted the control variate method and considered each parameter as an independent variable, which is not comprehensive for 2D materials growth optimization. Herein, we synthesized a representative 2D material, monolayer hexagonal boron nitride (hBN), on single-crystalline Cu (111) by epitaxial chemical vapor deposition and varied the growth parameters to regulate the hBN domain sizes. Furthermore, we explored the correlation between two growth parameters and provided the growth windows for large flake sizes by the Gaussian process. Here, this new analysis approach based on machine learning provides a more comprehensive understanding of the growth mechanism for 2D materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Microphysics of Stratiform Precipitation During OLYMPEX: Compatibility Between Triple‐Frequency Radar and Airborne In Situ Observations

Abstract The link between stratiform precipitation microphysics and multifrequency radar observables is thoroughly investigated by exploiting simultaneous airborne radar and in situ observations collected from two aircraft during the OLYMPEX/RADEX (Olympic Mountain Experiment/Radar Definition Experiment 2015) field campaign. Above the melting level, in situ images and triple‐frequency radar signatures both indicate the presence of moderately rimed aggregates. Various mass‐size relationships of ice particles and snow scattering databases are used to compute the radar reflectivity from the in situ particle size distribution. At Ku and Ka band, the best agreement with radar observations is found when using the self‐similar Rayleigh‐Gans approximation for moderately rimed aggregates. At W band, a direct comparison is challenging because of the non‐Rayleigh effects and of the probable attenuation due to ice aggregates and supercooled liquid water between the two aircraft. A variational method enables the retrieval of the full precipitation profile above and below the melting layer, by combining the observations from the three radars. Even with three radar frequencies, the retrieval of rain properties is challenging over land, where the integrated attenuation is not available. Otherwise, retrieved mean volume diameters and water contents of both solid and liquid precipitation are in agreement with in situ observations and indicate local changes of the degree of riming of ice aggregates, on the scale of 5 km. Finally, retrieval results are analyzed to explore the validity of using continuity constraints on the water mass flux and diameter within the melting layer in order to improve retrievals of ice properties.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

The phase diagram of quantum chromodynamics in one dimension on a quantum computer

The quantum chromodynamics (QCD) phase diagram, which reveals the state of strongly interacting matter at different temperatures and densities, is key to answering open questions in physics, ranging from the behaviour of particles in neutron stars to the conditions of the early universe. However, classical simulations of QCD face significant computational barriers, such as the sign problem at finite matter densities. Quantum computing offers a promising solution to overcome these challenges. Here, we take an important step toward exploring the QCD phase diagram with quantum devices by preparing thermal states in one-dimensional non-Abelian gauge theories. We experimentally simulate the thermal states of SU(2) and SU(3) gauge theories at finite densities on a trapped-ion quantum computer using a variational method. This is achieved by introducing two features: Firstly, we add motional ancillae to the existing qubit register to efficiently prepare thermal probability distributions. Secondly, we introduce charge-singlet measurements to enforce colour-neutrality constraints. This work pioneers the quantum simulation of QCD at finite density and temperature for two and three colours, laying the foundation to explore QCD phenomena on quantum platforms.

Quantum information↗
DOE OSTI2022

Preparation of metrological states in dipolar-interacting spin systems

Abstract Spin systems are an attractive candidate for quantum-enhanced metrology. Here we develop a variational method to generate metrological states in small dipolar-interacting spin ensembles with limited qubit control. For both regular and disordered spatial spin configurations the generated states enable sensing beyond the standard quantum limit (SQL) and, for small spin numbers, approach the Heisenberg limit (HL). Depending on the circuit depth and the level of readout noise, the resulting states resemble Greenberger-Horne-Zeilinger (GHZ) states or Spin Squeezed States (SSS). Sensing beyond the SQL holds in the presence of finite spin polarization and a non-Markovian noise environment. The developed black-box optimization techniques for small spin numbers ( N ≤ 10) are directly applicable to diamond-based nanoscale field sensing, where the sensor size limits N and conventional squeezing approaches fail.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Thermodynamical properties of liquid lanthanides-A variational approach

Thermodynamical properties like Entropy (S), Internal energy (E) and Helmholtz free energy (F) of liquid lanthanides using a variation principle based on the Gibbs-Bogoliubuv (GB) inequality with Percus Yevick hard sphere reference system have been reported in the present investigation. To describe electron-ion interaction we have used our newly constructed parameter free model potential along with Sarkar et al. local field correction function. Lastly, we conclude that our newly constructed model potential is capable to explain the thermodynamical properties of liquid lanthanides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Effects of the built-in electric field on polaron effects in a wurtzite ZnO/Mg{sub x}Zn{sub 1−x}O quantum well

The effects of the built-in electric field on the polarons in wurtzite ZnO/Mg{sub x}Zn{sub 1−x}O quantum wells are studied numerically via the improved Lee-Low-Pines intermediate coupling variational method. The contributions of the different branches of the optical phonons to the polaron energies of the ZnO/Mg{sub x}Zn{sub 1−x}O quantum wells are calculated as functions of well width d and composition x. The anisotropy effects of the electronic effective masses, the dielectric constants, and the frequencies of the different branches of the phonon modes (including both the longitudinal-like and transverse-like confined optical phonon modes, the interface optical phonon modes and the half-space phonon modes) on the polaron energies are considered in the calculations. Comparisons between the cases with and without the built-in electric field (F ≠ 0 and F = 0) are made for the optical phonon contributions to the polaron energies for the different branches of the phonon modes. The results show that the built-in electric field has marked effects on the contributions of the phonons with the different modes; in detail, it makes positive contributions to the interface and the half-space phonons, but negative contributions to the confined phonons, and thus its effect on the total phonon contribution is not obvious. Detailed comparisons of the contributions of the symmetric and antisymmetric phonon modes to the polaron energies as functions of d and x are also presented and a heuristic argument is provided to explain the numerical results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Theory of torsional control for G 16 -type molecules

Here, we introduce a four-dimensional quantum model for describing the torsional control with moderately strong, non-resonant laser pulses of G 16 -type molecules in the electronic ground state, based on the symmetry-adapted variational method. We define conditions for which lower-dimensional models, commonly used to simulate the strong-field control of molecular torsions, are reliable approximations to a four-dimensional treatment. In particular, we study the role of different types of rotational-torsional couplings—the field-free coupling and the field-induced coupling—and show that the conclusions recently drawn on the role of rotational-torsional couplings in the process of torsional alignment are not correct in general. Furthermore, we demonstrate how important an adequate description of the molecular polarizability is for reliably predicting the torsional alignment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

ADM Analysis of gravity models within the framework of bimetric variational formalism

Bimetric variational formalism was recently employed to construct novel bimetric gravity models. In these models an affine connection is generated by an additional tensor field which is independent of the physical metric. In this work we demonstrate how the ADM decomposition can be applied to study such models and provide some technical intermediate details. Using ADM decomposition we are able to prove that a linear model is unstable as has previously been indicated by perturbative analysis. Moreover, we show that it is also very difficult if not impossible to construct a non-linear model which is ghost-free within the framework of bimetric variational formalism. However, we demonstrate that viable models are possible along similar lines of thought. To this end, we consider a set up in which the affine connection is a variation of the Levi-Civita one. As a proof of principle we construct a gravity model with a massless scalar field obtained this way.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Accessing the gluon momentum fraction of nucleons through the gradient flow

We calculate the gluon momentum fraction of the nucleon using lattice QCD, with a nonperturbative renormalization technique based on the gradient flow. The gluon momentum fraction is determined on a single Wilson-clover ensemble using 𝑁 𝑓 =2 +1 flavors with pion mass 358 MeV and lattice spacing 0.094 fm. We employ the variational method to reduce excited-state contamination and apply the distillation framework to ensure a large operator basis. To reduce systematic uncertainties, we apply Bayesian model averaging to all fit procedures. We apply matching coefficients to the flow-time dependent lattice results to recover the gluon momentum fraction in the $\overline{MS}$-scheme at 2 GeV. Our final result is ⟨𝑥⟩ 𝑔 ⁢(𝜇 =2 GeV) =0.482⁢(35), where we quote only statistical uncertainties.

Lattice QCD↗