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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 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Effects of the local structure dependence of evaporation fields on field evaporation behavior

Accurate three dimensional reconstructions of atomic positions and full quantification of the information contained in atom probe microscopy data rely on understanding the physical processes taking place during field evaporation of atoms from needle-shaped specimens. However, the modeling framework for atom probe microscopy has only limited quantitative justification. Building on the continuum field models previously developed, we introduce a more physical approach with the selection of evaporation events based on density functional theory calculations. This model reproduces key features observed experimentally in terms of sequence of evaporation, evaporation maps, and depth resolution, and provides insights into the physical limit for spatial resolution.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Wireless current sensing by near field induction from a spin transfer torque nano-oscillator

We demonstrate that spin transfer torque nano-oscillators (STNO) can act as wireless sensors for local current. The STNO acts as a transducer that converts weak direct currents into microwave field oscillations that we detect using an inductive coil. We detect direct currents in the range of 300–700 μA and report them wirelessly to a receiving induction coil at distances exceeding 6.5 mm. This current sensor could find application in chemical and biological sensing and industrial inspection.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Portable diagnostic package for Thomson scattering and optical emission spectroscopy on Princeton field-reversed configuration 2 (PFRC 2)

An Advanced Research Projects Agency-Energy funded diagnostic system has been deployed to the Princeton field-reversed configuration 2 (PFRC-2) device, located at Princeton Plasma Physics Laboratory. The Portable Diagnostic Package (PDP), designed at Oak Ridge National Laboratory, allows for the measurement of Thomson Scattering (TS) for electron density and temperature and Optical Emission Spectroscopy (OES) for ion temperature, impurity density, and ion velocity. A tunable spectrometer on the PDP with three gratings provides the flexibility to measure low (1 eV) and high (1000 eV) electron temperature ranges from TS. Additionally, using a second spectrometer, the OES diagnostic can survey light emission from various ion excitation levels for wide wavelength ranges. The electron density (<2 × 10 19 m –3 ) of plasmas generated in PFRC-2 has been below the PDP TS discrimination threshold, which has made TS signal detection challenging against a high-background of laser stray light. The laser stray light was iteratively reduced by making modifications to the entrance and exit geometry on PFRC-2. Rayleigh scattering experiments on PFRC have yielded the TS discrimination sensitivity to be >1 × 10 20 m –3 for the PDP. A recently implemented narrow-band notch spectral filter that masks the second harmonic 532 nm Nd:YAG laser wavelength has increased the system’s TS light discrimination sensitivity 65 times compared to the instance when the notch filter was not implemented. The hardware implementation including design changes to the flight tubes and Brewster windows will be discussed, along with results from Rayleigh and rotational Raman scattering sensitivity analyses, which were used to establish a quantitative figure of merit on the system performance. Further, the Raman scattering calibration with the notch filter has improved the PDP electron density threshold to 1 ± 0.5 × 10 18 m –3 .

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

UVUDF: Ultraviolet imaging of the Hubble ultra deep field with wide-field camera 3

We present an overview of a 90 orbit Hubble Space Telescope treasury program to obtain near-ultraviolet imaging of the Hubble Ultra Deep Field using the Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters. This survey is designed to: (1) investigate the episode of peak star formation activity in galaxies at 1 < z < 2.5; (2) probe the evolution of massive galaxies by resolving sub-galactic units (clumps); (3) examine the escape fraction of ionizing radiation from galaxies at z ∼ 2-3; (4) greatly improve the reliability of photometric redshift estimates; and (5) measure the star formation rate efficiency of neutral atomic-dominated hydrogen gas at z ∼ 1-3. In this overview paper, we describe the survey details and data reduction challenges, including both the necessity of specialized calibrations and the effects of charge transfer inefficiency. We provide a stark demonstration of the effects of charge transfer inefficiency on resultant data products, which when uncorrected, result in uncertain photometry, elongation of morphology in the readout direction, and loss of faint sources far from the readout. We agree with the STScI recommendation that future UVIS observations that require very sensitive measurements use the instrument's capability to add background light through a 'post-flash'. Preliminary results on number counts of UV-selected galaxies and morphology of galaxies at z ∼ 1 are presented. We find that the number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely consistent with the number predicted by published luminosity functions. We also confirm that the image mosaics have sufficient sensitivity and resolution to support the analysis of the evolution of star-forming clumps, reaching 28-29th magnitude depth at 5σ in a 0.''2 radius aperture depending on filter and observing epoch.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Matching field effects at tesla-level magnetic fields in critical current density in high-Tc superconductors containing self-assembled columnar defects

We have investigated the superconductive transport properties of YBa2Cu3O7 films containing self-assembled columnar arrays of second phase SrZrO3 or BaSnO3 precipitates. A matching condition between columnar pinning sites (aligned at or near the c axis) and external magnetic flux, tilted with respect to them, is identified in the critical current JC.H/ data. The results for the material containing SrZrO3-based pins are analyzed within a simple intuitive model. At matching, the critical current is enhanced above the model prediction. In complementary contact-free investigations of BaSnO3-doped material, matching effects are observed over a wide range of temperatures in the field dependence of JC.H/. The deduced matching fields agree reasonably well with the densities of columnar pins directly observed by scanning electron microscopy.

Sinclair, J.↗
DOE OSTI2019

Phase field model of uranium carbide solidification through a combined KKS and orientation field approach

A Phase Field model is developed combining the Orientation Field approach to modeling solidification with the Kim, Kim, Suzuki (KKS) method of modeling binary alloys. These combined methods produce a model capable of simulating randomly oriented second phase dendrites with discrete control of the solid-liquid interface energy and thickness. The example system of carbon (C) in a liquid uranium (U) melt is used as a test for the model. The formation of uranium carbide (UC) within a liquid U melt is simulated for isothermal conditions and compares well with experiments.

Bair, Jacob L. (ORCID:0000000333273323)↗
DOE OSTI2012

Multi-field inflation with random potentials: field dimension, feature scale and non-Gaussianity

We explore the super-horizon evolution of the two-point and three-point correlation functions of the primordial density perturbation in randomly-generated multi-field potentials. We use the Transport method to evolve perturbations and give full evolutionary histories for observables. Identifying the separate universe assumption as being analogous to a geometrical description of light rays, we give an expression for the width of the bundle, thereby allowing us to monitor evolution towards the adiabatic limit, as well as providing a useful means of understanding the behaviour in f{sub NL}. Finally, viewing our random potential as a toy model of inflation in the string landscape, we build distributions for observables by evolving trajectories for a large number of realisations of the potential and comment on the prospects for testing such models. We find the distributions for observables to be insensitive to the number of fields over the range 2 to 6, but that these distributions are highly sensitive to the scale of features in the potential. Most sensitive to the scale of features is the spectral index, with more than an order of magnitude increase in the dispersion of predictions over the range of feature scales investigated. Least sensitive was the non-Gaussianity parameter f{sub NL}, which was consistently small; we found no examples of realisations whose non-Gaussianity is capable of being observed by any planned experiment.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

A field range bound for general single-field inflation

We explore the consequences of a detection of primordial tensor fluctuations for general single-field models of inflation. Using the effective theory of inflation, we propose a generalization of the Lyth bound that applies to models of inflation coupled to Einstein gravity. Our strongest bound applies to all single-field models with two-derivative kinetic terms for the scalar fluctuations and is always stronger than the corresponding bound for slow-roll models. This shows that non-trivial dynamics of the inflaton can't evade the Lyth bound. We also present a weaker, but more universal bound that holds when the Null Energy Condition (NEC) is satisfied at horizon crossing.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Holistic scan optimization of nacelle-mounted lidars for inflow and wake characterization at the RAAW and AWAKEN field campaigns

In this article, we provide a methodological framework for designing the scanning strategies of nacelle-mounted scanning lidars for wind energy field experiments, and apply it at two major experimental field campaigns. For the Rotor Aerodynamics, Aeroelastics, and Wake project (RAAW), we leverage two scanning lidars on one turbine to characterize the incoming turbulence and the turbine wake. For the American WAKE experimeNt (AWAKEN), we use four scanning lidars on top of four turbines in a large wind power plant to investigate both individual wakes and wind-plant-scale flow features.

17 WIND ENERGY↗
DOE OSTI2025

High-redshift millennium and astrid galaxies in effective field theory at the field level

Effective field theory (EFT) modeling is expected to be a useful tool in the era of future higher-redshift galaxy surveys such as DESI-II and Spec-S5 due to its robust description of various large-scale structure tracers. However, large values of EFT bias parameters of higher-redshift galaxies could jeopardize the convergence of the perturbative expansion. Here, in this paper we measure the bias parameters and other EFT coefficients from samples of two types of star-forming galaxies in the state-of-the-art MilleniumTNG and astrid hydrodynamical simulations. Our measurements are based on the field-level EFT forward model that allows for precision EFT parameter measurements by virtue of cosmic variance cancellation. Specifically, we consider approximately representative samples of Lyman-break galaxies (LBGs) and Lyman-𝛼 emitters (LAEs) that are consistent with the observed (angular) clustering and number density of these galaxies at 𝑧 = 3. Reproducing the linear biases and number densities observed from existing LAE and LBG data, we find quadratic bias parameters that are roughly consistent with those predicted from the halo model coupled with a simple halo occupation distribution model. We also find nonperturbative velocity contributions (fingers of God) of a similar size for LBGs to the familiar case of luminous red galaxies. However, these contributions are quite small for LAEs despite their large satellite fraction values of up to ∼ 30%. Our results indicate that the effective momentum reach 𝑘 max at 𝑧 = 3 for LAEs (LBGs) will be in the range 0.3−0.6⁢ℎ Mpc −1 (0.2−0.8⁢ℎ Mpc −1 ), suggesting that EFT will perform well for high-redshift galaxy clustering. This work provides the first step toward obtaining realistic simulation-based priors on EFT parameters for LAEs and LBGs.

Sullivan, James M. [Massachusetts Inst. of Technol↗
DOE OSTI2011

Parity-selective enhancement of field-free molecular orientation in an intense two-color laser field

We investigated the characteristics of molecular orientation induced by a nonresonant two-color femtosecond laser field. By analyzing the rotational dynamics of asymmetric linear molecules, we revealed that the critical parameter in characterizing the molecular orientation was the hyperpolarizability of molecules that selected the excitation paths of rotational states between parity-changing and parity-conserving transitions. Especially, in the case of molecules with small hyperpolarizability, a significant enhancement of orientation was achieved at the half-rotational period, instead of the full-rotational period. This deeper understanding of the hyperpolarizability-dependent characteristics of molecular orientation in a two-color scheme can provide an effective method to achieve significantly enhanced field-free orientation for various polar molecules.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Strong-field- versus weak-field-ionization pump-probe spectroscopy

Ionization can serve as a universal probe of excited-state dynamics in molecules, such as internal conversion, dissociation, and isomerization. These processes are of fundamental importance to a wide array of dynamics in biology, chemistry, and physics. In recent years, there has been significant debate about the relative merits of strong-field ionization (SFI), which involves multiphoton absorption, versus weak-field ionization (WFI), where a single photon is absorbed, as probes of these dynamics. SFI is advantageous because it uses wavelengths that are relatively easy to generate, and one can always ionize the molecule with sufficient intensity. However, for SFI it is difficult to calculate observables, such as the time-dependent ion yield, since the calculation of the ionization dynamics including multiphoton processes is computationally expensive and difficult to carry out for many molecular geometries. WFI has the advantage that calculations of observables are tractable. However, the generation and implementation of the appropriate wavelengths (photon energies) can be challenging, and the fixed energy of the probe can lead to technical complications in following the dynamics from excited states back down to the ground state. Here we present a quantitative comparison of the two approaches for following the excited-state dynamics of two molecules, diiodomethane and uracil. The combination of internal conversion and dissociation in these molecules provides an ideal comparison of WFI and SFI as a probe. We compare the measurements with calculations of the dynamics. Furthermore, our work indicates that while SFI and WFI provide qualitatively similar information about the excited-state dynamics, only WFI results can be compared quantitatively with present-day calculations.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Accurate and fast numerical solution of Poisson's equation for arbitrary, space-filling Voronoi polyhedra: Near-field corrections revisited

We present an accurate and rapid solution of Poisson's equation for space-filling, arbitrarily shaped, convex Voronoi polyhedra (VP); the method is O ( N VP ) , where N VP is the number of distinct VP representing the system. In effect, we resolve the long-standing problem of fast but accurate numerical solution of the near-field corrections, contributions to the potential due to near VP—typically those involving multipole-type conditionally convergent sums, or use of fast Fourier transforms. Our method avoids all ill-convergent sums, is simple, accurate, efficient, and works generally, i.e., for periodic solids, molecules, or systems with disorder or imperfections. We demonstrate the practicality of the method by numerical calculations compared to exactly solvable models.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Coupling between phonon and crystal-field excitations in multiferroic PrFe 3 ( BO 3 ) 4

Far-infrared reflection and ellipsometry measurements on multiferroic PrFe 3 ( BO 3 ) 4 and SmFe 3 ( BO 3 ) 4 single crystals were used to investigate the interaction between lattice phonons and electronic excitations associated with 4 f crystal-field transitions. A temperature-dependent interference between two types of excitations was observed in PrFe 3 ( BO 3 ) 4 in which the frequency of 4 f crystal-field electronic excitation of Pr 3 + falls into the TO-LO frequency interval of the optical phonon mode near 50 cm - 1 (1.5 THz). Experimental data were explained on the basis of a theoretical model of coupled electron-phonon modes. The fitting procedure revealed the value 14.8 cm - 1 for the electron-phonon coupling constant. This rather large value points to an essential role played by the electron-phonon interaction in the physics of multiferroics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Heat-flux control and solid-state cooling by regulating chemical potential of photons in near-field electromagnetic heat transfer

We consider near-field heat transfer with nonzero chemical potential for photons, as can occur between two semiconductor bodies, held at different temperatures with at least one of the bodies under external bias.We show that the dependence of radiative heat flux on chemical potential enables electronic control of both the direction and magnitude of near-field heat transfer between the two bodies. Moreover such a configuration can operate as a solid-state cooling device whose efficiency can approach the Carnot limit in the ideal case. Furthermore, significant cooling can also be achieved in the presence of inherent nonidealities including Auger recombination and parasitic phonon-polariton heat transfer.

42 ENGINEERING↗