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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

The effect of new interstellar medium parameters on the heliosphere and energetic neutral atoms from the interstellar boundary

We present new results from three-dimensional simulations of the solar wind interaction with the local interstellar medium (LISM) using recent observations by NASA's Interstellar Boundary EXplorer (IBEX) mission estimates of the velocity and temperature of the LISM. We investigate four strengths of the LISM magnetic field, from 1 to 4 μG, and adjust the LISM proton and hydrogen densities so that the distance to the termination shock (TS) in the directions of the Voyager spacecraft is just below 90 AU, and the density of hydrogen at the TS is close to 0.09 cm{sup –3} in the nose direction. The orientation of the magnetic field is chosen to point toward the center of the ribbon of enhanced energetic neutral atom (ENA) flux seen in the IBEX data. Our simulations show that the plasma and neutral properties in the outer heliosheath vary considerably as a function of the LISM magnetic field strength. We also show that the heliotail points downwind in all cases, though its structure is strongly affected by the external magnetic field. Comparison and consistency between the simulated ENA flux and the circularity of the ribbon as measured by IBEX are most consistent with a LISM magnetic field strength aligned with the center of the ribbon and a magnitude in the range 2.5-3 μG.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Atomic matter-wave revivals with definite atom number in an optical lattice

We study the collapse and revival of interference patterns in the momentum distribution of atoms in optical lattices using a projection technique to properly account for the fixed total number of atoms in the system. We consider the common experimental situation in which weakly interacting bosons are loaded into a shallow lattice, which is suddenly made deep. The collapse and revival of peaks in the momentum distribution is then driven by interactions in a lattice with essentially no tunneling. The projection technique allows to us to treat inhomogeneous (trapped) systems exactly in the case that noninteracting bosons are loaded into the system initially, and we use time-dependent density-matrix renormalization group techniques to study the system in the case of finite tunneling in the lattice and finite initial interactions. For systems of more than a few sites and particles, we find good agreement with results calculated via a naive approach, in which the state at each lattice site is described by a coherent state in the particle occupation number. However, for systems on the order of ten lattice sites, we find experimentally measurable discrepancies to the results predicted by this standard approach.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Resonance-mediated atomic ionization dynamics induced by ultraintense x-ray pulses

We describe the methodology of our recently developed Monte Carlo rate equation (MCRE) approach, which systematically incorporates bound-bound resonances to model multiphoton ionization dynamics induced by high-fluence, high-intensity x-ray free-electron laser (XFEL) pulses. These resonances are responsible for ionization far beyond that predicted by the sequential single photon absorption model and are central to a quantitative understanding of atomic ionization dynamics in XFEL pulses. We also present calculated multiphoton ionization dynamics for Kr and Xe atoms in XFEL pulses for a variety of conditions, to compare the effects of bandwidth, pulse duration, pulse fluence, and photon energy. This comprehensive computational investigation reveals areas in the photon energy–pulse fluence landscape where resonances are critically important. We also uncover a mechanism, preservation of inner-shell vacancies (PIVS), whereby radiation damage is enhanced at higher XFEL intensities and identify the sequence of core-outer–Rydberg, core-valence, and core-core resonances encountered during multiphoton x-ray ionization.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

Neutrino-impact ionization of atoms in searches for neutrino magnetic moment

The ionization of atomic electrons by scattering of neutrinos is revisited. This process is the one studied in the experimental searches for a neutrino magnetic moment using germanium detectors. Current experiments are sensitive to the ionization energy comparable with the atomic energies, and the effects of the electron binding should be taken into account. We find that the so-called stepping approximation to the neutrino-impact ionization is in fact exact in the semiclassical limit and also that the deviations from this approximation are very small already for the lowest bound Coulomb states. We also consider the effects of electron-electron correlations and argue that the resulting corrections to the ionization of independent electrons are quite small. In particular, we estimate that in germanium these are at a 1% level at the energy transfer down to a fraction of keV. Exact sum rules are also presented as well as analytical results for a few lowest hydrogenlike states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Nonlinear Quantum Optics in a Waveguide: Distinct Single Photons Strongly Interacting at the Single Atom Level

We propose a waveguide-QED system where two single photons of distinct frequency or polarization interact strongly. The system consists of a single ladder-type three level atom coupled to a waveguide. When both optical transitions are coupled strongly to the waveguide's mode, we show that a control photon tuned to the upper transition induces a {pi} phase shift and tunneling of a probe photon tuned to the otherwise reflective lower transition. Furthermore, the system exhibits single photon scattering by a classical control beam. Waveguide-QED schemes could be an alternative to high quality cavities or dense atomic ensembles in quantum information processing.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Glassy Behavior in a Binary Atomic Mixture

We experimentally study one-dimensional, lattice-modulated Bose gases in the presence of an uncorrelated disorder potential formed by localized impurity atoms, and compare to the case of correlated quasidisorder formed by an incommensurate lattice. While the effects of the two disorder realizations are comparable deeply in the strongly interacting regime, both showing signatures of Bose-glass formation, we find a dramatic difference near the superfluid-to-insulator transition. In this transition region, we observe that random, uncorrelated disorder leads to a shift of the critical lattice depth for the breakdown of transport as opposed to the case of correlated quasidisorder, where no such shift is seen. Our findings, which are consistent with recent predictions for interacting bosons in one dimension, illustrate the important role of correlations in disordered atomic systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Trapping Rydberg Atoms in an Optical Lattice

Rubidium Rydberg atoms are laser excited and subsequently trapped in a one-dimensional optical lattice (wavelength 1064 nm). Efficient trapping is achieved by a lattice inversion immediately after laser excitation using an electro-optic technique. The trapping efficiency is probed via analysis of the trap-induced shift of the two-photon microwave transition 50S{yields}51S. The inversion technique allows us to reach a trapping efficiency of 90%. The dependence of the efficiency on the timing of the lattice inversion and on the trap laser power is studied. The dwell time of 50D{sub 5/2} Rydberg atoms in the lattice is analyzed using lattice-induced photoionization.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

On the reproducibility of protein crystal structures: five atomic resolution structures of trypsin

Details of five very high-resolution accurate structures of bovine trypsin are compared in the context of the reproducibility of models obtained from crystals grown under identical conditions. Structural studies of proteins usually rely on a model obtained from one crystal. By investigating the details of this model, crystallographers seek to obtain insight into the function of the macromolecule. It is therefore important to know which details of a protein structure are reproducible or to what extent they might differ. To address this question, the high-resolution structures of five crystals of bovine trypsin obtained under analogous conditions were compared. Global parameters and structural details were investigated. All of the models were of similar quality and the pairwise merged intensities had large correlation coefficients. The C{sup α} and backbone atoms of the structures superposed very well. The occupancy of ligands in regions of low thermal motion was reproducible, whereas solvent molecules containing heavier atoms (such as sulfur) or those located on the surface could differ significantly. The coordination lengths of the calcium ion were conserved. A large proportion of the multiple conformations refined to similar occupancies and the residues adopted similar orientations. More than three quarters of the water-molecule sites were conserved within 0.5 Å and more than one third were conserved within 0.1 Å. An investigation of the protonation states of histidine residues and carboxylate moieties was consistent for all of the models. Radiation-damage effects to disulfide bridges were observed for the same residues and to similar extents. Main-chain bond lengths and angles averaged to similar values and were in agreement with the Engh and Huber targets. Other features, such as peptide flips and the double conformation of the inhibitor molecule, were also reproducible in all of the trypsin structures. Therefore, many details are similar in models obtained from different crystals. However, several features of residues or ligands located in flexible parts of the macromolecule may vary significantly, such as side-chain orientations and the occupancies of certain fragments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Prospects for atomic resolution in-line holography for a 3D determination of atomic structures from single projections

Abstract It is now established that the 3D structure of homogeneous nanocrystals can be recovered from in-line hologram of single projections. The method builds on a quantitative contrast interpretation of electron exit wave functions. Since simulated exit wave functions of single and bilayers of graphene reveal the atomic structure of carbon-based materials with sufficient resolution, we explore theoretically how the approach can be expanded beyond periodic carbon-based materials to include non-periodic molecular structures. We show here theoretically that the 3D atomic structure of randomly oriented oleic acid molecules can be recovered from a single projection.

3D molecular imaging↗
DOE OSTI2019

Rethinking surface reactions in nanoscale dry processes toward atomic precision and beyond: a physics and chemistry perspective

In this review, we discuss the progress of emerging dry processes with atomic precision. Researchers in the field of plasma processing and surface science have addressed the increasingly challenging demands of material selectivity by utilization of synergistic enhancement of etching or deposition. The discussion encompasses major challenges in the plasma science and technology community. Here, the focus of the review is advances in atomic layer etching and area-selective deposition with activation or deactivation, especially in terms of materials scaling and variety. Control of high-aspect-ratio feature fabrication in semiconductor manufacturing and etched shapes of interior features at the nanoscale are needed. Issues related to profile distortion have received much attention. State-of-the-art techniques used in semiconductor manufacturing are reviewed and future challenges are outlined.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Free-Standing Bialkali Photocathodes Using Atomically Thin Substrates

This study reports successful deposition of high quantum efficiency (QE) bialkali antimonide K2CsSb photocathodes on graphene films. The results pave the way for an ultimate goal of encapsulating technologically relevant photocathodes for accelerator technology with an atomically thin protecting layer to enhance lifetime while minimizing QE losses. A QE of 17% at approximate to 3.1 eV (405 nm) is the highest value reported so far on graphene substrates and is comparable to that obtained on stainless steel and nickel reference substrates. The spectral responses of the photocathodes on graphene exhibit signature features of K2CsSb including the characteristic absorption at approximate to 2.5 eV. Materials characterization based on X-ray fluorescence and X-ray diffraction reveals that the composition and crystal quality of these photocathodes deposited on graphene is comparable to those deposited on a reference substrate. Quantitative agreement between optical calculations and QE measurements for the K2CsSb on free suspended graphene and a graphene-coated metal substrate further confirms the high-quality interface between the photocathodes and graphene. Finally, a correlation between the QE and graphene quality as characterized by Raman spectroscopy suggests that a lower density of atomistic defects in the graphene films leads to higher QE of the deposited K2CsSb photocathodes.

accelerator technology↗