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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 OSTI2015

Grand canonical Monte Carlo using solvent repacking: Application to phase behavior of hard disk mixtures

A new “solvent repacking Monte Carlo” strategy for performing grand canonical ensemble simulations in condensed phases is introduced and applied to the study of hard-disk systems. The strategy is based on the configuration-bias approach, but uses an auxiliary biasing potential to improve the efficiency of packing multiple solvent particles in the cavity formed by removing one large solute. The method has been applied to study the coexistence of ordered and isotropic phases in three binary mixtures of hard disks with a small mole fraction (x{sub L} < 0.02) of the larger “solute” component. A chemical potential of 12.81 ± 0.01 k{sub B}T was found to correspond to the freezing transition of the pure hard disk “solvent.” Simulations permitted the study of partitioning of large disks between ordered and isotropic phases, which showed a distinct non-monotonic dependence on size; the isotropic phase was enriched approximately 10-fold, 20-fold, and 5-fold over the coexisting ordered phases at diameter ratios d = 1.4, 2.5, and 3, respectively. Mixing of large and small disks within both phases near coexistence was strongly non-ideal in spite of the dilution. Structures of systems near coexistence were analyzed to determine correlations between large disks’ positions within each phase, the orientational correlation length of small disks within the fluid phases, and the nature of translational order in the ordered phase. The analyses indicate that the ordered phase coexists with an isotropic phase resembling a nanoemulsion of ordered domains of small disks, with large disks enriched at the disordered domain interfaces.

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

In-situ structural investigations of ferroelasticity in soft and hard rhombohedral and tetragonal PZT

Despite the technological importance of hard and soft PZT, Pb(Zr,Ti)O{sub 3}, ceramics, the mechanisms of ferroelectric hardening and softening remain widely discussed in the literature. The hardening and softening phenomena have traditionally been investigated in relation with dielectric manifestations such as aging of the dielectric susceptibility and constriction of the polarization-electric field hysteresis loop. Here, we present a systematic investigation of the ferroelectric and ferroelastic properties of soft and hard PZT in both the tetragonal and rhombohedral phases. A particular focus has been devoted to ferroelastic domain switching by characterizing the macroscopic mechanical constitutive behavior and in-situ synchrotron X-ray diffraction during compression. It is demonstrated that variation of the ordering state of point defects in PZT ceramics affects the switching behavior of both ferroelectric and ferroelastic domains under mechanical or electrical fields. Softening of the mechanical and electrical properties of originally hard PZT ceramics was conferred by quenching the materials from above the Curie temperature. The present findings are discussed with respect to the current understanding of hardening-softening transitions in ferroelectric materials.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Injection locking of an electronic maser in the hard excitation mode

The phenomenon of hard excitation is natural for many electronic oscillators. In particular, in a gyrotron, a maximal efficiency is often attained in the hard excitation regime. In this paper, we study the injection-locking phenomena using two models of an electronic maser in the hard excitation mode. First, bifurcation analysis is performed for the quasilinear model described by ordinary differential equations for the slow amplitude and phase. Two main scenarios of transition to the injection-locked mode are described, which are generalizations of the well-known phase-locking and suppression mechanisms. The results obtained for the quasilinear model are confirmed by numerical simulations of a gyrotron with fixed Gaussian structure of the RF field.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions

Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for models of electrolyte solution. In this paper, we provide definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation and isolate the effects of charge and cavitation, comparing to the Born (linear response) model. We show that using uncorrected Ewald summation leads to unphysical values for the single ion solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small non-linearity for small anions. The charge hydration asymmetry for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. Finally, this suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Radiation-damage-induced transitions in zircon: Percolation theory applied to hardness and elastic moduli as a function of density

Two in literature predicted percolation transitions in radiation-damaged zircon (ZrSiO 4 ) were observed experimentally by measurement of the indentation hardness as a function of density and their correlation with the elastic moduli. Percolations occur near 30% and 70% amorphous fractions, where hardness deviates from its linear correlation with the elastic modulus ( E ), the shear modulus ( G ) and the bulk modulus ( K ). Finally, the first percolation point p c1 generates a cusp in the hardness versus density evolution, while the second percolation point is seen as a change of slope.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Hard X-ray induced fast secondary electron cascading processes in solids

Recent studies confirmed that the materials used in the extreme UV and soft X-ray regime for precise characterization of intense free-electron laser pulses (e.g., Si 3 N 4 ) do not work efficiently in the hard X-ray regime, which is due to the fact that the impact of a hard X-ray photon is followed by a series of electron cascading processes. Following theoretical indication, we show that this limitation can be circumvented and the cascading time can be significantly reduced if the X-ray photon energy is double the ionization energy. We investigate an alternative material for pulse diagnostics, SnO 2 , using the Linac Coherent Light Source at photon energies of 5 keV and 9 keV. We prove the validity of the concept and show that it has a large potential for practical applications. In conclusion, by applying the proposed criteria, the temporal accuracy of the non-invasive pulse diagnostic tools can be improved in current and emerging hard X-ray facilities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Optomechanical Design of Compact Laminar Flexure Bending Mechanism for Elliptically Bent Hard X-ray Mirrors

As a part of the Argonne Strategic Partnership Project (SPP) 85E77, collaboration between Argonne National Laboratory (ANL) and Shanghai Institute of Applied Physics (SINAP), has produced designs for a precision compact flexure bending mechanism to provide elliptically shaped 90-mm and 160-mm long hard x-ray mirrors. The design utilizes Argonne's laminar nanopositioning flexure technique. The flexure mirror bending mechanism will be incorporated into the beamline upgrade project at the Shanghai Synchrotron Radiation Facility (SSRF). Additionally, an Argonne Laboratory-Directed Research and Development (LDRD) project at the Advanced Photon Source (APS) has adopted a modified optomechanical design of the precision compact mirror benders for 300-mm-long hard x-ray mirrors with integrated profile monitoring and feedback, which are described in this paper. The mirror benders are designed with configurations for open-loop or closed-loop controls. Capacitive sensors can be applied to the mirror benders to ensure positioning reproducibility. Design specifications as well as finite element analyses results of the compact mirror benders for hard x-ray mirrors with trapezoid and rectangular shapes are discussed in this paper.

X-ray optics, nanopositioning flexure stage↗
DOE OSTI2020

Thermomechanical response of thickly tamped targets and diamond anvil cells under pulsed hard x-ray irradiation

In the laboratory study of extreme conditions of temperature and density, the exposure of matter to high intensity radiation sources has been of central importance. Here, we interrogate the performance of multi-layered targets in experiments involving high intensity, hard x-ray irradiation, motivated by the advent of extremely high brightness hard x-ray sources, such as free electron lasers and 4th-generation synchrotron facilities. Intense hard x-ray beams can deliver significant energy in targets having thick x-ray transparent layers (tampers) around samples of interest for the study of novel states of matter and materials’ dynamics. Heated-state lifetimes in such targets can approach the microsecond level, regardless of radiation pulse duration, enabling the exploration of conditions of local thermal and thermodynamic equilibrium at extreme temperature in solid density matter. The thermal and mechanical responses of such thick layered targets following x-ray heating, including hydrodynamic relaxation and heat flow on picosecond to millisecond timescales, are modeled using radiation hydrocode simulation, finite element analysis, and thermodynamic calculations. Assessing the potential for target survival over one or more exposures and resistance to damage arising from heating and resulting mechanical stresses, this study doubles as an investigation into the performance of diamond anvil high pressure cells under high x-ray fluences. Long used in conjunction with synchrotron x-ray radiation and high power optical lasers, the strong confinement afforded by such cells suggests novel applications at emerging high intensity x-ray facilities and new routes to studying thermodynamic equilibrium states of warm, very dense matter.

Meza-Galvez, J. (ORCID:000000032699849X)↗
DOE OSTI2013

GAMMA-RAY OBSERVATIONS OF CYGNUS X-1 ABOVE 100 MeV IN THE HARD AND SOFT STATES

We present the results of multi-year gamma-ray observations by the AGILE satellite of the black hole binary system Cygnus X-1. In a previous investigation we focused on gamma-ray observations of Cygnus X-1 in the hard state during the period mid-2007/2009. Here we present the results of the gamma-ray monitoring of Cygnus X-1 during the period 2010/mid-2012 which includes a remarkably prolonged 'soft state' phase (2010 June-2011 May). Previous 1-10 MeV observations of Cyg X-1 in this state hinted at a possible existence of a non-thermal particle component with substantial modifications of the Comptonized emission from the inner accretion disk. Our AGILE data, averaged over the mid-2010/mid-2011 soft state of Cygnus X-1, provide a significant upper limit for gamma-ray emission above 100 MeV of F{sub soft} < 20 Multiplication-Sign 10{sup -8} photons cm{sup -2} s{sup -1} , excluding the existence of prominent non-thermal emission above 100 MeV during the soft state of Cygnus X-1. We discuss theoretical implications of our findings in the context of high-energy emission models of black hole accretion. We also discuss possible gamma-ray flares detected by AGILE. In addition to a previously reported episode observed by AGILE in 2009 October during the hard state, we report a weak but important candidate for enhanced emission which occurred at the end of 2010 June (2010 June 30 10:00-2010 July 2 10:00 UT) exactly coinciding with a hard-to-soft state transition and before an anomalous radio flare. An appendix summarizes all previous high-energy observations and possible detections of Cygnus X-1 above 1 MeV.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Comparison of time/phase lags in the hard state and plateau state of GRS 1915+105

We investigate the complex behavior of energy- and frequency-dependent time/phase lags in the plateau state and the radio-quiet hard (χ) state of GRS 1915+105. In our timing analysis, we find that when the source is faint in the radio, quasi-periodic oscillations (QPOs) are observed above 2 Hz and typically exhibit soft lags (soft photons lag hard photons), whereas QPOs in the radio-bright plateau state are found below 2.2 Hz and consistently show hard lags. The phase lag at the QPO frequency is strongly anti-correlated with that frequency, changing sign at 2.2 Hz. However, the phase lag at the frequency of the first harmonic is positive and nearly independent of that frequency at ∼0.172 rad, regardless of the radio emission. The lag energy dependence at the first harmonic is also independent of radio flux. However, the lags at the QPO frequency are negative at all energies during the radio-quiet state, but lags at the QPO frequency during the plateau state are positive at all energies and show a 'reflection-type' evolution of the lag energy spectra with respect to the radio-quiet state. The lag energy dependence is roughly logarithmic, but there is some evidence for a break around 4-6 keV. Finally, the Fourier-frequency-dependent phase lag spectra are fairly flat during the plateau state, but increase from negative to positive during the radio-quiet state. We discuss the implications of our results in light of some generic models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Modeling the multi-band afterglow of GRB 091127: Evidence of a hard electron energy spectrum with an injection break

The afterglows of gamma-ray bursts (GRBs) are believed to originate from the synchrotron emission of shock-accelerated electrons produced by the interaction between the outflow and the external medium. The accelerated electrons are usually assumed to follow a power-law energy distribution with an index of p. Observationally, although most GRB afterglows have a p larger than 2, there are still a few GRBs suggestive of a hard (p<2) electron spectrum. The well-sampled broad-band afterglow data for GRB 091127 show evidence of a hard electron spectrum and strong spectral evolution, with a spectral break moving from high to lower energies. The spectral break evolves very fast and cannot be explained by the cooling break in the standard afterglow model, unless evolving microphysical parameters are assumed. In addition, the multi-band afterglow light curves show an achromatic break at around 33 ks. Based on the model of a hard electron spectrum with an injection break, we interpret the observed spectral break as the synchrotron frequency corresponding to the injection break, and the achromatic break as a jet break caused by the jet-edge effect. It is shown that the spectral evolution and the multi-band afterglow light curves of GRB 091127 can be well reproduced by this model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

IS THE LATE NEAR-INFRARED BUMP IN SHORT-HARD GRB 130603B DUE TO THE LI-PACZYNSKI KILONOVA?

Short-hard gamma-ray bursts (GRBs) are widely believed to be produced by the merger of two binary compact objects, specifically by two neutron stars or by a neutron star orbiting a black hole. According to the Li-Paczynski kilonova model, the merger would launch sub-relativistic ejecta and a near-infrared/optical transient would then occur, lasting up to days, which is powered by the radioactive decay of heavy elements synthesized in the ejecta. The detection of a late bump using the Hubble Space Telescope (HST) in the near-infrared afterglow light curve of the short-hard GRB 130603B is indeed consistent with such a model. However, as shown in this Letter, the limited HST near-infrared light curve behavior can also be interpreted as the synchrotron radiation of the external shock driven by a wide mildly relativistic outflow. In such a scenario, the radio emission is expected to peak with a flux of ∼100 μJy, which is detectable for current radio arrays. Hence, the radio afterglow data can provide complementary evidence on the nature of the bump in GRB 130603B. It is worth noting that good spectroscopy during the bump phase in short-hard bursts can test the validity of either model above, analogous to spectroscopy of broad-lined Type Ic supernova in long-soft GRBs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Interlayer Exchange Coupling in Magnetic Hard-Soft Bilayered Structures

Broadband ferromagnetic resonance (FMR) and high-temperature (T) FMR measurements are carried out to study interlayer exchange coupling (IEC) in a magnetic hard-soft bilayered system where the hard layer is a FePt thin film with strong perpendicular anisotropy and the soft layer is a thin film made of Fe, Co, or their alloys. The data indicate that the effective exchange field (H ex ) produced by the IEC on the soft layer increases with a decrease in the thickness or saturation induction (4πM s ) of the soft layer. With an increase in T, H ex drops by an amount larger than 4πM s . The effective damping constant of the soft layer increases with H ex and can vary by two orders of magnitude. In samples with H ex > 4πM s , the damping constant is insensitive to the choice of material of the soft layer. In samples with H ex < 4πM s , the damping constant strongly depends on the choice of material. When T is increased from room temperature to the Curie temperature of the hard layer, the FMR linewidth drops significantly in samples where H ex is relatively large, but remains constant or even increases slightly at high T in samples where H ex is very small. Furthermore, the effects of H ex on the damping and linewidth can be understood by considering two distinct components in the overall damping, an intrinsic component mainly due to spin-flip magnon-electron scattering and an extrinsic component due to IEC-associated spin pumping at the interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Imprints of high-momentum nucleons in nuclei on hard photons from heavy-ion collisions near the Fermi energy

The short-range correlation (SRC) induced by the tensor force in the isosinglet neutron-proton interaction channel leads to a high-momentum tail (HMT) in the single-nucleon momentum distributions n(k) in nuclei. Owing to the remaining uncertainties about the tensor force, the shape of the nucleon HMT may be significantly different from the dilute interacting Fermi gas model prediction n(k) ~ 1/k 4 similar to the HMT in cold atoms near the unitary limit. Within an isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck transport model incorporating approximately the nucleon HMT, we investigate hard photon emissions in 14 N + 12 C and 48 Ca + 124 Sn reactions at beam energies around the Fermi energy. Imprints of different shapes of the HMT on the energy spectrum, angular distribution and transverse momentum spectrum of hard photons are studied. Furthermore, while the angular distribution does not carry any information about the shape of the nucleon HMT, the energy spectra and especially the mid-rapidity transverse momentum spectra of hard photons are found to bare strong imprints of the shapes of nucleon HMTs in the two colliding nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Optimization of Error-Bounded Lossy Compression for Hard-to-Compress HPC Data

Since today’s scientific applications are producing vast amounts of data, compressing them before storage/transmission is critical. Results of existing compressors show two types of HPC data sets: highly compressible and hard to compress. In this work, we carefully design and optimize the error-bounded lossy compression for hard-tocompress scientific data. We propose an optimized algorithm that can adaptively partition the HPC data into best-fit consecutive segments each having mutually close data values, such that the compression condition can be optimized. Another significant contribution is the optimization of shifting offset such that the XOR-leading-zero length between two consecutive unpredictable data points can be maximized. We finally devise an adaptive method to select the best-fit compressor at runtime for maximizing the compression factor. We evaluate our solution using 13 benchmarks based on real-world scientific problems, and we compare it with 9 other state-of-the-art compressors. Experiments show that our compressor can always guarantee the compression errors within the user-specified error bounds. Most importantly, our optimization can improve the compression factor effectively, by up to 49% for hard-tocompress data sets with similar compression/decompression time cost.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

The differential absorption hard x-ray spectrometer at the Z facility

The Differential Absorption Hard X-ray (DAHX) spectrometer is a diagnostic developed to measure time-resolved radiation between 60 keV and 2 MeV at the Z Facility. It consists of an array of 7 Si PIN diodes in a tungsten housing that provides collimation and coarse spectral resolution through differential filters. DAHX is a revitalization of the Hard X-Ray Spectrometer (HXRS) that was fielded on Z prior to refurbishment in 2006. DAHX has been tailored to the present radiation environment in Z to provide information on the power, spectral shape, and time profile of the hard emission by plasma radiation sources driven by the Z Machine.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Towards directed energy deposition of metals using polymer-based supports: porosity of 316L stainless steel deposited on carbon-fiber-reinforced ABS

Directed energy deposition (DED) is increasingly valuable to many industries because of its high deposition rates relative to other metal additive manufacturing processes, but the design space of DED is limited. For instance, steep overhangs are difficult or impossible to manufacture. Polymer-based support structures could help address this challenge. The viability of DED on polymer composite substrates has begun to be explored, specifically with 316L stainless steel on carbon-fiber-reinforced ABS substrates. Monolithic metal components can be deposited on the polymer, but it was found that gas release during polymer degradation causes porosity due to gas entrapment in the metal. An interlayer cooling time was introduced to reduce polymer degradation and decrease the porosity due to gas entrapment, but this led to porosity from lack of fusion. The results of this work provide insight into process parameter selection and scan strategy development to enable the use of polymer support structures in blown-powder DED.

Kurfess, Rebecca↗
DOE OSTI2014

Novel strategy for low-temperature, high-rate growth of dense, hard, and stress-free refractory ceramic thin films

Growth of fully dense refractory thin films by means of physical vapor deposition (PVD) requires elevated temperatures T{sub s} to ensure sufficient adatom mobilities. Films grown with no external heating are underdense, as demonstrated by the open voids visible in cross-sectional transmission electron microscopy images and by x-ray reflectivity results; thus, the layers exhibit low nanoindentation hardness and elastic modulus values. Ion bombardment of the growing film surface is often used to enhance densification; however, the required ion energies typically extract a steep price in the form of residual rare-gas-ion-induced compressive stress. Here, the authors propose a PVD strategy for the growth of dense, hard, and stress-free refractory thin films at low temperatures; that is, with no external heating. The authors use TiN as a model ceramic materials system and employ hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS and DCMS) in Ar/N{sub 2} mixtures to grow dilute Ti{sub 1−x}Ta{sub x}N alloys on Si(001) substrates. The Ta target driven by HIPIMS serves as a pulsed source of energetic Ta{sup +}/Ta{sup 2+} metal–ions, characterized by in-situ mass and energy spectroscopy, while the Ti target operates in DCMS mode (Ta-HIPIMS/Ti-DCMS) providing a continuous flux of metal atoms to sustain a high deposition rate. Substrate bias V{sub s} is applied in synchronous with the Ta-ion portion of each HIPIMS pulse in order to provide film densification by heavy-ion irradiation (m{sub Ta} = 180.95 amu versus m{sub Ti} = 47.88 amu) while minimizing Ar{sup +} bombardment and subsequent trapping in interstitial sites. Since Ta is a film constituent, primarily residing on cation sublattice sites, film stress remains low. Dense Ti{sub 0.92}Ta{sub 0.08}N alloy films, 1.8 μm thick, grown with T{sub s} ≤ 120 °C (due to plasma heating) and synchronized bias, V{sub s} = 160 V, exhibit nanoindentation hardness H = 25.9 GPa and elastic modulus E = 497 GPa compared to 13.8 and 318 GPa for underdense Ti-HIPIMS/Ti-DCMS TiN reference layers (T{sub s} < 120 °C) grown with the same V{sub s}, and 7.8 and 248 GPa for DCMS TiN films grown with no applied bias (T{sub s} < 120 °C). Ti{sub 0.92}Ta{sub 0.08}N residual stress is low, σ = −0.7 GPa, and essentially equal to that of Ti-HIPIMS/Ti-DCMS TiN films grown with the same substrate bias.

36 MATERIALS SCIENCE↗