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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

High pressure melting curves of silver, gold and copper

In this work, based on the Lindemann's formula of melting and the pressure-dependent Grüneisen parameter, we have investigated the pressure effect on melting temperature of silver, gold and copper metals. The analytical expression of melting temperature as a function of volume compression has been derived. Our results are compared with available experimental data as well as with previous theoretical studies and the good and reasonable agreements are found. We also proposed the potential of this approach on predicting melting of copper at very high pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Excited electronic states from a variational approach based on symmetry-projected Hartree–Fock configurations

Recent work from our research group has demonstrated that symmetry-projected Hartree–Fock (HF) methods provide a compact representation of molecular ground state wavefunctions based on a superposition of non-orthogonal Slater determinants. The symmetry-projected ansatz can account for static correlations in a computationally efficient way. Here we present a variational extension of this methodology applicable to excited states of the same symmetry as the ground state. Benchmark calculations on the C{sub 2} dimer with a modest basis set, which allows comparison with full configuration interaction results, indicate that this extension provides a high quality description of the low-lying spectrum for the entire dissociation profile. We apply the same methodology to obtain the full low-lying vertical excitation spectrum of formaldehyde, in good agreement with available theoretical and experimental data, as well as to a challenging model C{sub 2v} insertion pathway for BeH{sub 2}. The variational excited state methodology developed in this work has two remarkable traits: it is fully black-box and will be applicable to fairly large systems thanks to its mean-field computational cost.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Computer program for the sensitivity calculation of a CR-39 detector in a diffusion chamber for radon measurements

Computer software for calculation of the sensitivity of a CR-39 detector closed in a diffusion chamber to radon is described in this work. The software consists of two programs, both written in the standard Fortran 90 programming language. The physical background and a numerical example are given. Presented software is intended for numerous researches in radon measurement community. Previously published computer programs TRACK-TEST.F90 and TRACK-VISION.F90 [D. Nikezic and K. N. Yu, Comput. Phys. Commun. 174, 160 (2006); D. Nikezic and K. N. Yu, Comput. Phys. Commun. 178, 591 (2008)] are used here as subroutines to calculate the track parameters and to determine whether the track is visible or not, based on the incident angle, impact energy, etching conditions, gray level, and visibility criterion. The results obtained by the software, using five different V functions, were compared with the experimental data found in the literature. Application of two functions in this software reproduced experimental data very well, while other three gave lower sensitivity than experiment.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Trojan horse particle invariance: The impact on nuclear astrophysics

In the current picture of nuclear astrophysics indirect methods and, in particular, the Trojan Horse Method cover a crucial role for the measurement of charged particle induced reactions cross sections of astrophysical interest, in the energy range required by the astrophysical scenarios. To better understand its cornerstones and its applications to physical cases many tests were performed to verify all its properties and the possible future perspectives. The key to the method is the quasi-free break-up and some of its properties will be investigated in the present work. In particular, the Trojan Horse nucleus invariance will be studied and previous studies will be extended to the cases of the binary d(d, p)t and {sup 6}Li(d,α){sup 4}He reactions, which were tested using different quasi-free break-up's, namely {sup 6}Li and {sup 3}He. The astrophysical S(E)-factor were then extracted with the Trojan Horse formalism applied to the two different break-up schemes and compared with direct data as well as with previous indirect investigations. The very good agreement confirms the independence of binary indirect cross section on the chosen spectator particle also for these reactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

AGB stars and presolar grains

Among presolar materials recovered in meteorites, abundant SiC and Al{sub 2}O{sub 3} grains of AGB origins were found. They showed records of C, N, O, {sup 26}Al and s-element isotopic ratios that proved invaluable in constraining the nucleosynthesis models for AGB stars [1, 2]. In particular, when these ratios are measured in SiC grains, they clearly reveal their prevalent origin in cool AGB circumstellar envelopes and provide information on both the local physics and the conditions at the nucleosynthesis site (the H- and He-burning layers deep inside the structure). Among the properties ascertained for the main part of the SiC data (the so-called mainstream ones), we mention a large range of {sup 14}N/{sup 15}N ratios, extending below the solar value [3], and {sup 12}C/{sup 13}C ratios ≳ 30. Other classes of grains, instead, display low carbon isotopic ratios (≳ 10) and a huge dispersion for N isotopes, with cases of large {sup 15}N excess. In the same grains, isotopes currently feeded by slow neutron captures reveal the characteristic pattern expected from this process at an efficiency slightly lower than necessary to explain the solar main s-process component. Complementary constraints can be found in oxide grains, especially Al{sub 2}O{sub 3} crystals. Here, the oxygen isotopes and the content in {sup 26}Al are of a special importance for clarifying the partial mixing processes that are known to affect evolved low-mass stars. Successes in modeling the data, as well as problems in explaining some of the mentioned isotopic ratios through current nucleosynthesis models are briefly outlined.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Recent results from Super-Kamiokande

The Super-Kamiokande experiment has collected more than 11 live-years of atmospheric neutrino data. Atmospheric neutrinos cover a wide phase space in both energy and distance travelled, the parameters relevant for studying neutrino oscillations. We present here recent measurements of the three-flavor neutrino oscillation parameters using this atmospheric neutrino data, as well as new limits on mixing with a fourth sterile neutrino state.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Investigating high speed phenomena in laser plasma interactions using dilation x-ray imager (invited)

The DIlation X-ray Imager (DIXI) is a new, high-speed x-ray framing camera at the National Ignition Facility (NIF) sensitive to x-rays in the range of ≈2–17 keV. DIXI uses the pulse-dilation technique to achieve a temporal resolution of less than 10 ps, a ≈10× improvement over conventional framing cameras currently employed on the NIF (≈100 ps resolution), and otherwise only attainable with 1D streaked imaging. The pulse-dilation technique utilizes a voltage ramp to impart a velocity gradient on the signal-bearing electrons. The temporal response, spatial resolution, and x-ray sensitivity of DIXI are characterized with a short x-ray impulse generated using the COMET laser facility at Lawrence Livermore National Laboratory. At the NIF a pinhole array at 10 cm from target chamber center (tcc) projects images onto the photocathode situated outside the NIF chamber wall with a magnification of ≈64×. DIXI will provide important capabilities for warm-dense-matter physics, high-energy-density science, and inertial confinement fusion, adding important capabilities to temporally resolve hot-spot formation, x-ray emission, fuel motion, and mix levels in the hot-spot at neutron yields of up to 10{sup 17}. We present characterization data as well as first results on electron-transport phenomena in buried-layer foil experiments.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Path-integral calculation of the second virial coefficient including intramolecular flexibility effects

We present a path-integral Monte Carlo procedure for the fully quantum calculation of the second molecular virial coefficient accounting for intramolecular flexibility. This method is applied to molecular hydrogen (H{sub 2}) and deuterium (D{sub 2}) in the temperature range 15–2000 K, showing that the effect of molecular flexibility is not negligible. Our results are in good agreement with experimental data, as well as with virials given by recent empirical equations of state, although some discrepancies are observed for H{sub 2} between 100 and 200 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Assessment of approximate computational methods for conical intersections and branching plane vectors in organic molecules

Quantum-chemical computational methods are benchmarked for their ability to describe conical intersections in a series of organic molecules and models of biological chromophores. Reference results for the geometries, relative energies, and branching planes of conical intersections are obtained using ab initio multireference configuration interaction with single and double excitations (MRCISD). They are compared with the results from more approximate methods, namely, the state-interaction state-averaged restricted ensemble-referenced Kohn-Sham method, spin-flip time-dependent density functional theory, and a semiempirical MRCISD approach using an orthogonalization-corrected model. It is demonstrated that these approximate methods reproduce the ab initio reference data very well, with root-mean-square deviations in the optimized geometries of the order of 0.1 Å or less and with reasonable agreement in the computed relative energies. A detailed analysis of the branching plane vectors shows that all currently applied methods yield similar nuclear displacements for escaping the strong non-adiabatic coupling region near the conical intersections. Our comparisons support the use of the tested quantum-chemical methods for modeling the photochemistry of large organic and biological systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Direct electrical observation of plasma wave-related effects in GaN-based two-dimensional electron gases

In this work, signatures of plasma waves in GaN-based high electron mobility transistors were observed by direct electrical measurement at room temperature. Periodic grating-gate device structures were fabricated and characterized by on-wafer G-band (140–220 GHz) s-parameter measurements as a function of gate bias voltage and device geometry. A physics-based equivalent circuit model was used to assist in interpreting the measured s-parameters. The kinetic inductance extracted from the measurement data matches well with theoretical predictions, consistent with direct observation of plasma wave-related effects in GaN-channel devices at room temperature. This observation of electrically significant room-temperature plasma-wave effects in GaN-channel devices may have implications for future millimeter-wave and THz device concepts and designs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Line mixing effects in isotropic Raman spectra of pure N{sub 2}: A classical trajectory study

Line mixing effects in the Q branch of pure N{sub 2} isotropic Raman scattering are studied at room temperature using a classical trajectory method. It is the first study using an extended modified version of Gordon's classical theory of impact broadening and shift of rovibrational lines. The whole relaxation matrix is calculated using an exact 3D classical trajectory method for binary collisions of rigid N{sub 2} molecules employing the most up-to-date intermolecular potential energy surface (PES). A simple symmetrizing procedure is employed to improve off-diagonal cross-sections to make them obeying exactly the principle of detailed balance. The adequacy of the results is confirmed by the sum rule. The comparison is made with available experimental data as well as with benchmark fully quantum close coupling [F. Thibault, C. Boulet, and Q. Ma, J. Chem. Phys. 140, 044303 (2014)] and refined semi-classical Robert-Bonamy [C. Boulet, Q. Ma, and F. Thibault, J. Chem. Phys. 140, 084310 (2014)] results. All calculations (classical, quantum, and semi-classical) were made using the same PES. The agreement between classical and quantum relaxation matrices is excellent, opening the way to the analysis of more complex molecular systems.

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

The method for measuring the groove density of variable-line-space gratings with elimination of the eccentricity effect

To eliminate the eccentricity effect, a new method for measuring the groove density of a variable-line-space grating was adapted. Based on grating equation, groove density is calculated by measuring the internal angles between zeroth-order and first-order diffracted light for two different wavelengths with the same angle of incidence. The measurement system mainly includes two laser sources, a phase plate, plane mirror, and charge coupled device. The measurement results of a variable-line-space grating demonstrate that the experiment data agree well with theoretical values, and the value of measurement error (ΔN/N) is less than 2.72 × 10{sup −4}.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Lessons from LHC elastic and diffractive data

In the light of LHC data, we discuss the global description of all high-energy elastic and diffractive data, using a one-pomeron model, but including multi-pomeron interactions. The LHC data indicate the need of a k{sub t}(s) behaviour, where k{sub t} is the gluon transverse momentum along the partonic ladder structure which describes the pomeron. We also discuss tensions in the data, as well as the t dependence of the slope of dσ{sub el}/dt in the small t domain.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Study of multi-functionality of lanthanum ferrite (LaFeO{sub 3})

In the present work, multifunctional behaviors of LaFeO{sub 3} (LFO) are investigated by studying its dielectric and photocatalytic properties, respectively. LFO is synthesized by microwave-assisted co-precipitation route. Orthorhombic structure is confirmed by X-ray diffraction (XRD) and data is well fitted using Rietveld refinement by Full-Prof suite. Frequency and Temperature dependence dielectric behavior are systematically studied. The dielectric constant of LFO was found to be 2500 – 3000 with dissipation factor less than 5%. Photodegradation of toxic dye (Methylene Blue) using as-prepared LFO is also investigated. UV-visible absorption spectra are used to study the photodegradation behaviour. Photodegradation of methylene blue (MB) taken from textile industries by LFO are reported. The colossal value of dielectric constant of LFO exhibits high potential to use as room temperature capacitive component for device miniaturization in microelectronics as well as photodegradation ability shows good photocatalyst.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

GiBUU and shallow inelastic scattering

In this talk we shortly describe the physics contents of the GiBUU transport code, used to describe lepton scattering off nuclei. Particular attention will be given to validation of the GiBUU in pion-, electron- and photon-induced reactions, which serve as a benchmark for neutrino-induced ones. We mainly concentrate on those properties of benchmark reactions, which are relevant to the region of Shallow Inelastic Scattering (SIS). Our results in this region are presented for integrated and differential cross sections. Comparison with recent MINOS inclusive data, as well as predictions for the differential cross sections measurable in Minerνa and NoνA experiments are made.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Magnetite nanoparticles coated glass wool for As(V) removal from drinking water

Arsenic (As) removal from contaminated groundwater is a key environmental concern worldwide. In this study, glass wool was coated with magnetite nanoparticles under argon gas flow and magnetite coated glass wool have been investigated for application as an adsorbent for As(V) removal from water. The adsorbent was characterized by using Scanning Electron Microscopy (SEM) and arsenic contaminated water treated with adsorbent was analyzed by Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The ICP-MS results showed that 10 g/L of adsorbent removed 99.4% of As(V) within 5 hours at pH-7 and initial arsenic concentration of 360µg/L. Adsorption kinetics data fitted well in pseudo-first-order kinetics model with high correlation coefficient (R{sup 2} = 0.995). As magnetite nanoparticles coated glass wool showed favorable adsorption behavior for As(V), it can be a promising tool for water purification.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Efficient calculation of nuclear spin-rotation constants from auxiliary density functional theory

The computation of the spin-rotation tensor within the framework of auxiliary density functional theory (ADFT) in combination with the gauge including atomic orbital (GIAO) scheme, to treat the gauge origin problem, is presented. For the spin-rotation tensor, the calculation of the magnetic shielding tensor represents the most demanding computational task. Employing the ADFT-GIAO methodology, the central processing unit time for the magnetic shielding tensor calculation can be dramatically reduced. In this work, the quality of spin-rotation constants obtained with the ADFT-GIAO methodology is compared with available experimental data as well as with other theoretical results at the Hartree-Fock and coupled-cluster level of theory. It is found that the agreement between the ADFT-GIAO results and the experiment is good and very similar to the ones obtained by the coupled-cluster single-doubles-perturbative triples-GIAO methodology. With the improved computational performance achieved, the computation of the spin-rotation tensors of large systems or along Born-Oppenheimer molecular dynamics trajectories becomes feasible in reasonable times. Three models of carbon fullerenes containing hundreds of atoms and thousands of basis functions are used for benchmarking the performance. Furthermore, a theoretical study of temperature effects on the structure and spin-rotation tensor of the H{sup 12}C–{sup 12}CH–DF complex is presented. Here, the temperature dependency of the spin-rotation tensor of the fluorine nucleus can be used to identify experimentally the so far unknown bent isomer of this complex. To the best of our knowledge this is the first time that temperature effects on the spin-rotation tensor are investigated.

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

Local structure of temperature and pH-sensitive colloidal microgels

The temperature dependence of the local intra-particle structure of colloidal microgel particles, composed of interpenetrated polymer networks, has been investigated by small-angle neutron scattering at different pH and concentrations, in the range (299÷315) K, where a volume phase transition from a swollen to a shrunken state takes place. Data are well described by a theoretical model that takes into account the presence of both interpenetrated polymer networks and cross-linkers. Two different behaviors are found across the volume phase transition. At neutral pH and T ≈ 307 K, a sharp change of the local structure from a water rich open inhomogeneous interpenetrated polymer network to a homogeneous porous solid-like structure after expelling water is observed. Differently, at acidic pH, the local structure changes almost continuously. These findings demonstrate that a fine control of the pH of the system allows to tune the sharpness of the volume-phase transition.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗