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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 OSTI2013

Near-infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources

Context. We present that spectral energy distribution and its variability are basic tools for understanding the physical processes operating in active galactic nuclei (AGN). Aims. In this paper we report the results of a one-year near-infrared (NIR) and optical monitoring of a sample of 22 AGN known to be gamma-ray emitters, aimed at discovering correlations between optical and gamma-ray emission. Methods. We observed our objects with the Rapid Eye Mount (REM) telescope in J,H,K, and R bands nearly twice every month during their visibility window and derived light curves and spectral indexes. We also analyzed the gamma-ray data from the Fermi gamma-ray Space Telescope, making weekly averages. Results. Six sources were never detected during our monitoring, proving to be fainter than their historical Two micron all sky survey (2MASS) level. All of the sixteen detected sources showed marked flux density variability, while the spectral indexes remained unchanged within our sensitivity limits. Steeper sources showed, on average, a larger variability. From the NIR light curves we also computed a variability speed index for each detected source. Only one source (PKS 0208-512) underwent an NIR flare during our monitoring. Half of the sources showed a regular flux density trend on a one-year time scale, but do not show any other peculiar characteristic. The broadband spectral index α ro appears to be a good proxy of the NIR spectral index only for BL Lac objects. No clear correlation between NIR and gamma-ray data is evident in our data, save for PKS 0537-441, PKS 0521-360, PKS 2155-304, and PKS 1424-418. In conclusion, the gamma-ray/NIR flux ratio showed a large spread, QSO being generally gamma-louder than BL Lac, with a marked correlation with the estimated peak frequency (ν peak ) of the synchrotron emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Applications of TIERRAS for underground particle cascade simulations

In this communication we present some example applications of TIERRAS, a software package for the simulation of High Energy particle cascades underground and underwater. The examples illustrate how this package can be used to study the phenomenology of particle cascades from Extended Air Showers propagated several meters underground, including the effect of the surface ''albedo'' particles that are generated when a cascade reaches ground level. These up-going particles can have a measurable effect on surface or shallow underground detectors. Finally, to show the package ability ro perform simulations of particle cascades in ice, an application for neutrino radio detection is briefly introduced.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Gas-phase photodissociation of CH{sub 3}COCN at 308 nm by time-resolved Fourier-transform infrared emission spectroscopy

By using time-resolved Fourier-transform infrared emission spectroscopy, the fragments of HCN(v= 1, 2) and CO(v= 1-3) are detected in one-photon dissociation of acetyl cyanide (CH{sub 3}COCN) at 308 nm. The S{sub 1}(A'), {sup 1}(n{sub O}, {pi}*{sub CO}) state at 308 nm has a radiative lifetime of 0.46 {+-} 0.01 {mu}s, long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of Ar collision-induced internal conversion is estimated to be (1-7) x 10{sup -12} cm{sup 3} molecule{sup -1} s{sup -1}. The measurements of O{sub 2} dependence exclude the production possibility of these fragments via intersystem crossing. The high-resolution spectra of HCN and CO are analyzed to determine the ro-vibrational energy deposition of 81 {+-} 7 and 32 {+-} 3 kJ/mol, respectively. With the aid of ab initio calculations, a two-body dissociation on the energetic ground state is favored leading to HCN + CH{sub 2}CO, in which the CH{sub 2}CO moiety may further undergo secondary dissociation to release CO. The production of CO{sub 2} in the reaction with O{sub 2} confirms existence of CH{sub 2} and a secondary reaction product of CO. The HNC fragment is identified but cannot be assigned, as restricted to a poor signal-to-noise ratio. Because of insufficient excitation energy at 308 nm, the CN and CH{sub 3} fragments that dominate the dissociation products at 193 nm are not detected.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Photodissociation of gaseous CH{sub 3}COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels

Upon one-photon excitation at 248 nm, gaseous CH{sub 3}C(O)SH is dissociated following three pathways with the products of (1) OCS + CH{sub 4}, (2) CH{sub 3}SH + CO, and (3) CH{sub 2}CO + H{sub 2}S that are detected using time-resolved Fourier-transform infrared emission spectroscopy. The excited state {sup 1}(n{sub O}, {pi}{sup *}{sub CO}) has a radiative lifetime of 249 {+-} 11 ns long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of collision-induced internal conversion is estimated to be 1.1 Multiplication-Sign 10{sup -10} cm{sup 3} molecule{sup -1} s{sup -1}. Among the primary dissociation products, a fraction of the CH{sub 2}CO moiety may undergo further decomposition to CH{sub 2}+ CO, of which CH{sub 2} is confirmed by reaction with O{sub 2} producing CO{sub 2}, CO, OH, and H{sub 2}CO. Such a secondary decomposition was not observed previously in the Ar matrix-isolated experiments. The high-resolution spectra of CO are analyzed to determine the ro-vibrational energy deposition of 8.7 {+-} 0.7 kcal/mol, while the remaining primary products with smaller rotational constants are recognized but cannot be spectrally resolved. The CO fragment detected is mainly ascribed to the primary production. A prior distribution method is applied to predict the vibrational distribution of CO that is consistent with the experimental findings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

A new ab initio potential energy surface for the collisional excitation of HCN by para- and ortho-H{sub 2}

We present a new four-dimensional potential energy surface for the collisional excitation of HCN by H{sub 2}. Ab initio calculations of the HCN–H{sub 2} van der Waals complex, considering both molecules as rigid rotors, were carried out at the explicitly correlated coupled cluster with single, double, and perturbative triple excitations [CCSD(T)-F12a] level of theory using an augmented correlation-consistent triple zeta (aVTZ) basis set. The equilibrium structure is linear HCN–H{sub 2} with the nitrogen pointing towards H{sub 2} at an intermolecular separation of 7.20 a{sub 0}. The corresponding well depth is −195.20 cm{sup −1}. A secondary minimum of −183.59 cm{sup −1} was found for a T-shape configuration with the H of HCN pointing to the center of mass of H{sub 2}. We also determine the rovibrational energy levels of the HCN–para-H{sub 2} and HCN–ortho-H{sub 2} complexes. The calculated dissociation energies for the para and ortho complexes are 37.79 cm{sup −1} and 60.26 cm{sup −1}, respectively. The calculated ro-vibrational transitions in the HCN–H{sub 2} complex are found to agree by more than 0.5% with the available experimental data, confirming the accuracy of the potential energy surface.

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

Product fine-structure resolved photodissociation dynamics: The A band of H{sub 2}O

The photodissociation dynamics of H{sub 2}O in its first absorption band is investigated on an accurate potential energy surface based on a large number of high-level ab initio points. Several ro-vibrational states of the parent molecule are considered. Different from most previous theoretical studies, the spin-orbit and Λ-doublet populations of the open-shell OH fragment are reported from full-dimensional wave packet calculations. The populations of the two spin-orbit manifolds are in most cases close to the statistical limit, but the Λ-doublet is dominated by the A{sup ″} component, thanks largely to the fast in-plane dissociation of H{sub 2}O(A{sup ~1}A{sup ′′}). Comparisons with experimental data and a Franck-Condon model are generally very good, although some discrepancies exist.

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

On the robust optimization to the uncertain vaccination strategy problem

In order to prevent an epidemic of infectious diseases, the vaccination coverage needs to be minimized and also the basic reproduction number needs to be maintained below 1. This means that as we get the vaccination coverage as minimum as possible, thus we need to prevent the epidemic to a small number of people who already get infected. In this paper, we discuss the case of vaccination strategy in term of minimizing vaccination coverage, when the basic reproduction number is assumed as an uncertain parameter that lies between 0 and 1. We refer to the linear optimization model for vaccination strategy that propose by Becker and Starrzak (see [2]). Assuming that there is parameter uncertainty involved, we can see Tanner et al (see [9]) who propose the optimal solution of the problem using stochastic programming. In this paper we discuss an alternative way of optimizing the uncertain vaccination strategy using Robust Optimization (see [3]). In this approach we assume that the parameter uncertainty lies within an ellipsoidal uncertainty set such that we can claim that the obtained result will be achieved in a polynomial time algorithm (as it is guaranteed by the RO methodology). The robust counterpart model is presented.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

The role of the transition state in polyatomic reactions: Initial state-selected reaction probabilities of the H + CH{sub 4} → H{sub 2} + CH{sub 3} reaction

Full-dimensional calculations of initial state-selected reaction probabilities on an accurate ab initio potential energy surface (PES) have been communicated recently [R. Welsch and U. Manthe, J. Chem. Phys. 141, 051102 (2014)]. These calculations use the quantum transition state concept, the multi-layer multi-configurational time-dependent Hartree approach, and graphics processing units to speed up the potential evaluation. Here further results of these calculations and an extended analysis are presented. State-selected reaction probabilities are given for many initial ro-vibrational states. The role of the vibrational states of the activated complex is analyzed in detail. It is found that rotationally cold methane mainly reacts via the ground state of the activated complex while rotationally excited methane mostly reacts via H–H–CH{sub 3}-bending excited states of the activated complex. Analyzing the different contributions to the reactivity of the vibrationally states of methane, a complex pattern is found. Comparison with initial state-selected reaction probabilities computed on the semi-empirical Jordan-Gilbert PES reveals the dependence of the results on the specific PES.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Theoretical investigation of the relaxation of the bending mode of CH{sub 2}(X{sup ~}) by collisions with helium

We have earlier determined the dependence on the bending angle of the interaction of the methylene radical (CH{sub 2}) in its X{sup ~3}B{sub 1} state with He [L. Ma, P. J. Dagdigian, and M. H. Alexander, J. Chem. Phys. 136, 224306 (2012)]. By integration over products of the bending vibrational wave function, in a quantum close-coupled treatment we have calculated cross sections for the ro-vibrational relaxation of CH{sub 2}(X{sup ~}). Specifically, we find that cross sections for a loss of one vibrational quantum (v{sub b} = 2 → 1 and 1 → 0) are roughly two orders of magnitude smaller, and those for a loss of two vibrational quanta (v{sub b} = 2 → 0) four orders of magnitude smaller, than those for pure rotational relaxation. In addition, no clear cut dependence on the energy gap is seen.

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

Communication: Visible line intensities of the triatomic hydrogen ion from experiment and theory

The visible spectrum of H{sub 3}{sup +} is studied using high-sensitivity action spectroscopy in a cryogenic radiofrequency multipole trap. Advances are made to measure the weak ro-vibrational transitions from the lowest rotational states of H{sub 3}{sup +} up to high excitation energies providing visible line intensities and, after normalisation to an infrared calibration line, the corresponding Einstein B coefficients. Ab initio predictions for the Einstein B coefficients are obtained from a highly precise dipole moment surface of H{sub 3}{sup +} and found to be in excellent agreement, even in the region where states have been classified as chaotic.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Toward accurate thermochemistry of the {sup 24}MgH, {sup 25}MgH, and {sup 26}MgH molecules at elevated temperatures: Corrections due to unbound states

The total partition functions Q(T) and their first two moments Q{sup ′}(T) and Q{sup ″}(T), together with the isobaric heat capacities C{sub p}(T), are computed a priori for three major MgH isotopologues on the temperature range of T = 100–3000 K using the recent highly accurate potential energy curve, spin-rotation, and non-adiabatic correction functions of Henderson et al. [J. Phys. Chem. A 117, 13373 (2013)]. Nuclear motion computations are carried out on the ground electronic state to determine the (ro)vibrational energy levels and the scattering phase shifts. The effect of resonance states is found to be significant above about 1000 K and it increases with temperature. Even very short-lived states, due to their relatively large number, have significant contributions to Q(T) at elevated temperatures. The contribution of scattering states is around one fourth of that of resonance states but opposite in sign. Uncertainty estimates are given for the possible error sources, suggesting that all computed thermochemical properties have an accuracy better than 0.005% up to 1200 K. Between 1200 and 2500 K, the uncertainties can rise to around 0.1%, while between 2500 K and 3000 K, a further increase to 0.5% might be observed for Q{sup ″}(T) and C{sub p}(T), principally due to the neglect of excited electronic states. The accurate thermochemical data determined are presented in the supplementary material for the three isotopologues of {sup 24}MgH, {sup 25}MgH, and {sup 26}MgH at 1 K increments. These data, which differ significantly from older standard data, should prove useful for astronomical models incorporating thermodynamic properties of these species.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Theoretical study on the ground state of the polar alkali-metal-barium molecules: Potential energy curve and permanent dipole moment

In this paper, we systematically investigate the electronic structure for the {sup 2}Σ{sup +} ground state of the polar alkali-metal-alkaline-earth-metal molecules BaAlk (Alk = Li, Na, K, Rb, and Cs). Potential energy curves and permanent dipole moments (PDMs) are determined using power quantum chemistry complete active space self-consistent field and multi-reference configuration interaction methods. Basic spectroscopic constants are derived from ro-vibrational bound state calculation. From the calculations, it is shown that BaK, BaRb, and BaCs molecules have moderate values of PDM at the equilibrium bond distance (BaK:1.62 D, BaRb:3.32 D, and BaCs:4.02 D). Besides, the equilibrium bond length (4.93 Å and 5.19 Å) and dissociation energy (0.1825 eV and 0.1817 eV) for the BaRb and BaCs are also obtained.

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

Quantum cascade laser based monitoring of CF{sub 2} radical concentration as a diagnostic tool of dielectric etching plasma processes

Dielectric etching plasma processes for modern interlevel dielectrics become more and more complex by the introduction of new ultra low-k dielectrics. One challenge is the minimization of sidewall damage, while etching ultra low-k porous SiCOH by fluorocarbon plasmas. The optimization of this process requires a deeper understanding of the concentration of the CF{sub 2} radical, which acts as precursor in the polymerization of the etch sample surfaces. In an industrial dielectric etching plasma reactor, the CF{sub 2} radical was measured in situ using a continuous wave quantum cascade laser (cw-QCL) around 1106.2 cm{sup −1}. We measured Doppler-resolved ro-vibrational absorption lines and determined absolute densities using transitions in the ν{sub 3} fundamental band of CF{sub 2} with the aid of an improved simulation of the line strengths. We found that the CF{sub 2} radical concentration during the etching plasma process directly correlates to the layer structure of the etched wafer. Hence, this correlation can serve as a diagnostic tool of dielectric etching plasma processes. Applying QCL based absorption spectroscopy opens up the way for advanced process monitoring and etching controlling in semiconductor manufacturing.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Renner-Teller modelling of recent experimental spectra of H{sub 2}S{sup +}

Recently there has been a renewal of interest in the spectroscopy and dynamics of the formation and fragmentation of the hydrogen sulphide ion, including. rotationally resolved spectra of higher vibrational states of the ∼A{sup 2}A{sub 1}−∼X{sup 2}B{sub 1} system than were obtained previously, and a comprehensive imaging study of the photo-fragmentation routes of highly excited H{sub 2}S{sup +}. In collaboration with Ch. Jungen and A. Alijah I have extended our previous l basis approach to the calculation of the effects of orbital angular momentum in H{sub 2}S{sup +} to include the stretch - bender extensions, with the options of using either the K- or l basis. This new code is being used to calculate the complicated orbital angular momentum and spin-orbit coupling effects responsible for the ro-vibronic pattern measured in some of the new experimental results.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Negative hydrogen ion production mechanisms

Negative hydrogen/deuterium ions can be formed by processes occurring in the plasma volume and on surfaces facing the plasma. The principal mechanisms leading to the formation of these negative ions are dissociative electron attachment to ro-vibrationally excited hydrogen/deuterium molecules when the reaction takes place in the plasma volume, and the direct electron transfer from the low work function metal surface to the hydrogen/deuterium atoms when formation occurs on the surface. The existing theoretical models and reported experimental results on these two mechanisms are summarized. Performance of the negative hydrogen/deuterium ion sources that emerged from studies of these mechanisms is reviewed. Contemporary negative ion sources do not have negative ion production electrodes of original surface type sources but are operated with caesium with their structures nearly identical to volume production type sources. Reasons for enhanced negative ion current due to caesium addition to these sources are discussed.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Direct numerical simulation of turbulent flow in a rotating square duct

A fully developed turbulent flow in a rotating straight square duct is simulated by direct numerical simulations at Re{sub τ} = 300 and 0 ≤ Ro{sub τ} ≤ 40. The rotating axis is parallel to two opposite walls of the duct and normal to the main flow. Variations of the turbulence statistics with the rotation rate are presented, and a comparison with the rotating turbulent channel flow is discussed. Rich secondary flow patterns in the cross section are observed by varying the rotation rate. The appearance of a pair of additional vortices above the pressure wall is carefully examined, and the underlying mechanism is explained according to the budget analysis of the mean momentum equations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Power efficiency improvements with the radio frequency H{sup −} ion source

CW 13.56 MHz radio frequency-driven H{sup −} ion source is under development at the University of Jyväskylä for replacing an existing filament-driven ion source at the MCC30/15 cyclotron. Previously, production of 1 mA H{sup −} beam, which is the target intensity of the ion source, has been reported at 3 kW of RF power. The original ion source front plate with an adjustable electromagnet based filter field has been replaced with a new front plate with permanent magnet filter field. The new structure is more open and enables a higher flux of ro-vibrationally excited molecules towards the plasma electrode and provides a better control of the potential near the extraction due to a stronger separation of the main plasma from the plasma electrode. While the original system provided better control over the e{sup −}/H{sup −} ratio, the new configuration has led to a higher production efficiency of 1 mA H{sup −} at 1.75 kW RF power. The latest results and upgrade plans are presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Electron cyclotron resonance heating by magnetic filter field in a negative hydrogen ion source

The influence of magnetic filter field on plasma properties in the heating region has been investigated in a planar-type inductively coupled radio-frequency (RF) H{sup −} ion source. Besides filtering high energy electrons near the extraction region, the magnetic filter field is clearly observed to increase the electron temperature in the heating region at low pressure discharge. With increasing the operating pressure, enhancement of electron temperature in the heating region is reduced. The possibility of electron cyclotron resonance (ECR) heating in the heating region due to stray magnetic field generated by a filter magnet located at the extraction region is examined. It is found that ECR heating by RF wave field in the discharge region, where the strength of an axial magnetic field is approximately ∼4.8 G, can effectively heat low energy electrons. Depletion of low energy electrons in the electron energy distribution function measured at the heating region supports the occurrence of ECR heating. The present study suggests that addition of axial magnetic field as small as several G by an external electromagnet or permanent magnets can greatly increase the generation of highly ro-vibrationally excited hydrogen molecules in the heating region, thus improving the performance of H{sup −} ion generation in volume-produced negative hydrogen ion sources.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗