Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “MULTIPLETS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Self-Healing Behavior of Ethylene-Based Ionomers

The self-healing behavior of poly(ethylene-co-methacrylic acid) (EMAA)-based ionomers holds tremendous potential for use in a wide variety of unique applications. However, to effectively utilize this self-healing behavior and to design novel materials which possess this ability, the mechanism by which they heal must first be understood ionomers are a class of polymers that can be described as copolymers containing less than 15 mol% ionic content whereby the bulk properties are governed by ionic interactions within the polymer. These ionic groups aggregate into discrete regions known as multiplets which overlap forming clusters that act as physical cross-links profoundly influencing the bulk physical properties. These clusters possess an order-disorder transition (T(sub i)) where the clustered regions may rearrange themselves given time and stimuli. Recognizing the strong influence of these ionic regions on other well understood ionomer properties, their role in self-heating behavior will be assessed. The self-healing behavior is observed following projectile puncture. It has been suggested that during impact energy is passed to the ionomer material, heating it to the melt state. After penetration, it is proposed that the ionic regions maintain their attractions and flow together patching the hole. Thus, the importance of this ionic character and is unique interaction must be established. This will be accomplished through examination of materials with varying ionic content and through the analysis of the T(sub i). The specific ionomer systems examined include a number of ethylene-based materials. Materials of varying ionic content, including the non-ionic base copolymers, will be examined by peel tests, projectile impact and DSC analysis. The information will also be compared with some basic data on LDPE material.

Kalista, Stephen J., Jr.↗
NASA NTRS1996

Electron-Impact-Induced Emission Cross Sections of Neon in the Extreme Ultraviolet

We have measured the extreme ultraviolet (EUV) spectrum of neon produced by electron excitation. The measurements were obtained under optically thin conditions, and at a spectral resolution of 0.5 nm full width at half maximum (FWHM). The most prominent features of the EUV spectrum between 45-80 nm are the resonance lines of Ne I at 73.6 and 74.4 nm and a multiplet of Ne II at 46.14 nm (the average value for the line center of the two closely spaced ion lines at 46.07 and 46.22 nm). Absolute emission cross sections of these lines at 300 eV were measured and compared to other previous measurements.

Neon extreme ultraviolet (EUV) spectrum EUV resona↗
NASA NTRS2008

A Comparison of EAST Shock-Tube Radiation Measurements with a New Air Radiation Model

This paper presents a comparison between the recent EAST shock tube radiation measurements (Grinstead et al., AIAA 2008-1244) and the HARA radiation model. The equilibrium and nonequilibrium radiation measurements are studied for conditions relevant to lunar-return shock-layers; specifically shock velocities ranging from 9 to 11 kilometers per second at initial pressures of 0.1 and 0.3 Torr. The simulated shock-tube flow is assumed one-dimensional and is calculated using the LAURA code, while a detailed nonequilibrium radiation prediction is obtained in an uncoupled manner from the HARA code. The measured and predicted intensities are separated into several spectral ranges to isolate significant spectral features, mainly strong atomic line multiplets. The equations and physical data required for the prediction of these strong atomic lines are reviewed and their uncertainties identified. The 700-1020 nm wavelength range, which accounts for roughly 30% of the radiative flux to a peak-heating lunar return shock-layer, is studied in detail and the measurements and predictions are shown to agree within 15% in equilibrium. The plus or minus 1.5% uncertainty on the measured shock velocity is shown to cause up to a plus or minus 30% difference in the predicted radiation. This band of predictions contains the measured values in almost all cases. For the highly nonequilibrium 0.1 Torr cases, the nonequilibrium radiation peaks are under-predicted by about half. This under-prediction is considered acceptable when compared to the order-of-magnitude over-prediction obtained using a Boltzmann population of electronic states. The reasonable comparison in the nonequilibrium regions provides validation for both the non-Boltzmann modeling in HARA and the thermochemical nonequilibrium modeling in LAURA. The N2 (+)(1-) and N2(2+) molecular band systems are studied in the 290 480 nm wavelength range for both equilibrium and nonequilibrium regimes. The non-Boltzmann rate models for these systems, which have significant uncertainties, are tuned to improve the comparison with measurements.

Johnston, Christopher O.↗
NASA NTRS2008

Middle UV to Near-IR Spectrum of Electron-Excited SO2

We investigated the electron impact-induced fluorescence spectrum of SO2 to provide excitation cross sections for modeling Io's mission spectrum and analyzing Cassini Imaging Science Subsystem observations. The electron-excited middle-ultraviolet visible optical near-infrared (VOIR) emission spectrum of SO2 gas was generated in the laboratory and studied from 2000 to 11,000 A at a resolution of (Delta)(lamda) approximately 2.5 A full width at half maximum (FWHM). The VOIR laboratory spectrum longward of 6000 A consists entirely of S I, II and O I, II multiplets for electron impact energies above approximately 15 eV. Between 2000 and 6000 A, we find previously identified molecular bands from both SO and SO2. This work represents a significant improvement in spectral resolution over our earlier work done at 18 A FWHM. From a measurement of the medium-resolution spectrum, we provide detailed 25- and 100-eV emission cross sections for spectral features from 2000 to 11,000 A . On the basis of these data, we suggest future ground-based and satellite telescopic observations in the VOIR that are of promise for understanding Io's atmosphere.

sulpher dioxide↗
NASA NTRS2008

The ALI-ARMS Code for Modeling Atmospheric non-LTE Molecular Band Emissions: Current Status and Applications

The Accelerated Lambda Iteration (ALI) technique was developed in stellar astrophysics at the beginning of 1990s for solving the non-LTE radiative transfer problem in atomic lines and multiplets in stellar atmospheres. It was later successfully applied to modeling the non-LTE emissions and radiative cooling/heating in the vibrational-rotational bands of molecules in planetary atmospheres. Similar to the standard lambda iterations ALI operates with the matrices of minimal dimension. However, it provides higher convergence rate and stability due to removing from the iterating process the photons trapped in the optically thick line cores. In the current ALI-ARMS (ALI for Atmospheric Radiation and Molecular Spectra) code version additional acceleration of calculations is provided by utilizing the opacity distribution function (ODF) approach and "decoupling". The former allows replacing the band branches by single lines of special shape, whereas the latter treats non-linearity caused by strong near-resonant vibration-vibrational level coupling without additional linearizing the statistical equilibrium equations. Latest code application for the non-LTE diagnostics of the molecular band emissions of Earth's and Martian atmospheres as well as for the non-LTE IR cooling/heating calculations are discussed.

Kutepov, A. A.↗
NASA NTRS2008

Study of Molecular Line Parameters down to Very Low Temperature

The impact of precise spectroscopic measurements on the P(9) multiplet in the v3 band of 12CH4, obtained using a newly developed cold Herriott cell coupled with a tunable diode laser spectrometer, is examined in the context of remote sensing of methane in the atmosphere. More specifically, the influence of the air-broadening temperature dependence, of line narrowing and of line-mixing effects is assessed when fitting high resolution atmospheric spectra recorded from a balloon in the solar occultation mode. This is achieved by considering residuals and retrieved methane volume mixing ratio profiles. By combining data from previous studies together with new measurements, the expression for the temperature dependence of the broadening coefficient has been revisited. It is shown that a correcting factor applied to the usual law gives better results, when considering all the available measurements from room temperature down to about 10-20 K, as compared to the usual expression of the width versus temperature. These results clearly demonstrate that collision broadening is more sensitive to long-range attractive forces when the temperature is decreased.

Mondelain, D.↗
DOE OSTI2011

High-Pressure Evolution of Fe2O3 Electronic Structure Revealed by X-ray Absorption

We report the first high pressure measurement of the Fe K-edge in hematite (Fe{sub 2}O{sub 3}) by X-ray absorption spectroscopy in partial fluorescence yield geometry. The pressure-induced evolution of the electronic structure as Fe{sub 2}O{sub 3} transforms from a high-spin insulator to a low-spin metal is reflected in the x-ray absorption pre-edge. The crystal field splitting energy was found to increase monotonically with pressure up to 48 GPa, above which a series of phase transitions occur. Atomic multiplet, cluster diagonalization, and density-functional calculations were performed to simulate the pre-edge absorption spectra, showing good qualitative agreement with the measurements. The mechanism for the pressure-induced phase transitions of Fe{sub 2}O{sub 3} is discussed and it is shown that ligand hybridization significantly reduces the critical high-spin/low-spin gap pressure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

High-pressure Evolution of Fe2O3 Electronic Structure Revealed by X-ray Absorption

We report the high-pressure measurement of the Fe K edge in hematite (Fe{sub 2}O{sub 3}) by x-ray absorption spectroscopy in partial fluorescence yield geometry. The pressure-induced evolution of the electronic structure as Fe{sub 2}O{sub 3} transforms from a high-spin insulator to a low-spin metal is reflected in the x-ray absorption pre-edge. The crystal-field splitting energy was found to increase monotonically with pressure up to 48 GPa, above which a series of phase transitions occur. Atomic multiplet, cluster diagonalization, and density-functional calculations were performed to simulate the pre-edge absorption spectra, showing good qualitative agreement with the measurements. The mechanism for the pressure-induced electronic phase transitions of Fe{sub 2}O{sub 3} is discussed and it is shown that ligand hybridization significantly reduces the critical high-spin/low-spin transition pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Spectroscopy of 26F to Probe Proton-Neutron Forces Close to the Drip Line

A long-lived J 4 1 isomer, T1=2 2:2 1 ms, has been discovered at 643.4(1) keV in the weakly bound 26 9 F nucleus. It was populated at Grand Acce le rateur National d Ions Lourds in the fragmentation of a 36S beam. It decays by an internal transition to the J 1 1 ground state [82(14)%], by decay to 26Ne, or -delayed neutron emission to 25Ne. From the -decay studies of the J 1 1 and J 4 1 states, new excited states have been discovered in 25;26Ne. Gathering the measured binding energies of the J 1 1 4 1 multiplet in 26 9 F, we find that the proton-neutron 0d5=20d3=2 effective force used in shell-model calculations should be reduced to properly account for the weak binding of 26 9 F. Microscopic coupled cluster theory calculations using interactions derived from chiral effective field theory are in very good agreement with the energy of the low-lying 1 1 , 2 1 , 4 1 states in 26F. Including three-body forces and coupling to the continuum effects improve the agreement between experiment and theory as compared to the use of two-body forces only.

Hagen, Gaute↗
DOE OSTI2016

Preface and Summary

Primary Physics with Secondary Beams of K L 's Not all of physics can be explored by primary beams of electrons and protons, however much these have taught us over the past 60 years. Electron-positron colliders give access to restricted sets of quantum numbers. From proton-proton collisions we have long learned about all manner of high energy reactions. However, access to excited mesons and baryons has been most universally achieved with pion and kaon secondary beams, and latterly pho-ton beams both virtual and real. Nowadays the wealth of information on polarized photon beams on polarized targets has totally revolutionized baryon spectroscopy, especially in the lightest flavor sector. The measurement of polarization asymmetries has constrained partial wave analyses far beyond anything conceivable with pion beams. Nevertheless, these only give access to the product of photocouplings of each excited baryon and its coupling to the hadron final state, such as πN , ππN , ηN , etc. Contemporaneously, in the meson sector, the COMPASS experiment with pion beams on protons at 190 GeV/c, together with heavy flavor decays in e + e - annihilation, have given access to multi-meson final states, like 2π, 3π, with greater precision than ever before. This has given hints and suggestions of new resonances, like the a 1 (1420). To understand the constituent structure of hadrons requires information on the relationship of each meson and baryon to those with different flavors, but the same J P quantum numbers. At its simplest, this is to understand the quark model multiplet structure, where this is appropriate. What is more, so ubiquitous are ππ, πK, KK, ηπ, ηK, ... final states as the decay products of almost every hadron, that knowledge of the properties of these is critical to every analysis. Unitarity colors and shapes the universality of such final state interactions in each set of quantum numbers. This means that however precise our measurements of γN → πη () N , with GlueX for instance, we cannot really determine the fine resonant structure of such a process without some information on πη and πη scattering too. Nor can we determine any flavor partners without information on the corresponding Kη () channels. For that secondary kaon beams are essential. While J-PARC has a whole program of charged strange particle and hypernuclear reactions, photon beams allow unique access to other channels. It was realized long ago that intense photon beams like that about to be delivered to Hall D at JLab, could produce secondary beams. The charged particles can readily be bent away, leaving a neutral particle beam dominated by K L : long lived kaons being produced far more copiously than neutrons above 3–4 GeV momentum. Such a facility provides access to a whole range of physics that is the subject of this meeting. The reactions that can be studied cover the meson spectrum and dynamics, the baryon spectrum and dynamics, and final state interactions that link mesons and baryons together. This includes particularly the channels Kπ, Kη, Kη in the meson sector. These explore the very limitations of chiral dynamics: the strange quark's current mass is 30-50 times that of the

42 ENGINEERING↗
DOE OSTI2017

Fast-neutron Multiplicity Counter for Passive and Active Measurements of Special Nuclear Material

We developed a fast-neutron multiplicity counter (FNMC) based on organic scintillators (liquid and stilbene). The system is able to detect correlated photon and neutron multiplets emitted by fission reactions. We tested the system both in passive and active operation mode, and present the results of the experiments, both carried out at the Zero Power Physics Reactor of Idaho National Laboratory. The system was operated in coincidence mode (with a gate time of 50 nanoseconds) and two calibration-based approaches were used to estimate the 240Pu effective (240Pueff) and 235U mass of the samples. In passive mode, we assayed two types of plutonium metal plates, i.e. PAHN and PANN, with a 240Pueff mass of 4.7 g and 25.05 g per plate, respectively. The 239Pu mass percentage was 74% for the PAHN and 95% for the PANN series. We measured neutrons emitted in coincidence by several plate assemblies, having an overall 240Pueff mass in the 4.7 g to 500 g range. In active mode, we characterized several uranium samples. We used two AmLi sources (~50000 neutrons emitted per second) to induce fission in the samples. The first six measured samples were certified reference materials (CRM, set 149), having a constant enrichment, i.e. 93.2 wt%, and mass in the range between 0.5 and 4 kg. Additionally, we assayed three CRM-146 samples, with constant total mass of 500 g and an enrichment of 20.1 wt%, 52.8 wt% and 93.2 wt%. In both configurations, the system succeeded in estimating the fissile mass of an unknown sample with a statistical uncertainty lower than 1% (4-minute assay) and 7% (10-minute assay), in passive and active mode, respectively. In passive mode, the statistical uncertainty is lower than the one achieved by standard 3He counters for plutonium metal samples of similar mass. The difference between the estimated and the declared 240Pueff mass, i.e., the bias error, measured by the fast neutron multiplicity counter was consistently lower compared to the bias error of a standard thermal system.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Validation of the Fast-Neutron Multiplicity Expressions for Fissile Mass Estimation

Neutron multiplicity analysis is a non-destructive assay technique that involves measurement of the multiplets of neutrons that are emitted from fission of fissile material. Typically, multiplicity analysis is conducted by means of a neutron multiplicity counting (NMC) system that uses capture-based thermal-neutron detectors (e.g., 3He-gas detectors). To relieve the reliance on such detectors, we have developed a fast-neutron multiplicity counting (FNMC) system that uses scatter-based, organic scintillators to directly detect the fast fission neutrons emitted from the sample. One challenge with FNMC systems, however, is that they are prone to effects of neutron cross-talk, where a single neutron may scatter and cause more than one detection event. This leads to an overestimate of the fission rate (F) and inaccurate estimation of other sample parameters such as the leakage multiplication (M) and the alpha-ratio (a) when using the traditional capture-based NMC equations. We have formulated fully generalized multiplicity expressions that account for cross-talk effects for any arbitrary order N. The validity of these expressions were verified with MCNPX-PoliMi simulations and experimental measurements; this paper will present the validation of the proposed generalized multiplicity expressions. Californium-252 and Pu metal plates were measured using the FNMC system and the data was used for neutron multiplicity analysis to estimate sample parameters F, M, and a. We demonstrate that accounting for neutron cross-talk effects of order N = 2 and 3 improves the accuracy of the estimated sample parameters.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Spin Flavor Composition of Excited Baryons

The excited baryon masses are analyzed in the framework of the 1/Nc expansion using the available physical masses and also the masses obtained in lattice QCD for different quark masses. The baryon states are organized into irreducible representations of SU(6)×O(3), where the [56,?P=0+] ground state and excited baryons, and the [56,2+] and [70,1?] excited states are analyzed. The analyses are carried out to O1/Nc and first order in the quark masses. The issue of state identifications is discussed. Numerous parameter independent mass relations result at those orders, among them the well known Gell-Mann-Okubo and Equal Spacing relations, as well as additional relations involving baryons with different spins. It is observed that such relations are satisfied at the expected level of precision. Predictions for physically unknown states for each multiplet are obtained. From the quark-mass dependence of the coefficients in the baryon mass formulas an increasingly simpler picture of the spin-flavor composition of the baryons is observed with increasing pion mass (equivalently, increasing mu,d masses), as measured by the number of significant mass operators.

Goity, Jose↗
DOE OSTI2024

Excitons in 2D Magnets

Theoretical abilities that we built: In our QSGW formalism, the electronic eigenfunctions are calculated self-consistently in presence of the ladder e-h vertex corrections to the screened Coulomb exchange. Charge and self-energies are recalculated iterated until the desired tolerance is achieved in the one-particle Green's function. Further, to include the multi-determinantal (spin-flip structure of multiplets) nature of many body correlations we combine QSGW with DMFT. Below we explore various classes of strongly correlated magnetic systems where excitons are sufficiently described within either the QSGW or the QSGW +DMFT approach. In the process, we establish the digrammatic requirements for a minimum-sufficient theory for describing excitons in large classes of materials.

2D magnets↗
DOE OSTI2011

The mass splittings of SU(3) baryons within a chiral soliton model

In the framework of a chiral soliton model ({sub {chi}S}M), the complete mass splittings of SU(3) baryons are investigated, the isospin and SU(3) flavor symmetry breaking being simultaneously considered with a 'model-independent approach'. The dynamical quantities appearing in the expressions for the masses are adjusted to the masses of the baryon octet, the decuplet baryon {Sigma}* and the masses of {Theta}{sup +} and N{sup *} as inputs rather than by extracting them from a calculated self-consistent soliton profile. We estimate the masses of the baryon decuplet and antidecuplet without any further adjustable free parameter and it turns out that calculated mass values of the baryon decuplet are in very good agreement with experimental data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Energy release from hadron-quark phase transition in neutron stars and the axial w mode of gravitational waves

Describing the hyperonic and quark phases of neutron stars with an isospin- and momentum-dependent effective interaction for the baryon octet and the MIT bag model, respectively, and using the Gibbs conditions to construct the mixed phase, we study the energy release from a neutron star owing to the hadron-quark phase transition. Moreover, the frequency and damping time of the first axial w mode of gravitational waves are studied for both hyperonic and hybrid stars. We find that the energy release is much more sensitive to the bag constant than the density dependence of the nuclear symmetry energy. Also, the frequency of the w mode is found to be significantly different with or without the hadron-quark phase transition and depends strongly on the value of the bag constant. Effects of the density dependence of the nuclear symmetry energy become, however, important for large values of the bag constant that lead to higher hadron-quark transition densities.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Weak kaon production off the nucleon

The weak kaon production off the nucleon induced by neutrinos is studied at the low and intermediate energies of interest for some ongoing and future neutrino oscillation experiments. This process is also potentially important for the analysis of proton decay experiments. We develop a microscopical model based on the SU(3) chiral Lagrangians. The basic parameters of the model are f{sub {pi},} the pion decay constant, Cabibbo's angle, the proton and neutron magnetic moments, and the axial vector coupling constants for the baryons octet, D and F, that are obtained from the analysis of the semileptonic decays of neutron and hyperons. The studied mechanisms are the main source of kaon production for neutrino energies up to 1.2 to 1.5 GeV for the various channels and the cross sections are large enough to be amenable to be measured by experiments such as Minerva and T2K.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Tensor charges and form factors of SU(3) baryons in the self-consistent SU(3) chiral quark-soliton model

We investigate the tensor form factors of the baryon octet within the framework of the chiral quark-soliton model, emphasizing those of the nucleon, taking linear 1/N{sub c} rotational as well as linear m{sub s} corrections into account, and applying the symmetry-conserving quantization. We explicitly calculate the tensor form factors H{sub T}{sup q}(Q{sup 2}) corresponding to the generalized parton distributions H{sub T}(x,{xi},t). The tensor form factors are obtained for the momentum transfer up to Q{sup 2{<=}}1 GeV{sup 2} and at a renormalization scale of 0.36 GeV{sup 2}. We find for the tensor charges {delta}u=1.08, {delta}d=-0.32, and {delta}s=-0.01 and discuss their physical consequences, comparing them with those from other models. Results for tensor charges for the baryon octet are also given.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗