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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 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Severity of liver disease affects HCV kinetics in patients treated with intravenous silibinin monotherapy

HCV kinetic analysis and modeling during antiviral therapy have not been performed in decompensated cirrhotic patients awaiting liver transplantation. Here, viral and host parameters were compared in patients treated with daily intravenous silibinin (SIL) monotherapy for 7 days according to the severity of their liver disease. Data were obtained from 25 patients, 12 non-cirrhotic, 8 with compensated cirrhosis and 5 with decompensated cirrhosis. The standard-biphasic model with time-varying SIL effectiveness (from 0 to ε max ) was fit to viral kinetic data. Our results show that baseline viral load and age were significantly associated with the severity of liver disease (p<0.0001). A biphasic viral decline was observed in most patients with a higher first phase decline patients with less severe liver disease. The maximal effectiveness, ε max , was significantly (p≤0.032) associated with increasing severity of liver disease (ε max [s.e.]=0.86[0.05], ε max =0.69[0.06] and ε max =0.59[0.1]). The 2nd phase decline slope was not significantly different among groups (mean 1.88±0.15 log 10 IU/ml/wk, p=0.75) as was the rate of change of SIL effectiveness (k=2.12/day[standard error, SE=0.18/day]). HCV-infected cell loss rate (δ[SE]=0.62/day[0.05/day]) was high and similar among groups. We conclude that the high loss rate of HCV-infected cells suggests that sufficient dose and duration of SIL might achieve viral suppression in advanced liver disease.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1991

A self-consistent model for the particles and fields upstream of an outgassing comet. I - Gyrotropic and isotropic ion distributions

The magnetic field and solar wind flow parameters in the vicinity of a weakly outgassing comet are determined using a self-consistent model which treats the cometary ions kinetically. Two different assumptions are made concerning the cometary ion distribution function; the pickup cometary ions from either a velocity space gyrotropic ring distribution or a velocity space isotropic shell distribution in the solar wind frame of reference. The individual currents due to the solar wind and cometary ions, which determine the magnetic field, are calculated in each case. Using theoretically determined parameters which reflect the conditions expected to comet Kopff (a typical short-period comet and one possible target for the future CRAF/Cassini mission) for various heliocentric distances, the way in which global field and flow characteristics are influenced by the nature of the cometary ion distribution function is determined.

Flammer, K. R.↗
DOE OSTI2014

Comparative analysis of condensation models within DSMC

Two condensation process modeling approaches within DSMC methodology are compared. The first is based on the modified nucleation theory which correctly describes small clusters and the second on the kinetic theory and considers not only supercritical clusters, but clusters of all sizes including dimers. The relaxation of the size distribution function is calculated for the spatially homogeneous cases, where the monomer parameters are kept constant. As an example the vapour of Cu atoms is considered and importance of taking into account of the internal energies of clusters is shown. Peculiarities of the classical and kinetic approaches are discussed herein.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Two-dimensional positive column structure in a discharge tube with radius discontinuity

The low-pressure (40 and 90 Pa) low-current (4 and 10 mA) direct current discharge in a tube with a sharp change of its radius is studied both numerically and experimentally. A fully self-consistent hybrid numerical model of a two-dimensional non-uniform positive column in neon is developed using a nonlocal approach. The model combines kinetic simulation of the electrons (under two-terms approach) and fluid description of the neon ions and permits to calculate the distribution of all plasma parameters in the direct current discharges in the cameras with cylindrical geometry and radius discontinuity. The simulation results are compared with the measured 585.3 nm neon spectral line absolute intensities and excited 1s{sub 3} metastable neon atom number densities. Non-local electron kinetics in the transition region and formation of standing strata are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Etching of a-Si:H thin films by hydrogen plasma: A view from in situ spectroscopic ellipsometry

When atomic hydrogen interacts with hydrogenated amorphous silicon (a-Si:H), the induced modifications are of crucial importance during a-Si:H based devices manufacturing or processing. In the case of hydrogen plasma, the depth of the modified zone depends not only on the plasma processing parameters but also on the material. In this work, we exposed a-Si:H thin films to H{sub 2} plasma just after their deposition. In situ UV-visible spectroscopic ellipsometry measurements were performed to track the H-induced changes in the material. The competition between hydrogen insertion and silicon etching leads to first order kinetics in the time-evolution of the thickness of the H-modified zone. We analyzed the correlation between the steady state structural parameters of the H-modified layer and the main levers that control the plasma-surface interaction. In comparison with a simple doped layer, exposure of a-Si:H based junctions to the same plasma treatment leads to a thinner H-rich subsurface layer, suggesting a possible charged state of hydrogen diffusing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

An active learning high-throughput microstructure calibration framework for solving inverse structure–process problems in materials informatics

Determining a process–structure–property relationship is the holy grail of materials science, where both computational prediction in the forward direction and materials design in the inverse direction are essential. Problems in materials design are often considered in the context of process–property linkage by bypassing the materials structure, or in the context of structure–property linkage as in microstructure-sensitive design problems. However, there is a lack of research effort in studying materials design problems in the context of process–structure linkage, which has a great implication in reverse engineering. In this paper, given a target microstructure, we propose an active learning high-throughput microstructure calibration framework to derive a set of processing parameters, which can produce an optimal microstructure that is statistically equivalent to the target microstructure. The proposed framework is formulated as a noisy multi-objective optimization problem, where each objective function measures a deterministic or statistical difference of the same microstructure descriptor between a candidate microstructure and a target microstructure. Furthermore, to significantly reduce the physical waiting wall-time, we enable the high-throughput feature of the microstructure calibration framework by adopting an asynchronously parallel Bayesian optimization to exploit high-performance computing resources. Case studies in additive manufacturing and grain growth are used to demonstrate the applicability of the proposed framework, where kinetic Monte Carlo (kMC) simulation is used as a forward predictive model, such that for a given target microstructure, the target processing parameters that produced this microstructure are successfully recovered.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Predicting the effect of angular momentum on the dissociation dynamics of highly rotationally excited radical intermediates

We present a model which accurately predicts the net speed distributions of products resulting from the unimolecular decomposition of rotationally excited radicals. The radicals are produced photolytically from a halogenated precursor under collision-free conditions so they are not in a thermal distribution of rotational states. The accuracy relies on the radical dissociating with negligible energetic barrier beyond the endoergicity. We test the model predictions using previous velocity map imaging and crossed laser-molecular beam scattering experiments that photolytically generated rotationally excited CD{sub 2}CD{sub 2}OH and C{sub 3}H{sub 6}OH radicals from brominated precursors; some of those radicals then undergo further dissociation to CD{sub 2}CD{sub 2} + OH and C{sub 3}H{sub 6} + OH, respectively. We model the rotational trajectories of these radicals, with high vibrational and rotational energy, first near their equilibrium geometry, and then by projecting each point during the rotation to the transition state (continuing the rotational dynamics at that geometry). This allows us to accurately predict the recoil velocity imparted in the subsequent dissociation of the radical by calculating the tangential velocities of the CD{sub 2}CD{sub 2}/C{sub 3}H{sub 6} and OH fragments at the transition state. The model also gives a prediction for the distribution of angles between the dissociation fragments’ velocity vectors and the initial radical’s velocity vector. These results are used to generate fits to the previously measured time-of-flight distributions of the dissociation fragments; the fits are excellent. The results demonstrate the importance of considering the precession of the angular velocity vector for a rotating radical. We also show that if the initial angular momentum of the rotating radical lies nearly parallel to a principal axis, the very narrow range of tangential velocities predicted by this model must be convoluted with a J = 0 recoil velocity distribution to achieve a good result. The model relies on measuring the kinetic energy release when the halogenated precursor is photodissociated via a repulsive excited state but does not include any adjustable parameters. Even when different conformers of the photolytic precursor are populated, weighting the prediction by a thermal conformer population gives an accurate prediction for the relative velocity vectors of the fragments from the highly rotationally excited radical intermediates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Numerical investigation of non-perturbative kinetic effects of energetic particles on toroidicity-induced Alfvén eigenmodes in tokamaks and stellarators

The resonant interaction of shear Alfvén waves with energetic particles is investigated numerically in tokamak and stellarator geometry using a non-perturbative MHD-kinetic hybrid approach. The focus lies on toroidicity-induced Alfvén eigenmodes (TAEs), which are most easily destabilized by a fast-particle population in fusion plasmas. While the background plasma is treated within the framework of an ideal-MHD theory, the drive of the fast particles, as well as Landau damping of the background plasma, is modelled using the drift-kinetic Vlasov equation without collisions. Building on analytical theory, a fast numerical tool, STAE-K, has been developed to solve the resulting eigenvalue problem using a Riccati shooting method. The code, which can be used for parameter scans, is applied to tokamaks and the stellarator Wendelstein 7-X. High energetic-ion pressure leads to large growth rates of the TAEs and to their conversion into kinetically modified TAEs and kinetic Alfvén waves via continuum interaction. To better understand the physics of this conversion mechanism, the connections between TAEs and the shear Alfvén wave continuum are examined. It is shown that, when energetic particles are present, the continuum deforms substantially and the TAE frequency can leave the continuum gap. The interaction of the TAE with the continuum leads to singularities in the eigenfunctions. To further advance the physical model and also to eliminate the MHD continuum together with the singularities in the eigenfunctions, a fourth-order term connected to radiative damping has been included. The radiative damping term is connected to non-ideal effects of the bulk plasma and introduces higher-order derivatives to the model. Thus, it has the potential to substantially change the nature of the solution. For the first time, the fast-particle drive, Landau damping, continuum damping, and radiative damping have been modelled together in tokamak- as well as in stellarator geometry.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Fluctuation approach to description of nonideal plasma. II: Collisional recombination in nonequilibrium plasma

A model capable of describing the kinetics of collisional recombination in nonideal plasmas by the methods of molecular dynamics is developed. The dependence of the collisional recombination rate on the coupling parameter is found to differ substantially from the extrapolation of the three-body recombination rate in nonideal plasmas. A sharp decrease in the recombination rate in strongly nonideal plasmas is revealed. As the coupling parameter decreases, collisional recombination transforms into three-body recombination.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Kinetic particle simulation of discharge and wall erosion of a Hall thruster

The primary lifetime limiting factor of Hall thrusters is the wall erosion caused by the ion induced sputtering, which is predominated by dielectric wall sheath and pre-sheath. However, so far only fluid or hybrid simulation models were applied to wall erosion and lifetime studies in which this non-quasi-neutral and non-equilibrium area cannot be treated directly. Thus, in this study, a 2D fully kinetic particle-in-cell model was presented for Hall thruster discharge and lifetime simulation. Because the fully kinetic lifetime simulation was yet to be achieved so far due to the high computational cost, the semi-implicit field solver and the technique of mass ratio manipulation was employed to accelerate the computation. However, other artificial manipulations like permittivity or geometry scaling were not used in order to avoid unrecoverable change of physics. Additionally, a new physics recovering model for the mass ratio was presented for better preservation of electron mobility at the weakly magnetically confined plasma region. The validity of the presented model was examined by various parametric studies, and the thrust performance and wall erosion rate of a laboratory model magnetic layer type Hall thruster was modeled for different operation conditions. The simulation results successfully reproduced the measurement results with typically less than 10% discrepancy without tuning any numerical parameters. It is also shown that the computational cost was reduced to the level that the Hall thruster fully kinetic lifetime simulation is feasible.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Isotope Effects on the Crystallization Kinetics of Selectively Deuterated Poly(ε-Caprolactone)

Deuterium labeling of semi-crystalline polymers can dramatically affect their crystallization behaviors. However, the influence of different labeled positions in a partially deuterated polymer on its crystallization is still far from understood. Here, we synthesized a series of selectively deuterated poly(ε-caprolactones) (PCLs) through ring-opening polymerization of ε-caprolactone with controlled deuteration sites, including fully protiated (D0), fully deuterated (D10), tetra deuteration at the 3- and 7- caprolactone ring positions (D4) and hexa deuteration at the 4-, 5-, and 6- caprolactone ring positions (D6). All the PCLs showed a similar lamellar structure and parameters. Differential scanning calorimetry (DSC) analysis revealed that the equilibrium melting temperature $T^{0}_{m}$, melting temperature T m , crystallization temperature T c , and crystallization kinetics changed systemically with the deuterium content except for D4, which indicates that the presence of—CD 2 —moieties on either side of ester group in the polymer chain combined with isotopic inhomogeneity could influence the chain packing. The nonmonotonic trend of T m as a function of deuterium content could be attributed to the difference in a hydrogen-bond like intermolecular interaction between different PCLs. Partially deuterated PCLs (D4 and D6) showed an Avrami index near 2. After analyzing the parameters at the same supercooling temperature Δ T c , the existence of two crystallization regimes of PCLs were detected.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Mutual-information based optimal experimental design for hyperpolarized $$^{13}$$C-pyruvate MRI

Abstract A key parameter of interest recovered from hyperpolarized (HP) MRI measurements is the apparent pyruvate-to-lactate exchange rate, $$k_{{\textrm PL}}$$ k P L , for measuring tumor metabolism. This manuscript presents an information-theory-based optimal experimental design approach that minimizes the uncertainty in the rate parameter, $$k_{{\textrm PL}}$$ k P L , recovered from HP-MRI measurements. Mutual information is employed to measure the information content of the HP measurements with respect to the first-order exchange kinetics of the pyruvate conversion to lactate. Flip angles of the pulse sequence acquisition are optimized with respect to the mutual information. A time-varying flip angle scheme leads to a higher parameter optimization that can further improve the quantitative value of mutual information over a constant flip angle scheme. However, the constant flip angle scheme, 35 and 28 degrees for pyruvate and lactate measurements, leads to an accuracy and precision comparable to the variable flip angle schemes obtained from our method. Combining the comparable performance and practical implementation, optimized pyruvate and lactate flip angles of 35 and 28 degrees, respectively, are recommended.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2020

Passive NO x adsorption on Pd/H-ZSM-5: Experiments and modeling

A combined experimental and modeling study of the passive NO x adsorber (PNA) is presented that advances the understanding and prediction of the effects of various operating parameters and material properties of H-ZSM-5 and Pd/H-ZSM-5. Experiments reveal the NO x uptake process to be kinetically limited. Two microkinetic schemes are developed to explain the NO x uptake and release and NO 2 generation data. Both schemes are incorporated into a 1+1 D monolith model to predict and validate NO x uptake and temperature programmed desorption (TPD) data. Scheme I involves Z – [PdOH] + , Z – Pd 2+ Z – and Z – Pd + with Z – Pd + as the strongest NO binding site. Scheme II involves reduction of PdO 2 to PdO and nitrate formation. Model tuning utilizes a combination of infrared spectroscopy measurements and density functional theory (DFT) estimates of energy barriers. Lastly, the model is validated at different conditions including feed parameters and Pd loading.

42 ENGINEERING↗
NASA NTRS1976

Preliminary scaling laws for plasma current, ion kinetic temperature, and plasma number density in the NASA Lewis bumpy torus plasma

Parametric variation of independent variables which may affect the characteristics of bumpy torus plasma have identified those which have a significant effect on the plasma current, ion kinetic temperature, and plasma number density, and those which do not. Empirical power law correlations of the plasma current, and the ion kinetic temperature and number density were obtained as functions of potential applied to the midplane electrode rings, the background neutral gas pressure, and the magnetic field strength. Additional parameters studied included the type of gas, the polarity of the midplane electrode rings, the mode of plasma operation, and the method of measuring the plasma number density. No significant departures from the scaling laws appear to occur at the highest ion kinetic temperatures or number densities obtained to date.

Roth, J. R.↗
DOE OSTI2024

Discoveries in Blast-Driven Turbulence of Astrophysical Relevance

The fluid mixing caused by variable-density instabilities is important in a wide variety of scenarios from ocean mixing and astrophysical phenomena to nuclear fusion techniques and atomic weapons. This thesis explores the mixing resulting from a specific instability known as the Blast Driven Instability (BDI). This work investigates the variable density mixing in an explosively driven environment due to the fluid instabilities at the material interfaces. Specifically, diverging Richtmyer-Meshkov (impulsive-acceleration environment) and Rayleigh-Taylor (variable-acceleration environment) instabilities (present in supernova and inertial confinement fusion) are studied using advanced high-speed diagnostics in carefully designed laboratory experiments. The BDI morphology is presented through a time development of Mie scattering images, and steps through the parameter space (varying density ratio and driver speed), highlighting the development of the structures that form during mixing. A scaling criterion is used to relate the two systems of vastly different spatiotemporal scales. Velocity fields in the BDI have been captured for the first time using the high temporal resolution PIV technique. Subsequent analysis of the dynamics of the instability from the velocity fields illustrates the distribution of kinetic energy, the transition to turbulence, and the characteristic growth of the instability are discussed. This study furthers understanding of how blast-driven instability pertains to supernova and inertial confinement fusion science. The morphology of the BDI has been characterized for the first time. This work steps through the parameter space covered in Mie scattering experiments, and how the different parameters contribute to development of structures and mixing. It also examines a scaling of the Atwood number for expanding predictive capabilities to other experimental conditions and simulations. The first collection of velocity fields acquired for the BDI are recorded, and subsequent analysis evaluating the distribution of kinetic energy throughout space and time for two density ratios from the overall parameter space, as well as the transition to turbulence, estimated from a Reynolds number calculated based on momentum mixing are all presented. This information is useful in advancing the development of models to predict physics of high energy density applications where experiments are not always readily available. This research has successfully demonstrated understanding for the time criteria defining regimes where the shock driven (Richtmyer-Meshkov instability) and the buoyancy driven (Rayleigh-Taylor instability) dominates through a parametric study of density variation (Atwood number) and driver speed (Mach number). All this furthers understanding of how the BDI pertains to SN and ICF.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Cosmological stability bound in massive gravity and bigravity

We give a simple derivation of a cosmological bound on the graviton mass for spatially flat FRW solutions in massive gravity with an FRW reference metric and for bigravity theories. This bound comes from the requirement that the kinetic term of the helicity zero mode of the graviton is positive definite. The bound is dependent only on the parameters in the massive gravity potential and the Hubble expansion rate for the two metrics. We derive the decoupling limit of bigravity and FRW massive gravity, and use this to give an independent derivation of the cosmological bound. We recover our previous results that the tension between satisfying the Friedmann equation and the cosmological bound is sufficient to rule out all observationally relevant FRW solutions for massive gravity with an FRW reference metric. In contrast, in bigravity this tension is resolved due to different nature of the Vainshtein mechanism. We find that in bigravity theories there exists an FRW solution with late-time self-acceleration for which the kinetic terms for the helicity-2, helicity-1 and helicity-0 are generically nonzero and positive making this a compelling candidate for a model of cosmic acceleration. We confirm that the generalized bound is saturated for the candidate partially massless (bi)gravity theories but the existence of helicity-1/helicity-0 interactions implies the absence of the conjectured partially massless symmetry for both massive gravity and bigravity.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2015

Effects of Mesoscale Eddies in the Active Mixed Layer: Test of the Parametrisation in Eddy Resolving Simulations

In eddy resolving simulations, we test a mixed layer mesoscale parametrisation, developed recently by Canuto and Dubovikov [Ocean Model., 2011, 39, 200-207]. With no adjustable parameters, the parametrisation yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy (EKE). We compare terms of the parametrisation diagnosed from coarse-grained fields with the eddy mesoscale fluxes diagnosed directly from the high resolution model. An expression for the EKE in terms of mean fields has also been found to get a closed parametrisation in terms of the mean fields only. In 40 numerical experiments we simulated two types of flows: idealised flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1-2 degrees and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are positively correlated with the parametrisation with higher (0.5-0.74) correlations at the experiments with larger baroclinic radius Rossby. After being averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations are consistent with the parametrisation for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parametrisation unless vertical turbulent mixing in the upper layer becomes strong enough in comparison with mesoscale advection. In the latter case, numerical simulations demonstrate that the deviation of the fluxes from the parametrisation is controlled by dimensionless parameter estimating the ratio of vertical turbulent mixing term to mesoscale advection. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed.

simulation↗