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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 1,585 records · Page 88
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

C–H Bond Activation Facilitated by Bis(phosphinoamide) Heterobimetallic Zr/Co Complexes

The activation of C–H bonds using first-row transition metals poses a formidable challenge in the development of sustainable catalytic methods. Early/late heterobimetallic complexes provide a Lewis acidic binding site for directing groups, facilitating the activation of C–H bonds at an appended first-row transition metal center. In this work, the reactivity of the ZrIV/Co–I heterobimetallic complexes (THF)(I)Zr(XylNP i Pr 2 ) 2 Co(PR 3 ) (1-PR 3 ; Xyl = 3,5-dimethylphenyl; PR 3 = PMe 3 , PPh 2 Me) toward directed C–H bond activation is explored with pyridine and terminal alkyne derivatives. 1-PMe 3 reacts reversibly with 4-methylpyridine to afford the C–H activated complex (4-Me-C 5 H 4 N)(I)Zr(XylNP i Pr 2 ) 2 (μ-4-Me-C 5 H 3 N)Co(PMe 3 )(H) (3-PMe 3 ). By using the more Lewis basic substrate 4-tert-butylpyridine, (I)Zr(XylNP i Pr 2 )2(μ-4- t Bu-C 5 H 3 N)Co(PMe 3 )(H) (4-PMe 3 ) is formed irreversibly. In addition to pyridine derivatives, 1-PPh 2 Me can activate the C–H bond of terminal alkynes to form (THF)(I)Zr(XylNPiPr 2 ) 2 (μ-R'C≡C)Co(PPh 2 Me)(H) (R' = Ph (5-PPh 2 Me); R' = SiMe 3 (6-PPh 2 Me)).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1997

Crystal Growth and Characterization of Bil3

Bismuth tri-iodide (BiI3) have been grown by physical vapor transport (PVT), and by the Bridgman (melt) method. These crystals along with pure and stoichiometric BiI3 powder have been investigated by differential scanning calorimetry (DSC). The DSC results show that pure BiI3 powder has no phase transition and melts around 408 C. While we found no evidence for the high temperature dissociation of BiI3, the DSC measurements show that crystals grown from melt method contain a significantly large amount of Bi-rich phases than crystals grown from PVT method, as indicated by phase transition detected at 270, 285, 298 and 336 C.

Hayes, Julia↗
DOE OSTI2017

Parallel replica dynamics method for bistable stochastic reaction networks: Simulation and sensitivity analysis

Stochastic reaction networks that exhibit bistable behavior are common in systems biology, materials science, and catalysis. Sampling of stationary distributions is crucial for understanding and characterizing the long-time dynamics of bistable stochastic dynamical systems. However, simulations are often hindered by the insufficient sampling of rare transitions between the two metastable regions. In this paper, we apply the parallel replica method for a continuous time Markov chain in order to improve sampling of the stationary distribution in bistable stochastic reaction networks. The proposed method uses parallel computing to accelerate the sampling of rare transitions. Furthermore, it can be combined with the path-space information bounds for parametric sensitivity analysis. With the proposed methodology, we study three bistable biological networks: the Schlögl model, the genetic switch network, and the enzymatic futile cycle network. We demonstrate the algorithmic speedup achieved in these numerical benchmarks. More significant acceleration is expected when multi-core or graphics processing unit computer architectures and programming tools such as CUDA are employed

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1998

Cross Sections for Electron Impact Excitation of Ions Relevant to Planetary Atmospheres Observation

The goal of this research grant was to calculate accurate oscillator strengths and electron collisional excitation strengths for inelastic transitions in atomic species of relevance to Planetary Atmospheres. Large scale configuration-interaction atomic structure calculations have been performed to obtain oscillator strengths and transition probabilities for transitions among the fine-structure levels and R-matrix method has been used in the calculations of electron-ion collision cross sections of C II, S I, S II, S III, and Ar II. A number of strong features due to ions of sulfur have been detected in the spectra of Jupiter satellite Io. The electron excitation cross sections for the C II and S II transitions are studied in collaboration with the experimental atomic physics group at the Jet Propulsion Laboratory. There is excellent agreement between experiment and theory which provide an accurate and broad-base test of the ability of theoretical methods used in the calculation of atomic processes. Specifically, research problems have been investigated for: electron impact excitation cross sections of C II: electron impact excitation cross sections of S III; energy levels and oscillator strengths for transitions in S III; collision strengths for electron collisional excitation of S II; electron impact excitation of inelastic transitions in Ar II; oscillator strengths of fine-structure transitions in neutral sulfur; cross sections for inelastic scattering of electrons from atomic nitrogen; and excitation of atomic ions by electron impact.

Tayal, Swaraj S.↗
NASA NTRS1987

Stability characteristics of a supersonic boundary layer and their relation to the position of the laminar-turbulent transition point

By comparing the calculated results with experimental data, it is demonstrated that the position of the laminar-boundary transition point of a boundary layer can be estimated by using the e-exp-n method. The effect of the Mach number, pressure gradient, and heat transfer on the laminar-turbulent transition is discussed. It is found that under conditions of strong cooling, the effect of the pressure gradient on the position of the transition point is less pronounced than in the absence of heat transfer.

Lysenko, V. I.↗
NASA NTRS1987

Prediction and control of transition in hypersonic boundary layers

In this paper, the role of compressible linear stability theory in prediction of boundary layer transition at supersonic and hypersonic speeds is investigated. Computations for sharp cones, using the e exp N method with N = 10, show that the first oblique Tollmien-Schlichting mode is responsible for transition at adiabatic wall conditions for freestream Mach numbers up to 7. For cold walls, the two-dimensional second mode dominates the transition process at lower hypersonic Mach numbers due to the well-known destabilizing effect of cooling on the second mode. It is shown that pressure gradient and suction may be used to stabilize this mode. Some results on the real gas effects on hypersonic boundary-layer stability are presented.

Malik, Mujeeb R.↗
DOE OSTI2015

Disorder - driven phase transition in La{sub 0.37}Bi{sub 0.15}Sm{sub 0.15}Ca{sub 0.33}MnO{sub 3}

We report the effect of disorder on the properties of La{sub 0.37}Bi{sub 0.15}Sm{sub 0.15}Ca{sub 0.33}MnO{sub 3} manganite synthesized by sol – gel method. The critical properties were investigated through various techniques such as modified - Arrott plot, Kouvel - Fisher method and critical isotherm analysis. The sample show second- order phase transition near critical point. The decrease in magnetization (M), Curie temperature (T{sub C}), evolution of spin or cluster glass behavior and the nature of phase transition compared to first - order transition in La{sub 0.67}Ca{sub 0.33}MnO{sub 3} are ascribed to the disorder caused by the size mismatch of the A-site cations with Bi and Sm doping at La- site.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2003

A Comparison of Active and Passive Methods for Control of Hypersonic Boundary Layers on Airbreathing Configurations

Active and passive methods for control of hypersonic boundary layers have been experimentally examined in NASA Langley Research Center wind tunnels on a Hyper-X model. Several configurations for forcing transition using passive discrete roughness elements and active mass addition, or blowing, methods were compared in two hypersonic facilities, the 20-Inch Mach 6 Air and the 31-Inch Mach 10 Air tunnels. Heat transfer distributions, obtained via phosphor thermography, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. The comparisons between the active and passive methods for boundary layer control were conducted at test conditions that nearly match the nominal Mach 7 flight trajectory of an angle-of-attack of 2-deg and length Reynolds number of 5.6 million. For the passive roughness examination, the primary parametric variation was a range of trip heights within the calculated boundary layer thickness for several trip concepts. The prior passive roughness study resulted in a swept ramp configuration being selected for the Mach 7 flight vehicle that was scaled to be roughly 0.6 of the calculated boundary layer thickness. For the active jet blowing study, the blowing manifold pressure was systematically varied for each configuration, while monitoring the mass flow, to determine the jet penetration height with schlieren and transition movement with the phosphor system for comparison to the passive results. All the blowing concepts tested were adequate for providing transition onset near the trip location with manifold stagnation pressures on the order of 40 times the model static pressure or higher.

Berry, Scott A.↗
DOE OSTI2015

Surface oxidation energetics and kinetics on MoS{sub 2} monolayer

In this work, surface oxidation of monolayer MoS{sub 2} (one of the representative semiconductors in transition-metal dichalcogenides) has been investigated using density functional theory method. Oxygen interaction with MoS{sub 2} shows that, thermodynamically, the surface tends to be oxidized. However, the dissociative absorption of molecular oxygen on the MoS{sub 2} surface is kinetically limited due to the large energy barrier at low temperature. This finding elucidates the air stability of MoS{sub 2} surface in the atmosphere. Furthermore, the presence of defects significantly alters the surface stability and adsorption mechanisms. The electronic properties of the oxidized surface have been examined as a function of oxygen adsorption and coverage as well as substitutional impurities. Our results on energetics and kinetics of oxygen interaction with the MoS{sub 2} monolayer are useful for the understanding of surface oxidation, air stability, and electronic properties of transition-metal dichalcogenides at the atomic scale.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1993

Viscous hypersonic shock-shock interaction on a blunt body at high altitude

The shock interaction produced when an incident oblique shock impinges on a blunt body, such as an engine inlet cowl lip of a hypersonic vehicle, is investigated for high altitude flight conditions. A perfect gas, Navier-Stokes numerical simulation of this problem at various altitudes representing continuum through transitional conditions is performed using the modified flux vector splitting method of Steger and Warming (1979). Two series of solutions are produced. First, a number-of-shock-positions are studied at a particular altitude and Mach number. Second, given a fixed shock position and Mach number, the interaction is investigated at several altitudes ranging from continuum to transitional flow conditions. It is shown that the interaction becomes fundamentally different as the density is lowered, and its effect on the overheating problem is progressively diminished. The maximum stagnation point heating at the highest altitude is reached only when the incident shock misses the cowl lip completely, and any interaction with the cowl bow shock that does occur takes place downstream and thus has little effect on the conditions at the stagnation point.

Comeaux, Keith A.↗
DOE OSTI2018

TL/OSL properties of beta irradiated Al2O3:Tm3+ phosphor synthesized by microwave combustion method

Highlights: • TL emission spectra of γ – rayed Al{sub 2}O{sub 3}:Tm{sup 3+} shows Tm{sup 3+} characteristic transitions. • Doping of Tm{sup 3+} ions causes enhancement of TL/OSL. • TL/OSL kinetic parameters are analyzed by CGCD method. • TL mechanism of γ/β – rayed Al{sub 2}O{sub 3}:Tm{sup 3+} was proposed. • TL/OSL dosimetric properties of Al{sub 2}O{sub 3}:Tm{sup 3+} suggests that the material is appropriate for medical dosimetry. - Abstract: This work discusses synthesis of stable α-phase of Al{sub 2}O{sub 3}:Tm{sup 3+} by combustion method using temperature controlled microwave oven. The crystalline phase was analyzed by X-ray diffraction (XRD) technique and average crystallite size was found to be 147 nm. Observations using scanning electron microscope (SEM) image suggest formation of agglomerated particles and energy dispersive x-ray spectroscopy (EDS) confirmed the incorporation of Tm{sup 3+} in Al{sub 2}O{sub 3}. Thermoluminescence emission (TLE) spectrum of γ – irradiated Al{sub 2}O{sub 3}:Tm{sup 3+} shows characteristic emissions of Tm{sup 3+}, Cr{sup 3+} and Mn{sup 4+}. TL glow curves of γ – irradiated Al{sub 2}O{sub 3}:Tm{sup 3+} exhibit a prominent peak at 453 K along with a shoulder at 496 K. The glow curves of β – irradiated Al{sub 2}O{sub 3}:Tm{sup 3+} were studied in different emission regions using U340 + BG39 (UV band pass), CS759 + BG39 (Blue band pass) and BG39 (Visible band pass) optical glass filters. A prominent peak was observed at 471 K in for all mentioned emission regions and an additional shoulder was observed at 511 K with CS759 + BG39 and BG39 filters. TL glow curve of β – irradiated Al{sub 2}O{sub 3}:Tm{sup 3+} using only BG39 filter had more counts than CS759 + BG39 and U340 + BG39 filters. Further, the effect of Tm{sup 3+} impurity on TL response was studied. TL kinetic parameters were estimated by using computerized glow curve deconvolution (CGCD) technique. The activation energy and frequency factor of prominent peak (471 K) were found to be 1.31 eV and 3.50 × 10{sup 13} s{sup −1} respectively. Optically stimulated luminescence (OSL) characteristics of β – irradiated Al{sub 2}O{sub 3}:Tm{sup 3+} were studied using U340 + BG39 and CS759 + BG39 filters. Highest OSL intensity was observed in UV. OSL curves were deconvoluted by general order decay equation. Life time and photoionization cross section of the traps responsible for OSL were found to be 5.30 s and 3.98 × 10{sup −18} cm{sup 2} respectively. The process of ionization of electron from Tm{sup 3+}, electron trap in host lattice and its recombination mechanism is proposed. Phosphorescence decay of beta irradiated sample was also studied. The lifetime of phosphorescence decay was found to be 140 s for the prominent peak and TL intensity decays 25% after the phosphorescence. TL/OSL dosimetric properties viz. linearity with dose, reusability and minimum detectable dose of the phosphor were characterized for medical dosimetry application.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Thermally averaged collision strengths for extreme-ultraviolet line of Fe ix

Collision strengths and thermally averaged collision strengths for a large number of extreme-ultraviolet lines of Fe ix arising by electron impact have been reported. The thermally averaged collision strengths are calculated at electron temperatures in the range 10{sup 4}–10{sup 7} K for the 122,043 forbidden and allowed transitions between the 370 fine-structure levels. The atomic parameters for Fe ix play an important role in modeling of various astrophysical plasmas, including especially the solar corona. The B-spline Breit–Pauli R-matrix method has been used in the calculation of collision strengths. The target wave functions and transition probabilities have been determined by combining the multiconfiguration Hartree–Fock method with the B-spline box-based multichannel expansions. We have included 370 fine-structure levels of Fe ix in the energy region up to 3s{sup 2}3p{sup 5}5s states. The close-coupling expansion includes levels of the 3s{sup 2}3p{sup 6}, 3s{sup 2}3p{sup 5}3d,4l,5s, 3s3p{sup 6}3d,4s,4p, 3s{sup 2}3p{sup 4}3d{sup 2}, 3s3p{sup 5}3d{sup 2} configurations and some low-lying levels of the 3s{sup 2}3p{sup 3}3d{sup 3} configuration in our collision strengths and transition probabilities calculations. There is a good agreement with the previous R-matrix collision strength calculations by Storey et al. and Del Zanna et al. for transitions between the lowest 17 levels of the 3s{sup 2}3p{sup 6}, 3s{sup 2}3p{sup 5}3d, and 3s3p{sup 6}3d configurations, especially for electron temperatures log T(K) ≥ 5.0. The transitions between the first 17 levels are dominated by Rydberg series of resonances converging to the levels of the 3s{sup 2}3p{sup 4}3d{sup 2} configuration. The present results and the calculation of Del Zanna et al. show significant differences for many weaker forbidden and intercombination transitions with thermally averaged collision strengths smaller than 0.01.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Time-Dependent Electric Bus and Charging Station Deployment Problem

Battery electric buses (BEBs) have gained popularity due to their emission-free and energy-efficient features. Many transit authorities worldwide have set goals to gradually replace their bus fleets with BEBs. Considering the potential decline in BEB battery and charger prices, this study proposes a time-dependent bus fleet transition model to determine the optimal bus fleet transition plan, which includes selecting the bus lines to be electrified, determining the timing and type of BEBs to be purchased, and deploying on-route fast chargers and depot chargers. The model is a bi-objective integer linear program that considers the trade-off between electrified transit mileages and bus electrification costs. A normalized normal constraint method is applied to solve the bi-objective optimization model. The effectiveness of the proposed model is tested using a real-world bus network. Additionally, sensitivity analyses are conducted to better understand the impact of different parameter values on the optimal solutions. Our proposed model can provide transit authorities with a powerful tool to make informed decisions about their BEB fleet replacement plans.

ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2024

Pore‐Scale Modeling of Carbon Dioxide and Hydrogen Transport During Geologic Gas Storage

Abstract Geologic storage of CO 2 and H 2 are climate‐positive techniques for meeting the energy transition. While similar formations could be considered for both gases, the flow dynamics could differ due to differences in their thermophysical properties. We conduct a rigorous pore‐scale study of water/CO 2 and water/H 2 systems at relevant reservoir conditions in a Bentheimer rock sample using the lattice Boltzmann method to quantify the effects of capillary, viscous, inertial, and wetting forces during gas invasion. At similar conditions, H 2 invasion is weaker compared to CO 2 due to unfavorable viscosity ratios. Increasing flow rate, however, increases the breakthrough saturation for both gas systems in the range of capillary numbers studied. At isolated conditions of flow rate, viscosity ratio, and wettability, local inertial effects are found to be critical and show consistent increase in the invaded gas saturation. The effect of inertial forces persits for both gases across all field conditions tested.

58 GEOSCIENCES↗
DOE OSTI2022

Simulations of x-ray absorption spectra for CO desorbing from Ru(0001) with transition-potential and time-dependent density functional theory approaches

The desorption of a carbon monoxide molecule from a Ru(0001) surface was studied by means of X-ray Absorption Spectra (XAS) computed with Transition Potential (TP-DFT) and Time Dependent (TD-DFT) DFT methods. By unraveling the evolution of the CO electronic structure upon desorption, we observed that at 2.3 Å from the surface, the CO molecule has already predominantly gas-phase character. While C 1s XAS is quite insensitive to changes in the C–O bond length, the O 1s excitation is very sensitive with the π* coming down in energy upon CO bond stretching, which competes with the increase in orbital energy due to the repulsive interaction with the metallic surface. We show in a systematic way that the TP-DFT method can describe the XAS rather well at the endpoints (chemisorbed and gas phase) but is affected by artificial charge transfer and/or incorrect spin treatment in the transition region in cases like CO, where there are low-lying π* orbitals and large exchange interactions between the core 1s and valence-acceptor π* orbitals. As an alternative, we demonstrate by comparing with experimental data that a linear response approach using TD-DFT employing common exchange-correlation functionals and finite-size clusters can yield a good description of the spectral evolution of the 1s → π* transition with correct spin and gas-to-chemisorbed chemical shifts in good agreement with experiment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

Transition From NASA Space Communication Systems to Commerical Communication Products

Transitioning from twenty-five years of space communication system architecting, engineering and development to creating and marketing of commercial communication system hardware and software products is no simple task for small, high-tech system engineering companies whose major source of revenue has been the U.S. Government. Yet, many small businesses are faced with this onerous and perplexing task. The purpose of this talk/paper is to present one small business (LinCom) approach to taking advantage of the systems engineering expertise and knowledge captured in physical neural networks and simulation software by supporting numerous National Aeronautics and Space Administration (NASA) and the Department of Defense (DoD) projects, e.g., Space Shuttle, TDRSS, Space Station, DCSC, Milstar, etc. The innovative ingredients needed for a systems house to transition to a wireless communication system products house that supports personal communication services and networks (PCS and PCN) development in a global economy will be discussed. Efficient methods for using past government sponsored space system research and development to transition to VLSI communication chip set products will be presented along with notions of how synergy between government and industry can be maintained to benefit both parties.

Ghazvinian, Farzad↗
NASA NTRS2019

Scale-Resolving Simulations of Laminar-to-Turbulent Transition in Swept-Wing Flow

Aerodynamic shape optimization of swept Natural Laminar Flow (NLF) wing design plays an important role for the development of future energy-efficient commercial transport aircraft. Lack of predictive laminar-to-turbulent transition modeling capabilities is still limiting the extent to which design can rely on computational tools, while making costly wind tunnel and flight tests a necessity. Prediction of transition on practical 3D wing geometries using the e (sup N) method coupled with laminar boundary layer and linear stability codes or local statistical correlation CFD (Computational Fluid Dynamics) models such as the gamma - Re (sub theta) Langtry-Menter model have proven challenging, whereas transitional hybrid RANS-LES solvers have shown encouraging but still mitigated results.

Scale-resolving↗
NASA NTRS2021

Precipitable Water Vapor Variation in the Clear-Cloud Transition Zone From the ARM Shortwave Spectrometer

A new technique to retrieve precipitable water vapor (PWV)amount in the clear-cloud transition zone using ground-based zenith spectral radiance is developed. The method uses zenith radiances at the water vapor band at 720 nm and adjacent non-absorbing band at 750 nm.Radiative transfer calculations show that the relative difference in zenith radiance between the two bands depends on PWV and the variations in cloud optical depth introduce a small change in the relative difference which is independent of PWV amount. This allows us to retrieve PWV variations in the cloud-clear transition zone for clouds over dark ocean surface. We applied this method to a Cu cloud case with zenith radiance observations by the Shortwave Array Spectroradiometer-Zenith (SASZe) during the Marine ARM GPCI Investigation of Clouds (MAGIC) field campaign. We found that there is about 10% change in PWV amount from known-cloudy region to known-clear sky in cloud edges.

Atmosphere↗