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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Two-dimensional internal compressible viscous flows using semi-elliptic analysis

Subsonic viscous flows through planar cascades are examined by means of a semielliptic form of the Navier-Stokes equations, which is obtained by neglecting the streamwise diffusion of momentum and energy in their respective equations and providing upstream interaction through the pressure field. The influence of downstream conditions is propagated upstream in the subsonic flow, via a streamwise implicit determination of the pressure field, in order to permit departure-free solutions for the overall flow problem. The continuity equation is thereby satisfied directly. Governing equations are written in strong conservation law form, in terms of general, nonorthogonal transformed coordinates and Cartesian velocity components.

Ghia, K. N.↗
DOE OSTI2024

Anisotropic, multiband, and strong-coupling superconductivity of the Pb 0.64 ⁢Bi 0.36 alloy

This paper presents theoretical and experimental studies on the superconductivity of Pb ⁢0.64 ⁢Bi 0.36 alloy, which is a prototype of strongly coupled superconductors and exhibits one of the strongest coupling under ambient pressure among the materials studied so far. The critical temperature, the specific heat in the superconducting state, and the magnetic critical fields are experimentally determined. Deviations from the single-gap s-wave BCS-like behavior are observed. The electronic structure, phonons, and electron-phonon interactions are analyzed in relation to the metallic Pb, explaining why the Pb-Bi alloy exhibits such a large value of the electron-phonon coupling parameter λ ≃ 2. Superconductivity is studied using the isotropic Eliashberg formalism as well as the anisotropic density functional theory for superconductors. Here, we find that while Pb is a two-gap superconductor with well-defined separate superconducting gaps, in the Pb-Bi alloy an overlapped three-gap-like structure is formed with a strong anisotropy. Furthermore, the chemical disorder, inherent to this alloy, leads to strong electron scattering, which is found to reduce the critical temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Chain rigidity controlled aggregation ability and solid-state microstructures for efficient stretchable conjugated polymer films

Stretchable conjugated polymer films with good electrical performance under mechanical deformation are highly desirable for soft electronics. However, the mechanical and electrical properties of these films, particularly in conjugated polymer:elastomer blends, are not fully understood at molecular level. Here, this study explores the relationships among molecular structure, aggregation ability, film microstructure, and the electrical/mechanical properties of three diketopyrrolopyrrole-based conjugated polymers (P1, P2, P3) with decreasing backbone rigidity and their corresponding polymer:elastomer blends. The most flexible polymer P3 shows strong aggregation, which forms highly crystalline fibers to produce fragile neat film and produces large isolated crystallites restricting charge transport in blend film. As chain rigidity increases, the P1 and P2 polymers show weaker aggregation, and produce smaller crystallites in neat films with enhanced ductility. P1 and P2 based blend films display nanocrystallites polymer networks with dispersed elastomer domains. As a result, we achieved near-constant charge mobility before and after stretching under 50 % strain for P2-based blend films with well-controlled pathways for both charge transport and energy dissipation. This study demonstrates the critical role of backbone rigidity in regulating the properties of stretchable conjugated polymer films, paving the way for more reliable and deformable materials in soft electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Structural Insight into a Sixteen Cyanine Dye Construct via Exciton–Exciton Annihilation

Molecular (dye) aggregates play a prominent role in light harvesting and are of interest in quantum information science; however, there are limited reports hat programmably assemble many (>4) dye aggregates featuring strong coupling and exciton delocalization. Using oligonucleotides with four Cy5s covalently linked in series along the phosphate backbone, we bring four, eight, and sixteen Cy5s in close proximity by assembling four-armed junctions. We elucidate their structure via gel electrophoresis and steady-state and transient optical spectroscopy. We find that Cy5 has a strong propensity to form tetramer clusters, where the exciton is delocalized over all four Cy5s, that the exciton is not delocalized beyond tetramer clusters in the eight and sixteen Cy5 constructs, and that the sixteen Cy5 construct may consist of pairs of tetramer clusters that are isolated from one another. Many-dye aggregates such as these may serve useful as antennae for their intense light absorption and spatially directed energy transfer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Mechanochemical Solid Form Screening of Zeolitic Imidazolate Frameworks Using Structure-Directing Liquid Additives

We demonstrate a systematic application of the mechanochemical liquid-assisted grinding (LAG) methodology to screen for forms of zinc imidazolate (ZnIm 2 ), of fundamental importance as the simplest member of the zeolitic imidazolate framework materials family. The exploration of 45 different liquid additives, selected based on their molecular structure and physicochemical properties has resulted in eight different ZnIm 2 topological forms, appearing in 13 crystallographically distinct solid forms (including two previously unknown forms of the crb (BCT) topology), amorphous phases, and the interrupted moc-Zn 4 Im 8 HIm. All prepared topological forms were also explored computationally, using dispersion-corrected periodic density functional theory (DFT) calculations, enabling the rationalization of screening outcomes, and setting the stage for future prediction of additive-directed metal–organic framework (MOF) synthesis. This first systematic exploration of LAG in screening for three-dimensional MOFs demonstrates the potential of the liquid additive to not only accelerate materials synthesis, but also to direct it toward topologically different MOFs. The discovery of novel forms of a material that already exhibits at least 21 crystallographically and functionally different forms provides a strong testimony on the power of mechanochemistry in metal–organic materials discovery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Extracting the femtometer structure of strange baryons using the vacuum polarization effect

Abstract One of the fundamental goals of particle physics is to gain a microscopic understanding of the strong interaction. Electromagnetic form factors quantify the structure of hadrons in terms of charge and magnetization distributions. While the nucleon structure has been investigated extensively, data on hyperons are still scarce. It has recently been demonstrated that electron-positron annihilations into hyperon-antihyperon pairs provide a powerful tool to investigate their inner structure. We present a method useful for hyperon-antihyperon pairs of different types which exploits the cross section enhancement due to the effect of vacuum polarization at theJ/ψresonance. Using the 10 billionJ/ψevents collected with the BESIII detector, this allows a precise determination of the hyperon structure function. The result is essentially a precise snapshot of the$$\bar{\Lambda }{\Sigma }^{0}\,(\Lambda {\bar{\Sigma }}^{0})$$ Λ ¯ Σ 0 ( Λ Σ ¯ 0 ) transition process, encoded in the transition form factor ratio and phase. Their values are measured to beR = 0.860 ± 0.029(stat.) ± 0.015(syst.),$$\Delta {\Phi }_{\bar{\Lambda }{\Sigma }^{0}}=(1.011\pm 0.094({{\rm{stat.}}})\pm 0.010({{\rm{syst.}}}))\,{{\rm{r}}}ad$$ Δ Φ Λ ¯ Σ 0 = ( 1.011 ± 0.094 ( stat. ) ± 0.010 ( syst. ) ) r a d and$$\Delta {\Phi }_{\Lambda {\bar{\Sigma }}^{0}}=(2.128\pm 0.094({{\rm{stat.}}})\pm 0.010({{\rm{syst.}}}))\,{{\rm{r}}}ad$$ Δ Φ Λ Σ ¯ 0 = ( 2.128 ± 0.094 ( stat. ) ± 0.010 ( syst. ) ) r a d . Furthermore, charge-parity (CP) breaking is investigated in this reaction and found to be consistent with CP symmetry.

Science & Technology - Other Topics↗
DOE OSTI2024

Tethered balloon measurements reveal enhanced aerosol occurrence aloft interacting with Arctic low-level clouds

Low-level clouds in the Arctic affect the surface energy budget and vertical transport of heat and moisture. The limited availability of cloud-droplet-forming aerosol particles strongly impacts cloud properties and lifetime. Vertical particle distributions are required to study aerosol–cloud interaction over sea ice comprehensively. This article presents vertically resolved measurements of aerosol particle number concentrations and sizes using tethered balloons. The data were collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition in the summer of 2020. Thirty-four profiles of aerosol particle number concentration were observed in 2 particle size ranges: 12–150 nm (N 12−150 ) and above 150 nm (N >150 ). Concurrent balloon-borne meteorological measurements provided context for the continuous profiles through the cloudy atmospheric boundary layer. Radiosoundings, cloud remote sensing data, and 5-day back trajectories supplemented the analysis. The majority of aerosol profiles showed more particles above the lowest temperature inversion, on average, double the number concentration compared to below. Increased N 12−150 up to 3,000 cm −3 were observed in the free troposphere above low-level clouds related to secondary particle formation. Long-range transport of pollution increased N >150 to 310 cm −3 in a warm, moist air mass. Droplet activation inside clouds caused reductions of N >150 by up to 100%, while the decrease in N 12−150 was less than 50%. When low-level clouds were thermodynamically coupled with the surface, profiles showed 5 times higher values of N 12−150 in the free troposphere than below the cloud-capping temperature inversion. Enhanced N 12−150 and N >150 interacting with clouds were advected above the lowest inversion from beyond the sea ice edge when clouds were decoupled from the surface. Vertically discontinuous aerosol profiles below decoupled clouds suggest that particles emitted at the surface are not transported to clouds in these conditions. It is concluded that the cloud-surface coupling state and free tropospheric particle abundance are crucial when assessing the aerosol budget for Arctic low-level clouds over sea ice.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1973

Pulsatile Newtonian frictional losses in a rigid tube.

Analytic expressions for the instantaneous average velocity and friction factor have been obtained for pulsatile Newtonian laminar flow with mean flow. Experimental pulsatile pressure gradients were found to be complex wave forms whose characteristics strongly influenced the experimental pulsatile average velocity and friction factor. Experimental and theoretical reduced instantaneous friction factor histories varied in a non-sinusoidal manner throughout the pulse cycle and exhibited extremum points. At high pulsation pressure ratios, substantial deviation occurred in the portion of the pulse cycle where the instantaneous average velocity approached zero. At low pulsation pressure ratios, the experimental and theoretical time average friction factor equaled unity and was independent of pulsation modulus. One potential application of this result is in the study of blood flow through small blood vessels.

Phillips, E. M.↗
NASA NTRS1973

On detonation waves supported by diffusion flames.

An eigenvalue condition to determine propagation velocity of detonation waves in a tube is derived for the case where the oxidizer and fuel are in the gaseous and condensed phase, respectively, so that the combustion occurs only within the peripheral boundary layer. It is shown that the self-sustained shock propagation is possible if core streamtube constriction, due to combustion in the boundary layer, is strong enough to form a converging nozzle, and for a sonic throat to exist.

Fujitsuna, Y.↗
NASA NTRS1979

Analysis of combustion instability in liquid fuel rocket motors

The development of an analytical technique used in the solution of nonlinear velocity-sensitive combustion instability problems is presented. The Galerkin method was used and proved successful. The pressure wave forms exhibit a strong second harmonic distortion and a variety of behaviors are possible depending on the nature of the combustion process and the parametric values involved. A one dimensional model provides insight into the problem by allowing a comparison of Galerkin solutions with more exact finite difference computations.

Wong, K. W.↗
NASA NTRS1979

Analysis of Combustion Instability in Liquid Fuel Rocket Motors

The development of a technique to be used in the solution of nonlinear velocity-sensitive combustion instability problems is described. The orthogonal collocation method was investigated. It found that the results are heavily dependent on the location of the collocation points and characteristics of the equations, so the method was rejected as unreliabile. The Galerkin method, which has proved to be very successful in analysis of the pressure sensitive combustion instability was found to work very well. It was found that the pressure wave forms exhibit a strong second harmonic distortion and a variety of behaviors are possible depending on the nature of the combustion process and the parametric values involved. A one-dimensional model provides further insight into the problem by allowing a comparison of Galerkin solutions with more exact finite-difference computations.

Wong, K. W.↗
NASA NTRS1980

An explanation for the alternating north-south asymmetry of Io's sodium cloud

The hot Jovian plasma torus discovered by Voyager 1 is responsible for the periodic intensity variations of Io's sodium cloud, which are correlated with Io's magnetic latitude. The plasma torus must be a long-lived phenomenon in spite of its apparent absence at the time of the Pioneer flybys. The hot electrons (100,000 K) must be concentrated about one Jupiter radius from the magnetic equator in order to produce the observed variations. Electron impact ionization in the hot plasma torus is strong enough to form and to maintain Io's ionosphere; the hot plasma torus may be the dominant agent forming the ionosphere. Io's bound atmosphere is dense enough that the plasma torus electrons cannot cause a noticeable variation in its Na emission intensity.

Trafton, L.↗
NASA NTRS1982

IUE observations of reflection nebulae

Low-resolution IUE spectra in the SWP and LWR ranges were obtained of several reflection nebulae in the vicinity of their respective illuminating stars. Data for NGC 7023 (HD200775), NGC 1435 (Merope, 23 Tau), NGC 1432 (Maia, 20 Tau) and the Electra (17 Tau) nebula were found to display significant differences in the shape of their normalized nebular spectra. If the dust in these nebulae is similar from one object to the next, these differences can be most readily explained by differences in the line-of-sight dust distribution, coupled with a wavelength-dependent phase function, changing from a strongly forward throwing form (g = 0.6-0.7) in the visible to a more nearly isotropic shape (g approximately 0.25) at 1400A.

Witt, A. N.↗
NASA NTRS1983

A new stream function formulation for the Euler equations

A new stream function formulation is developed for the solution of Euler's equations in the transonic flow region. The stream function and the density are the dependent variables in this method, while the governing equations for adiabatic flow are the momentum equations which are solved in the strong conservation law form. The application of this method does not require a knowledge of the vorticity. The algorithm is combined with the automatic grid solver (GRAPE) of Steger and Sorenson (1979) in order to study arbitrary geometries. Results of the application of this method are presented for the NACA 0012 airfoil at various Mach numbers and angles of attack, and cylinders. In addition, detailed comparisons are made with other solutions of the Euler equations.

Atkins, H. L.↗
NASA NTRS1984

Transonic flow calculations using a flux vector splitting method for the Euler equations

A study of the flux vector splitting method of Steger and Warming for the solution of the time dependent Euler equations in strong conservation law form for arbitrary two-dimensional geometries is presented. The procedure employed here differs from that of Buning and Steger in that it uses a different algorithm and employs implicit boundary conditions. Moreover, the method, as implemented here, does not contain any explicit smoothing or any adjustable parameters. Calculations were carried out for an NACA 0012 airfoil at various Mach numbers and angles of attack, and cylinders. Steady symmetric solutions were obtained for the full cylinder at a freestream Mach number of .5 without imposing a symmetry condition. In general, good agreement with other methods was obtained.

Seaford, C. M.↗
NASA NTRS1985

The model-independence of cosmic ray source determinations

The direct inversion method of Margolis is used to explore the dependence of Z less than or equal to 28 source abundance determinations on the choice of the pathlength distribution. The source abundances do not depend strongly on the form of the truncation used, although some truncation at the lower energies (compared to a leaky box) is necessary. The decrease of mean grammage with increasing energy is required by the observations. The effects of errors and he use of other secondary to primary ratios is discussed.

Margolis, S. H.↗
NASA NTRS1985

The Heart Mountain fault: Implications for the dynamics of decollement

The Hart Mountain docollement in Northwestern Wyoming originally comprised a plate of rock up to 750m thick and 1300 sq kilometers in area. This plate moved rapidly down a slope no steeper than 2 deg. during Early Eocene time, transporting some blocks at least 50m from their original positions. Sliding occurred just before a volcanic erruption and was probably accompanied by seismic events. The initial movement was along a bedding plane fault in the Bighorn Dolomite, 2 to 3 meters above its contact with the Grove Creek member of the Snowy Range formation. The major pecularity of this fault is that it lies in the strong, cliff-forming Bighorn Dolomite, rather than in the weaker underlying shales. The dynamics of decollement are discussed.

Melosh, H. J.↗