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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

Cosmological cross-correlations and nearest neighbour distributions

ABSTRACT Cross-correlations between data sets are used in many different contexts in cosmological analyses. Recently, k-nearest neighbour cumulative distribution functions (kNN-CDF) were shown to be sensitive probes of cosmological (auto) clustering. In this paper, we extend the framework of NN measurements to describe joint distributions of, and correlations between, two data sets. We describe the measurement of joint kNN-CDFs, and show that these measurements are sensitive to all possible connected N-point functions that can be defined in terms of the two data sets. We describe how the cross-correlations can be isolated by combining measurements of the joint kNN-CDFs and those measured from individual data sets. We demonstrate the application of these measurements in the context of Gaussian density fields, as well as for fully non-linear cosmological data sets. Using a Fisher analysis, we show that measurements of the halo-matter cross-correlations, as measured through NN measurements are more sensitive to the underlying cosmological parameters, compared to traditional two-point cross-correlation measurements over the same range of scales. Finally, we demonstrate how the NN cross-correlations can robustly detect cross-correlations between sparse samples – the same regime where the two-point cross-correlation measurements are dominated by noise.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

Effect of buoyancy on fuel containment in an open-cycle gas-core nuclear rocket engine.

Analysis aimed at determining the scaling laws for the buoyancy effect on fuel containment in an open-cycle gas-core nuclear rocket engine, so conducted that experimental conditions can be related to engine conditions. The fuel volume fraction in a short coaxial flow cavity is calculated with a programmed numerical solution of the steady Navier-Stokes equations for isothermal, variable density fluid mixing. A dimensionless parameter B, called the Buoyancy number, was found to correlate the fuel volume fraction for large accelerations and various density ratios. This parameter has the value B = 0 for zero acceleration, and B = 350 for typical engine conditions.

Putre, H. A.↗
NASA NTRS1993

Mixing and transient interface condensation of a liquid hydrogen tank

Experiments were conducted to investigate the effect of axial jet-induced mixing on the pressure reduction of a thermally stratified liquid hydrogen tank. The tank was nearly cylindrical, having a volume of about 0.144 cu m with 0.559 m in diameter and 0.711 m long. A mixer/pump unit, which had a jet nozzle outlet of 0.0221 m in diameter was located 0.178 m from the tank bottom and was installed inside the tank to generate the axial jet mixing and tank fluid circulation. The liquid fill and jet flow rate ranged from 42 to 85 percent (by volume) and 0.409 to 2.43 cu m/hr, respectively. Mixing tests began with the tank pressure ranging from 187.5 to 238.5 kPa at which the thermal stratification results in 4.9 to 6.2 K liquid sub cooling. The mixing time and transient vapor condensation rate at the liquid-vapor interface are determined. Two mixing time correlations, based on the thermal equilibrium and pressure equilibrium, are developed. Both mixing time correlations are expressed as functions of system and buoyancy parameters and compared well with other experimental data. The steady state condensation rate correlation of Sonin et al. based on steam-water data is modified and expressed as a function of jet subcooling. The limited liquid hydrogen data of the present study shows that the modified steady state condensation rate correlation may be used to predict the transient condensation rate in a mixing process if the instantaneous values of jet sub cooling and turbulence intensity at the interface are employed.

Lin, C. S.↗
DOE OSTI2018

Evidence of an Improper Displacive Phase Transition in Cd 2 Re 2 O 7 via Time-Resolved Coherent Phonon Spectroscopy

We have used a combination of ultrafast coherent phonon spectroscopy, ultrafast thermometry, and time-dependent Landau theory to study the inversion symmetry breaking phase transition at T c = 200 K in the strongly spin-orbit coupled correlated metal Cd 2 Re 2 O 7 . We establish that the structural distortion at T c is a secondary effect through the absence of any softening of its associated phonon mode, which supports a purely electronically driven mechanism. However, the phonon lifetime exhibits an anomalously strong temperature dependence that decreases linearly to zero near T c . Here, we show that this behavior naturally explains the spurious appearance of phonon softening in previous Raman spectroscopy experiments and should be a prevalent feature of correlated electron systems with linearly coupled order parameters.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Applications of the direct photon absorption technique for measuring bone mineral content in vivo. Determination of body composition in vivo

The bone mineral content, BMC, determined by monoenergetic photon absorption technique, of 29 different locations on the long bones and vertebral columns of 24 skeletons was measured. Compressive tests were made on bone from these locations in which the maximum load and maximum stress were measured. Also the ultimate strain, modulus of elasticity and energy absorbed to failure were determined for compact bone from the femoral diaphysis and cancellous bone from the eighth through eleventh thoracic vertebrae. Correlations and predictive relationships between these parameters were examined to investigate the applicability of using the BMC at sites normally measured in vivo, i.e. radius and ulna in estimating the BMC and/or strength of the spine or femoral neck. It was found that the BMC at sites on the same bone were highly correlated r = 0.95 or better; the BMC at sites on different bones were also highly interrelated, r = 0.85. The BMC at various sites on the long bones could be estimated to between 10 and 15 per cent from the BMC of sites on the radius or ulna.

Cameron, J. R.↗
NASA NTRS2018

Boundary of the Slow Solar Wind

This work argues that there are two fundamental states of the non-transient solar wind, and that these can be distinguished by a number of criteria. Here we define the states, which will be termed slow and fast, or SSW and FSW, for lack of better terms, by the level of velocity fluctuations, v, in them, with the slow wind having systematically lower fluctuations than the fast wind. Almost all winds with speeds less than 450 km s1 are in the slow class, and winds with speeds greater than 600 km s1 are fast, but we argue that in between, consistent with other work, the v classification is more fundamental than speed. We show that the fluctuation categorization coincides well with classes based on Alfvénicy, proton specific entropy, ion thermal speed, and ionic composition. This correlated behavior among these solar wind parameters exists regardless of it being associated with a heliospheric current sheet or a pseudostreamer. This work provides evidence that both the so-called SSW I and SSW II scenarios coexist for the SSW formation. In addition, that the dynamical properties (thermal, magnetic, and turbulence properties) correlate well with properties set at the inner corona (ion ionization states and FIP bias)implies that there exists a boundary layer on the Sun within which the SSW is formed. This boundary layer would set up the coronal conditions for the source and transport of the SSW.

Ko, Yuan-Kuen↗
DOE OSTI2017

Ginzburg–Landau expansion in strongly disordered attractive Anderson–Hubbard model

We have studied disordering effects on the coefficients of Ginzburg–Landau expansion in powers of superconducting order parameter in the attractive Anderson–Hubbard model within the generalized DMFT+Σ approximation. We consider the wide region of attractive potentials U from the weak coupling region, where superconductivity is described by BCS model, to the strong coupling region, where the superconducting transition is related with Bose–Einstein condensation (ВЕС) of compact Cooper pairs formed at temperatures essentially larger than the temperature of superconducting transition, and a wide range of disorder—from weak to strong, where the system is in the vicinity of Anderson transition. In the case of semielliptic bare density of states, disorder’s influence upon the coefficients A and В of the square and the fourth power of the order parameter is universal for any value of electron correlation and is related only to the general disorder widening of the bare band (generalized Anderson theorem). Such universality is absent for the gradient term expansion coefficient C. In the usual theory of “dirty” superconductors, the С coefficient drops with the growth of disorder. In the limit of strong disorder in BCS limit, the coefficient С is very sensitive to the effects of Anderson localization, which lead to its further drop with disorder growth up to the region of the Anderson insulator. In the region of BCS–ВЕС crossover and in ВЕС limit, the coefficient С and all related physical properties are weakly dependent on disorder. In particular, this leads to relatively weak disorder dependence of both penetration depth and coherence lengths, as well as of related slope of the upper critical magnetic field at superconducting transition, in the region of very strong coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Separation of volatile organic contaminants from water using a direct-contact dehumidifier: An experimental study and modeling

A packed-bed, direct-contact dehumidifier (PB-DCD) has been developed to selectively condense water from a gaseous mixture of organic contaminants. In this process, hot air is humidified by mixing with wastewater vapor in a static mixer and is dehumidified by subcooled fresh water passing through the PB-DCD in a counter-current configuration. The goal of this study is to understand the relationship between various operating parameters and how they affect separation of isopropyl alcohol (IPA) from the gaseous mixture with the purpose of expanding the investigation to other contaminants in the future. The process has been successfully used to separate IPA from wastewater. Different parameters including the concentration of IPA in water, feed temperature, air-to-vapor ratio, and cooling-water-to-vapor mass ratio, as well as residence time were examined to determine their influence on contaminant separation and clean water recovery rate. The Buckingham Pi theorem was applied to reduce the number of studying variables by generating non-dimensional groups. Experiments were performed to determine the relationship between the non-dimensional parameters and model mass transfer in the system. Mass transfer coefficients for multicomponent gaseous mixture condensation in a packed-bed direct contact condenser column are calculated and a modified correlation of mass transfer is developed. The parameters of the mass transfer model are obtained from operating conditions of the PB-DCD, stream conditions and thermodynamic properties. A modified Sherwood correlation is developed to predict IPA separation from a gaseous mixture consisting of air, water, and IPA. The modified Sherwood correlation is applied to successfully predict the Sherwood number with a mean absolute error equal to 6.6 %. According to the experimental results, the maximum IPA separation achieved was 76.3 %, which corresponds to a water recovery rate of 58.7 %.

42 ENGINEERING↗
DOE OSTI2017

Equation of state and hyperfine parameters of high-spin bridgmanite in the Earth’s lower mantle by synchrotron X-ray diffraction and Mössbauer spectroscopy

In this study, we performed synchrotron X-ray diffraction (XRD) and Mössbauer spectroscopy (SMS) measurements on two single-crystal bridgmanite samples [ Embedded Image and Embedded Image ] to investigate the combined effect of Fe and Al on the hyperfine parameters, lattice parameters, and equation of state (EoS) of bridgmanite up to 130 GPa. Our SMS results show that Fe2+ and Fe3+ in Bm6 and Al-Bm11 are predominantly located in the large pseudo-dodecahedral sites (A-site) at lower-mantle pressures. The observed drastic increase in the hyperfine quadrupole splitting (QS) between 13 and 32 GPa can be associated with an enhanced local distortion of the A-site Fe2+ in Bm6. In contrast to Bm6, the enhanced lattice distortion and the presence of extremely high QS values of Fe2+ are not observed in Al-Bm11 at high pressures. Our results here support the notion that the occurrence of the extremely high QS component of approximately 4 mm/s in bridgmanite is due to the lattice distortion in the high-spin (HS) A-site Fe2+, instead of the occurrence of the intermediate-spin state. Both A-site Fe2+ and Fe3+ in Bm6 and Al-Bm11 remain in the HS state at lower-mantle pressures. Together with XRD results, we present the first experimental evidence that the enhanced lattice distortion of A-site Fe2+ does not cause any detectable variation in the EoS parameters, but is associated with anomalous variations in the bond length, tilting angle, and shear strain in the octahedra of Bm6. Analysis of the obtained EoS parameters of bridgmanite at lower-mantle pressures indicates that the substitution of Fe in bridgmanite will cause an enhanced density and a reduced bulk sound velocity (VΦ), whereas the Al and Fe substitution has a reduced effect on density and a negligible effect on VΦ. These experimental results provide new insight into the correlation between lattice, hyperfine, and EoS parameters of bridgmanite in the Earth’s lower mantle.

58 GEOSCIENCES↗
DOE OSTI2020

Unravelling competing microscopic interactions at a phase boundary: A single-crystal study of the metastable antiferromagnetic pyrochlore Yb 2 Ge 2 O 7

We report inelastic neutron scattering measurements from our newly synthesized single crystals of the structurally metastable antiferromagnetic pyrochlore Yb 2 Ge 2 O 7 . We determine the four symmetry-allowed nearest-neighbor anisotropic exchange parameters via fits to linear spin wave theory supplemented by fits of the high-temperature specific heat using the numerical linked-cluster expansion method. The exchange parameters so-determined are strongly correlated to the values determined for the g-tensor components, as previously noted for the related Yb pyrochlore Yb 2 Ti 2 O 7 . To address this issue, we directly determined the g-tensor from electron paramagnetic resonance of 1% Yb-doped Lu 2 Ge 2 O 7 , thus enabling an unambiguous determination of the exchange parameters. Our results show that Yb 2 Ge 2 O 7 resides extremely close to the classical phase boundary between an antiferromagnetic Γ 5 phase and a splayed ferromagnet phase. By juxtaposing our results with recent ones on Yb 2 Ti 2 O 7 , our work illustrates that the Yb pyrochlore oxides represent ideal systems for studying quantum magnets in close proximity to classical phase boundaries.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1978

OSO 8 X-ray spectra of clusters of galaxies. I - Observations of twenty clusters: Physical correlations

OSO 8 X-ray spectra from 2 to 20 keV have been analyzed for 26 clusters of galaxies. For 20 clusters temperatures, emission integrals, iron abundances, and low-energy absorption measurements are presented. The data give, in general, better fits to thermal bremsstrahlung than to power-law models. Eight clusters have positive iron emission-line detections at the 90% confidence level, and all 20 cluster spectra are consistent with Fe/H = 0.000014 by number with the possible exception of Virgo. Thus it is confirmed that X-ray emission in this energy band is predominantly thermal radiation from hot intracluster gas rather than inverse Compton radiation. Physical correlations between X-ray spectral parameters and other cluster properties are examined. It is found that (1) the X-ray temperature is approximately proportional to the square of the velocity dispersion of the galaxies; (2) the emission integral is a strong function of the X-ray temperature; (3) the X-ray temperature and emission integral are better correlated with cluster central-galaxy density than with richness; and (4) the fraction of galaxies which are spirals is correlated with the observed ram pressure in the cluster core.

Mushotzky, R. F.↗
DOE OSTI2016

Multiscale metrologies for process optimization of carbon nanotube polymer composites

Carbon nanotube (CNT) polymer nanocomposites are attractive multifunctional materials with a growing range of commercial applications. With the increasing demand for these materials, it is imperative to develop and validate methods for on-line quality control and process monitoring during production. In this work, a novel combination of characterization techniques is utilized, that facilitates the non-invasive assessment of CNT dispersion in epoxy produced by the scalable process of calendering. First, the structural parameters of these nanocomposites are evaluated across multiple length scales (10 -10 m to 10 -3 m) using scanning gallium-ion microscopy, transmission electron microscopy and small-angle neutron scattering. Then, a non-contact resonant microwave cavity perturbation (RCP) technique is employed to accurately measure the AC electrical conductivity of the nanocomposites. Quantitative correlations between the conductivity and structural parameters find the RCP measurements to be sensitive to CNT mass fraction, spatial organization and, therefore, the processing parameters. These results, and the non-contact nature and speed of RCP measurements identify this technique as being ideally suited for quality control of CNT nanocomposites in a nanomanufacturing environment. In conclusion, when validated by the multiscale characterization suite, RCP may be broadly applicable in the production of hybrid functional materials, such as graphene, gold nanorod, and carbon black nanocomposites.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Fracture mechanics parameters for small fatigue cracks

This paper presents a review of some common small-crack test specimens, the underlying causes of the small-crack effect, and the fracture-mechanics parameters that have been used to correlate or predict their growth behavior. This review concentrates on continuum mechanics concepts and on the nonlinear behavior of small cracks. The paper reviews some stress-intensity factor solutions for small-crack test specimens and develops some simple elastic-plastic J integral and cyclic J integral expressions that include the influence of crack-closure. These parameters were applied to small-crack growth data on two aluminum alloys, and a fatigue life prediction methodology is demonstrated. For these materials, the crack-closure transient from the plastic wake was found to be the major factor in causing the small-crack effect.

Newman, J. C., Jr.↗
NASA NTRS1994

Relationship between clouds and sea surface temperatures in the western tropical Pacific

Analysis of four years of earth radiation budget, cloud, and sea surface temperature data confirms that cloud parameters change dramatically when and where sea surface temperatures increase above approximately 300K. These results are based upon monthly mean values within 2.5 deg x 2.5 deg grid points over the 'warm pool' region of the western tropical Pacific. The question of whether sea surface temperatures are influenced, in turn, by the radiative effects of these clouds (Ramanathan and Collins) is less clear. Such a feedback, if it exists, is weak. The reason why clouds might have so little influence, despite large changes in their longwave and shortwave radiative effects, might be that the sea surface responds to both the longwave heating and the shortwave cooling effects of clouds, and the two effects nearly cancel. There are strong correlations between the rate of change of sea surface temperature and any of the radiation budget parameters that are highly correlated with the incident solar flux-implying that season and latitude are the critical factors determining sea surface temperatures. With the seasonal or both seasonal and latitudinal variations removed, the rate of change of sea surface temperature shows no correlation with cloud-related parameters in the western tropical Pacific.

Arking, Albert↗
NASA NTRS2000

Modal Analysis and Model Correlation of the Mir Space Station

This paper will discuss on-orbit dynamic tests, modal analysis, and model refinement studies performed as part of the Mir Structural Dynamics Experiment (MiSDE). Mir is the Russian permanently manned Space Station whose construction first started in 1986. The MiSDE was sponsored by the NASA International Space Station (ISS) Phase 1 Office and was part of the Shuttle-Mir Risk Mitigation Experiment (RME). One of the main objectives for MiSDE is to demonstrate the feasibility of performing on-orbit modal testing on large space structures to extract modal parameters that will be used to correlate mathematical models. The experiment was performed over a one-year span on the Mir-alone and Mir with a Shuttle docked. A total of 45 test sessions were performed including: Shuttle and Mir thruster firings, Shuttle-Mir and Progress-Mir dockings, crew exercise and pushoffs, and ambient noise during night-to-day and day-to-night orbital transitions. Test data were recorded with a variety of existing and new instrumentation systems that included: the MiSDE Mir Auxiliary Sensor Unit (MASU), the Space Acceleration Measurement System (SAMS), the Russian Mir Structural Dynamic Measurement System (SDMS), the Mir and Shuttle Inertial Measurement Units (IMUs), and the Shuttle payload bay video cameras. Modal analysis was performed on the collected test data to extract modal parameters, i.e. frequencies, damping factors, and mode shapes. A special time-domain modal identification procedure was used on free-decay structural responses. The results from this study show that modal testing and analysis of large space structures is feasible within operational constraints. Model refinements were performed on both the Mir alone and the Shuttle-Mir mated configurations. The design sensitivity approach was used for refinement, which adjusts structural properties in order to match analytical and test modal parameters. To verify the refinement results, the analytical responses calculated using original and refined math models were compared with the measured responses. The results from this study show that the refined models predict more accurately the dynamics of the actual structure. The MiSDE test and analysis results provided the information and experience on test design, flight testing, and data analysis for the ISS and other future spacecraft, which are critical to the verification of analytical models and structural loads.

Kim, Hyoung M.↗
DOE OSTI2014

Aperiodic signals processing via parameter-tuning stochastic resonance in a photorefractive ring cavity

Based on solving numerically the generalized nonlinear Langevin equation describing the nonlinear dynamics of stochastic resonance by Fourth-order Runge-Kutta method, an aperiodic stochastic resonance based on an optical bistable system is numerically investigated. The numerical results show that a parameter-tuning stochastic resonance system can be realized by choosing the appropriate optical bistable parameters, which performs well in reconstructing aperiodic signals from a very high level of noise background. The influences of optical bistable parameters on the stochastic resonance effect are numerically analyzed via cross-correlation, and a maximum cross-correlation gain of 8 is obtained by optimizing optical bistable parameters. This provides a prospective method for reconstructing noise-hidden weak signals in all-optical signal processing systems.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Quasars probing quasars. VII. The pinnacle of the cool circumgalactic medium surrounds massive z ∼ 2 galaxies

We survey the incidence and absorption strength of the metal-line transitions C II 1334 and C IV 1548 from the circumgalactic medium (CGM) surrounding z ∼ 2 quasars, which act as signposts for massive dark matter halos M {sub halo} ≈ 10{sup 12.5} M {sub ☉}. On scales of the virial radius (r {sub vir} ≈ 160 kpc), we measure a high covering fraction f{sub C} = 0.73 ± 0.10 to strong C II 1334 absorption (rest equivalent width W {sub 1334} ≥ 0.2 Å), implying a massive reservoir of cool (T ∼ 10{sup 4} K) metal enriched gas. We conservatively estimate a metal mass exceeding 10{sup 8} M {sub ☉}. We propose that these metals trace enrichment of the incipient intragroup/intracluster medium that these halos eventually inhabit. This cool CGM around quasars is the pinnacle among galaxies observed at all epochs, as regards covering the fraction and average equivalent width of H I Lyα and low-ion metal absorption. We argue that the properties of this cool CGM primarily reflect the halo mass, and that other factors such as feedback, star-formation rate, and accretion from the intergalactic medium are secondary. We further estimate that the CGM of massive, z ∼ 2 galaxies accounts for the majority of strong Mg II absorption along random quasar sightlines. Last, we detect an excess of strong C IV 1548 absorption (W {sub 1548} ≥ 0.3 Å) over random incidence to the 1 Mpc physical impact parameter and measure the quasar-C IV cross-correlation function: ξ{sub C} {sub IV-Q}(r)=(r/r{sub 0}){sup −γ} with r{sub 0}=7.5{sub −1.4}{sup +2.8} h{sup −1} Mpc and γ=1.7{sub −0.2}{sup +0.1}. Consistent with previous work on larger scales, we infer that this highly ionized C IV gas traces massive (10{sup 12} M {sub ☉}) halos.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Supernovae and their host galaxies – VII. The diversity of Type Ia supernova progenitors

ABSTRACT We present an analysis of the light curve (LC) decline rates (Δm15) of 407 normal and peculiar supernovae (SNe) Ia and global parameters of their host galaxies. As previously known, there is a significant correlation between the Δm15 of normal SNe Ia and global ages (morphologies, colours, and masses) of their hosts. On average, those normal SNe Ia that are in galaxies from the Red Sequence (early-type, massive, old hosts) have faster declining LCs in comparison with those from the Blue Cloud (late-type, less massive, younger hosts) of the colour–mass diagram. The observed correlations between the Δm15 of normal SNe Ia and hosts’ parameters appear to be due to the superposition of at least two distinct populations of faster and slower declining normal SNe Ia from older and younger stellar components. We show, for the first time, that the Δm15 of 91bg- and 91T-like SNe is independent of host morphology and colour. The distribution of hosts on the colour–mass diagram confirms the known tendency for 91bg-like SNe to occur in globally red/old galaxies, while 91T-like events prefer blue/younger hosts. On average, the youngest global ages of 02cx-like SNe hosts and their positions in the colour–mass diagram hint that these events likely originate from young population, but they differ from 91T-like events in the LC decline rate. Finally, we discuss the possible explosion channels and present our favoured SN Ia models that have the potential to explain the observed SN–host relations.

Hakobyan, A. A.↗