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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 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Effective dielectric function of TiO{sub 2} nanoparticles under laser pumping in the fundamental absorption band

A nonlinear optical response of TiO{sub 2} nanoparticles under pumping by 355-nm laser radiation is experimentally investigated. Using the data obtained by z -scanning with simultaneous measurement of the scattering intensity, the effective permitivity of particles is reconstructed as a function of the pump intensity. It is found that graphical mapping of the relationship between the real and imaginary parts of the permitivity can be obtained using an affine transformation of a similar map of the frequency-dependent dielectric function for the Lorentz model. It is shown that an increase in the pump intensity should lead to a red shift of the absorption maximum of nanoparticles and a rise in the plasma frequency, which is estimated (using a single-oscillator Lorenz model) from the obtained values of the real and imaginary parts of the effective permitivity for the probe radiation wavelength in use. (paper)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Improving our fundamental understanding of the role of aerosol-cloud interactions in the climate system

The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth’s clouds is the most uncertain component of the overall global radiative forcing from pre-industrial time. General Circulation Models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol-cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol-cloud interactions with high fidelity but do not include interactions with the larger scale and are therefore limited from a climatic point of view. Lastly, we suggest strategies for improving estimates of aerosol-cloud relationships in climate models, for new remote sensing and in situ measurements, and for quantifying and reducing model uncertainty.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

New nutrients exert fundamental control on dissolved organic carbon accumulation in the surface Atlantic Ocean

The inventories of carbon residing in organic matter dissolved in the ocean [dissolved organic carbon (DOC)] and in the atmosphere as CO 2 are of the same order of magnitude, such that small changes in the DOC pool could have important consequences in atmospheric carbon and thus climate. DOC in the global ocean is largely formed in the sunlit euphotic zone, but identifying predictable controls on that production is an important yet unrealized goal. In this paper, we use a testable and causative correlation between the net production of DOC and the consumption of new nutrients in the euphotic zone of the Atlantic Ocean. We demonstrate that new nutrients introduced to the euphotic zone by upwelling in divergence zones and by winter convective overturn of the water column, and the primary production associated with those nutrients, are the ultimate driver of DOC distributions across the Atlantic basins. Finally, as new nutrient input will change with a changing climate, the role of DOC in the ocean’s biological pump should likewise be impacted.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Adaptive nonequilibrium design of actin-based metamaterials: Fundamental and practical limits of control

The adaptive and surprising emergent properties of biological materials self-assembled in far-from-equilibrium environments serve as an inspiration for efforts to design nanomaterials. In particular, controlling the conditions of self-assembly can modulate material properties, but there is no systematic understanding of either how to parameterize external control or how controllable a given material can be. Here, we demonstrate that branched actin networks can be encoded with metamaterial properties by dynamically controlling the applied force under which they grow and that the protocols can be selected using multi-task reinforcement learning. These actin networks have tunable responses over a large dynamic range depending on the chosen external protocol, providing a pathway to encoding “memory” within these structures. Interestingly, we obtain a bound that relates the dissipation rate and the rate of “encoding” that gives insight into the constraints on control—both physical and information theoretical. Taken together, these results emphasize the utility and necessity of nonequilibrium control for designing self-assembled nanostructures.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Exhaust Gas Recirculation Cooler Fouling in Diesel Applications: Fundamental Studies Deposit Properties and Microstructure

This paper reports on the results of experimental efforts aimed at improving the understanding of the mechanisms and conditions at play in the fouling of EGR coolers. An experimental apparatus was constructed to utilize simplified surrogate heat exchanger tubes in lieu of full-size heat exchangers. The use of these surrogate tubes allowed removal of the tubes after exposure to engine exhaust for study of the deposit layer and its properties. The exhaust used for fouling the surrogate tubes was produced using a modern medium-duty diesel engine fueled with both ultra-low sulfur diesel and biodiesel blends. At long exposure times, no significant difference in the fouling rate was observed between fuel types and HC levels. Surface coatings for the tubes were also evaluated to determine their impact on deposit growth. No surface treatment or coating produced a reduction in the fouling rate or any evidence of deposit removal. In addition, microstructural analysis of the fouling layers was performed using optical and electron microscopy in order to better understand the deposition mechanism. The experimental results are consistent with thermophoretic deposition for deposit formation, and van der Waals attraction between the deposit surface and exhaust-borne particulate.

EGR↗
DOE OSTI2012

Kinetics of heterogeneous nucleation in supersaturated vapor: Fundamental limits to neutral particle detection revisited

We examine the nucleated (with barrier) activation of perfectly wetting (zero contact angle) particles ranging from essentially bulk size down to approximately 1-nm mass diameter. While similar studies trace back to the pioneering work of Fletcher, we present here a novel approach to the analysis based on general area constructions that enable key thermodynamic properties, including surface and bulk contributions to nucleation work, to be interpreted geometrically with reference to the Kelvin curve. The kinetics of activation are described in more detail in terms of the mean first passage time (MFPT) for barrier crossing. MFPT theory and benchmark calculations are used to develop and test a new approximate-but-simpler-to-use analytic expression for the barrier crossing rate. The present study is motivated by recent condensation particle counter (CPC) studies that appear to finally establish the long-predicted detection of 'sub-Kelvin' particles in the nano-size regime. Corresponding states thermodynamic and kinetic scaling approaches are used to facilitate the correlation and selection of optimal CPC working fluids and operating conditions based on a new metric for heterogeneous nucleation, the signal-to-noise ratio, and physical and chemical properties.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Separation of Americium from Europium using Camphor-BisTriazinyl Pyridine: A Fundamental Study

Among the different components present in spent nuclear fuel, long-lived trivalent actinides are particularly difficult to separate from the shorter-lived lanthanide fission products due to their similar chemical properties. We achieved selective extraction of americium from acidic solution (up to 2M HNO 3 ) containing tenth molar quantities of lanthanides using neutral pyridine-based ligands dissolved in polar diluents. Nitrogen-based Bis Triazinyl Pyridine (BTP) ligands are desirable for both their excellent An/Ln selectivity and incinerability. Our results pertaining to ligand solubility, kinetics, hydrolytic stability, and extraction performance in various nitric acid environments are presented.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

APS: High-Energy X-rays Expediting Applied and Fundamental Research

The Advanced Photon Source (APS) at Argonne National Laboratory (ANL) was designed and built as one of the first large 3rd generation synchrotrons operated at 7 GeV. The United States Department of Energy (DOE) Office of Science funded the construction and continues to fund the operation of this national facility. Furthermore, the beamlines were originally operated by Collaborative Access Teams (CAT), which allowed a strong involvement of research institutes, universities, and industry. Today 43 of 68 beamlines are operated by the X-ray Science Division (XSD) and 35 beamlines are directly funded by the DOE Office of Science. The APS became operational in 1995, and was planned right from the beginning with 4 beamlines dedicated to high-energy x-rays above 40 keV: 1-ID designed to study engineering materials science, 6-ID-D for magnetism and condensed matter research, 11-ID-B dedicated to magnetic Compton scattering using an Elliptical Multipole Wiggler, and 11-ID-C for materials science and condensed matter physics. These stations were later joined by the bending magnet beamlines 6-BM for white beam studies and 17-BM for rapid powder diffraction. CAT operated beamlines such as 15-ID for crystallography or 16-ID for high-pressure studies also use the high-energy x-ray regime frequently. The program in Compton scattering ended in 2004 and the wiggler was replaced by an undulator. 11-ID-B became the first dedicated station for Pair Distribution Function (PDF) Analysis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Determination of fundamental mechanical properties of biomass using the cubical triaxial tester to model biomass flow

The flowability of biomass is an indicator of how amenable biomass is to handling. The flowability measurements are often determined with empirical or tertiary experiments. This status quo impedes employing engineering principles to advance the design and operation of biomass handling systems. It is imperative to establish an experimental protocol minimizing empirical aspects of flowability characterization to account for the variability of biomass. This study demonstrates the operational principles of the large chamber cubical triaxial tester and the procedure of triaxial tests to quantify bulk flow behaviors of two milled biomass feedstocks, namely corn stover 2 mm (CS) and Douglas fir 1 mm (DF). The Mohr-Coulomb (MC), Drucker-Prager (DP) and modified Cam Clay (mCC) models are calibrated for both biomasses. Analysis indicates that CS will exhibit a cohesive flow with a larger cohesion coefficient of MC (3.8 ± 3.5 kPa) than DF (0.42 ± 0.9 kPa) and a larger d value of DP (6.9 kPa) than DF (0.0 kPa), respectively. CS exhibits a higher spring-back index of mCC (0.39 ± 0.05) than DF (0.27 ± 0.05) also suggesting handling issues, which agrees with the experiences in the industry. This study demonstrates the capability of a CTT in a quantitative investigation of biomass handling characteristics.

09 BIOMASS FUELS↗
DOE OSTI2015

THREE FUNDAMENTAL PERIODS IN AN 87 YEAR LIGHT CURVE OF THE SYMBIOTIC STAR MWC 560

We construct a visual light curve of the symbiotic star MWC covering the last 87 years of its history. The data were assembled from the literature and from the AAVSO data bank. Most of the periodic components of the system brightness variation can be accounted for by the operation of three basic clocks of the periods P1 = 19,000 days, P2 = 1943 days, and P3 = 722 days. These periods can plausibly, and consistently with the observations, be attributed to three physical mechanisms in the system: the working of a solar-like magnetic dynamo cycle in the outer layers of the giant star of the system, the binary orbit cycle, and the sidereal rotation cycle of the giant star. MWC 560 is the seventh symbiotic star with historical light curves that reveal similar basic characteristics of the systems. The light curves of all these stars are well interpreted on the basis of the current understanding of the physical processes that are the major sources of the optical luminosity of these symbiotic systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

METHANOL AS A TRACER OF FUNDAMENTAL CONSTANTS

The methanol molecule CH{sub 3}OH has a complex microwave spectrum with a large number of very strong lines. This spectrum includes purely rotational transitions as well as transitions with contributions of the internal degree of freedom associated with the hindered rotation of the OH group. The latter takes place due to the tunneling of hydrogen through the potential barriers between three equivalent potential minima. Such transitions are highly sensitive to changes in the electron-to-proton mass ratio, {mu} = m{sub e}/m{sub p}, and have different responses to {mu}-variations. The highest sensitivity is found for the mixed rotation-tunneling transitions at low frequencies. Observing methanol lines provides more stringent limits on the hypothetical variation of {mu} than ammonia observation with the same velocity resolution. We show that the best-quality radio astronomical data on methanol maser lines constrain the variability of {mu} in the Milky Way at the level of |{Delta}{mu}/{mu}| < 28 x 10{sup -9} (1{sigma}) which is in line with the previously obtained ammonia result, |{Delta}{mu}/{mu}| < 29 x 10{sup -9} (1{sigma}). This estimate can be further improved if the rest frequencies of the CH{sub 3}OH microwave lines will be measured more accurately.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

FUNDAMENTAL PARAMETERS OF THE EXOPLANET HOST K GIANT STAR {iota} DRACONIS FROM THE CHARA ARRAY

We measured the angular diameter of the exoplanet host star {iota} Dra with Georgia State University's Center for High Angular Resolution Astronomy Array interferometer and, using the star's parallax and photometry from the literature, calculated its physical radius and effective temperature. We then combined our results with stellar oscillation frequencies from Zechmeister et al. and orbital elements from Kane et al. to determine the masses for the star and exoplanet. Our value for the central star's mass is 1.82 {+-} 0.23 M{sub Sun }, which means the exoplanet's minimum mass is 12.6 {+-} 1.1 M{sub Jupiter}. Using our new effective temperature, we recalculated the habitable zone for the system, though it is well outside the star-planet separation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

FUNDAMENTAL PARAMETERS AND CHEMICAL COMPOSITION OF ARCTURUS

We derive a self-consistent set of atmospheric parameters and abundances of 17 elements for the red giant star Arcturus: T{sub eff} = 4286 {+-} 30 K, log g = 1.66 {+-} 0.05, and [Fe/H] = -0.52 {+-} 0.04. The effective temperature was determined using model atmosphere fits to the observed spectral energy distribution from the blue to the mid-infrared (0.44 to 10 {mu}m). The surface gravity was calculated using the trigonometric parallax of the star and stellar evolution models. A differential abundance analysis relative to the solar spectrum allowed us to derive iron abundances from equivalent width measurements of 37 Fe I and 9 Fe II lines, unblended in the spectra of both Arcturus and the Sun; the [Fe/H] value adopted is derived from Fe I lines. We also determine the mass, radius, and age of Arcturus: M = 1.08 {+-} 0.06 M{sub Sun }, R = 25.4 {+-} 0.2 R{sub Sun }, and {tau} = 7.1{sup +1.5}{sub -1.2} Gyr. Finally, abundances of the following elements are measured from an equivalent width analysis of atomic features: C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Zn. We find the chemical composition of Arcturus typical of that of a local thick-disk star, consistent with its kinematics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CONFIRMING FUNDAMENTAL PROPERTIES OF THE EXOPLANET HOST STAR {epsilon} ERIDANI USING THE NAVY OPTICAL INTERFEROMETER

We measured the angular diameter of the exoplanet host star {epsilon} Eridani using the Navy Optical Interferometer. We determined its physical radius, effective temperature, and mass by combining our measurement with the star's parallax, photometry from the literature, and the Yonsei-Yale isochrones, respectively. We used the resulting stellar mass of 0.82 {+-} 0.05 M{sub Sun} plus the mass function from Benedict et al. to calculate the planet's mass, which is 1.53 {+-} 0.22 M{sub Jupiter}. Using our new effective temperature, we also estimated the extent of the habitable zone for the system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

A LINK TO THE PAST: USING MARKOV CHAIN MONTE CARLO FITTING TO CONSTRAIN FUNDAMENTAL PARAMETERS OF HIGH-REDSHIFT GALAXIES

We have developed a new method for fitting spectral energy distributions (SEDs) to identify and constrain the physical properties of high-redshift (4 < z < 8) galaxies. Our approach uses an implementation of Bayesian based Markov Chain Monte Carlo that we have dubbed '{pi}MC{sup 2}'. It allows us to compare observations to arbitrarily complex models and to compute 95% credible intervals that provide robust constraints for the model parameters. The work is presented in two sections. In the first, we test {pi}MC{sup 2} using simulated SEDs to not only confirm the recovery of the known inputs but to assess the limitations of the method and identify potential hazards of SED fitting when applied specifically to high-redshift (z > 4) galaxies. In the second part of the paper we apply {pi}MC{sup 2} to thirty-three 4 < z < 8 objects, including the spectroscopically confirmed Grism ACS Program for Extragalactic Science Ly{alpha} sample (4 < z < 6), supplemented by newly obtained Hubble Space Telescope/WFC3 near-IR observations, and several recently reported broadband selected z > 6 galaxies. Using {pi}MC{sup 2}, we are able to constrain the stellar mass of these objects and in some cases their stellar age and find no evidence that any of these sources formed at a redshift larger than z = 8, a time when the universe was Almost-Equal-To 0.6 Gyr old.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

AKARI OBSERVATIONS OF BROWN DWARFS. III. CO, CO{sub 2}, AND CH{sub 4} FUNDAMENTAL BANDS AND PHYSICAL PARAMETERS

We investigate variations in the strengths of three molecular bands, CH{sub 4} at 3.3 {mu}m, CO at 4.6 {mu}m, and CO{sub 2} at 4.2 {mu}m, in 16 brown dwarf spectra obtained by AKARI. Spectral features are examined along the sequence of source classes from L1 to T8. We find that the CH{sub 4} 3.3 {mu}m band is present in the spectra of brown dwarfs later than L5, and the CO 4.6 {mu}m band appears in all spectral types. The CO{sub 2} absorption band at 4.2 {mu}m is detected in late-L and T-type dwarfs. To better understand brown dwarf atmospheres, we analyze the observed spectra using the Unified Cloudy Model. The physical parameters of the AKARI sample, i.e., atmospheric effective temperature T {sub eff}, surface gravity log g, and critical temperature T {sub cr}, are derived. We also model IRTF/SpeX and UKIRT/CGS4 spectra in addition to the AKARI data in order to derive the most probable physical parameters. Correlations between the spectral type and the modeled parameters are examined. We confirm that the spectral-type sequence of late-L dwarfs is not related to T {sub eff}, but instead originates as a result of the effect of dust.

79 ASTRONOMY AND ASTROPHYSICS↗