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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Bifurcation and Pattern Symmetry Selection in Reaction-Diffusion Systems with Kinetic Anisotropy

Abstract Ordering and self-organization are critical in determining the dynamics of reaction-diffusion systems. Here we show a unique pattern formation mechanism, dictated by the coupling of thermodynamic instability and kinetic anisotropy. Intrinsically different from the physical origin of Turing instability and patterning, the ordered patterns we obtained are caused by the interplay of the instability from uphill diffusion, the symmetry breaking from anisotropic diffusion, and the reactions. To understand the formation of the void/gas bubble superlattices in crystals under irradiation, we establish a general theoretical framework to predict the symmetry selection of superlattice structures associated with anisotropic diffusion. Through analytical study and phase field simulations, we found that the symmetry of a superlattice is determined by the coupling of diffusion anisotropy and the reaction rate, which indicates a new type of bifurcation phenomenon. Our discovery suggests a means for designing target experiments to tailor different microstructural patterns.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Controlling Directionality and Dimensionality of Radiation by Perturbing Separable Bound States in the Continuum

Here, a bound state in the continuum (BIC) is an unusual localized state that is embedded in a continuum of extended states. Here, we present the general condition for BICs to arise from wave equation separability. Then we show that by exploiting perturbations of certain symmetry such BICs can be turned into resonances that radiate with a tailorable directionality and dimensionality. Using this general framework, we construct new examples of separable BICs and resonances that can exist in optical potentials for ultracold atoms, photonic systems, and systems described by tight binding. Such resonances with easily reconfigurable radiation allow for applications such as the storage and release of waves at a controllable rate and direction, as well systems that switch between different dimensions of confinement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Nanoscale heat transfer – from computation to experiment

Heat transfer can differ distinctly at the nanoscale from that at the macroscale. Recent advancement in computational and experimental techniques has enabled a large number of interesting observations and understanding of heat transfer processes at the nanoscale. We will first discuss recent advances in computational and experimental methods used in nanoscale thermal transport studies, followed by reviews of novel thermal transport phenomena at the nanoscale observed in both computational and experimental studies, and discussion on current understanding of these novel phenomena. Our perspectives on challenges and opportunities on computational and experimental methods are also presented.

42 ENGINEERING↗
DOE OSTI2015

An efficient low-temperature route to nitrogen-doping and activation of mesoporous carbons for CO 2 capture

We report an innovative strategy for post-synthesis nitrogen-doping of mesoporous carbons (MCs) with high yields (>90%) at low temperatures (230–380 °C) by using a strong base, sodium amide (NaNH 2 ), was developed. The as-prepared N-doped MCs exhibit a significantly enhanced CO 2 adsorption performance in terms of capacity and selectivity when compared to their parent MCs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A high-performance spectrally-selective solar absorber based on a yttria-stabilized zirconia cermet with high-temperature stability

Spectrally-selective solar absorbers are widely used in solar hot water and concentrating solar power (CSP) systems. However, their performance at high temperatures (>450 °C) is still not satisfactory due to high infrared (IR) emittance and lack of long-term thermal stability. In this work, we explore yttria-stabilized zirconia (YSZ) cermet-based spectrally-selective surfaces for high-temperature solar absorber applications. The developed multilayer selective surface comprises two sunlight-absorbing W–Ni–YSZ cermet layers with different W–Ni volume fractions inside the YSZ matrix, two anti-reflection coatings (ARCs), and one tungsten IR reflection layer for reduced IR emittance and improved thermal stability, deposited on a polished stainless steel (SS) substrate. The fabricated solar absorbers are tested for their long-term thermal stability at 600 °C. We find a distinct change in the surface morphology of the solar absorbers when oxygen is highly deficient in the YSZ-ARC layers. The oxygen deficiency can be effectively overcome through increasing the oxygen partial pressure during sputtering, which leads to a stable solar absorber with a solar absorptance of ~0.91 and a total hemispherical emittance of ~0.13 at 500 °C. Those values are obtained at the actual operating temperature using an absolute and direct method that measures the total hemispherical emittance with high accuracy. In contrast, most reports on solar absorber development in the literature to date use only near room-temperature spectroscopy techniques that have been shown to significantly underestimate the total hemispherical emittance. This makes our experimentally demonstrated total hemispherical emittance value the lowest ever reported for a high-temperature stable solar absorber with solar absorptance above 0.9.

14 SOLAR ENERGY↗
DOE OSTI2015

Thermal conductivity reduction by isoelectronic elements V and Ta for partial substitution of Nb in half-Heusler Nb (1-x)/2 V (1-x)/2 Ta x CoSb

Recently, we found a new n-type thermoelectric half-Heusler NbCoSb with a valence electron count of 19, different from the usual 18. In this paper, we focus on the effect of partial substitution of Nb by isoelectronic elements V and Ta on the reduction of the thermal conductivity of Nb(1-x)/2V(1-x)/2TaxCoSb. We found that the isoelectronic elements V and Ta for partial substitution of Nb can dramatically decrease the thermal conductivity from 7.0 W m-1 K-1 to 3.3 W m-1 K-1 at room temperature for Nb0.44V0.44Ta0.12CoSb, but unfortunately a large power factor decrease also occurred. Consequently, a peak ZT of ~0.5 is achieved at 700 °C for Nb0.44V0.44Ta0.12CoSb, which is about 25% higher than the ~0.4 reported earlier for NbCoSb.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗