Search NASA⌕ Search

SEARCH · Search NASA

Results for “intermediate phase”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Measurements of I/SVOCs in biomass-burning smoke using solid-phase extraction disks and two-dimensional gas chromatography

Biomass-burning organic-aerosol (OA) emissions are known to exhibit semi-volatile behavior that impacts OA loading during plume transport. Because such semi-volatile behavior depends in part on OA composition, improved speciation of intermediate and semi-volatile organic compounds (I/SVOCs) emitted during fires is needed to assess the competing effects of primary OA volatilization and secondary OA production. In this study, 18 laboratory fires were sampled in which a range of fuel types were burned. Emitted I/SVOCs were collected onto Teflon filters and solid-phase extraction (SPE) disks to qualitatively characterize particulate and gaseous I/SVOCs, respectively. Derivatized filter extracts were analyzed using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC-TOFMS). Quality control tests were performed using biomass-burning relevant standards and demonstrate the utility of SPEdisks for untargeted analysis of air samples. The observed chromatographic profiles of I/SVOCs in coniferous fuel-derived smoke samples were well correlated with each other, but poorly correlated with other fuel types(e.g., herbaceous and chaparral fuels). Emissions of benzenediol isomers were also shown to be fuel dependent. The combined Teflon and SPE filter data captured differences in gas-particle partitioning of the benzene diolisomers, with hydroquinone having a significantly higher particle-phase fraction than catechol due to its lower volatility. Additionally, the speciated volatility distribution of I/SVOCs in smoke from a rotten-log fire was estimated to evaluate the composition of potentially volatilized primary OA, which was entirely attributed to oxygenated (or other heteroatomic) compounds. The isomer-dependent partitioning and the speciated volatility distributions both suggest the need for better understanding of gas-phase and heterogenous reaction pathways of biomass-burning-derived I/SVOCs in order to represent the atmospheric chemistry of smoke in models.

09 BIOMASS FUELS↗
DOE OSTI2014

EARLY-PHASE PHOTOMETRY AND SPECTROSCOPY OF TRANSITIONAL TYPE Ia SN 2012ht: DIRECT CONSTRAINT ON THE RISE TIME

We report photometric and spectroscopic observations of the nearby Type Ia Supernova (SN Ia) 2012ht from –15.8 days to +49.1 days after B-band maximum. The decline rate of the light curve is Δm {sub 15}(B) = 1.39 ± 0.05 mag, which is intermediate between normal and subluminous SNe Ia, and similar to that of the ''transitional'' Type Ia SN 2004eo. The spectral line profiles also closely resemble those of SN 2004eo. We were able to observe SN 2012ht at a very early phase, when it was still rising and was about three magnitudes fainter than at the peak. The rise time to the B-band maximum is estimated to be 17.6 ± 0.5 days and the time of the explosion is MJD 56277.98 ± 0.13. SN 2012ht is the first transitional SN Ia whose rise time is directly measured without using light curve templates, and the fifth SN Ia overall. This rise time is consistent with those of the other four SNe within the measurement error, even including the extremely early detection of SN 2013dy. The rising part of the light curve can be fitted by a quadratic function, and shows no sign of a shock-heating component due to the interaction of the ejecta with a companion star. The rise time is significantly longer than that inferred for subluminous SNe such as SN 1991bg, which suggests that a progenitor and/or explosion mechanism of transitional SNe Ia are more similar to normal SNe Ia rather than to subluminous SNe Ia.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Strain relaxation in multilayer III–N structures on Si(111) substrates

X-ray diffractometry and X-ray scattering reciprocal space maps have been used to study strain relaxation in a complex buffer composed of seven intermediate layers of Al{sub x}Ga{sub 1−x}N composition with different values of x, decreasing with an increase in the distance from the substrate. The layers have been grown by hydride metalorganic vapor phase epitaxy on silicon and sapphire substrates. Differences in the structural quality of the first four layers of a multilayer buffer grown on different substrates have been revealed. A gradual smoothing out of these differences in the next three layers with an increase in the layer serial number has been shown. The last grown intermediate Al{sub x}Ga{sub 1−x}N layer and the GaN layer grown on it have identical thicknesses and degrees of mosaicity, regardless of the substrate type. Device structures grown on a complex buffer demonstrate emission in approximately the same wavelength range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Unique Phase Behavior of Inverse Tapered Block Copolymers: Self-Consistent Field Theory and Molecular Dynamics Simulations

Using theory and simulation, we study the microphase separated structures of inverse tapered block copolymers. These are AB block copolymers with a gradient region inserted between the pure A and B blocks that smoothly changes in composition from B to A, with the B-side of the taper bonded to the pure A block. Tapering is a means to increase miscibility between polymer blocks, and by controlling the length of the taper, the phase behavior and domain spacing can be adjusted. As opposed to better known ABAB tetrablock copolymers that also have four alternating A-rich and B-rich regions, here the intermediate region has a partially mixed composition, promoting relatively diblock-like behavior for shorter inverse tapers or low segregation strength but unique behavior as a function of increasing segregation strength for some systems. In particular, for systems in which 50% of the backbone is the taper, the larger of the two pure end blocks - composed of the overall majority component - can phase separate analogously to the minority component of a diblock copolymer, creating cylinder and network phases in which the majority component’s pure block is the minority phase in a matrix of a relatively disordered mixture of the tapered region and the minority component’s pure block.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Combustion chemistry of alkenes and alkadienes

Alkenes formed, during the refining of crude oil, by cracking the heavier fractions are present in transportation fuels in significant amounts, up to as much as 15–20% in gasoline. Moreover, alkenes are also the major intermediate products of the oxidation of alkanes, which play a significant role in autoignition chemistry. This review has assessed the recent progress in gas-phase detailed kinetic model development for species with C=C double bond, mostly C2–C10 alkenes and 1,3-butadiene. The compiled knowledge on alkene combustion chemistry enabled a better understanding of the influence of the number and the position of the C=C double bond on the chemical kinetics and hence combustion behavior of alkenes in engines. At first, the article gives an extensive overview of fundamental combustion experiments by considering studies of C2–C10 alkenes and 1,3-butadiene in shock tubes, rapid compression machines, laminar flames, and jet-stirred and flow reactors. The value of the data from such experiments is critically discussed. Secondly, this article highlights the important reaction classes involved in alkene oxidation over low-, intermediate- and high-temperature ranges. Combustion chemistry covering C2 to C10 alkenes, with a special emphasis on C2 to C7 isomers is discussed by presenting a large body of experimental and modeling investigations. Detailed chemistry differences between alkene isomers and also between alkenes and alkanes are also addressed. Thirdly, the article presents important reaction pathways for PAH precursor formation in different alkenes. Finally, a summary of the distinguishing features of alkene combustion chemistry and an outlook towards future research in this area are presented. In conclusion, this review is focused on linear and branched chain alkenes, and the chemistry of cyclo-alkenes is not included.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Field-induced quantum critical point in the itinerant antiferromagnet Ti 3 Cu 4

New phases of matter emerge at the edge of magnetic instabilities, which can occur in materials with moments that are localized, itinerant or intermediate between these extremes. In local moment systems, such as heavy fermions, the magnetism can be tuned towards a zero-temperature transition at a quantum critical point (QCP) via pressure, chemical doping, and, rarely, magnetic field. By contrast, in itinerant moment systems, QCPs are more rare, and they are induced by pressure or doping; there are no known examples of field induced transitions. This means that no universal behaviour has been established across the whole itinerant-to-local moment range—a substantial gap in our knowledge of quantum criticality. Here we report an itinerant antiferromagnet, Ti 3 Cu 4 , that can be tuned to a QCP by a small magnetic field. We see signatures of quantum criticality and the associated non-Fermi liquid behaviour in thermodynamic and transport measurements, while band structure calculations point to an orbital-selective, spin density wave ground state, a consequence of the square net structural motif in Ti 3 Cu 4 . Ti 3 Cu 4 thus provides a platform for the comparison and generalisation of quantum critical behaviour across the whole spectrum of magnetism.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Elucidating the role of reactive nitrogen intermediates in hetero-cyclization during hydrothermal liquefaction of food waste

Hydrothermal liquefaction (HTL) has emerged as a promising strategy for converting abundant, water-rich organic streams into an energy-dense, sustainable, biocrude. Despite major strides in improving oil yields and process intensification, a key underlying challenge persists in relating the composition of the feedstock to the ultimate fate of nitrogen, which is especially important for biocrude quality. To elucidate how nitrogen partitions into the respective gas, aqueous, oil and solid hydrothermal products, food waste was treated under HTL conditions (15 wt% solids, 575 K reaction temperature, and 1 hour reaction time) and elemental, chromatographic and mass spectroscopy analyses were performed on the products to establish dominant product classes and to close mass, carbon, and nitrogen balances. Liquid products (aqueous and biocrude) were found to contain nearly 60% of the nitrogen, with a majority of the biocrude-phase nitrogen in the form of amides. Ab initio thermodynamic and kinetic simulations on model reactants were used to evaluate potential reaction pathways involving reactive nitrogen intermediates. A subsequent kinetic model was evaluated at reaction temperatures ranging 300–1000 K and for a range of feedstock compositions to identify primary reaction pathways. The Maillard reaction is revealed to be the dominant pathway for converting reactive nitrogen intermediates into observed products, especially those in which nitrogen is present as a heterocyclic aromatic. Subsequent product analysis by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) confirms strong agreement among the experimental data, kinetic model and proposed Maillard pathways.

09 BIOMASS FUELS↗
DOE OSTI2021

Combustion in the ZrF 4 -Mg-Si and ZrF 4 -Al-Si systems for preparation of zirconium silicides

The exothermic reactions in the ZrF 4 –Mg-Si and ZrF 4 -Al-Si systems are investigated by a fast temperature recording (thermocouple) technique, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). A quenching method is used to arrest the combustion process and conduct a layer-by-layer analysis of the products by x-ray diffraction (XRD) and electron microscopy. Two seemingly similar reactive systems exhibited considerably different combustion characteristics, composition, and morphology. Based on these investigations, we propose and discuss phase formation mechanisms at the early stages for each system. Three different pathways involving the reaction of ZrF 4 with other reagents and the Mg 2 Si intermediate are identified to occur in the ZrF 4 –Mg-Si system. Contrary to the complex mechanism in the ZrF 4 –Mg-Si system, the early stage of the combustion process for the ZrF 4 -Al-Si system involves the interaction of ZrF 4 with Al-Si eutectic melt. The exothermic reaction between reduced solid Zr and Si melt is the primary heat-generating step for both systems in spite of substantial differences in the early stages of the reactions. The silicon content in the reactive mixtures governs the phase composition of products. The ZrSi 2 phase, with a high growth rate, forms first on the Zr particle surfaces and then grows by a reactive diffusion mechanism. The ZrSi 2+ Zr reaction produces silicon-lean phases (e.g., ZrSi) when the silicon supply is limited. The combustion temperature also has a considerable influence on the phase compositions of the products. High combustion temperature in the ZrF 4 +2Mg+Si mixture enables the formation of multiphase products (α-ZrSi and β-ZrSi), whereas the relatively lower temperatures in the 3ZrF 4 +4Al+3Si mixture yields a single-phase α-ZrSi. As a result, lower combustion temperatures also make the ZrF 4 -Al-Si system more advantageous for the preparation of zirconium silicides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Early stage structural development of prototypical zeolitic imidazolate framework (ZIF) in solution

Given the wide-ranging potential applications of metal organic frameworks (MOFs), an emerging imperative is to understand their formation with atomic scale precision. This will aid in designing syntheses for next-generation MOFs with enhanced properties and functionalities. Major challenges are to characterize the early-stage seeds, and the pathways to framework growth, which require synthesis coupled with in situ structural characterization sensitive to nanoscale structures in solution. Here we report measurements of an in situ synthesis of a prototypical MOF, ZIF-8, utilizing synchrotron X-ray atomic pair distribution function (PDF) analysis optimized for sensitivity to dilute species, complemented by mass spectrometry, electron microscopy, and density functional theory calculations. We observe that despite rapid formation of the crystalline product, a high concentration of Zn(2-MeIm) 4 (2-MeIm=2-methylimidazolate) initially forms and persists as stable clusters over long times. A secondary, amorphous phase also pervades during the synthesis, which has a structural similarity to the final ZIF-8 and may act as an intermediate to the final product.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Growth modes and epitaxy of FeAl thin films on a-cut sapphire prepared by pulsed laser and ion beam assisted deposition

FeAl films around equiatomic composition are grown on a-cut (112{sup ¯}0) sapphire substrates by ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD) at ambient temperature. Subsequent successive annealing is used to establish chemical order and crystallographic orientation of the films with respect to the substrate. We find a strongly [110]-textured growth for both deposition techniques. Pole figures prove the successful preparation of high quality epitaxial films by PLD with a single in-plane orientation. IBAD-grown films, however, exhibit three in-plane orientations, all of them with broad angular distributions. The difference of the two growth modes is attributed to the existence of a metastable intermediate crystalline orientation as concluded from nonassisted sputter depositions at different substrate temperatures. The formation of the chemically ordered crystalline B2 phase is accompanied by the expected transition from ferromagnetic to paramagnetic behavior of the films. In accordance with the different thermally induced structural recovery, we find a step-like magnetic transition to paramagnetic behavior after annealing for 1 h at T{sub A} = 300 °C for IBAD deposition, while PLD-grown films show a gradual decrease of ferromagnetic signals with rising annealing temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electron-Phonon Systems on a Universal Quantum Computer

We present an algorithm that extends existing quantum algorithms for simulating fermion systems in quantum chemistry and condensed matter physics to include bosons in general and phonons in particular. We introduce a qubit representation for the low-energy subspace of phonons which allows an efficient simulation of the evolution operator of the electron-phonon systems. As a consequence of the Nyquist-Shannon sampling theorem, the phonons are represented with exponential accuracy on a discretized Hilbert space with a size that increases linearly with the cutoff of the maximum phonon number. The additional number of qubits required by the presence of phonons scales linearly with the size of the system. The additional circuit depth is constant for systems with finite-range electron-phonon and phonon-phonon interactions and linear for long-range electron-phonon interactions. Our algorithm for a Holstein polaron problem was implemented on an Atos quantum learning machine quantum simulator employing the quantum phase estimation method. The energy and the phonon number distribution of the polaron state agree with exact diagonalization results for weak, intermediate, and strong electron-phonon coupling regimes.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

Scalable stable comb-to-tone integrated RF photonic drive for superconducting qubits

The recent advent of quantum computing has the potential to overhaul security, communications, and scientific modeling. Superconducting qubits are a leading platform that is advancing noise-tolerant intermediate-scale quantum processors. The implementation requires scaling to large numbers of superconducting qubits, circuit depths, and gate speeds, wherein high-purity RF signal generation and effective cabling transport are desirable. Fiber photonic-enhanced RF signal generation has demonstrated the principle of addressing both signal generation and transport requirements, supporting intermediate qubit numbers and robust packaging efforts; however, fiber-based approaches to RF signal distribution are often bounded by their phase instability. Here, we present a silicon photonic integrated circuit-based version of a photonic-enhanced RF signal generator that demonstrates the requisite stability, as well as a path towards the necessary signal fidelity.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Mechanisms Governing the Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems

This research project, which includes collaborators from INL and ORNL, focuses on the study of alloy 617 and alloy 800H that are candidates for applications as intermediate heat exchangers in GEN IV nuclear reactors, with an emphasis on the effects of grain size, grain boundaries and second phases on the creep properties; the mechanisms of dislocation creep, diffusional creep and cavitation; the onset of tertiary creep; and theoretical modeling for long-term predictions of materials behavior and for high temperature alloy design.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2015

Radiation-Hardened Circuitry Using Mask-Programmable Analog Arrays: Report 3

As the recent accident at Fukushima Daiichi so vividly demonstrated, telerobotic technologies capable of withstanding high radiation environments need to be readily available to enable operations, repair, and recovery under severe accident scenarios when human entry is extremely dangerous or not possible. Telerobotic technologies that enable remote operation in high dose rate environments have undergone revolutionary improvement over the past few decades. However, much of this technology cannot be employed in nuclear power environments because of the radiation sensitivity of the electronics and the organic insulator materials currently in use. This is a report of the activities involving Task 3 of the Nuclear Energy Enabling Technologies (NEET) 2 project Radiation Hardened Circuitry Using Mask-Programmable Analog Arrays. Evaluation of the performance of the system for both pre- and post-irradiation as well as operation at elevated temperature will be performed. Detailed performance of the system will be documented to ensure the design meets requirements prior to any extended evaluation. A suite of tests will be developed which will allow evaluation before and after irradiation and during temperature. Selection of the radiation exposure facilities will be determined in the early phase of the project. Radiation exposure will consist of total integrated dose (TID) up to 200 kRad or above with several intermediate doses during test. Dose rates will be in various ranges determined by the facility that will be used with a target of 30 kRad/hr. Many samples of the pre-commercial devices to be used will have been tested in previous projects to doses of at least 300 kRad and temperatures up to 125C. The complete systems will therefore be tested for performance at intermediate doses. Extended temperature testing will be performed up to the limit of the commercial sensors. The test suite performed at each test point will consist of operational testing of the three basic measurement functions plus electronic functional testing (power dissipation, voltage offset changes, noise variations, etc.). This suite will be developed as part of this task.

42 ENGINEERING↗
NASA NTRS1989

On the orthorhombic phase in ZrO2-based alloys

During TEM observation, a tetragonal (t) to orthorhombic (o) phase transformation often occurs in thin portions of ZrO2-containing foils. This transformation is stress-induced and in some senses artifactual, in that the reaction product is actually a high-pressure phase, relative to monoclinic (m) ZrO2, that can form from metastable t-ZrO2 in the TEM because its density is intermediate between t- and m-ZrO2. Examples of the formation of o-ZrO2 in a number of different systems are given.

Heuer, A. H.↗
NASA NTRS1994

Analyzing Seals With Two-Phase Flows

SEAL computer program analyzes steady-state performance of face seal with two-phase leakage flow. Calculates general trends of performance under both low- and high-leakage conditions and, by extrapolation, behavior in intermediate region. Parameters investigated include subcooling, coning of seal faces, speeds of rotation, conductivities of seal materials, and widths of seal faces. Program incorporates idealized mathematical models, and based on finite-difference approach. Written in FORTRAN 77.

Lau, S.↗
NASA NTRS1983

Analytic modeling of soot nucleation under fuel rich conditions

The objective of the present research is to construct a soot nucleation model according to a proposed chemical kinetic scheme to delineate quantitatively the nucleation mechanism in the soot formation process. Instead of following the traditional views which generally associate sooting with the homogeneous nucleation process in phase transformation or polymerization, we choose a chemical kinetic approach. In our proposed scheme the number of carbon atoms in the intermediate species between the fuel molecule and soot nuclei is continuously increased by radical additions. The number of hydrogen atoms in the intermediate species on the other hand is steadily decreased by radical dehydrogenation. When the number of carbon atoms in each of the intermediate molecules has exceeded a certain limit and the number of hydrogen atoms has fallen below a certain level, they may coagulate with one and another to form a larger molecule which is regarded as the initial soot nuclei in the present theory. Further coagulation and surface growth of the nuclei will lead to observable soot particles.

Yang, C. H.↗
NASA NTRS1999

Dynamics of Quasi-biennial Oscillations in Tropical Ocean-Atmosphere Coupled System

In this study, quasi-biennial oscillation (QBO) in atmosphere-ocean coupled system is investigated using intermediate coupled model. Observation studies show that the easterly zonal winds anomalies prevail over the equatorial western Pacific during the warm phase of El Nino/Southern Oscillation (ENSO). At the time scale of QBO, SST variations and east Asia Summer monsoon rainfall are closely linked to the eastward propagating zonal winds anomalies originated from Indian ocean. To investigate the effect of zonal wind anomalies over western Pacific on the evolution of ENSO, simple anomalous winds are added to the western part of model domain as external forcing. Wind forcing is parameterized as a function of SST anomalies in the eastern Pacific with time lag. Time lag is adopted to mimic the relation between east Asian monsoon and ENSO. The results shows that the winds anomalies make coupled system oscillate through generating forced Kelvin waves even without the western boundary reflection of Rossby waves. Kelvin waves generated by external forcing are also crucial for the model to oscillate as well as Rossby wave reflections at the western boundary. When the monsoon forced Kelvin wave is strong during the northern winter, the coupled system damped out very quickly. In certain range of external winds amplitude and time lag, the model El Nino shows QBO features. It is suggested that the external wind forcing which is related to summer monsoon flow over western Pacific intensify the negative feedback process of off-equatorial Rossby waves and modify the ENSO periodicity.

Kim, K.-M.↗