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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Dependence of Lamellar Eutectic Growth with Convection on Boundary Conditions and Geometric Confinement: A Phase-Field Lattice-Boltzmann Study

Simulating eutectic growth with convection is challenging because of the enormous computing demand resulting from the required domain size compared with the eutectic scale. In this study, a phase-field lattice-Boltzmann approach was employed to reproduce the eutectic growth with convection (both natural and forced). To enable and accelerate large-scale simulations, a parallel-adaptive mesh refinement algorithm was developed to combine with this numerical approach. The effects of the boundary conditions and the geometric confinement on the eutectic growth with convection were systematically investigated in the Al-Cu eutectic alloy. Results showed that both boundary conditions and the geometric confinement altered the eutectic evolution by affecting the distributions of the solute and velocity ahead of the eutectic solid/liquid interface. As the first attempt to explore the two factors on the eutectic growth with convection, our thorough investigation lays a foundation for modeling the coupled convection–solute eutectic evolution.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Austempering Temperature and Time on the Microstructure and Mechanical Properties of Ductile Iron Weldment Using Developed Coated Electrode

Sound welded joints of ductile iron were first made by developing coated electrodes as well as weld procedure. The weldments were then austenitized at 900 °C for 2-h holding time followed by austempering at 300 and 350 °C for three different holding times (1.5, 2 and 2.5 h) at each austempering temperature. The influence of austempering temperature and time on the microstructural and mechanical properties was studied. Microstructural characterization, phase analysis, microhardness and mechanical properties were performed to understand the effect of austempering heat treatment on microstructure, austempering kinetics and mechanical properties of welded joints. In spite of significant variation in microstructures among all the three zones of DI weldment before austempering, the response of both weld metal and HAZ to austempering heat treatment similar to a base metal was noted. However, a significant variation in matrix structures (bainitic ferrite, retained austenite) as well as graphite nodules among the three zones was observed with changing the austempering temperature and holding time. Also, 100% joint efficiency of the welded joints was achieved at both 300 and 350 °C for 2-h holding time. Hardness and charpy impact toughness mostly depended on the volume fraction of retained austenite and carbon content. Based on the results of tensile and charpy impact testing, 350 °C and 2-h holding time could be considered as an optimum austempering condition for ADI weldment.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Phase 1-2 Study of Stereotactic Ablative Radiotherapy Including Regional Lymph Node Irradiation in Patients With High-Risk Prostate Cancer (SATURN): Early Toxicity and Quality of Life

Five-fraction stereotactic ablative radiation therapy appears to be gaining popularity in treatment of prostate cancer, but it has not been extensively tested in the context of pelvic radiation. The objective of this prospective prostate and pelvic SABR study is to report the acute toxicity, late toxicity, and quality of life (QoL) after study completion.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Time-Resolved SAXS/WAXS Study of the Phase Behavior and Microstructural Evolution of Drug/PEG Solid Dispersions

Simultaneous small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) was employed to elucidate the physical state and location of various small molecule drugs blended with polyethylene glycol (PEG), as well as the time dependent microstructural evolution of the systems. Samples were prepared by comelting physical mixtures of the drug and PEG, followed by solidification at 25 C. The model drugs selected encompassed a wide variety of physicochemical properties in terms of crystallization tendency and potential for interaction with PEG. It was observed that compounds which crystallized rapidly and had weak interactions with PEG tended to be excluded from the interlamellar region of the PEG matrix. In contrast, drugs which had favorable interactions with PEG were incorporated into the interlamellar regions of the polymer up until the point at which the drug crystallized whereby phase separation occurred. These factors are likely to impact the effectiveness of drug/PEG systems as drug delivery systems.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures

Establishing the phase diagram of hydrogen is a major challenge for experimental and theoretical physics. Experiment alone cannot establish the atomic structure of solid hydrogen at high pressure, because hydrogen scatters X-rays only weakly. Instead, our understanding of the atomic structure is largely based on density functional theory (DFT). By comparing Raman spectra for low-energy structures found in DFT searches with experimental spectra, candidate atomic structures have been identified for each experimentally observed phase. Unfortunately, DFT predicts a metallic structure to be energetically favoured at a broad range of pressures up to 400 GPa, where it is known experimentally that hydrogen is non-metallic. Here we show that more advanced theoretical methods (diffusion quantum Monte Carlo calculations) find the metallic structure to be uncompetitive, and predict a phase diagram in reasonable agreement with experiment. This greatly strengthens the claim that the candidate atomic structures accurately model the experimentally observed phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Study of second phase in bioabsorbable magnesium alloys: Phase stability evaluation via Dmol{sup 3} calculation

Thermodynamical stabilities of four conventional second phases as well as magnesium matrix in bioabsorbable magnesium alloys were investigated theoretically via computer calculation method. Model of individual phase and systems including phase and four water molecular (phase-4H{sub 2}O) were established to simulate the in vitro and in vivo environment. Local orbital density functional theory approach was applied to calculate the total energy for the individual phase and phase-4H{sub 2}O system. The results demonstrated that all the second phases possessed higher phase stability compared with magnesium matrix, but the phase stability was quite different for different types of second phases or second phase-4H{sub 2}O systems. Furthermore, a schematic process of inflammation reaction caused by magnesium alloy implants was proposed for the further evaluation on biocompatibility of different second phases.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A numerical study of the phase behaviors of drug particle/star triblock copolymer mixtures in dilute solutions for drug carrier application

The complex microstructures of drug particle/ABA star triblock copolymer in dilute solutions have been investigated by a theoretical approach which combines the self-consistent field theory and the hybrid particle-field theory. Simulation results reveal that, when the volume fraction of drug particles is smaller than the saturation concentration, the drug particle encapsulation efficiency is 100%, and micelle loading capacity increases with increasing particle volume fraction. When the volume fraction of drug particles is equal to the saturation concentration, the micelles attain the biggest size, and micelle loading capacity reaches a maximum value which is independent of the copolymer volume fraction. When the volume fraction of drug particles is more than the saturation concentration, drug particle encapsulation efficiency decreases with increasing volume fraction of drug particles. Furthermore, it is found that the saturation concentration scales linearly with the copolymer volume fraction. The above simulation results are in good agreement with experimental results.

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

A study of the phase transition and magnetocaloric effect in multiferroic La{sub 2}MnNiO{sub 6} single crystals

Magnetic and magnetocaloric properties of single crystal double perovskite La{sub 2}MnNiO{sub 6} have been investigated in details. Its ordered phase with a high Curie temperature (T{sub C} = 280 K) exhibits a significant refrigerant capacity around room temperature. A model based on the mean field theory approximation has been used in order to quantify the magnetic and magnetocaloric properties in the ordered La{sub 2}MnNiO{sub 6}. The magnetization and entropy changes were satisfactorily simulated as a function of temperature and magnetic field. On the other hand, the presence of cationic disorder in La{sub 2}MnNiO{sub 6} phases allows to shift the Curie point to low temperature without a significant change in the magnetocaloric performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Strain-assisted current-induced magnetization reversal in magnetic tunnel junctions: A micromagnetic study with phase-field microelasticity

Effect of substrate misfit strain on current-induced in-plane magnetization reversal in CoFeB-MgO based magnetic tunnel junctions is investigated by combining micromagnetic simulations with phase-field microelasticity theory. It is found that the critical current density for in-plane magnetization reversal decreases dramatically with an increasing substrate strain, since the effective elastic field can drag the magnetization to one of the four in-plane diagonal directions. A potential strain-assisted multilevel bit spin transfer magnetization switching device using substrate misfit strain is also proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Time-resolved x-ray diffraction and Raman studies of the phase transition mechanisms of methane hydrate

The mechanisms by which methane hydrate transforms from an sI to sH structure and from an sH to filled-ice Ih structure were examined using time-resolved X-ray diffractometry (XRD) and Raman spectroscopy in conjunction with charge-coupled device camera observation under fixed pressure conditions. The XRD data obtained for the sI–sH transition at 0.8 GPa revealed an inverse correlation between sI and sH, suggesting that the sI structure is replaced by sH. Meanwhile, the Raman analysis demonstrated that although the 12-hedra of sI are retained, the 14-hedra are replaced sequentially by additional 12-hedra, modified 12-hedra, and 20-hedra cages of sH. With the sH to filled-ice Ih transition at 1.8 GPa, both the XRD and Raman data showed that this occurs through a sudden collapse of the sH structure and subsequent release of solid and fluid methane that is gradually incorporated into the filled-ice Ih to complete its structure. This therefore represents a typical reconstructive transition mechanism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

High temperature phase stability in Li{sub 0.12}Na{sub 0.88}NbO{sub 3}: A combined powder X-ray and neutron diffraction study

The phase stabilities of ecofriendly piezoelectric material of lithium doped sodium niobate for composition Li{sub 0.12}Na{sub 0.88}NbO{sub 3} (LNN12) have been investigated by a combination of powder X-ray and neutron diffraction techniques in the temperature range of 300–1100 K. We observed interesting changes with appearance or disappearance of the super-lattice reflections in the powder diffraction patterns. Unambiguous experimental evidence is shown for coexistence of paraelectric and ferroelectric orthorhombic phases in the temperature range of 525 K to 675 K. We identified the correct crystal structure of LNN12 with temperature and correlated it with observed anomaly in the physical properties. Identification of crystal structure also helps in the mode assignments in Raman and infrared spectroscopies. We argued that application of chemical pressure as a result of Li substitution in NaNbO{sub 3} matrix favors the freezing of zone centre phonons in contrast to the freezing of zone boundary phonons in pure NaNbO{sub 3} with the variation of temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

In-situ X-ray diffraction studies of the phase transformations and structural states of B2, R and B19′ phases in Ti{sub 49.5}Ni{sub 50.5} alloy

The martensitic transformation, Debye–Waller factor, mean-square atomic displacements and the coefficient of thermal expansion on cooling of the Ti{sub 49.5}Ni{sub 50.5} shape memory alloy were examined using in-situ X-ray diffraction. It was revealed B2→R (T{sub R} ≡ T = 273 ± 10 K) along with B2→B19’ (M{sub s} ≡ T = 273 ± 10 K) transitions occur. It was found that Debye–Waller factor and mean-square displacement of B2 phase undergo significant increase as functions of temperature when phase transition B2→R and B2→B19’ take place. The analysis of the thermal expansion coefficient of the B2 phase indicates that the value of a increases almost linearly while cooling.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Electronic spectra of 2- and 3-tolunitrile in the gas phase. I. A study of methyl group internal rotation via rovibronically resolved spectroscopy

Rotationally resolved fluorescence excitation spectra of the origin bands in the S{sub 1}←S{sub 0} transition of 2-tolunitrile (2TN) and 3-tolunitrile (3TN) have been recorded in the collision-free environment of a molecular beam. Analyses of these data provide the rotational constants of each molecule and the potential energy curves governing the internal rotation of the attached methyl groups in both electronic states. 2TN exhibits much larger barriers along this coordinate than 3TN. Interestingly, the electronic transition dipole moment in both molecules is markedly influenced by the position of the attached methyl group rather than the position of the cyano group; possible reasons for this intriguing behavior are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗