Search NASA⌕ Search

SEARCH · Search NASA

Results for “formatting”

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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Monitoring solvent dynamics and ion associations in the formation of cubic octamer polyanion in tetramethylammonium silicate solutions

NMR methods were utilized to monitor the in situ structural and dynamic changes of various species in highly alkaline tetramethylammonium (TMA) silicate solutions. Quantitative 29Si NMR, 1H, 2H, and 17O relaxation NMR, and 1H and 29Si diffusion NMR of silicates, TMA, H2O and D2O demonstrate that the growth of the cubic octamer Q38 is accompanied by reduced water mobility and increasing TMA coordination number per Q38, which reaches an equilibrium value of 4.5 at 15 °C. Temperature-dependent measurements further reveal that the increased control over speciation by TMA at lower temperatures results from the more stable ion associations via slower solvent motions.

Chen, Ying↗
DOE OSTI2018

Exciton photoluminescence and benign defect complex formation in zinc tin nitride

Emerging photovoltaic materials need to prove their viability by demonstrating excellent electronic properties. In ternary and multinary semiconductors, disorder and off-stoichiometry often cause defects that limit the potential for high-efficiency solar cells. We report on Zn-rich ZnSnN 2 (Zn/(Zn + Sn) = 0.67) photoluminescence, high-resolution X-ray diffraction, and electronic structure calculations based on Monte-Carlo structural models. The mutual compensation of Zn excess and O incorporation affords a desirable reduction of the otherwise degenerate n-type doping, but also leads to a strongly off-stoichiometric and disordered atomic structure. It is therefore remarkable that we observe only near-edge photoluminescence from well-resolved excitons and shallow donors and acceptors. Based on first principles calculations, this result is explained by the mutual passivation of Zn Sn and O N defects that renders both electronically benign. The calculated bandgaps range between 1.4 and 1.8 eV, depending on the degree of non-equilibrium disorder. The experimentally determined value of 1.5 eV in post-deposition annealed samples falls within this interval, indicating that further bandgap engineering by disorder control should be feasible via appropriate annealing protocols.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Production, formation, and transport of high-brightness atomic hydrogen beam studies for the relativistic heavy ion collider polarized source upgrade

The RHIC polarized H{sup −} ion source had been successfully upgraded to higher intensity and polarization by using a very high brightness fast atomic beam source developed at BINP, Novosibirsk. In this source the proton beam is extracted by a four-grid multi-aperture ion optical system and neutralized in the H{sub 2} gas cell downstream from the grids. The proton beam is extracted from plasma emitter with a low transverse ion temperature of ∼0.2 eV which is formed by plasma jet expansion from the arc plasma generator. The multi-hole grids are spherically shaped to produce “geometrical” beam focusing. Proton beam formation and transport of atomic beam were experimentally studied at test bench.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Zonal flow formation in the presence of ambient mean shear

The effect of mean shear flows on zonal flow formation is considered in the contexts of plasma drift wave turbulence and quasi-geostrophic turbulence models. The generation of zonal flows by modulational instability in the presence of large-scale mean shear flows is studied using the method of characteristics as applied to the wave kinetic equation. It is shown that mean shear flows reduce the modulational instability growth rate by shortening the coherency time of the wave spectrum with the zonal shear. The scalings of zonal flow growth rate and turbulent vorticity flux with mean shear are determined in the strong shear limit.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Formation of ultracold {sup 7}Li{sup 85}Rb molecules in the lowest triplet electronic state by photoassociation and their detection by ionization spectroscopy

We report the formation of ultracold {sup 7}Li{sup 85}Rb molecules in the a{sup 3}Σ{sup +} electronic state by photoassociation (PA) and their detection via resonantly enhanced multiphoton ionization (REMPI). With our dual-species Li and Rb magneto-optical trap apparatus, we detect PA resonances with binding energies up to ∼62 cm{sup −1} below the {sup 7}Li 2s {sup 2}S{sub 1/2} + {sup 85}Rb 5p {sup 2}P{sub 1/2} asymptote. In addition, we use REMPI spectroscopy to probe the a{sup 3}Σ{sup +} state and excited electronic 3{sup 3}Π and 4{sup 3}Σ{sup +} states and identify a{sup 3}Σ{sup +} (v″ = 7–13), 3{sup 3}Π (v{sub Π}′ = 0–10), and 4{sup 3}Σ{sup +} (v{sub Σ}′ = 0–5) vibrational levels. Our line assignments agree well with ab initio calculations. These preliminary spectroscopic studies on previously unobserved electronic states are crucial to discovering transition pathways for transferring ultracold LiRb molecules created via PA to deeply bound rovibrational levels of the electronic ground state.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Brownmillerite Phase Formation and Evolution in Epitaxial Strontium Ferrite Heterostructures

By controlling the synthesis and process conditions, we show that the oxygen vacancy channels (OVCs) of Brownmillerite-structured SrFeO2.5+? (0=??0.5) thin films can be oriented differently on the same LaAlO3(001) substrate due to either a bottom up or top down synthesis route. The brownmillerite structure formation and evolution processes yield distinctively different optical and electronic properties, owing to the difference in the oxygen content and OVC configuration in the resultant films. Moreover, we also show that in situ transmission electron microscopy (TEM) can induce oxygen loss and drive a phase transition from perovskite SrFeO3 to brownmillerite SrFeO2.5+? with mixed horizontally and vertically aligned OVCs. The dimensionality change during the TEM sample preparation makes the bottom up and top down model not applicable. Our results offer further insight into the phase stability and oxygen-diffusion mechanisms, which is important for the predictive synthesis of novel functional materials.

SrFeO3-d, compressive strain, oxygen vacancy chann↗
DOE OSTI2013

Formation of compact clusters from high resolution hybrid cosmological simulations

The early universe hosted a large population of small dark matter 'minihalos' that were too small to cool and form stars on their own. These existed as static objects around larger galaxies until acted upon by some outside influence. Outflows, which have been observed around a variety of galaxies, can provide this influence in such a way as to collapse, rather than disperse, the minihalo gas. Gray and Scannapieco performed an investigation in which idealized spherically symmetric minihalos were struck by enriched outflows. Here we perform high-resolution cosmological simulations that form realistic minihalos, which we then extract to perform a large suite of simulations of outflow-minihalo interactions including non-equilibrium chemical reactions. In all models, the shocked minihalo forms molecules through non-equilibrium reaction, and then cools to form dense, chemically homogenous clumps of star-forming gas. The formation of these high-redshift clusters may be observable with the next generation of telescopes and the largest of them should survive to the present-day, having properties similar to halo globular clusters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

An evolutionary model for collapsing molecular clouds and their star formation activity. II. Mass dependence of the star formation rate

We discuss the evolution and dependence on cloud mass of the star formation rate (SFR) and efficiency (SFE) of star-forming molecular clouds (MCs) within the scenario that clouds are undergoing global collapse and that the SFR is controlled by ionization feedback. We find that low-mass clouds (M {sub max} ≲ 10{sup 4} M {sub ☉}) spend most of their evolution at low SFRs, but end their lives with a mini-burst, reaching a peak SFR ∼10{sup 4} M {sub ☉} Myr{sup –1}, although their time-averaged SFR is only (SFR) ∼ 10{sup 2} M {sub ☉} Myr{sup –1}. The corresponding efficiencies are SFE{sub final} ≲ 60% and (SFE) ≲ 1%. For more massive clouds (M {sub max} ≳ 10{sup 5} M {sub ☉}), the SFR first increases and then reaches a plateau because the clouds are influenced by stellar feedback since earlier in their evolution. As a function of cloud mass, (SFR) and (SFE) are well represented by the fits (SFR) ≈ 100(1 + M {sub max}/1.4 × 10{sup 5} M {sub ☉}){sup 1.68} M {sub ☉} Myr{sup –1} and (SFE) ≈ 0.03(M {sub max}/2.5 × 10{sup 5} M {sub ☉}){sup 0.33}, respectively. Moreover, the SFR of our model clouds follows closely the SFR-dense gas mass relation recently found by Lada et al. during the epoch when their instantaneous SFEs are comparable to those of the clouds considered by those authors. Collectively, a Monte Carlo integration of the model-predicted SFR(M) over a Galactic giant molecular cloud mass spectrum yields values for the total Galactic SFR that are within half an order of magnitude of the relation obtained by Gao and Solomon. Our results support the scenario that star-forming MCs may be in global gravitational collapse and that the low observed values of the SFR and SFE are a result of the interruption of each SF episode, caused primarily by the ionizing feedback from massive stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Formation of short-range magnetic order and avoided ferromagnetic quantum criticality in pressurized LaCrGe 3

LaCrGe 3 has attracted attention as a paradigm example of the avoidance of ferromagnetic (FM) quantum criticality in an itinerant magnet. In this work, we combined thermodynamic (specific heat and thermal expansion), transport, x-ray, and neutron scattering as well as μSR measurements to obtain insights on the temperature-pressure phase diagram of LaCrGe 3 . Consistent with previous studies of the phase diagram by transport measurements, our thermodynamic data shows clearly that the FM transition at T FM changes its character from second order to first order when it is suppressed to low temperatures by pressure. In addition, previous studies demonstrated that for high pressures a new phase occurs below T 2 , which was proposed to be a long-wavelength antiferromagnetic state (AFM q ). In this paper, we provide evidence from our thermodynamic data that this phase transition is preceded by yet another phase transition at T 1 >T 2 . Our μSR data indicate that full magnetic volume fraction is only established below T 2 , but that this magnetism is characterized by a short correlation length. Within the experimental resolution, our neutron-scattering data is not able to identify any magnetic Bragg peaks. Overall, the microscopic magnetic data is therefore consistent with the formation of FM clusters in the proximity of the avoided FM quantum critical point in LaCrGe 3 . This conclusion is at odds with the previous proposal of AFM q order and raises questions on the role of disorder in this stochiometric compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

X-ray diffraction study of laser-driven solid-state diffusional mixing and new phase formation in Ni-Pt multilayers [X-ray diffraction study of laser-driven solid-state diffusional mixing and new phase formation]

An in situ optical pump and x-ray probe technique has been utilized to study photoinitiated solid-state diffusion in a Ni-Pt multilayer system. Hard x-ray diffraction has been used to follow the systematic growth of the NiPt alloy as a function of laser intensity and total energy deposited. It is observed that new phase growth can be driven in as little as one laser pulse, and that repeated photoexcitation can completely convert the entire multilayer structure into a single metallic alloy. In conclusion, the data suggest that lattice strain relaxation takes place prior to atomic diffusion and the formation of a NiPt alloy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗