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At least 1,783 records · Page 99

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NASA NTRS2002

Temperature Variations from HST Imagery and Spectroscopy of NGC 7009

We present new HST/WFPC2 imagery and STIS long-slit spectroscopy of the planetary nebula NGC 7009. The primary goal was to obtain high spatial resolution of the intrinsic line ratio [O III] 4364/5008 and thereby evaluate the electron temperature (Te) and the mean-square Te variation (t(sup 2, sub A)) across the nebula. The observations here do not address Te fluctuation along the line of sight. The WFPC2 Te map is rather uniform; almost all values are between 9000 - 11,000 K, with the higher Te's closely coinciding with the inner He(++)-zone. The results indicate very small values - certainly less than 0.01 - for t(sup 2, sub A) throughout. Our STIS data allow an even more direct determination of Te and t(sup 2, sub A), albeit for a much smaller area than with WFPC2. We present results from binning the data along the slit into tiles that are 0.5 in square (matching the slit width). The average [O III] temperature using 45 tiles (excluding the central star and STIS fiducial bars) is 10,146 K; t(sup 2, sub A) is 0.0036. Although we have measured t(sup 2, sub A) in only 2-dimensions, we conclude that temperature fluctuations alone are unlikely to explain for NGC 7009 the large discrepancy between heavy element abundances inferred from emission lines that are collisionally excited compared with those that are due to recombination lines.

Rubin, R. H.↗

NASA NTRS2002

Origin of the Large Bandgap Bowing in Highly Mismatched Semiconductor Alloys

We use a combination of optical and soft x-ray fluorescence techniques to investigate the composition dependence of the band edge energies in ZnSe(1-x)Te(x) and ZnS(1-x)Te(x) alloys. The results reveal entirely different origins of the large bandgap bowing for alloys with small and large Te content. On the Te-rich side, the reduction of the bandgap is well explained by the band anticrossing interaction between the Se or S localized states and the ZnTe conduction band states. On the Se or S-rich side, an interaction between the localized Te states and the degenerate GAMMA valence bands of ZnSe or ZnS is responsible for the bandgap reduction and the rapid increase of the spin-orbit splitting with increasing Te concentration. Results of soft x-ray fluorescence experiments provide direct evidence for the valence band anticrossing interaction. The bandgap bowing over the entire composition range is accounted for by a linear interpolation between the conduction band anticrossing and valence band anticrossing models.

Wu, J.↗

NASA NTRS2004

Effects of Angle of Attack and Velocity on Trailing Edge Noise

Trailing edge (TE) noise measurements for a NACA 63-215 airfoil model are presented, providing benchmark experimental data for a cambered airfoil. The effects of flow Mach number and angle of attack of the airfoil model with different TE bluntnesses are shown. Far-field noise spectra and directivity are obtained using a directional microphone array. Standard and diagonal removal beamforming techniques are evaluated employing tailored weighting functions for quantitatively accounting for the distributed line character of TE noise. Diagonal removal processing is used for the primary database as it successfully removes noise contaminates. Some TE noise predictions are reported to help interpret the data, with respect to flow speed, angle of attack, and TE bluntness on spectral shape and peak levels. Important findings include the validation of a TE noise directivity function for different airfoil angles of attack and the demonstration of the importance of the directivity function s convective amplification terms.

Hutcheson, Florence V.↗

NASA NTRS2006

Effects of Angle of Attack and Velocity on Trailing Edge Noise

Hutcheson, Florence V.↗

NASA NTRS2015

Analysis of Advanced Thermoelectric Materials and Their Functional Limits

The world's demand for energy is increasing dramatically, but the best energy conversion systems operate at approximately 30% efficiency. One way to decrease energy loss is in the recovery of waste heat using thermoelectric (TE) generators. A TE generator is device that generates electricity by exploiting heat flow across a thermal gradient. The efficiency of a TE material for power generation and cooling is determined by the dimensionless Figure of Merit (ZT): ZT = S(exp. 2)sigmaT/κ: where S is the Seebeck coefficient, sigma is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. The parameters are not physically independent, but intrinsically coupled since they are a function of the transport properties of electrons. Traditional research on TE materials has focused on synthesizing bulk semiconductor-type materials that have low thermal conductivity and high electrical conductivity affording ZT values of 1. The optimization of the σ/κ ratio is difficult to achieve using current material formats, as these material constants are complementary. Recent areas of research are focusing on using nanostructural artifacts that introduce specific dislocations and boundary conditions that scatter the phonons. This disrupts the physical link between thermal (phonon) and electrical (electron) transport. The result is that κ is decreased without decreasing σ. These material formats give ZT values of up to 2 which represent approximately 18% energy gain from waste heat recovery. The next challenge in developing the next generation of TE materials with superior performance is to tailor the interconnected thermoelectric physical parameters of the material system. In order to approach this problem, the fundamental physics of each parameter S, sigma, and κ need to be physically understood in their context of electron/phonon interaction for the construction of new high ZT thermoelectric devices. Is it possible to overcome the physical limit imposed by of the effect of phonon lattice oscillation and energetic electrons towards thermal conductivity? Is the Seebeck coefficient, based on the difference in voltage over temperature gradient ( deltaV/deltaT), an intrinsic parameter of each material? All these parameters were manipulated using nano-bridge and twin-lattice structural concepts at the NASA Langley Research Center. This talk will review the current trend of TE research to optimize the ZT and discuss about new approaches on increasing ZT within functional limits of each parameter.

Kim, Hyun Jung↗

NASA NTRS2016

Development of Multi-Physics Dynamics Models for High-Frequency Large-Amplitude Structural Response Simulation

An analytic approach is demonstrated to reveal potential pyroshock-driven dynamic effects causing power losses in the Thermo-Electric (TE) module bars of the Mars Science Laboratory (MSL) Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). This study utilizes high-fidelity finite element analysis with SIERRA/PRESTO codes to estimate wave propagation effects due to large-amplitude suddenly-applied pyro shock loads in the MMRTG. A high fidelity model of the TE module bar was created with approximately 30 million degrees-of-freedom (DOF). First, a quasi-static preload was applied on top of the TE module bar, then transient tri-axial acceleration inputs were simultaneously applied on the preloaded module. The applied input acceleration signals were measured during MMRTG shock qualification tests performed at the Jet Propulsion Laboratory. An explicit finite element solver in the SIERRA/PRESTO computational environment, along with a 3000 processor parallel super -computing framework at NASA AMES, was used for the simulation. The simulation results were investigated both qualitatively and quantitatively. The predicted shock wave propagation results provide detailed structural responses throughout the TE module bar, and key insights into the dynamic response (i.e., loads, displacements, accelerations) of critical internal spring/piston compression systems, TE materials, and internal component interfaces in the MMRTG TE module bar. They also provide confidence on the viability of this high-fidelity modeling scheme to accurately predict shock wave propagation patterns within complex structures. This analytic approach is envisioned for modeling shock sensitive hardware susceptible to intense shock environments positioned near shock separation devices in modern space vehicles and systems.

Shock Waves↗

DOE OSTI2020

Materials Data on Sc6FeTe2 by Materials Project

Sc6FeTe2 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent Sc sites. In the first Sc site, Sc is bonded in a 4-coordinate geometry to two equivalent Fe and two equivalent Te atoms. Both Sc–Fe bond lengths are 2.62 Å. Both Sc–Te bond lengths are 3.04 Å. In the second Sc site, Sc is bonded in a 5-coordinate geometry to one Fe and four equivalent Te atoms. The Sc–Fe bond length is 2.96 Å. All Sc–Te bond lengths are 3.07 Å. Fe is bonded in a 9-coordinate geometry to nine Sc atoms. Te is bonded in a 9-coordinate geometry to nine Sc atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Sc6NiTe2 by Materials Project

Sc6NiTe2 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent Sc sites. In the first Sc site, Sc is bonded in a 4-coordinate geometry to two equivalent Ni and two equivalent Te atoms. Both Sc–Ni bond lengths are 2.63 Å. Both Sc–Te bond lengths are 3.03 Å. In the second Sc site, Sc is bonded in a 5-coordinate geometry to one Ni and four equivalent Te atoms. The Sc–Ni bond length is 3.05 Å. All Sc–Te bond lengths are 3.04 Å. Ni is bonded in a 9-coordinate geometry to nine Sc atoms. Te is bonded in a 9-coordinate geometry to nine Sc atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Dy6FeTe2 by Materials Project

Dy6FeTe2 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent Dy sites. In the first Dy site, Dy is bonded in a 5-coordinate geometry to one Fe and four equivalent Te atoms. The Dy–Fe bond length is 3.31 Å. All Dy–Te bond lengths are 3.23 Å. In the second Dy site, Dy is bonded in a 4-coordinate geometry to two equivalent Fe and two equivalent Te atoms. Both Dy–Fe bond lengths are 2.79 Å. Both Dy–Te bond lengths are 3.26 Å. Fe is bonded in a 9-coordinate geometry to nine Dy atoms. Te is bonded in a 9-coordinate geometry to nine Dy atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Lu8Te by Materials Project

Lu8Te crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are three inequivalent Lu sites. In the first Lu site, Lu is bonded in a 12-coordinate geometry to eight Lu and two equivalent Te atoms. There are a spread of Lu–Lu bond distances ranging from 3.29–3.62 Å. Both Lu–Te bond lengths are 3.12 Å. In the second Lu site, Lu is bonded in a 1-coordinate geometry to twelve Lu and one Te atom. There are four shorter (3.36 Å) and two longer (3.69 Å) Lu–Lu bond lengths. The Lu–Te bond length is 3.49 Å. In the third Lu site, Lu is bonded in a 11-coordinate geometry to eleven Lu atoms. Both Lu–Lu bond lengths are 3.69 Å. Te is bonded in a 9-coordinate geometry to nine Lu atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Sc6Te2Os by Materials Project

Sc6OsTe2 crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. there are two inequivalent Sc sites. In the first Sc site, Sc is bonded in a 4-coordinate geometry to two equivalent Os and two equivalent Te atoms. Both Sc–Os bond lengths are 2.68 Å. Both Sc–Te bond lengths are 3.01 Å. In the second Sc site, Sc is bonded in a 5-coordinate geometry to one Os and four equivalent Te atoms. The Sc–Os bond length is 2.97 Å. All Sc–Te bond lengths are 3.10 Å. Os is bonded in a 9-coordinate geometry to nine Sc atoms. Te is bonded in a 9-coordinate geometry to nine Sc atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ni(TePd)2 by Materials Project

Pd2NiTe2 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. Pd is bonded in a 10-coordinate geometry to three equivalent Pd, two equivalent Ni, and five equivalent Te atoms. There are one shorter (2.93 Å) and two longer (3.09 Å) Pd–Pd bond lengths. Both Pd–Ni bond lengths are 2.93 Å. There are a spread of Pd–Te bond distances ranging from 2.67–3.03 Å. Ni is bonded in a 10-coordinate geometry to four equivalent Pd, two equivalent Ni, and four equivalent Te atoms. Both Ni–Ni bond lengths are 2.58 Å. All Ni–Te bond lengths are 2.54 Å. Te is bonded in a 7-coordinate geometry to five equivalent Pd and two equivalent Ni atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Co(TePd)2 by Materials Project

Pd2CoTe2 crystallizes in the orthorhombic Ibam space group. The structure is three-dimensional. Co is bonded in a 10-coordinate geometry to two equivalent Co, four equivalent Pd, and four equivalent Te atoms. Both Co–Co bond lengths are 2.63 Å. All Co–Pd bond lengths are 2.92 Å. All Co–Te bond lengths are 2.49 Å. Pd is bonded in a 10-coordinate geometry to two equivalent Co, three equivalent Pd, and five equivalent Te atoms. There are one shorter (2.91 Å) and two longer (3.12 Å) Pd–Pd bond lengths. There are a spread of Pd–Te bond distances ranging from 2.68–2.96 Å. Te is bonded in a 7-coordinate geometry to two equivalent Co and five equivalent Pd atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Hf5Te4 by Materials Project

Hf5Te4 is Titanium telluride structured and crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 5-coordinate geometry to five equivalent Te atoms. There are four shorter (2.92 Å) and one longer (2.93 Å) Hf–Te bond lengths. In the second Hf site, Hf is bonded in a distorted square co-planar geometry to four equivalent Te atoms. All Hf–Te bond lengths are 3.13 Å. Te is bonded in a 6-coordinate geometry to six Hf atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on TlTe by Materials Project

TlTe crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Tl1+ is bonded in a 6-coordinate geometry to eight Te1- atoms. There are a spread of Tl–Te bond distances ranging from 3.46–4.11 Å. There are three inequivalent Te1- sites. In the first Te1- site, Te1- is bonded in a 10-coordinate geometry to eight equivalent Tl1+ and two equivalent Te1- atoms. Both Te–Te bond lengths are 3.11 Å. In the second Te1- site, Te1- is bonded in a 2-coordinate geometry to eight equivalent Tl1+ and six Te1- atoms. There are two shorter (3.11 Å) and four longer (3.40 Å) Te–Te bond lengths. In the third Te1- site, Te1- is bonded in a 10-coordinate geometry to eight equivalent Tl1+ and two equivalent Te1- atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Gd2SiTeO4 by Materials Project

Gd2SiTeO4 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. there are two inequivalent Gd3+ sites. In the first Gd3+ site, Gd3+ is bonded in a 6-coordinate geometry to four equivalent Te2- and six O2- atoms. There are two shorter (3.27 Å) and two longer (3.71 Å) Gd–Te bond lengths. There are a spread of Gd–O bond distances ranging from 2.43–2.49 Å. In the second Gd3+ site, Gd3+ is bonded in a 6-coordinate geometry to three equivalent Te2- and six O2- atoms. There are a spread of Gd–Te bond distances ranging from 3.13–3.36 Å. There are a spread of Gd–O bond distances ranging from 2.44–2.64 Å. Si4+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.65 Å) and two longer (1.67 Å) Si–O bond length. Te2- is bonded in a 1-coordinate geometry to seven Gd3+, two equivalent Te2-, and twelve O2- atoms. Both Te–Te bond lengths are 3.74 Å. There are a spread of Te–O bond distances ranging from 3.29–3.83 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to three Gd3+, one Si4+, and three equivalent Te2- atoms. In the second O2- site, O2- is bonded in a 1-coordinate geometry to three Gd3+, one Si4+, and three equivalent Te2- atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on TlTe by Materials Project

TlTe crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. Tl1+ is bonded in a 7-coordinate geometry to three equivalent Tl1+ and seven Te1- atoms. There are one shorter (3.58 Å) and two longer (3.79 Å) Tl–Tl bond lengths. There are a spread of Tl–Te bond distances ranging from 3.49–3.72 Å. There are three inequivalent Te1- sites. In the first Te1- site, Te1- is bonded in a 10-coordinate geometry to eight equivalent Tl1+ and two equivalent Te1- atoms. Both Te–Te bond lengths are 3.16 Å. In the second Te1- site, Te1- is bonded to four equivalent Tl1+ and four Te1- atoms to form corner-sharing TeTl4Te4 hexagonal bipyramids. There are two shorter (3.02 Å) and two longer (3.16 Å) Te–Te bond lengths. In the third Te1- site, Te1- is bonded in a 9-coordinate geometry to eight equivalent Tl1+ and one Te1- atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on MnTePd by Materials Project

PdMnTe is half-Heusler structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mn is bonded to four equivalent Pd and six equivalent Te atoms to form a mixture of distorted corner and face-sharing MnTe6Pd4 tetrahedra. All Mn–Pd bond lengths are 2.75 Å. All Mn–Te bond lengths are 3.17 Å. Pd is bonded in a body-centered cubic geometry to four equivalent Mn and four equivalent Te atoms. All Pd–Te bond lengths are 2.75 Å. Te is bonded in a 10-coordinate geometry to six equivalent Mn and four equivalent Pd atoms.

36 MATERIALS SCIENCE↗