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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Effect of Tilt Angle on the Morphology of SiC Epitaxial Films Grown on Vicinal (0001) SiC Substrates

In this study of 4H-SiC and 6H-SiC epitaxial films we found that film morphology was strongly dependent on the tilt angle of the substrate. Large surface steps (up to 25 nm high) due to step bunching were more prevalent at smaller tilt angles. Also, 4H films were more susceptible than 6H to 3C-SiC inclusions during growth. The lateral growth of steps from screw dislocations in low-tilt-angle substrates demonstrated that step bunching on the atomic scale was anisotropic with respect to growth direction for both 4H-SiC and 6H-SiC. A model explaining this behavior is presented. We observed and directly measured the Burgers vector of a 'super' screw dislocation in a 6H-SiC epilayer.

Powell, J. A.↗
NASA NTRS1980

Radar observations of Saturn's rings at intermediate tilt angles

The 12.6-cm-wavelength radar observations of Saturn's rings, corresponding to ring-plane tilt angles of 18.2, 11.7, and 5.6 degrees, respectively, are reported. Measurements of geometric albedo and circular polarization ratio are used to investigate acceptable ring models and radar scattering properties of individual particles. Attention is given to the dependence of the rings' polarization properties on wavelength or tilt angle, or both. All large-particle monolayer models of Saturn's rings are ruled out; however, extended-layer models postulating ice or metal particles are compatible with the radar albedo measurements and are less severely restricted by the polarization data.

Ostro, S. J.↗
NASA NTRS1991

Controlled growth of 3C-SiC and 6H-SiC films on low-tilt-angle vicinal (0001) 6H-SiC wafers

It has been found that, with proper pregrowth surface treatment, 6H-SiC single-crystal films can be grown by chemical vapor deposition (CVD) at 1450 C on vicinal (0001) 6H-SiC with tilt angles as small as 0.1 deg. Previously, tilt angles of greater than 1.5 deg were required to achieve 6H on 6H at this growth temperature. In addition, 3C-SiC could be induced to grow within selected regions on the 6H substrate. the 3C regions contained few (or zero) double-positioning boundaries and a low density of stacking faults. A new growth model is proposed to explain the control of SiC polytype in this epitaxial film growth process.

Powell, J. A.↗
NASA NTRS1972

Precipitation of low energy electrons at high latitudes: Effects of substorms, interplanetary magnetic field and dipole tilt angle

Data from the auroral particles experiment on OGO-4 were used to study effects of substorm activity, interplanetary magnetic field latitutde, and dipole tilt angle on high-latitude precipitation of 700 eV electrons. It was found that: (1) The high-latitude zone of 700 eV electron precipitation in late evening and early morning hours moves equatorward by 5 to 10 deg during substorms. (2) The low-latitude boundary of polar cusp electron precipitation at 9 to 15 hours MLT also moves equatorward by several degrees during substorms and, in the absence of significant substorm activity, after a period of southward interplanetary magnetic field. (3) With times containing substorm activity or a southward interplanetary magnetic field eliminated, the low-latitude boundary of polar cusp electron precipitation is found to move by approximately 4 deg over the total yearly range of tilt angles. At maximum winter and summer conditions the invariant latitude of the boundary is shown to shift by approximately -3 deg and +1 deg respectively from its equinox location.

Burch, J. L.↗
DOE OSTI2026

ICRF near-field effects sensitivity to magnetic tilt-angle

This paper complements the study reported in G. Urbanczyk et al 2025 Nucl. Fusion 65 046018 by investigating how near-field effects from Ion Cyclotron Range of Frequency (ICRF) antennas depend on the magnetic geometry, particularly focusing on the sensitivity of rectified sheath potentials and associated impurity production to variations in magnetic field tilt-angle. Simulations were conducted using Petra-M, employing a flat model of the ASDEX Upgrade (AUG) three-strap antenna, and COMSOL, utilizing a curved model of the WEST antenna. Results demonstrate indications of sensitivity of the rectified sheath potentials and impurity sputtering to the alignment of Faraday screen bars with the magnetic field lines, emphasizing the necessity for careful consideration of geometric alignment in antenna design for fusion devices. This trend is consistent with experimental data measured with various diagnostics.

Urbanczyk, Guillaume [Universite de Lorraine, Nanc↗
DOE OSTI2024

Tuning Perovskites’ Hydration-Induced Chemical Expansion with Octahedral Tilt Angles

Hydration-induced strains in proton-conducting oxides compromise chemo-mechanical stability when these materials are applied in protonic ceramic electrochemical cells. Here, to develop design principles for zero-strain materials, we systematically studied the hydration coefficients of chemical expansion (CCEs) in perovskite (Sr, Ba)(Ce, Zr, Y)O 3–x solid solutions with in situ dilatometry and thermogravimetric analysis in the range of 430–630 °C. By including and decoupling a wide range of tolerance factors and lattice parameters, we were able to identify a minimum in hydration CCEs (0–0.02) at intermediate tolerance factor values (t ≈ 0.95). Conversely, despite expectations of lower CCEs in larger unit cells, no general trend in CCE versus lattice parameter was found, and opposite trends could be seen for Sr(Ce, Zr, Y)O 3–x versus Ba(Ce, Zr, Y)O 3–x separately. In situ neutron diffraction (ND) enabled atomistic insight. Upon decreasing t, chemical strain anisotropy increased, but this trend did not match the U-shaped dependence of macroscopic CCEs on t. Instead, perovskites with intermediate t, hosting intermediate octahedral tilt angles in the nominally dry state, underwent the largest change in the B–O–B angles during hydration. Accommodating hydration through decreasing B–O–B angles is beneficial because it does not result in large lattice parameter changes. We propose an intermediate tolerance factor as a simple structural descriptor to enable near-zero hydration strains in proton-conducting perovskites.

36 MATERIALS SCIENCE↗
NASA NTRS1979

Low tilt angle photometry and the thickness of Saturn's rings

Nine photographic plates taken by Focas and Dollfus (1969) at the moment of the 1966 passage of the earth through the ring plane of Saturn have been remeasured. The value 0.8 (+2.3, -0.8) km is obtained for the ring thickness. The observed transmitted radiation through the rings at two distances from the planet suggests that there are density fluctuations in Ring A with the low density areas having an optical thickness less than 0.13. The radiation reflected by the outermost part of the ring layer can be explained in terms of particles similar to those in the bulk of the rings. The time of the passage of the earth through the ring plane was found to be December 18 at 07h plus or minus 4h UT in 1966.

Lumme, K.↗
NASA NTRS1979

Azimuthal brightness variations of Saturn's rings. III - Observations at tilt angle B approximately equal to 11.5 deg

The brightness variation in Saturn's ring A with orbital phase of the ring particles does not change significantly as the declination of the earth, B, decreases from about 16.5 to 11.5 deg and is noticeably more pronounced than when the rings are fully open. The present data are also not inconsistent with earlier results suggesting that the amplitude of this azimuthal effect diminishes near opposition.

Lumme, K.↗
NASA NTRS1995

Eye movements and motion perception induced by off-vertical axis rotation (OVAR) at small angles of tilt after spaceflight

The nystagmus and motion perception of two astronauts were recorded during Earth-vertical axis rotation and during off-vertical axis rotation (OVAR) before and after 7 days of spaceflight. Postflight, the peak velocity and duration of per- and postrotatory nystagmus during velocity steps about the Earth-vertical axis were the same as preflight values. During OVAR at constant velocity (45/s, tilt angles successively 5, 10, and 15 degrees), the mean horizontal slow-phase eye velocity (bias), produced by the 'velocity storage mechanism' in the vestibular system, and the peak-to-peak amplitude (modulation) in horizontal eye velocity and position, generated from the output of otolith afferents, were also the same before as after flight. There were, however, changes in the vertical eve position and in the perceived body motion during OVAR. The angle of the perceived body path described as a cone was larger in both astronauts postflight. One astronaut experienced either a large cone angle with its axis upright, or a smaller cone angle with its axis tilted backwards, accompanied by an upward vertical eye drift. These results suggest an increase in the sensitivity of the otolithic system after spaceflight and a longer period of readaptation to Earth's gravity for otolith-induced responses than for canal-induced responses. Our data support the hypothesis that just after spaceflight the CNS generally interprets changes in the otolith signals to be due to translation rather than to tilt.

manned↗
NASA NTRS1970

Perception of the upright and susceptibility to motion sickness as functions of angle of tilt and angular velocity in off-vertical rotation

Motion sickness susceptibility of four normal subjects was measured in terms of duration of exposure necessary to evoke moderate malaise (MIIA) as a function of velocity in a chair rotated about a central axis tilted 10 deg with respect to gravitational upright. The subjects had little or no susceptibility to this type of rotation at 2.5 and 5.0 rpm, but with further increases in rate, the MIIA endpoint was always reached and with ever shorter test durations. Minimal provocative periods for all subjects were found at 15 or 20 rpm. Higher rotational rates dramatically reversed the vestibular stressor effect, and the subjects as a group tended to reach a plateau of relatively low susceptibility at 40 and 45 rpm. At these higher velocities, furthermore, the subjects essentially lost their sensation of being tilted off vertical. In the second half of the study, the effect of tilt angle was varied while the rotation rate was maintained at a constant 17.5 rpm. Two subjects were completely resistant to symptoms of motion sickness when rotated at 2.5 deg off vertical; with greater off-vertical angles, the susceptibility of all subjects increased sharply at first, then tapered off in a manner reflecting a Fechnerian function.

Earl F. Miller II↗
DOE OSTI2021

Solar Transposition Modeling via Deep Neural Networks With Sky Images

This article presents a notable advance toward the development of a new method of increasing the single-axis tracking photovoltaic (PV) system power output by improving the determination and near-term prediction of the optimum module tilt angle. The tilt angle of the plane receiving the greatest total irradiance changes with Sun position and atmospheric conditions including cloud formation and movement, aerosols, and particulate loading, as well as varying albedo within a module's field of view. In this article, we present a multi-input convolutional neural network that can create a profile of plane-of-array irradiance versus surface tilt angle over a full 180° arc from horizon to horizon. As input, the neural network uses the calculated solar position and clear-sky irradiance values, along with sky images. The target irradiance values are provided by the multiplanar irradiance sensor (MPIS). In order to account for varying irradiance conditions, the MPIS signal is normalized by the theoretical clear-sky global horizontal irradiance. Using this information, the neural network outputs an N -dimensional vector, where N is the number of points to approximate the MPIS curve via Fourier resampling. The output vector of the model is smoothed with a Gaussian kernel to account for error in the downsamping and subsequent upsampling steps, as well as to smooth the unconstrained output of the model. Furthermore, these profiles may be used to perform near-term prediction of angular irradiance, which can then inform the movement of a PV tracker.

42 ENGINEERING↗
DOE OSTI2020

Materials Data on Ta36B4C35 by Materials Project

Ta26C25Ta9C8TaBC(B)2BC1 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of two boron molecules; one BC1 sheet oriented in the (0, 0, 1) direction; one Ta26C25 sheet oriented in the (0, 0, 1) direction; one Ta9C8 sheet oriented in the (0, 0, 1) direction; and one TaBC sheet oriented in the (0, 0, 1) direction. In the BC1 sheet, B3+ is bonded in a trigonal planar geometry to three equivalent C4- atoms. All B–C bond lengths are 1.83 Å. C4- is bonded in a distorted trigonal planar geometry to three equivalent B3+ atoms. In the Ta26C25 sheet, there are eighteen inequivalent Ta+3.56+ sites. In the first Ta+3.56+ site, Ta+3.56+ is bonded in a 3-coordinate geometry to three equivalent C4- atoms. There are one shorter (2.14 Å) and two longer (2.15 Å) Ta–C bond lengths. In the second Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 1°. All Ta–C bond lengths are 2.23 Å. In the third Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 1°. There are five shorter (2.25 Å) and one longer (2.26 Å) Ta–C bond lengths. In the fourth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. All Ta–C bond lengths are 2.25 Å. In the fifth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.24 Å) and three longer (2.26 Å) Ta–C bond lengths. In the sixth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.24 Å) and three longer (2.25 Å) Ta–C bond lengths. In the seventh Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. In the eighth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. In the ninth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. In the tenth Ta+3.56+ site, Ta+3.56+ is bonded to six equivalent C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. In the eleventh Ta+3.56+ site, Ta+3.56+ is bonded to six equivalent C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.23 Å) and three longer (2.24 Å) Ta–C bond lengths. In the twelfth Ta+3.56+ site, Ta+3.56+ is bonded to six equivalent C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.23 Å. In the thirteenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.23 Å. In the fourteenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.23 Å. In the fifteenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.23 Å) and three longer (2.24 Å) Ta–C bond lengths. In the sixteenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.23 Å. In the seventeenth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.23 Å) and two longer (2.24 Å) Ta–C bond lengths. In the eighteenth Ta+3.56+ site, Ta+3.56+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Ta–C bond lengths are 2.25 Å. There are fifteen inequivalent C4- sites. In the first C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the third C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fourth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the fifth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the sixth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the seventh C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the eighth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the ninth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the tenth C4- site, C4- is bonded to six equivalent Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.23 Å) and three longer (2.24 Å) C–Ta bond lengths. In the eleventh C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the twelfth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the thirteenth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fourteenth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fifteenth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. All C–Ta bond lengths are 2.25 Å. In the Ta9C8 sheet, there are nine inequivalent Ta+3.56+ sites. In the first Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are five shorter (2.24 Å) and one longer (2.25 Å) Ta–C bond lengths. In the second Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Ta–C bond distances ranging from 2.23–2.26 Å. In the third Ta+3.56+ site, Ta+3.56+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Ta–C bond lengths are 2.26 Å. In the fourth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fifth Ta+3.56+ site, Ta+3.56+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. In the sixth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (2.23 Å) and three longer (2.24 Å) Ta–C bond lengths. In the seventh Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.23 Å) and four longer (2.24 Å) Ta–C bond lengths. In the eighth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.24 Å) and two longer (2.25 Å) Ta–C bond lengths. In the ninth Ta+3.56+ site, Ta+3.56+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Ta–C bond lengths are 2.24 Å. There are eight inequivalent C4- sites. In the first C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the second C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the third C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. All C–Ta bond lengths are 2.24 Å. In the fourth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. All C–Ta bond lengths are 2.24 Å. In the fifth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the sixth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 0°. In the seventh C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the eighth C4- site, C4- is bonded to six Ta+3.56+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the TaBC sheet, Ta+3.56+ is bonded in a single-bond geometry to one C4- atom. The Ta–C bond length is 2.08 Å. B3+ is bonded in a trigonal planar geometry to three equivalent C4- atoms. There are a spread of B–C bond distances ranging from 1.81–1.85 Å. C4- is bonded to one Ta+3.56+ and three equivalent B3+ atoms to form corner-sharing CTaB3 trigonal pyramids.

36 MATERIALS SCIENCE↗