SEARCH · Search NASA

Results for “Orientation gradients”

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.

SourceResearch connectionFrom yearThrough year

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

At least 235 records · Page 13

All sources NASA NTRS DOE OSTI

DOE OSTI2026

Quantitative characterization of gradient microstructures: A study on friction stir spot processing of pure cobalt

Heterogeneous microstructures in polycrystalline metals can enhance the strength and ductility, outperforming homogeneous structures of similar composition. This study investigates deformed cobalt via friction stir spot processing with varying dwell times to uncover the effects of plastic deformation and heat generation on the formation of morphological, phase, and grain boundary character gradients. A new approach to quantify the morphological gradients in materials, which describes grain morphology in terms of density followed by parametric regression, enables direct quantification of processing depth and gradient sharpness. Results show that longer processing times increase the steepness of morphological gradients and reduce the deformation depth for friction stir spot processing with low plunge depths and high tool rotational speeds. The amount of retained FCC is increased in the shorter processing conditions, primarily due to refined grain size, increased defect content, and reduced heat generation. Crystallographic texture analysis of the HCP phase indicated a dominant B-fiber described by (0001) ∥ shear plane normal in the extreme processing conditions and the formation of a P-fiber, shear direction ∥ ⟨11$\bar2$0⟩ for intermediate dwell times. The texture of the FCC phase for low processing times was a C texture {100}⟨011⟩ where longer processing times were dominated by a [001] fiber texture with a main {110}⟨100⟩ orientation and emergence of a slight [111] fiber in the longest processing condition. The approaches outlined in this work give insight into quantifying gradients and improve the understanding of highly deformed cobalt.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Spin Decoherence in VOPc@graphene Nanoribbon Complexes

Carbon nanoribbons or nanographene qubit arrays can facilitate quantum-to-quantum transduction between light, charge, and spin, making them an excellent testbed for fundamental science in quantum coherent systems and for the construction of higher-level qubit circuits. Here, in this work, we study spin decoherence due to coupling with a surrounding nuclear spin bath of an electronic molecular spin of a vanadyl phthalocyanine (VOPc) molecule integrated onto an armchair-edged graphene nanoribbon (GNR). Density functional theory (DFT) is used to obtain ground-state atomic configurations. Decay of spin coherence in Hahn echo experiments is then simulated using the cluster correlation expansion method with a spin Hamiltonian involving hyperfine and electric field gradient tensors calculated from DFT. We find that the decoherence time T 2 is anisotropic with respect to magnetic field orientation and determined only by the hydrogen nuclear spins on both VOPc and GNR. Large electron spin echo envelope modulation (ESEEM) due to nitrogen and vanadium nuclear spins is present at specific field ranges and can be completely suppressed by tuning the magnetic field. The relation between these field ranges and the hyperfine interactions is analyzed. The effects of interactions with the nuclear quadrupole moments are also studied, validating the applicability and limitations of the spin Hamiltonian when they are disregarded.

Hamiltonians↗

NASA NTRS1989

Hanging drop crystal growth apparatus and method

An apparatus (10) is constructed having a cylindrical enclosure (16) within which a disc-shaped wicking element (18) is positioned. A well or recess (22) is cut into an upper side (24) of this wicking element, and a glass cover plate or slip (28) having a protein drop disposed thereon is sealably positioned on the wicking element (18), with drop (12) being positioned over well or recess (22). A flow of control fluid is generated by a programmable gradient former (16), with this control fluid having a vapor pressure that is selectively variable. This flow of control fluid is coupled to the wicking element (18) where control fluid vapor diffusing from walls (26) of the recess (22) is exposed to the drop (12), forming a vapor pressure gradient between the drop (12) and the control fluid vapor. Initially, this gradient is adjusted to draw solvent from the drop (12) at a relatively high rate, and as the critical supersaturation point is approached (the point at which crystal nucleation occurs), the gradient is reduced to more slowly draw solvent from the drop (12). This allows discrete protein molecules more time to orient themselves into an ordered crystalline lattice, producing protein crystals which, when processed by X-ray crystallography, possess a high degree of resolution.

Carter, Daniel C.↗

NASA NTRS2018

Simultaneous Conventional and Plenoptic Background Oriented Schlieren Imaging

Plenoptic Background Oriented Schlieren (BOS) is an emerging schlieren technique that is capable of providing 3D qualitative and quantitative information about density gradients present in a wide range of fluid dynamics problems. In this work, the fundamental concepts of plenoptic BOS are reviewed before discussing an open-air experiment with a buoyant plume where both conventional BOS and plenoptic BOS measurements were acquired simultaneously. Both cameras had the same field-of-view for all experiments, and three different focal plane arrangements were explored: (1) the focal plane was set to the background positions and the plume varied between 11 different positions relative to this focal plane, (2) the focal plane was set to 635- millimeters in front of the background position, and (3) the nominal focal plane varied while the position of the plume remained fixed. Such discussion will provide insight on how the two techniques compare, and what additional work is required to better understand the results provided by these two imaging systems.

Klemkowsky, Jenna N.↗

NASA NTRS1991

Thermal and solutal convection with conduction effects inside a rectangular enclosure

We numerically investigate the effects of various boundary conditions on the flow field characteristics of the physical vapor transport process. We use a prescribed temperature profile as boundary condition on the enclosure walls, and we consider parametric variations applicable to ground-based and space microgravity conditions. For ground-based applications, density gradients in the fluid phase generate buoyancy-driven convection which in turn disrupts the uniformity of the mass flux at the interface depending on the orientation. Heat conduction in the crystal can affect the fluid flow near the interface of the crystal. When considering isothermal source and sink at the interfaces, we observe a diffusive mode and three modes (i.e., thermal, solutal, and thermo-solutal). The convective modes show opposing flow field trends between thermal and solutal convection; theoretically, these trends can be used to achieve a uniform mass flux near the crystal. However, under the physical conditions chosen, the mathematical condition necessary for uniform mass flux cannot be satisfied because of thermodynamic restrictions. When a longitudinal thermal gradient is prescribed on the boundary of the crystal, a non-uniform interface temperature results, which induces a symmetrical fluid flow near the interface for the vertical case. For space microgravity applications, we show that the flow field is dominated by the Stefan wind and a uniform mass flux results at the interface.

Mennetrier, Christophe↗

DOE OSTI2022

Logic operations with active topological defects

Logic operations performed by semiconductor-based transistors are the basis of modern computing. There is considerable interest in creating autonomous materials systems endowed with the capability to make decisions. In this work, we introduce the concept of using topological defects in active matter to perform logic operations. When an extensile active stress in a nematic liquid crystal is turned on, +1/2 defects can self-propel, in analogy to electron transport under a voltage gradient. By relying on hydrodynamic simulations of active nematics, we demonstrate that patterns of activity, when combined with surfaces imparting certain orientations, can be used to control the formation and transport of +1/2 defects. We further show that asymmetric high- and low-activity patterns can be used to create effective defect gates, tunnels, and amplifiers. The proposed active systems offer the potential to perform computations and transmit information in active soft materials, including actin-, tubulin-, and cell-based systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1974

Orbiter/Space lab momentum management for POP orientations

An angular momentum management scheme applicable to the orbiter/spacelab is described. The basis of the scheme is to periodically maneuver the vehicle through a small angle thereby using the gravity gradient torque to dump momentum from the control moment gyro (CMG) control system. The orbiter is operated with its principal vehicle axis perpendicular to the orbital plane. Numerous case runs were conducted on the hybrid simulation and representative cases are included.

Cox, J. W.↗

DOE OSTI2021

Pulsed Magnetic Gradiometry in Earth's Field [Poster]

We describe a novel pulsed magnetic gradiometer based on the optical interference of sidebands generated using two spatially separated alkali vapor cells. In contrast to traditional magnetic gradiometers, our approach provides a direct readout of the gradient field without the intermediate step of subtracting the outputs of two spatially separated magnetometers. Operation of the gradiometer in multiple field orientations is discussed. The noise floor is measured as low as 25$\frac{fT}{\sqrt{Hz-cm}}$ in a room without magnetic shielding.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1980

The effect of reduced gravity on solidification microstructures of NH4Cl-H2O alloys

The effect of gravity on the columnar-to-equiaxed microstructural transition was studied in small samples of NH4Cl-H2O. The behavior of the samples during laboratory (one gravity) experiments was contrasted with their behavior during a (low gravity) sounding rocket flight. In one gravity, the columnar zone accounted for 25 to 100 pct of the structure, depending on the superheat and orientation of the chill. Grain multiplication occurred by showering and by convection induced dendrite arm remelting. Convection was caused by both thermal gradients and solutal gradients. In low gravity, however, completely columnar structures were obtained; all grain multiplication mechanisms were entirely suppressed. Reduced gravity also modified the thermal conditions and caused the liquid to cool more slowly. This resulted in a steeper temperature gradient in the liquid ahead of the solidification interface. 'Big bang' type nucleation occurred in two of the samples, distributing nuclei throughout the liquid. Despite this, an equiaxed zone did not form, indicating that the most significant effect of low gravity on this experiment was modification of the thermal conditions.

Papazian, J. M.↗

NASA NTRS1984

Atmospheric Dynamics of Uranus and Neptune: Theoretical Considerations

The atmospheric dynamics of neptune and uranus are investigated. Uranus, because of its pole on orientation and low internal heat source, is in a dynamically different atmospheric regime from Jupiter and Saturn. Neptune resembles Jupiter and Saturn in orientation and internal heating, but its extremely long radiative time constant puts Neptune in a different class. Voyager observations of seasonal temperature gradients, equator to pole temperature gradients, infrared emission, Bond albedo, possible cloud structures (bands, spots, eddies), and cloud motions can be used to improve the ability to classify planetary atmospheres according to their dynamical regimes.

Andrew P Ingersoll↗

NASA NTRS2003

An Alternative Hypothesis for How Microgravity Improves Macromolecular Crystal Quality

There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests that for many proteins crystal nucleation and growth is by addition of associated species that are preformed by reversible concentration-driven self association processes in the bulk solution. We have developed a self-association model for the crystal nucleation and growth of the protein chicken egg lysozyme. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small an octamer in the 43 helix configuration (the proposed average sized growth unit) would have a M.W. approx. 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm (a 24-mer) commonly attach to the crystal. AFM results from Weichmann et al. (Ultramicroscopy 86, 159-166, 2001) suggest that associated species of up to 40-mers in size add to the (101) faces. These measurements reflect the sizes of units that both added and desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. On Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species is more likely to be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

Pusey, Marc↗

DOE OSTI2022

Fracture-based shape optimization built upon the topological derivative

In Silva et al. (2011) and Alidoost et al. (2020), the authors developed an approximation of the energy release rate field associated with a small edge or surface crack at any boundary location and with any orientation using the topological derivative. The approximation is computationally attractive because it requires only a single analysis on the non-cracked domain in contrast with conventional boundary-element and finite-element-based methods, which require a separate and costlier analysis for each crack length-location-orientation combination. Here, a shape optimization scheme for fracture-resistant structures is developed using the energy release rate approximation. In the gradient-based optimization scheme, the domain and its boundary are defined implicitly using level-set functions. The level-set functions of arbitrary geometries are constructed using Boolean operations from the level-set functions of simple primitives. This geometrical representation has the dual advantage of (i) allowing shapes to intersect and/or separate during the optimization and (ii) simplifying the computation of the shape sensitivities.

42 ENGINEERING↗

NASA NTRSDate not supplied

High-Frequency Secondary Instabilities Downstream of a Forward-Facing Step

Localized high-frequency velocity fluctuations were measured downstream of a forward-facing step on a 30◦swept flat plate with an imposed pressure gradient. Phase-locked time-resolved particle image velocimetry measurements were performed to determine the source of the fluctuations, which ultimately lead to transition. The steps result in localized regions of reversed flow for a short region downstream of the step. These regions are highly localized due to the impact of the stationary crossflow vortices. The velocity fluctuations typically increase significantly in amplitude shortly downstream of reattachment in these localized regions, indicating that the fluctuations are related to reattachment of the shear layer. The phase-averaged measurements confirm that the unsteadiness in the shear layer results in the shedding of a plethora of vortices, some oriented in the streamwise direction, and others in the spanwise direction. These vortices are impacted by the local properties of the mean flow, such as streamwise vorticity and streamwise velocity gradient. The origin of the unsteadiness in the shear layer is not definitively shown, but evidence suggests it is due to a shear-layer instability. Ultimately, the unsteadiness of the shear layer, and the vortices that are shed as a result of this unsteadiness, are responsible for transition in this scenario.

Jenna L Eppink↗

DOE OSTI2022

Multipolar Raman Scattering vs Interfacial Nanochemistry: Case of 4-Mercaptopyridine on Gold

Caution needs to be exercised in associating changes in plasmon-enhanced Raman spectra with chemical transformations. This is demonstrated through a detailed analysis of tip-enhanced Raman (TER) scattering from 4-mercaptopyridine (MPY) on gold. The substrate used consists of gold nanoplates atop a gold surface featuring heterogeneous grooves, all coated with a monolayer of MPY. The brightest spectra across the substrate exhibit features that can only be recovered by considering the generalized polarizability of oriented MPY molecules. Finally, the complex TER spectra we observe do not mark interfacial chemistry, but rather, multipolar TER scattering driven by local field gradients.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Melt-grown semi-insulating Mn:β-Ga 2 O 3 single crystals exhibiting unique visible absorptions and luminescence

In this study, several acceptor dopants have been explored in β-Ga 2 O 3 to produce semi-insulating substrates and epitaxial films. Fe and Mg make up the majority of research thus far; however, other transition metals provide potential alternatives for optimized performance. β-Ga 2 O 3 bulk single crystals were grown by the Czochralski and vertical gradient freeze methods with a nominal dopant concentration of 0.25 at. % Mn. Ultraviolet-visible-near infrared spectroscopy and photoluminescence revealed polarization- and orientation-dependent optical absorptions (pleochroism) coupled with an orange luminescence. All samples were electrically insulating, on the order of 10 9 –10 11 ohm cm at room temperature, indicative of acceptor doping. Actual dopant concentrations of the intentionally doped transition metal and background impurities were determined via glow discharge mass spectrometry, indicating the macroscale segregation behavior. High-temperature resistivity measurements indicated an experimental acceptor level of 1.7 ± 0.2 eV. Hydrogenation of samples resulted in an increase in the orange luminescence and O–H stretching modes observable in the infrared spectrum. Density functional theory calculations were performed to determine the likely site-occupancy and acceptor level of Mn in the bandgap.

36 MATERIALS SCIENCE↗

NASA NTRS1981

Holes help control temperature

Study of passive thermal control for the Solar Terrestrial Subsatellite (STSS) has found that array of "see through" holes substantially improves performance of system. Holes in payload mounting plates allow line of sight radiative heat transfer between hot and cold ends of spacecraft and between mounting plates and ends. Temperature gradients between plates are thereby reduced, as is temperature of each plate. Holes and selected exterior paints and finishes keep payload cool for all orientations and operating modes of STSS.

Chhatpar, C. K.↗

NASA NTRS1981

Superconducting tensor gravity gradiometer

The employment of superconductivity and other material properties at cryogenic temperatures to fabricate sensitive, low-drift, gravity gradiometer is described. The device yields a reduction of noise of four orders of magnitude over room temperature gradiometers, and direct summation and subtraction of signals from accelerometers in varying orientations are possible with superconducting circuitry. Additional circuits permit determination of the linear and angular acceleration vectors independent of the measurement of the gravity gradient tensor. A dewar flask capable of maintaining helium in a liquid state for a year's duration is under development by NASA, and a superconducting tensor gravity gradiometer for the NASA Geodynamics Program is intended for a LEO polar trajectory to measure the harmonic expansion coefficients of the earth's gravity field up to order 300.

Paik, H. J.↗

NASA NTRS1988

A comparative study of the influence of buoyancy driven fluid flow on GaAs crystal growth

A systematic investigation of the effect of gravity driven fluid flow on GaAs crystal growth was performed. It includes GaAs crystal growth in the microgravity environment aboard the Space Shuttle. The program involves a controlled comparative study of crystal growth under a variety of earth based conditions with variable orientation and applied magnetic field in addition to the microgravity growth. Earth based growth will be performed under stabilizing as well as destabilizing temperature gradients. The boules grown in space and on earth will be fully characterized to correlate the degree of convection with the distribution of impurities. Both macro- and micro-segregation will be determined. The space growth experiment will be flown in a self-contained payload container through NASA's Get Away Special program.

Kafalas, J. A.↗