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Results for “curved surfaces”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Fabrication and durability characterization of superhydrophobic and lubricant-infused surfaces

Hypothesis: Practical applications of non-wetting surfaces require good mechanical durability in the wet environments for which they are intended to be used. Durability of non-wetting surfaces is influenced by the surface features, interaction with the functionalization agent, and the lubricant properties that can be tuned independently to identify optimal combination. Experiments: In this study, superhydrophobic and lubricant-infused surfaces are fabricated on copper tubes using chemical etching and electrodeposition texturing techniques, six different functionalizing agents, and five different infused lubricants. Through 180 fabrication combinations and 102 durability tests, each parameter is systematically studied for contributions to initial non-wetting behavior and its durability in heated, wet environment, under high-energy water jet impingement, and under accelerated flow conditions. Findings: Among the adsorbing and curing functionalization agents investigated, n-Hexadecyl mercaptan that belongs to the sulfhydryl group and Sylgard-184, respectively, showed high durability in heated water immersion and under jet impingement tests. For lubricant-infused surfaces, lubricants with high surface tension demonstrated high durability in heated water immersion test, whereas durability in hydrodynamic conditions is closely correlated to lubricant viscosity. Results showed that a lubricant-infused surface will maintain its non-wetting properties in dropwise condensation conditions for approximately 1.5 years.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Transport of colloidal particles in microscopic porous medium analogs with surface charge heterogeneity: experiments and fundamental role of single-bead deposition

Understanding colloid transport in subsurface environments is challenging due to complex interactions between colloids, ground water, and porous media over several length scales. Here, we study the transport of colloidal particles through bead-assembled microfluidic porous media analogs (PMAs) with surface charge heterogeneity. The pore-scale dynamics of colloidal particle deposition were measured, as well as the breakthrough curves (BTC) and retention profiles (RP) of deposited colloidal particles at the scale of the entire PMA. From pore-scale experiments, the maximum surface coverage (?max = 0.51) was measured directly, from which the surface blocking function and deposition coefficient (kpore = 3.56 s-1) were obtained. Using these pore-scale parameters, the transport of colloidal particles was modeled using a one-dimensional advection-dispersion equation under the assumption of irreversible adsorption between oppositely charged beads and colloids, showing good agreement with experimental data. This work presents a new approach to fabricate chemically heterogeneous porous media in a microfluidic device that enables direct measurements of pore-scale colloidal deposition. The approach allows a quantitative prediction of colloidal breakthrough and retention via coupling of direct measurements and an advection-dispersion-deposition model.

Guo, Yang↗
DOE OSTI2024

Surfaceology for colored Yukawa theory

Arkani-Hamed and collaborators have recently shown that scattering amplitudes for colored theories can be expressed as integrals over combinatorial objects simply constructed from surfaces decorated by kinematic data. In this paper we extend the curve integral formalism to theories with colored fermionic matter and present a compact formula for the all-loop, all-genus, all-multiplicity amplitude integrand of a colored Yukawa theory. The curve integral formalism makes certain properties of the amplitudes manifest and repackages non-trivial numerators into a single combinatorial object. We also present an efficient formula for L-loop integrated amplitudes in terms of a sum over 2 L combinatorial determinants.

1/N Expansion↗
DOE OSTI2022

Spin canting of Ni/CoO/Fe films grown on curved MgO(0 0 1) substrate

Using element-resolved x-ray magnetic circular dichroism (XMCD) and x-ray magnetic linear dichroism (XMLD) measurements, we determined the spin orientations of Ni, CoO and Fe films in Ni/CoO/Fe films grown on a curved MgO(0 0 1) substrate. We find that the vicinal surface of MgO(0 0 1) substrate results in a spin canting towards out-of-plane direction in the Ni and CoO films as a result of the interfacial coupling. The Ni spin canting angle increases monotonically with the vicinal angle in the studied range of 0–17° and the CoO spin canting angle increases more rapidly towards saturation only at a few degrees of the vicinal angle. The uniaxial magnetic anisotropy induced in the Ni layer by the Ni/CoO interfacial coupling is quantitatively determined and is shown to increase monotonically with the vicinal angle. Our result provides a new pathway for tailoring the spin orientation by modifying the substrate surface symmetry in combining with the ferromagnetic/antiferromagnetic interfacial interaction in thin-film based spintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Occultation of a Large Star by the Large Plutino (28978) Ixion on 2020 October 13 UTC

We observed the occultation of the star Gaia DR2 4056440205544338944 by (28978) Ixion. The event was observed from two Lowell Observatory sites, using the 4.3 m Lowell Discovery Telescope (LDT), near Happy Jack, AZ, USA, and a 0.32 m telescope co-mounted with the Titan Monitoring telescope on Lowell’s Mars Hill campus in Flagstaff, AZ. The LDT chord, at 44.86 s, was roughly 30% longer than the longest predicted possible chord. Under the assumption of a spherical body, Ixion’s fitted diameter D = 709.6 ± 0.2 km. The LDT light-curve profile was used to place an upper limit on the surface pressure P < 2 μbar on any possible atmosphere of Ixion. At the distance of Ixion, the occulted star had a fitted projected diameter of 19.25 ± 0.3 km assuming uniform disk illumination, giving a stellar angular diameter of 0.675 ± 0.010 mas. Using the Gaia EDR3 parallax of 0.565 mas, the stellar radius is 130{sub −17}{sup +20} R{sub ⊙}. The measured size is consistent with prior spectral classification of this star as a reddened mid-M giant. This is one of only a modest number of M5 III stars to have a directly measured diameter, and is more distant than most.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

The Interplay Between Ferroelectricity and Electrochemical Reactivity on the Surface of Binary Ferroelectric Al x B 1–x N

Polarization dynamics and domain structure evolution in ferroelectric Al 0.93 B 0.07 N are studied using piezoresponse force microscopy and spectroscopies in ambient and controlled atmosphere environments. The application of negative unipolar and bipolar first-order reverse curve (FORC) waveforms leads to a protrusion-like feature on the Al 0.93 B 0.07 N surface and a reduction of electromechanical response due to electrochemical reactivity. A surface change is also observed on the application of fast alternating current bias. At the same time, the application of positive biases does not lead to surface changes. Comparatively in a controlled glove box atmosphere, stable polarization patterns can be observed, with minuscule changes in surface morphology. This surface morphology change is not isolated to applying biases to free surface, a similar topographical change is also observed at the electrode edges when cycling a capacitor in an ambient environment. The study suggests that surface electrochemical reactivity may have a significant impact on the functionality of this material in the ambient environment. However, even in the controlled atmosphere, the participation of the surface ions in polarization switching phenomena and ionic compensation is possible.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The Page curve of Hawking radiation from semiclassical geometry

We consider a gravity theory coupled to matter, where the matter has a higher-dimensional holographic dual. In such a theory, finding quantum extremal surfaces becomes equivalent to finding the RT/HRT surfaces in the higher-dimensional theory. Using this we compute the entropy of Hawking radiation and argue that it follows the Page curve, as suggested by recent computations of the entropy and entanglement wedges for old black holes. The higher-dimensional geometry connects the radiation to the black hole interior in the spirit of ER=EPR. The black hole interior then becomes part of the entanglement wedge of the radiation. Inspired by this, we propose a new rule for computing the entropy of quantum systems entangled with gravitational systems which involves searching for “islands” in determining the entanglement wedge.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

High-throughput surface characterization to identify porosity defects in additively manufactured 316L stainless steel

In the present study, a high throughput (HT) methodology is applied to rapidly assess the surface characteristics of 83 additively manufactured 316L stainless steel. The variation in surface roughness (S a ) showed a good correlation with a dimensionless number (π) and provided direct linkages to the internal porosity defects. Lack-of-fusion regime relates to high surface roughness (S a > 5 µm), low dimensionless number (π < 61), and the presence of cavities in between the melt pool tracks. Balling regime correlates to high surface roughness (S a > 5 µm), intermediate dimensionless number (61 < π < 146), and non-uniform melt pool track width. Keyhole regime shows low surface roughness (S a < 5 µm), high dimensionless number (π > 146), and a curved melt pool track. This approach accelerates the process parameter discovery and minimizes the porosity defects for the LPBF process. The impact of the defects on the as-processed tensile mechanical properties demonstrates that samples with porosity exhibit up to 10% less tensile strength and 30% less ductility than optimal samples.

316L stainless steel↗
DOE OSTI2022

Surface analysis insight note: Synthetic line shapes, integration regions and relative sensitivity factors

Here, methods for estimating photoemission intensity from X-ray photoelectron spectroscopy data are examined. The role played by “synthetic” bell-shaped curves, integration intervals, background curves, and the use of relative sensitivity factors (RSFs) in reporting percentage atomic concentration for a sample is presented. In particular, photoemission lines with differing energy distributions obtained from the NaCl sample surface are used to demonstrate how a comparison of photoemission intensities is dependent on the line shapes, background curves, and appropriate use of RSFs.

42 ENGINEERING↗
DOE OSTI2025

Mechanical design of a parallel flexure-based RADSI instrument for curved x-ray mirror metrology

Modern synchrotron x-ray beamlines demand reflective optics with higher surface profile accuracy to achieve diffraction-limited focusing. This necessitates advanced metrology instruments capable of delivering repeatable measurements in the nanometer to sub-nanometer range. Slope ranges exceeding 15 mrad (0.86°) and greater pose significant challenges for mirror metrology using conventional interferometric methods. Here, to address this, we present a new relative angle determinable stitching interferometry instrument featuring a parallel flexure-based mechanical design. This approach enhances vibration and thermal stability while maintaining a compact and lightweight system. Initial measurements of a cylindrical mirror with a 16 m radius of curvature and a slope range of 5 mrad demonstrate nanometer-level repeatability. Comprehensive system characterization suggests the potential for achieving sub-nanometer repeatability with further refinement to the instrument.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The EBLM project – IX. Five fully convective M-dwarfs, precisely measured with CHEOPS and TESS light curves

ABSTRACT Eclipsing binaries are important benchmark objects to test and calibrate stellar structure and evolution models. This is especially true for binaries with a fully convective M-dwarf component for which direct measurements of these stars’ masses and radii are difficult using other techniques. Within the potential of M-dwarfs to be exoplanet host stars, the accuracy of theoretical predictions of their radius and effective temperature as a function of their mass is an active topic of discussion. Not only the parameters of transiting exoplanets but also the success of future atmospheric characterization relies on accurate theoretical predictions. We present the analysis of five eclipsing binaries with low-mass stellar companions out of a subsample of 23, for which we obtained ultra-high-precision light curves using the CHEOPS satellite. The observation of their primary and secondary eclipses are combined with spectroscopic measurements to precisely model the primary parameters and derive the M-dwarfs mass, radius, surface gravity, and effective temperature estimates using the PYCHEOPS data analysis software. Combining these results to the same set of parameters derived from TESS light curves, we find very good agreement (better than 1 per cent for radius and better than 0.2 per cent for surface gravity). We also analyse the importance of precise orbits from radial velocity measurements and find them to be crucial to derive M-dwarf radii in a regime below 5 per cent accuracy. These results add five valuable data points to the mass–radius diagram of fully convective M-dwarfs.

Sebastian, D. (ORCID:0000000222149258)↗
DOE OSTI2021

Data–Driven Velocity Model Evaluation Using K–Means Clustering

In this work, we develop a data-driven clustering method to evaluate a velocity model using surface wave velocity dispersion. This is done by first computing theoretical dispersion curves for 1-D velocity profiles of all the grid locations and then splitting the resulting dispersion curves into a certain number of groups via the K-means clustering. The observed dispersion curves are also clustered following the same procedure and the velocity model is assessed by comparing the spatial patterns obtained for the observed and synthetic data sets. The method is applied to evaluate two community velocity models in southern California, CVM-S4.26 and CVM-H15.1, using phase velocity maps derived for 3–16 s Rayleigh waves. We found a good correlation in the spatial distribution of clusters between the result of CVM-S4.26 and that of the observed data, suggesting that the CVM-S4.26 fits the observed dispersion maps better than the CVM-H15.1 in terms of features extracted from the clustering analysis.

58 GEOSCIENCES↗
DOE OSTI2022

Probabilistic inversion of circular phase spectra: application to two-station phase-velocity dispersion estimation in western Canada

SUMMARY Periodic directional and temporal measurements are common in seismology, and necessitate specific statistical analyses that are appropriate for circular quantities. In this work, we explore the use of a von Mises distribution as a representation of errors on circular seismological observations. Specifically, we automate the estimation of surface-wave phase-velocity dispersion for the teleseismic two-station method, which generally suffers from a 2π phase ambiguity. The use of Bayesian inverse techniques, which aim to rigorously quantify model parameter uncertainty, have become widespread throughout seismology over the last decade. Here, we apply Bayesian inversion to measurements of surface-wave phase spectra in order to estimate 1-D, path-averaged Earth structure between station pairs. The dispersion curve and associated uncertainties are additional results of the inversion, which can then be used as input for subsequent analyses (e.g. tomography). We demonstrate this technique through application to surface-wave recordings from long-running seismic stations throughout western Canada. Our results for over 10 000 station pairs reveal first-order tectonic features consistent with previous studies, which provides confidence in our approach as well as an initial step towards resolving a full 3-D seismic velocity model for the region. This work also presents a foundation for the inversion of surface-wave phase spectra to estimate 3-D Earth structure directly. Finally, the ideas presented in this work are not limited to the inversion of surface-wave phase spectra, but can also be considered for Bayesian geophysical inversion of any circular quantities.

Gosselin, Jeremy M. (ORCID:0000000203754102)↗
DOE OSTI2022

Progress in Near-Equilibrium Ammonothermal (NEAT) Growth of GaN Substrates for GaN-on-GaN Semiconductor Devices

This paper reviews the near-equilibrium ammonothermal (NEAT) growth of bulk gallium nitride (GaN) crystals and reports the evaluation of 2″ GaN substrates and 100 mmbulk GaN crystal grown in our pilot production reactor. Recent progress in oxygen reduction enabled growing NEAT GaN substrates with lower residual oxygen, coloration, and optical absorption. The oxygen concentration was approximately 2 × 1018 cm−2, and the optical absorption coefficient was 1.3 cm−1 at 450 nm. Maps of full-width half maximum (FWHM) of X-ray diffraction rocking curveswere generated for grown crystals and finished wafers. The X-ray rocking curve maps confirmed high-quality and uniform microstructure across the entire surface of the bulk crystals and substrates. The average FWHM of the 50 best bulk crystals from the recent batch was 28 ± 4 arcsec for the 002 diffraction and 34 ± 5 arcsec for the 201 diffraction, with an average radius of curvature of 20 m. X-ray topography measured on both sides of the bulk crystals implied that the density of dislocations wasreduced by one order of magnitude during the NEAT growth. A typical NEAT GaN substrate shows dislocation density of about 2 × 105 cm−2.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Secondary reflectors for solar collectors and methods of making the same

The present disclosure relates to a device that includes a reflecting surface having a length aligned along a first axis (z), where a cross-section of the reflecting surface in a plane perpendicular to the first axis (z) forms a curve comprising a concave section positioned between a first endpoint and a second endpoint, at least a portion of the concave section is accurately approximated by a polynomial equation, an aperture is formed by a straight line connecting the first endpoint to the second endpoint, and the concave section is configured to focus a plurality of beams of light passing through the aperture onto a focal point.

Zhu, Guangdong↗
DOE OSTI2023

Secondary reflectors for solar collectors and methods of making the same

A secondary reflector for receiving light from a plurality of primary reflectors that includes a reflecting surface having a length aligned along a first axis (z), where a cross-section of the reflecting surface in a plane perpendicular to the first axis (z) forms a curve comprising a concave section positioned between a first endpoint and a second endpoint, at least a portion of the concave section is accurately approximated by a polynomial equation, an aperture is formed by a straight line connecting the first endpoint to the second endpoint, and the concave section is configured to focus a plurality of beams of light passing through the aperture onto a focal point.

Zhu, Guangdong↗
DOE OSTI2025

Curvature Induced Modifications of Chirality and Magnetic Configuration in Perpendicular Films

Designing curvature in three-dimensional (3D) magnetic nanostructures enables controlled manipulation of local energy landscapes, allowing for the modification of noncollinear spin textures relevant for next-generation spintronic devices. In this study, we experimentally investigate 3D magnetization textures in a Co/Pd multilayer film, exhibiting strong perpendicular magnetic anisotropy (PMA), deposited onto curved Cu nanowire meshes with diameters as small as 50 nm and lengths of several microns. Utilizing magnetic soft X-ray nanotomography, we achieve reconstructions of 3D magnetic domain patterns at approximately 30 nm spatial resolution. This approach provides detailed information on both the orientation and magnitude of magnetization within the film. Our results reveal that interfacial anisotropy in the Co/Pd multilayers drives the magnetization toward the local surface normal. In contrast to typical labyrinth domains observed in planar films, the presence of curved nanowires significantly alters the domain structure, with domains preferentially aligning along the nanowire axis in close proximity, while adopting random orientations farther away. We report direct experimental observation of a curvature-induced Dzyaloshinskii-Moriya interaction (DMI), which is quantified to be approximately one-third of the intrinsic DMI in Co/Pd stacks. The curvature induced DMI enhances stability of Néel-type domain walls. These experimental observations are further supported by micromagnetic simulations. Altogether, our findings demonstrate that introducing curvature into magnetic nanostructures provides a powerful strategy for tailoring complex magnetic behaviors, paving the way for the design of advanced 3D racetrack memory and neuromorphic computing devices.

Raftrey, David↗
DOE OSTI2024

Sensitivity of magnetohydrodynamic simulations of Joule-heated conductors to the vaporization curve in equations of state

Magnetohydrodynamic (MHD) simulations of electrically exploded aluminum and copper rods demonstrate a technique to validate equations of state (EOS) for rapidly Joule-heated conductors. The balance of internal and magnetic forces at the conductor-insulator interface drives the metal there along the vaporization phase boundary. Variations between critical points and vaporization curves in existing models predict differing densities and temperatures in MHD simulations for these models. Here, the inclusion of Maxwell constructs in the liquid-vapor biphase region of the EOS caused the rod surface to vaporize earlier in time than unmodified tables with van der Waals loops. Velocimetry of recent experiments is used to validate the location of the vaporization curve in existing EOS models and differentiate between the vapor dome treatments. Dielectric coatings applied to the metal surface restricted the conductor’s expansion and diverted the metal into the warm dense matter regime.

36 MATERIALS SCIENCE↗