Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ORIENTATION”

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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Effect of Solvent Composition on Non-DLVO Forces and Oriented Attachment of Zinc Oxide Nanoparticles

Oriented attachment (OA) occurs when nanoparticles in solution align their crystallographic axes prior to colliding and subsequently fuse into single crystals. Traditional colloidal theories such as DLVO provide a framework for evaluating OA but fail to capture key particle interactions due to the atomistic details of both the crystal structure and the interfacial solution structure. Using zinc oxide as a model system, we investigated the effect of the solvent on short-ranged and long-ranged particle interactions and the resulting OA mechanism. In situ TEM imaging showed that ZnO nanocrystals in toluene undergo long-range attraction comparable to 1kT at separations of 10 nm and 3kT near particle contact. These observations were rationalized by considering non-DLVO interactions, namely dipole-dipole forces and torques between the polar ZnO nanocrystals. Langevin dynamics simulations showed stronger interactions in toluene compared to methanol solvents, consistent with the experimental results. Concurrently, we performed atomic force microscopy measurements using ZnO-coated probes for the short-ranged interaction. Our data provided valuable insights into another type of non-DLVO interaction, namely the repulsive solvation force. Specifically, the solvation force was stronger in water compared to ethanol and methanol, due to the stronger hydrogen bonding and denser packing of water molecules at the interface. In conclusion, our results highlight the importance of non-DLVO forces in a general framework for understanding and predicting particle aggregation and attachment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Synthesis and Self-Assembly of Monodisperse Graphene Nanoribbons: Access to Submicron Architectures with Long-Range Order and Uniform Orientation

Fabricating organic semiconducting materials into large-scale well-organized architectures is critical for building high performance molecular electronics. While graphene nanoribbons (GNRs) hold enormous promise for various device applications, their assembly into a well-structured monolayer or multilayer architecture poses a substantial challenge. Here we report the preparation of length-defined monodisperse GNRs via the integrated iterative binomial synthesis (IIBS) strategy and their self-assembly into submicron-architectures with long-range order, uniform orientation as well as regular layers. Further, the use of short alkyl side chains benefits forming stable multi-layers through interlocking structures. By changing the length and backbone shapes of these monodisperse GNRs, various three-dimensional assemblies including multilayer stripes, monolayer stripes, and nanowires, can be achieved, leading to different photophysical properties and band gaps. The discovery of these intriguing self-assembly behaviors of length-defined GNRs is expected to open the door for various future applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Process‐Oriented Calibration of a Turbulence Scheme in the DOE's Global Storm‐Resolving Model Using Machine Learning

A process‐oriented calibration framework is developed for the Simplified Higher‐Order Closure (SHOC) turbulence scheme in DOE's Simple Cloud Resolving E3SM Atmospheric Model (SCREAM). This framework leverages machine learning surrogates and observational constraints to efficiently calibrate SHOC adjustable parameters across two convective regimes: clear‐sky dry convective boundary layer and fair‐weather shallow cumulus clouds from ARM observations. We use perturbed‐parameter ensembles of a doubly periodic version of SCREAM to train surrogates and apply Markov Chain Monte Carlo sampling guided by cost functions based on benchmarking large‐eddy simulations and observations to identify optimized parameter sets that perform well in both regimes. The calibrated SHOC parameters substantially improve boundary‐layer turbulence and cloud boundaries, and modeled cloud fraction and radiative effects align better with observations than the default. These results demonstrate that combining multiple process‐specific convective regimes with machine‐learning surrogates can reduce parametric uncertainties and yield a model more faithful to cloud–turbulence interactions.

58 GEOSCIENCES↗
DOE OSTI2019

Anomalous neutron scattering `halo' observed in highly oriented pyrolytic graphite

Highly oriented pyrolytic graphite (HOPG) has been used as monochromators, analyzers and filters at neutron and X-ray scattering facilities for more than half a century. Interesting questions remain. In this work, the first observation of anomalous neutron `halo' scattering of HOPG is reported. The scattering projects a ring onto the detector with a half-cone angle of 12.4°, which surprisingly persists to incident neutron wavelengths far beyond the Bragg cutoff for graphite (6.71 Å). At longer wavelengths the ring is clearly a doublet with a splitting roughly proportional to wavelength. Sample tilting leads to the shift of the ring, which is wavelength dependent with longer wavelengths providing a smaller difference between the ring shift and the sample tilting. The ring broadens and weakens with decreasing HOPG quality. The lattice dynamics of graphite play a role in causing the scattering ring, as shown by the fact that the ring vanishes once the sample is cooled to 30 K. A possible interpretation by multiple scattering including elastic and inelastic processes is proposed.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Background-Oriented Schlieren Velocimetry of Helium Coolant Flow in Additively Manufactured Channels

High-pressure helium gas cooling is an attractive solution for thermal management of the fusion blanket first wall, as this coolant is chemically and neutronically inert and separable from hydrogenic species. However, due to the low thermal mass of helium, geometric optimization of these channels is required to provide sufficient cooling at manageable flow rates and pumping burdens. Increasingly, analysis and optimization of these coolant channels rely on computational fluid dynamics (CFD) simulations, and these require relevant experimental data for turbulence model validation. Toward this end, a high-pressure helium gas flow visualization system has been employed to image the flow of helium in flow channels with one-sided heating, mimicking the blanket first wall environment. Flow of helium at 4 MPa pressure and flow rates up to 68 g/s (Reynolds number 57 000) is supplied to rectangular channel test sections, with uniform heating applied to the bottom wall of the channel at heat fluxes varied between roughly 50 and 130 kW/m2. A high-speed camera is used to image index of refraction (IOR) gradients in the fluid via background-oriented schlieren (BOS), and temperature and pressure instrumentation are used to characterize thermal-hydraulic performance of each channel. Cross correlation of time-resolved BOS images is then used to calculate time-averaged 2-D helium velocity fields. Flow in additively manufactured (AM) channels is examined in this manner, including both featureless channels and those containing baffling as a heat transfer enhancement. The flow distribution seen in the featureless case differs significantly from that seen in prior simulations, whereas the flow in the baffled case shows the predicted behavior of flow forced along the heated wall. This augmented flow distribution is seen to increase the heat transfer coefficient in the baffled test section. Here, strategies are discussed for ongoing and future validation of these simulations, with the aim of model deployment for blanket cooling design and optimization.

Additive manufacturing↗
DOE OSTI2018

Magnetic Phases and Inhomogeneous Micromagnetic Structures in a Ferrite Garnet Film with Orientation (210)

Possible magnetic states of a cubic ferromagnet with a uniaxial anisotropy induced along the [210] direction are theoretically investigated. It is demonstrated that the orientation phase diagram of a magnet is nontrivial and admits the existence of three types of magnetic phases that differ in transformational properties and the presence of quintuple points, isostructural phase transitions, etc. It is found that magnetic inhomogeneities, regardless of the values of parameters of the matter, have a common structure: they correspond to 180-degree domain boundaries with a noncircular trajectory of the magnetization vector. The features of homogeneous and inhomogeneous magnetic states, found in these materials, make it possible to explain the manifestation of a flexomagnetoelectric effect in them.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Method for Increasing the Efficiency of a Biaxial Solar Tracker with Exact Solar Orientation

Modern solar follow-up systems make it possible to increase a solar cell’s efficiency and, as a result, solar energy utilization. The paper considers modern solar follow-up methods and their operational principles. Trackers are separated onto uniaxial and biaxial according to the plane which tracking occurs. Biaxial trackers are the most efficient. The operational principles of active and passive trackers are studied. A laboratory model of a biaxial solar tracker with precise solar orientation is described, based on an algorithm for calculating the voltage with current sensors. The following are given in the paper: the current–voltage characteristic obtained for different solar array positions and using trackers; the relationships between the power and measured currents and voltages. The efficiency is calculated for different solar array positions and using a tracker.

14 SOLAR ENERGY↗
DOE OSTI2018

Molecular Orientations Change Reaction Kinetics and Mechanism: A Review on Catalytic Alcohol Oxidation in Gas Phase and Liquid Phase on Size-Controlled Pt Nanoparticles

Catalytic oxidation of alcohols is an essential process for energy conversion, production of fine chemicals and pharmaceutical intermediates. Although it has been broadly utilized in industry, the basic understanding for catalytic alcohol oxidations at a molecular level, especially under both gas and liquid phases, is still lacking. In this paper, we systematically summarized our work on catalytic alcohol oxidation over size-controlled Pt nanoparticles. The studied alcohols included methanol, ethanol, 1-propanol, 2-propanol, and 2-butanol. The turnover rates of different alcohols on Pt nanoparticles and also the apparent activation energy in gas and liquid phase reactions were compared. The Pt nanoparticle size dependence of reaction rates and product selectivity was also carefully examined. Water showed very distinct effects for gas and liquid phase alcohol oxidations, either as an inhibitor or as a promoter depending on alcohol type and reaction phase. A deep understanding of different alcohol molecular orientations on Pt surface in gas and liquid phase reactions was established using sum-frequency generation spectroscopy analysis for in situ alcohol oxidations, as well as density functional theory calculation. This approach can not only explain the entirely different behaviors of alcohol oxidations in gas and liquid phases, but can also provide guidance for future catalyst/process design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

A Method to Measure the Transverse Magnetic Field and Orient the Rotational Axis of Stars

Direct measurements of stellar magnetic fields are based on the splitting of spectral lines into polarized Zeeman components. With a few exceptions, Zeeman signatures are hidden in data noise, and a number of methods have been developed to measure the average, over the visible stellar disk, of longitudinal components of the magnetic field. At present, faint stars are only observable via low-resolution spectropolarimetry, which is a method based on the regression of the Stokes V signal against the first derivative of Stokes I . Here, we present an extension of this method to obtain a direct measurement of the transverse component of stellar magnetic fields by the regression of high-resolution Stokes Q and U as a function of the second derivative of Stokes I . We also show that it is possible to determine the orientation in the sky of the rotation axis of a star on the basis of the periodic variability of the transverse component due to its rotation. The method is applied to data, obtained with the Catania Astrophysical Observatory Spectropolarimeter along the rotational period of the well known magnetic star β CrB.

79 ASTRONOMY AND ASTROPHYSICS↗