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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

SU-F-R-08: Can Normalization of Brain MRI Texture Features Reduce Scanner-Dependent Effects in Unsupervised Machine Learning?

Purpose: To reduce differences in features calculated from MRI brain scans acquired at different field strengths with or without Gadolinium contrast. Methods: Brain scans were processed for 111 epilepsy patients to extract hippocampus and thalamus features. Scans were acquired on 1.5 T scanners with Gadolinium contrast (group A), 1.5T scanners without Gd (group B), and 3.0 T scanners without Gd (group C). A total of 72 features were extracted. Features were extracted from original scans and from scans where the image pixel values were rescaled to the mean of the hippocampi and thalami values. For each data set, cluster analysis was performed on the raw feature set and for feature sets with normalization (conversion to Z scores). Two methods of normalization were used: The first was over all values of a given feature, and the second by normalizing within the patient group membership. The clustering software was configured to produce 3 clusters. Group fractions in each cluster were calculated. Results: For features calculated from both the non-rescaled and rescaled data, cluster membership was identical for both the non-normalized and normalized data sets. Cluster 1 was comprised entirely of Group A data, Cluster 2 contained data from all three groups, and Cluster 3 contained data from only groups 1 and 2. For the categorically normalized data sets there was a more uniform distribution of group data in the three Clusters. A less pronounced effect was seen in the rescaled image data features. Conclusion: Image Rescaling and feature renormalization can have a significant effect on the results of clustering analysis. These effects are also likely to influence the results of supervised machine learning algorithms. It may be possible to partly remove the influence of scanner field strength and the presence of Gadolinium based contrast in feature extraction for radiomics applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Modification of the structural, textural, and mechanical properties of an Al{sub 2}O{sub 3}/Al composite on the addition of an Al-SBA-15-type mesoporous phase

The formation of the pore structure of metal–ceramic materials based on Al{sub 2}O{sub 3}/Al composites has been studied in detail by modifying them via the incorporation of SBA-15-type mesoporous materials. The composition, pore structure, pore size, and morphology of the composite particles have been studied using nitrogen adsorption/desorption isotherms, scanning electron microscopy, and X-ray diffraction. We have produced Al-SBA-15/Al{sub 2}O{sub 3}/Al monoliths that combine properties of both adsorbents and permeable materials, but the incorporation of Al-SBA-15 into an Al{sub 2}O{sub 3}/Al matrix reduces the permeability and mechanical strength of the composites.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Effect of Base Thickness on Photoconversion Efficiency in Textured Silicon-Based Solar Cells

A theory is developed, which describes the experimental external quantum efficiency, EQE(λ) as a function of photon wavelength for structured Si-based solar cells. Short-circuit current density as a function of base thickness, d, is calculated for the high-efficiency solar cells with the photoconversion efficiency η ≥ 25% The procedure allows one to carry out a complete optimization of such solar cells, in particular, to find the optimal base thickness, d{sub opt}.

14 SOLAR ENERGY↗
DOE OSTI2019

Radioactive beams and inverse kinematics: Probing the quantal texture of the nuclear vacuum

The properties of the quantum electrodynamic (QED) vacuum in general, and of the nuclear vacuum (ground) state in particular, are determined by virtual processes implying the excitation of a photon and of an electron-positron pair in the first case and of, for instance, the excitation of a collective quadrupole surface vibration and a particle-hole pair in the nuclear case. Signals of these processes can be detected in the laboratory in terms of what can be considered a nuclear analogue of Hawking radiation. An analogy which extends to other physical processes involving QED vacuum fluctuations like the Lamb shift, pair creation by \(\gamma\) -rays, van der Waals forces and the Casimir effect, to the extent that one concentrates on the eventual outcome resulting by forcing a virtual process to become real, and not on the role of the black hole in defining the event horizon. In the nuclear case, the role of this event is taken over at a microscopic and fully quantum mechanical level, by nuclear probes (reactions) acting on virtual particles of the zero point fluctuations (ZPF) of the nuclear vacuum in a similar irreversible, no-return, fashion as the event horizon does, letting the other particle, entangled with the first one, escape to infinity, and eventually be detected. With this proviso in mind one can posit that the reactions 1 H( 11 Be, 10 Be(2 + ;3.37MeV)) 2 H and 1 H( 11 Li, 9 Li(1/2 - ;2.69MeV)) 3 H together with the associated \( \gamma\) -decay processes suggest a possible nuclear analogy of Hawking radiation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

A New Method for Grain Texture Manipulation in Post-Deposition Niobium Films

Niobium films are frequently grown using forms of energetic condensation, with modest substrate temperatures to control grain structure. As an alternative, energetic deposition onto a cold substrate results in a dense amorphous film, with a much larger energy density than the re-crystallized state. Re-crystallization is then performed using a pulsed UV (HIPPO) laser, with minimal damage to the substrate. In addition, a graded interface between the substrate and Nb film is created during the early stages of energetic deposition. Experimental approach and apparatus are described.

Musson, J.↗
DOE OSTI2015

Crystal structure and texture changes during thermal cycling of TATB

Goals: Understand crystal structure and micro-structure changes during thermal cycling, understand reasons for ratcheting of TATB during thermal cycling, and Support of B61 LEP. Deliverables achieved: Completed in situ thermal cycling of loose powder and pressed pellet TATB on HIPPO, Quantified preferred orientation of pressed pellet, and quantified relative change of each of the six lattic parameters.

Materials Science(36)↗
DOE OSTI2017

Multiscale Characterization of Structural Compositional and Textural Heterogeneity of Nano-porous Geomaterials

The purpose of the project was to perform multiscale characterization of low permeability rocks to determine the effect of physical and chemical heterogeneity on the poromechanical and flow responses of shales and carbonate rocks with a broad range of physical and chemical heterogeneity . An integrated multiscale imaging of shale and carbonate rocks from nanometer to centimeter scales include s dual focused ion beam - scanning electron microscopy (FIB - SEM) , micro computed tomography (micro - CT) , optical and confocal microscopy, and 2D and 3D energy dispersive spectroscopy (EDS). In addition, mineralogical mapping and backscattered imaging with nanoindentation testing advanced the quantitative evaluat ion of the relationship between material heterogeneity and mechanical behavior. T he spatial distribution of compositional heterogeneity, anisotropic bedding patterns, and mechanical anisotropy were employed as inputs for brittle fracture simulations using a phase field model . Comparison of experimental and numerical simulations reveal ed that proper incorporation of additional material information, such as bedding layer thickness and other geometrical attributes of the microstructures, can yield improvements on the numerical prediction of the mesoscale fracture patterns and hence the macroscopic effective toughness. Overall, a comprehensive framework to evaluate the relationship between mechanical response and micro-lithofacial features can allow us to make more accurate prediction of reservoir performance by developing a multi - scale understanding of poromechanical response to coupled chemical and mechanical interactions for subsurface energy related activities.

36 MATERIALS SCIENCE↗