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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Materials Fingerprinting Classification

Significant progress in many classes of materials could be made with the availability of experimentally-derived large datasets composed of atomic identities and three-dimensional coordinates. Methods for visualizing the local atomic structure, such as atom probe tomography (APT), which routinely generate datasets comprised of millions of atoms, are an important step in realizing this goal. However, state-of-the-art APT instruments generate noisy and sparse datasets that provide information about elemental type, but obscure atomic structures, thus limiting their subsequent value for materials discovery. The application of a materials fingerprinting process, a machine learning algorithm coupled with topological data analysis, provides an avenue by which here-to-fore unprecedented structural information can be extracted from an APT dataset. As a proof of concept, the material fingerprint is applied to high-entropy alloy APT datasets containing body-centered cubic (BCC) and face-centered cubic (FCC) crystal structures. A local atomic configuration centered on an arbitrary atom is assigned a topological descriptor, with which it can be characterized as a BCC or FCC lattice with near perfect accuracy, despite the inherent noise in the dataset. Finally, this successful identification of a fingerprint is a crucial first step in the development of algorithms which can extract more nuanced information, such as chemical ordering, from existing datasets of complex materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Classification of igneous rocks analyzed by ChemCam at Gale crater, Mars

Several recent studies have revealed that Mars is not a simple basalt-covered planet, but has a more complex geological history. In Gale crater on Mars, the Curiosity rover discovered 59 igneous rocks. This article focuses on their textures (acquired from the cameras such as MAHLI and MastCam) and their geochemical compositions that have been obtained using the ChemCam instrument. Light-toned crystals have been observed in most of the rocks. They correspond to feldspars ranging from andesines/oligoclases to anorthoclases and sanidines in the leucocratic vesiculated rocks. Darker crystals observed in all igneous rocks (except the leucocratic vesiculated ones) were analyzed by LIBS and mainly identified as Fe-rich pigeonites and Fe-augites. Iron oxides have been observed in all groups whereas F-bearing minerals have been detected only in few of them. From their textural analysis and their whole-rock compositions, all these 59 igneous rocks have been classified in five different groups; from primitive rocks i.e. dark aphanitic basalts/basanites, trachybasalts, tephrites and fine/coarse-grained gabbros/norites to more evolved materials i.e. porphyritic trachyandesites, leucocratic trachytes and quartz-diorites. The basalts and gabbros are found all along the traverse of the rover, whereas the felsic rocks are located before the Kimberley formation, i.e. close to the Peace Vallis alluvial fan deposits. This suggests that these alkali rocks have been transported by fluvial activity and could come from the Northern rim of the crater, and may correspond to deeper strata buried under basaltic regolith (Sautter et al., 2015). Some of the basaltic igneous rocks are surprisingly enriched in iron, presenting low Mg# similar to the nakhlite parental melt that cannot be produced by direct melting of the Dreibus and Wanke (1986) martian primitive mantle. The basaltic rocks at Gale are thus different from Gusev basalts. They could originate from different mantle reservoirs, or they could have undergone a more extensive fractional crystallization. Lastly, Gale basaltic rocks could have been the parental magma of residual liquid extending into alkali field towards trachyte composition as magma fractionated under anhydrous condition on its way to the surface before sub adiabatic ascent.

58 GEOSCIENCES↗
DOE OSTI2010

Pathologic Nodal Classification Is the Most Discriminating Prognostic Factor for Disease-Free Survival in Rectal Cancer Patients Treated With Preoperative Chemoradiotherapy and Curative Resection

Purpose: We retrospectively evaluated the effects of clinical and pathologic factors on disease-free survival (DFS) with the aim of identifying the most discriminating factor predicting DFS in rectal cancer patients treated with preoperative chemoradiotherapy (CRT) and curative resection. Methods and Materials: The study involved 420 patients who underwent preoperative CRT and curative resection between August 2001 and October 2006. Gender, age, distance from the anal verge, histologic type, histologic grade, pretreatment carcinoembryonic antigen (CEA) level, cT, cN, cStage, circumferential resection margin, type of surgery, preoperative chemotherapy, adjuvant chemotherapy, ypT, ypN, ypStage, and tumor regression grade (TRG) were analyzed to identify prognostic factors associated with DFS. To compare the discriminatory prognostic ability of four tumor response-related pathologic factors (ypT, ypN, ypStage, and TRG), the Akaike information criteria were calculated. Results: The 5-year DFS rate was 75.4%. On univariate analysis, distance from the anal verge, histologic type, histologic grade, pretreatment CEA level, cT, circumferential resection margin, type of surgery, preoperative chemotherapeutic regimen, ypT, ypN, ypStage, and TRG were significantly associated with DFS. Multivariate analysis showed that the four parameters ypT, ypN, ypStage, and TRG were, consistently, significant prognostic factors for DFS. The ypN showed the lowest Akaike information criteria value for DFS, followed by ypStage, ypT, and TRG, in that order. Conclusion: In our study, ypT, ypN, ypStage, and TRG were important prognostic factors for DFS, and ypN was the most discriminating factor.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Prognostic Relevance of Treatment Failure Patterns in Pediatric High-Grade Glioma: Is There a Role for a Revised Failure Classification System?

Purpose: We sought to investigate the pattern of treatment failure with respect to anatomic extent, radiation dose, and criteria for failure according to the Response Assessment in Neuro-Oncology (RANO). We evaluated the corresponding prognostic significance of these factors in patients with pediatric high-grade glioma (pHGG). Methods and Materials: Fifty-six patients with pHGG were enrolled in an institutional phase 1 to 2 prospective trial that included maximal safe resection and radiation therapy with concurrent and adjuvant erlotinib. The radiation therapy dose administered was 54 to 59.4 Gy at 1.8 Gy/d. Tumor progression was defined according to clinical symptoms and imaging features and was classified in relation to the original extent of the tumor, radiation prescription target volume coverage, and RANO criteria (RANOc). Results: With a median follow-up period of 90 months (range, 70-124 months), progression occurred in 48 patients (85.7%) while 8 (14.3%) were without progression. Central failure represented 42.6% of the total cohort, while in-field, marginal, and distant failures occurred in 7.4%, 9.3%, and 22.2%, respectively. Patients with biopsy or subtotal resection had increased rates of central failure and represented 14.81% and 16.67% of the total cohort, respectively. Tumor progression was classified as local, local plus distant, or distant. Among patients with local failure as a component of failure, 5 were considered to have marginal failure. Patients with frontal, temporal, and parietal disease had the highest rates of multifocal failure. A comparison between responses defined by RANOc demonstrated varied time to death (TTD) from progression. Conclusions: Pediatric high-grade glioma was shown to have high rates of central failure, particularly in cases with limited resection. Patients with central failure had a trend toward more prolonged TTD from failure relative to other failure patterns. The low marginal failure rates seen in this group suggest that less conservative radiation target margins may be possible. TTD from failure varied according to RANO type, suggesting that adult RANOc require modification before being applied to pHGG.

62 RADIOLOGY AND NUCLEAR MEDICINE↗