67 research outputs found
Quantitative powder diffraction using a (2+3) surface diffractometer and an area detector
X-ray diffractometers primarily designed for surface x-ray diffraction are
often used to measure the diffraction from powders, textured materials, and
fiber-texture samples in so-called scans. Unlike high-energy powder
diffraction only a fraction of the powder rings is typically measured and the
data consists of many detector images across the range. Such
diffractometers typically scan in directions not possible on a conventional
lab-diffractometer, which gives enhanced control of the scattering vector
relative to the sample orientation. There are, however, very few examples where
the measured intensity is directly used, such as for profile/Rietveld
refinement, as is common with other powder diffraction data. Although the
underlying physics is known, converting the data is time-consuming and the
appropriate corrections are dispersed across several publications, often not
with powder diffraction in mind. In this paper we present the angle
calculations and correction factors required to calculate meaningful
intensities for scans with a (2+3)-type diffractometer and an area
detector. We also discuss some of the limitations with respect to texture,
refraction, and instrumental resolution, and what kind of information one can
hope to obtain.Comment: Research paper, 15 pages, 12 figures, 3 table
Metastable Precursor Structures in Hydrogen-infused Super Duplex Stainless Steel Microstructure – An Operando Diffraction Experiment
We report the evolution of metastable precursor structures during hydrogen infusion in the near-surface region of a super duplex stainless steel. Grazing-incidence x-ray diffraction was employed to monitor, operando, the lattice degradation of the austenite and ferrite phases. Electrochemical hydrogen charging resulted in the splitting of the diffraction peaks of the austenite phase, suggesting the evolution of a metastable precursor structure. This may be explained by the formation of quasi-hydrides, which convert back into the austenite parent structure during hydrogen effusion. The ferrite showed less lattice deformation than the austenite and no phase transformation
hydride breathing during the template-assisted electrodeposition of Pd nanowires
We investigated the structural evolution of electrochemically fabricated Pd
nanowires by means of grazing-incidence transmission small-
and wide-angle x-ray scattering (GTSAXS and GTWAXS), x-ray fluorescence (XRF)
and 2-dimensional surface optical reflectance (2D-SOR). This shows how
electrodeposition and the hydrogen evolution reaction (HER) compete and
interact during Pd electrodepositon. During the bottom-up growth of the
nanowires, we show that -phase Pd hydride is formed. Suspending the
electrodeposition then leads to a phase transition from - to
-phase Pd hydride. Additionally, we find that grain coalescence later
hinders the incorporation of hydrogen in the Pd unit cell. GTSAXS and 2D-SOR
provide complementary information on the volume fraction of the pores occupied
by Pd, while XRF was used to monitor the amount of Pd electrodeposited.Comment: 17 pages, 11 figures, 4 appendice
Exploring Hydride Formation in Stainless Steel Revisits Theory of Hydrogen Embrittlement
Various mechanisms have been proposed for hydrogen embrittlement, but the
causation of hydrogen-induced material degradation has remained unclear. This
work shows hydrogen embrittlement due to phase instability (decomposition).
In-situ diffraction measurements revealed metastable hydrides formed in
stainless steel, typically declared as a non-hydride forming material. Hydride
formation is possible by increasing the hydrogen chemical potential during
electrochemical charging and low defect formation energy of hydrogen
interstitials. Our findings demonstrate that hydrogen-induced material
degradation can only be understood if measured in situ and in real-time during
the embrittlement process.Comment: 31 Pages, 18 Figures, Preprin
Phylogeography of the neotropical Anopheles triannulatus complex (Diptera: Culicidae) supports deep structure and complex patterns
Abstract Background The molecular phylogenetic relationships and population structure of the species of the Anopheles triannulatus complex: Anopheles triannulatus s.s., Anopheles halophylus and the putative species Anopheles triannulatus C were investigated. Methods\ud
\ud
The mitochondrial COI gene, the nuclear white gene and rDNA ITS2 of samples that include the known geographic distribution of these taxa were analyzed. Phylogenetic analyses were performed using Bayesian inference, Maximum parsimony and Maximum likelihood approaches. Results Each data set analyzed septely yielded a different topology but none provided evidence for the seption of An. halophylus and An. triannulatus C, consistent with the hypothesis that the two are undergoing incipient speciation. The phylogenetic analyses of the white gene found three main clades, whereas the statistical parsimony network detected only a single metapopulation of Anopheles triannulatus s.l. Seven COI lineages were detected by phylogenetic and network analysis. In contrast, the network, but not the phylogenetic analyses, strongly supported three ITS2 groups. Combined data analyses provided the best resolution of the trees, with two major clades, Amazonian (clade I) and trans-Andean + Amazon Delta (clade II). Clade I consists of multiple subclades: An. halophylus + An. triannulatus C; trans-Andean Venezuela; central Amazonia + central Bolivia; Atlantic coastal lowland; and Amazon delta. Clade II includes three subclades: Panama; cis-Andean Colombia; and cis-Venezuela. The Amazon delta specimens are in both clades, likely indicating local sympatry. Spatial and molecular variance analyses detected nine groups, corroborating some of subclades obtained in the combined data analysis. Conclusion Combination of the three molecular markers provided the best resolution for differentiation within An. triannulatus s.s. and An. halophylus and C. The latest two species seem to be very closely related and the analyses performed were not conclusive regarding species differentiation. Further studies including new molecular markers would be desirable to solve this species status question. Besides, results of the study indicate a trans-Andean origin for An. triannulatus s.l. The potential implications for malaria epidemiology remain to be investigated.This project has been financially supported by NIH grant AI ROI 54139–02 to JE Conn, PAPES IV Fiocruz-CNPq to RLO, and from the Fundação de Amparo à Pesquisa do Estado de São Paulo, FAPESP (Grant 2011/20397-7 to MAMS), CNPq (BPP no. 301666/2011-3 to MAMS).This research was performed under a Memorandum of Understanding between the Walter Reed Army Institute of Research and the Smithsonian Institution, with institutional support provided by both organizations. The material to be published reflects the views of the authors and should not be construed to represent those of the Department of the Army or the Department of Defense
Phylogeography of the neotropical Anopheles triannulatus complex (Diptera: Culicidae) supports deep structure and complex patterns
Abstract Background The molecular phylogenetic relationships and population structure of the species of the Anopheles triannulatus complex: Anopheles triannulatus s.s., Anopheles halophylus and the putative species Anopheles triannulatus C were investigated. Methods\ud
\ud
The mitochondrial COI gene, the nuclear white gene and rDNA ITS2 of samples that include the known geographic distribution of these taxa were analyzed. Phylogenetic analyses were performed using Bayesian inference, Maximum parsimony and Maximum likelihood approaches. Results Each data set analyzed septely yielded a different topology but none provided evidence for the seption of An. halophylus and An. triannulatus C, consistent with the hypothesis that the two are undergoing incipient speciation. The phylogenetic analyses of the white gene found three main clades, whereas the statistical parsimony network detected only a single metapopulation of Anopheles triannulatus s.l. Seven COI lineages were detected by phylogenetic and network analysis. In contrast, the network, but not the phylogenetic analyses, strongly supported three ITS2 groups. Combined data analyses provided the best resolution of the trees, with two major clades, Amazonian (clade I) and trans-Andean + Amazon Delta (clade II). Clade I consists of multiple subclades: An. halophylus + An. triannulatus C; trans-Andean Venezuela; central Amazonia + central Bolivia; Atlantic coastal lowland; and Amazon delta. Clade II includes three subclades: Panama; cis-Andean Colombia; and cis-Venezuela. The Amazon delta specimens are in both clades, likely indicating local sympatry. Spatial and molecular variance analyses detected nine groups, corroborating some of subclades obtained in the combined data analysis. Conclusion Combination of the three molecular markers provided the best resolution for differentiation within An. triannulatus s.s. and An. halophylus and C. The latest two species seem to be very closely related and the analyses performed were not conclusive regarding species differentiation. Further studies including new molecular markers would be desirable to solve this species status question. Besides, results of the study indicate a trans-Andean origin for An. triannulatus s.l. The potential implications for malaria epidemiology remain to be investigated.This project has been financially supported by NIH grant AI ROI 54139–02 to JE Conn, PAPES IV Fiocruz-CNPq to RLO, and from the Fundação de Amparo à Pesquisa do Estado de São Paulo, FAPESP (Grant 2011/20397-7 to MAMS), CNPq (BPP no. 301666/2011-3 to MAMS).This research was performed under a Memorandum of Understanding between the Walter Reed Army Institute of Research and the Smithsonian Institution, with institutional support provided by both organizations. The material to be published reflects the views of the authors and should not be construed to represent those of the Department of the Army or the Department of Defense
Social Bonding and Nurture Kinship: Compatibility between Cultural and Biological Approaches
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