35 research outputs found
Rhynie chert Prototaxites taiti dataset
No full text3D models of Prototaxites taiti from the 407 million year old Rhynie chert. Photogrammetry was used to capture the external 3D structure of two Rhynie chert blocks. Block North Sea Core (NSC) 36 and Lyon collection block 156. After describing the external surface of NSC36 we cut the specimen to investigate internal structure and produced another photogrammetry model of the cut specimen. Alongside our investigations with photogrammetry we produced a 3D model of complex tube branching within a medullary spot. This investigation was based on using confocal laser scanning microscopy to investigate thin section NMS G.2024.5.7 (MPEG0057). The dataset is related to the upcoming publication by Corentin C. Loron, Laura M. Cooper, Sean McMahon, Seán F. Jordan, Andrei V. Gromov, Matthew Humpage, Laetitia Pichevin, Hendrik Vondracek, Ruaridh Alexander, Edwin Rodriguez Dzul, Alexander T. Brasier, Alexander J. Hetherington. (In submission)
Asymptotic behavior of generalized capacities with applications to eigenvalue perturbations: The higher dimensional case
Get PDFWe provide a full series expansion of a generalization of the so-called u-capacity related to the Dirichlet-Laplacian in dimension three and higher, extending the results of Abatangelo et al. (2021); Abatangelo, Lena and Musolino (2022) dealing with the planar case. We apply the result in order to study the asymptotic behavior of perturbed eigenvalues when Dirichlet conditions are imposed on a small regular subset of the domain of the eigenvalue problem. (c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
Rhynie chert Prototaxites taiti dataset
No full text3D models of Prototaxites taiti from the 407 million year old Rhynie chert. Photogrammetry was used to capture the external 3D structure of two Rhynie chert blocks. Block North Sea Core (NSC) 36 and Lyon collection block 156. After describing the external surface of NSC36 we cut the specimen to investigate internal structure and produced another photogrammetry model of the cut specimen. Alongside our investigations with photogrammetry we produced a 3D model of complex tube branching within a medullary spot. This investigation was based on using confocal laser scanning microscopy to investigate thin section NMS G.2024.5.7 (MPEG0057). The dataset is related to the upcoming publication by Corentin C. Loron, Laura M. Cooper, Sean McMahon, Seán F. Jordan, Andrei V. Gromov, Matthew Humpage, Laetitia Pichevin, Hendrik Vondracek, Ruaridh Alexander, Edwin Rodriguez Dzul, Alexander T. Brasier, Alexander J. Hetherington. (In submission).>README.txt
A readme file providing information about the five image files.
>Images_of_sampled_fossils.zip
Images of fossils sampled by ATR-FTIR
>MPEG0057_2024_03_25__12_47_29_airyscan_Substack (1-114)_zstack.tif
Airyscan confocal z-stack produced from thin section National Museum Scotland (NMS) G.2024.5.7 (MPEG0057).
>MPEG0057 spot model.obj
3D model of medullary spot, produced from Airyscan confocal z-stack of thin section National Museum Scotland (NMS) G.2024.5.7 (MPEG0057)
>NSC36 whole block_scaled.oj
3D photogrammetry model of complete Rhynie chert Block North Sea Core (NSC) 36.
>NSC 36 cut_scaled.obj
3D photogrammetry model of Rhynie chert Block North Sea Core (NSC) 36, after the specimen had been cut.
>block 156 scaled.obj
3D photogrammetry model of Rhynie chert Lyon collection block 156
Geometric bounds for the magnetic Neumann eigenvalues in the plane
Get PDFWe consider the eigenvalues of the magnetic Laplacian on a bounded domain Omega of R-2 with uniform magnetic field beta > 0 and magnetic Neumann boundary conditions. We find upper and lower bounds for the ground state energy lambda(1) and we provide semiclassical estimates in the spirit of Kroger for the first Riesz mean of the eigenvalues. We also discuss upper bounds for the first eigenvalue for non-constant magnetic fields beta = beta(x) on a simply connected domain in a Riemannian surface. In particular: we prove the upper bound lambda(1) infinity and consists of the semiclassical limit 2 pi k/ |Omega| plus an oscillating term.We also construct several examples, showing the importance of the topology: in particular we show that an arbitrarily small tubular neighborhood of a generic simple closed curve has lowest eigenvalue bounded away from zero, contrary to the case of a simply connected domain of small area, for which lambda(1) is always small.(c) 2023 The Author(s). Published by Elsevier Masson SAS. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/)
Point defect engineering in Ge
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 121-127).In 1947, the first transistor was made of germanium, but soon silicon became the core material of computer chips because of its processability. However, as the typical dimensions of transistors are getting closer to the atomic size, the traditional approach of scaling down transistors to improve performance is reaching its limits, and other elements need to be used in conjunction with silicon. Germanium is one of the key materials to empower silicon based devices because it possesses electronic and optoelectronic properties complementary to those of silicon, among them higher carrier mobilities and a direct band gap (G-valley) at 1.55 [mu]m (the telecom C-band, therefore adding new capabilities to silicon integrated microphotonics). Furthermore, good quality Ge layers can be grown epitaxially on a Si substrate, allowing a monolithic integration of devices. However, compared to silicon, little is known about the point defects in germanium. The goal of the present doctoral work is to remedy this gap. To this end, we have used radiation (gamma rays, alpha particles, and neutrons) to controllably introduce point defects in crystalline germanium, which were then characterized by Deep-Level Transient Spectroscopy (DLTS), a technique that allows the determination of the activation energy, capture cross-section, and concentration of the said defects. By studying their electronic properties, annealing kinetics, and introduction rates, we were able to separate vacancy-containing from interstitial-containing defects and gain insight on their physical nature and formation process. We especially identified a di-interstitial defect and a tri-interstitial defect. In addition, we proved that in the case of alpha particles and neutron irradiation, the fact that defects are generated in a collision cascade influences their carrier capture rates and annealing behaviors. We have also characterized the impact of radiation on commercial germanium-on-silicon photodetectors, and showed that point defects associate with dislocations in epitaxial Ge-on-Si layers. Finally, we have investigated the passivation of midgap states by implanting germanium with fluorine, and showed how the interaction between the halogen element, the amorphous/crystalline interface during the solid phase epitaxy, and the implantation damage is key in obtaining a high performance materialby Corentin Monmeyran.Ph. D
Author Correction: Early fungi from the Proterozoic era in Arctic Canada
No full textInternational audienceFungi are crucial components of modern ecosystems. They may have had an important role in the colonization of land by eukaryotes, and in the appearance and success of land plants and metazoans(1-3). Nevertheless, fossils that can unambiguously be identified as fungi are absent from the fossil record until the middle of the Palaeozoic era(4,5). Here we show, using morphological, ultrastructural and spectroscopic analyses, that multicellular organic-walled microfossils preserved in shale of the Grassy Bay Formation (Shaler Supergroup, Arctic Canada), which dates to approximately 1,010-890 million years ago, have a fungal affinity. These microfossils are more than half a billion years older than previously reported unambiguous occurrences of fungi, a date which is consistent with data from molecular clocks for the emergence of this clade(6,7). In extending the fossil record of the fungi, this finding also pushes back the minimum date for the appearance of eukaryotic crown group Opisthokonta, which comprises metazoans, fungi and their protist relatives(8,9)
Fables d'Ésope 2: Les Hommes
No full textThis is a tight little book, 6 x 7¾. It contains eighty-six of Aesop's fables drawn from either Chambry's 1927 translation or a version done by Hachette in 1913 without attribution to an author. To go with those texts there are eleven full-page illustrations noted on 85 and a number of other designs along the way. Six of the full-page illustrations are colored. For an inexpensive edition, this book does a good job with the art! There is a T of C at the back. I am not sure that I have ever seen Aesop's work divided into animals and people before this! See the companion volume on animals.This is a hardbound book (hard cover)This book has a dust jacket (book cover)Language note: FrenchOriginal language: greTraduction, introduction et notes par Daniel Loayz
Synchrotron FTIR investigations of kerogen from Proterozoic organic-walled eukaryotic microfossils.
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On the multiplicity of the second eigenvalue of the Laplacian in non simply connected domains -with some numerics
No full textWe revisit an interesting example proposed by Maria Hoffmann-Ostenhof, the second author and Nikolai Nadirashvili of a bounded domain in R 2 for which the second eigenvalue of the Dirichlet Laplacian has multiplicity 3. We also analyze carefully the first eigenvalues of the Laplacian in the case of the disk with two symmetric cracks placed on a smaller concentric disk in function of their size
Organic-walled microfossils from the late Mesoproterozoic to early Neoproterozoic lower Shaler Supergroup (Arctic Canada): Diversity and biostratigraphic significance
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