216 research outputs found
Spatially Resolved Raman Spectroscopy of Single- and Few-Layer Graphene
We present Raman spectroscopy measurements on single- and few-layer graphene
flakes. Using a scanning confocal approach we collect spectral data with
spatial resolution, which allows us to directly compare Raman images with
scanning force micrographs. Single-layer graphene can be distinguished from
double- and few-layer by the width of the D' line: the single peak for
single-layer graphene splits into different peaks for the double-layer. These
findings are explained using the double-resonant Raman model based on ab-initio
calculations of the electronic structure and of the phonon dispersion. We
investigate the D line intensity and find no defects within the flake. A finite
D line response originating from the edges can be attributed either to defects
or to the breakdown of translational symmetry
Raman imaging of doping domains in graphene on SiO2
We present spatially resolved Raman images of the G and 2D lines of
single-layer graphene flakes. The spatial fluctuations of G and 2D lines are
correlated and are thus shown to be affiliated with local doping domains. We
investigate the position of the 2D line -- the most significant Raman peak to
identify single-layer graphene -- as a function of charging up to |n|~4 10^12
cm^-2. Contrary to the G line which exhibits a strong and symmetric stiffening
with respect to electron and hole-doping, the 2D line shows a weak and slightly
asymmetric stiffening for low doping. Additionally, the line width of the 2D
line is, in contrast to the G line, doping-independent making this quantity a
reliable measure for identifying single-layer graphene
Raman mapping of a single-layer to double-layer graphene transition
Abstract.: We report on confocal Raman spectroscopy on a few-layer graphene flake. Adjacent single- and double-layer graphene sections allow mapping the transition in vibrational and electronic properties to a second stacked graphene sheet and with it a weak interlayer coupling. Most prominently the width of the D' peak doubles upon going from a single to a double layer, which can be explained within the double-resonant Raman model. The intensities of the G and G' lines decrease at the crossover to a single layer. Contrary to the G' line the G peak position shifts to higher wave numbers, however, not uniformly over the entire section: its frequency fluctuates spatially. The Raman map of the D line intensity shows a non-zero contribution at the boundaries of the flake and the individual sections, which can be attributed either to defects and disorder or to the breakdown of translational symmetry, whereas within the flake no D line signal is detecte
Optimization of Generalized Multichannel Quantum Defect reference functions for Feshbach resonance characterization
This work stresses the importance of the choice of the set of reference
functions in the Generalized Multichannel Quantum Defect Theory to analyze the
location and the width of Feshbach resonance occurring in collisional
cross-sections. This is illustrated on the photoassociation of cold rubidium
atom pairs, which is also modeled using the Mapped Fourier Grid Hamiltonian
method combined with an optical potential. The specificity of the present
example lies in a high density of quasi-bound states (closed channel)
interacting with a dissociation continuum (open channel). We demonstrate that
the optimization of the reference functions leads to quantum defects with a
weak energy dependence across the relevant energy threshold. The main result of
our paper is that the agreement between the both theoretical approaches is
achieved only if optimized reference functions are used.Comment: submitte to Journal of Physics
Dissociation energy of the hydrogen molecule at 10 accuracy
The ionization energy of ortho-H has been determined to be
cm
from measurements of the GK(1,1)--X(0,1) interval by Doppler-free two-photon
spectroscopy using a narrow band 179-nm laser source and the ionization energy
of the GK(1,1) state by continuous-wave near-infrared laser spectroscopy.
(H) was used to derive the dissociation energy of
H, (H), at cm with a
precision that is more than one order of magnitude better than all previous
results. The new result challenges calculations of this quantity and represents
a benchmark value for future relativistic and QED calculations of molecular
energies.Comment: 6 pages, 5 figure
Structural and magnetic characterization of batch-fabricated nickel encapsulated multi-walled carbon nanotubes
We report on the growth and fabrication of Ni-filled multi-walled carbon nanotubes (Ni-MWNTs) with an average diameter of 115 nm and variable length of 400 nm-1μm. The Ni-MWNTs were grown using template-assisted electrodeposition and low pressure chemical vapor deposition (LPCVD) techniques. Anodized alumina oxide (AAO) templates were fabricated on Si using a current controlled process. This was followed by the electrodeposition of Ni nanowires (NWs) using galvanostatic pulsed current (PC) electrodeposition. Ni NWs served as the catalyst to grow Ni-MWNTs in an atmosphere of H2/C2H2 at a temperature of 700º C. Time dependent depositions were carried out to understand the diffusion and growth mechanism of Ni-MWNTs. Characterization was carried out using scanning electron microscopy (SEM), focused ion beam (FIB) milling, transmission electron microscopy (TEM), Raman spectroscopy and energy dispersive x-ray spectroscopy (EDX). TEM analysis revealed that the Ni nanowires possess a fcc structure. To understand the effects of the electrodeposition parameters, and also the effects of the high temperatures encountered during MWNT growth on the magnetic properties of the Ni-MWNTs, vibrating sample magnetometer (VSM) measurements were performed. The template-based fabrication method is repeatable, efficient, enables batch fabrication and provides good control on the dimensions of the Ni-MWNT
Spatial distribution of CD3- and CD8-positive lymphocytes as pretest for POLE wild-type in molecular subgroups of endometrial carcinoma.
INTRODUCTION
Over the years, the molecular classification of endometrial carcinoma has evolved significantly. Both POLEmut and MMRdef cases share tumor biological similarities like high tumor mutational burden and induce strong lymphatic reactions. While therefore use case scenarios for pretesting with tumor-infiltrating lymphocytes to replace molecular analysis did not show promising results, such testing may be warranted in cases where an inverse prediction, such as that of POLEwt, is being considered. For that reason we used a spatial digital pathology method to quantitatively examine CD3+ and CD8+ immune infiltrates in comparison to conventional histopathological parameters, prognostics and as potential pretest before molecular analysis.
METHODS
We applied a four-color multiplex immunofluorescence assay for pan-cytokeratin, CD3, CD8, and DAPI on 252 endometrial carcinomas as testing and compared it to further 213 cases as validation cohort from a similar multiplexing assay. We quantitatively assessed immune infiltrates in microscopic distances within the carcinoma, in a close distance of 50 microns, and in more distant areas.
RESULTS
Regarding prognostics, high CD3+ and CD8+ densities in intra-tumoral and close subregions pointed toward a favorable outcome. However, TCGA subtyping outperforms prognostication of CD3 and CD8 based parameters. Different CD3+ and CD8+ densities were significantly associated with the TCGA subgroups, but not consistently for histopathological parameter. In the testing cohort, intra-tumoral densities of less than 50 intra-tumoral CD8+ cells/mm2 were the most suitable parameter to assume a POLEwt, irrespective of an MMRdef, NSMP or p53abn background. An application to the validation cohort corroborates these findings with an overall sensitivity of 95.5%.
DISCUSSION
Molecular confirmation of POLEmut cases remains the gold standard. Even if CD3+ and CD8+ cell densities appeared less prognostic than TCGA, low intra-tumoral CD8+ values predict a POLE wild-type at substantial percentage rates, but not vice versa. This inverse correlation might be useful to increase pretest probabilities in consecutive POLE testing. Molecular subtyping is currently not conducted in one-third of cases deemed low-risk based on conventional clinical and histopathological parameters. However, this percentage could potentially be increased to two-thirds by excluding sequencing of predicted POLE wild-type cases, which could be determined through precise quantification of intra-tumoral CD8+ cells
CETOBaC - Centre d’études turques, ottomanes, balkaniques et centrasiatiques
Marc Aymes, chargé de recherche au CNRSBenjamin Gourisse, ATER à l’Université Paris-I/Panthéon-SorbonneEmmanuel Szurek, doctorant à l’EHESS Sociologie historique de l’État en Turquie depuis les Tanzimat Le séminaire s’est poursuivi en 2010-2011 pour sa troisième année consécutive. Il demeure articulé au programme ANR TRANSTUR, « Ordonner et transiger. Modalités de gouvernement et d’administration en Turquie et dans l’Empire ottoman du XIXe siècle à nos jours » (2008-2011), dont il permet de d..
Large-Scale Selective Sweep among Segregation Distorter Chromosomes in African Populations of Drosophila melanogaster
Segregation Distorter (SD) is a selfish, coadapted gene complex on chromosome 2 of Drosophila melanogaster that strongly distorts Mendelian transmission; heterozygous SD/SD+ males sire almost exclusively SD-bearing progeny. Fifty years of genetic, molecular, and theory work have made SD one of the best-characterized meiotic drive systems, but surprisingly the details of its evolutionary origins and population dynamics remain unclear. Earlier analyses suggested that the SD system arose recently in the Mediterranean basin and then spread to a low, stable equilibrium frequency (1–5%) in most natural populations worldwide. In this report, we show, first, that SD chromosomes occur in populations in sub-Saharan Africa, the ancestral range of D. melanogaster, at a similarly low frequency (∼2%), providing evidence for the robustness of its equilibrium frequency but raising doubts about the Mediterranean-origins hypothesis. Second, our genetic analyses reveal two kinds of SD chromosomes in Africa: inversion-free SD chromosomes with little or no transmission advantage; and an African-endemic inversion-bearing SD chromosome, SD-Mal, with a perfect transmission advantage. Third, our population genetic analyses show that SD-Mal chromosomes swept across the African continent very recently, causing linkage disequilibrium and an absence of variability over 39% of the length of the second chromosome. Thus, despite a seemingly stable equilibrium frequency, SD chromosomes continue to evolve, to compete with one another, or evade suppressors in the genome
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