Search results for "Ibers"
showing 10 items of 578 documents
Dscam1 Is Required for Normal Dendrite Growth and Branching But Not for Dendritic Spacing in Drosophila Motoneurons
2014
Down syndrome cell adhesion molecule, Dscam, serves diverse neurodevelopmental functions, including axon guidance and synaptic adhesion, as well as self-recognition and self-avoidance, depending on the neuron type, brain region, or species under investigation. InDrosophila, the extensive molecular diversity that results from alternative splicing of Dscam1 into >38,000 isoforms provides neurons with a unique molecular code for self-recognition in the nervous system. Each neuron produces only a small subset of Dscam1 isoforms, and distinct Dscam1 isoforms mediate homophilic interactions, which in turn, result in repulsion and even spacing of self-processes, while allowing contact with neig…
Practical application of electron microscopy to neuromuscular diseases.
2013
Concerning individual neuromuscular conditions, electron microscopy may be considered “essential,” “helpful,” or “wasteful.” “Essential” electron microscopy should provide a clear diagnosis, because of the disease specificity of the ultrastructural findings, in particular as to inclusions within muscle fibers, such as cylindrical spirals and reducing bodies. Electron microscopy may be “helpful” in detecting ultrastructural features preceding typical light microscopic findings, for instance, undulating tubules in endothelial cells. Congenital, metabolic, and inflammatory myopathies may often be more easily and more reliably diagnosed by means of the electron microscope. Diagnostically “waste…
Design of All-Normal Dispersion Microstructured Optical Fiber on Silica Platform for Generation of Pulse-Preserving Supercontinuum Under Excitation a…
2017
We investigated numerically the possibility of all normal dispersion fiber design for near-infrared supercontinuum generation based on a standard air-silica microstructure. The design procedure includes finding of target dispersion profile and subsequent finding of appropriate geometrical fiber design by inverse dispersion engineering. It was shown that the tailoring of dispersion profile could increase the spectral width of generated supercontinuum while maintaining perfect spectral flatness. Conditions necessary for wide and flat supercontinuum generation as well as restrictions imposed by chosen materials were discussed. As a result of design and optimization procedure, an air-silica des…
Polarization attraction using counter-propagating waves in optical fiber at telecommunication wavelengths
2008
International audience; In this work, we report the experimental observation of a polarization attraction process which can occur in optical fibers at telecommunication wavelengths. More precisely, we have numerically and experimentally shown that a polarization attractor, based on the injection of two counter-propagating waves around 1.55 mu m into a 2-m long high nonlinear fiber, can transform any input polarization state into a unique well-defined output polarization state.
Radiation effects on silica-based preforms and optical fibers-II: Coupling ab initio simulations and experiments
2008
International audience; Abstract—Experimental characterization through electron paramagnetic resonance (EPR) and confocal luminescence microscopy (CML) of a Ge-doped glass (preform and fiber) reveals the generation of several point defects by 10 keV X-ray radiation-induced attenuation: GeE', Ge(1), Ge(2), and Ge-ODC. The generation mechanisms of Ge-ODC and charged defects like GeE' centers are studied through ab initio simulation. Our calculations used a 108 atom supercell with a glass composition comparable to the Ge-doped core or to the pure-silica cladding of the canonical sample. The large size of our cell allows us to study the influence of the local environment surrounding the X-ODC d…
Steady-State X-Ray Radiation-Induced Attenuation in Canonical Optical Fibers
2020
The so-called canonical optical fibers (OFs) are samples especially designed to highlight the impact of some manufacturing process parameters on the radiation responses. Thanks to the results obtained on these samples, it is thus possible to define new procedures to better control the behaviors of OFs in radiation environments. In this article, we characterized the responses, under steady-state X-rays, of canonical samples representative of the most common fiber types differing by their core-dopants: pure silica, Ge, Al, and P. Their radiation-induced attenuation (RIA) spectra were measured online at both room temperature (RT) and liquid nitrogen temperature (LNT), in the energy range [~0.6…
Radiation effects on silica-based preforms and optical fibers-I: Experimental study with canonical samples
2008
International audience; Prototype samples of preforms and associated fibers have been designed and fabricated through MCVD process to investigate the role of fluorine (F) and germanium (Ge) doping elements on the radiation sensitivity of silica-based glasses. We characterized the behaviors of these canonical samples before, during and after 10 keV X-ray irradiation through several spectroscopic techniques, to obtain global information (in situ absorption measurements, electron paramagnetic resonance) or spatially-resolved information (confocal microscopy, absorption and luminescence on preform). These tests showed that, for the Ge-doped fiber and in the 300–900 nm range, the radiation-induc…
Transient and Steady-State Radiation Response of Phosphosilicate Optical Fibers: Influence of H2 Loading
2019
The radiation response of a phosphorus-doped multimode optical fiber is investigated under both transient (pulsed X-rays) and steady-state ( $\gamma $ - and X-rays) irradiations. The influence of a H2 preloading on the fiber radiation-induced attenuation (RIA) in the 300–2000-nm wavelength range has been characterized. To better understand the impact of this treatment, online behaviors of fiber samples containing different amounts of gas are compared from glass saturation (100%) to less than 1%. In addition to these in situ experiments, additional postirradiation spectroscopic techniques have been performed such as electron paramagnetic resonance or luminescence measurements to identify the…
Transient Radiation Responses of Optical Fibers: Influence of MCVD Process Parameters
2012
International audience; A dedicated set of fibers elaborated via the Modified Chemical Vapor Deposition (MCVD) technique is used to study the influence of composition and drawing parameters on their responses to an X-ray pulse representative of the radiation environments associated with Megajoule class lasers. These canonical fibers were designed to highlight the impact of these parameters on the amplitude and kinetics of the transient pulsed X-ray Radiation Induced Attenuation (RIA) at room temperature. From preforms differing by their core composition, three optical fibers were elaborated by varying the tension and speed during the drawing process. No or only slight RIA change results fro…
Influence of the manufacturing process on the radiation sensitivity of fluorine-doped silica-based optical fibers
2011
International audience; In this work, we analyze the origins of the observed differences between the radiation sensitivities of fluorine-doped optical fibers made with different fabrication processes. We used several experimental techniques, coupling in situ radiation-induced absorption measurements with post mortem confocal microscopy luminescence measurements. Our data showed that the silica intrinsic defects are generated both from precursor sites and from strained regular Si-O-Si linkages. Our work also provides evidence for the preponderant role of the chlorine in determining the optical losses at about 3.5 eV. The results show that the manufacturing process of these fibers strongly af…