Imagining ‘non-nationality’: Cosmopolitanism as a source of identity and belonging

Current literature tends to see cosmopolitan identity formation as an individual endeavour of developing a stance of openness, and transcending discourses of national and other cultural identities. This article challenges the essentialism inherent in this model by proposing a different framing of cosmopolitan identity formation that shifts the focus to how people collectively mobilize cosmopolitanism as a resource for cultural identity construction. The article is based on an anthropological study of transnational professionals who are part of a diverse expatriate community in Amsterdam. The analysis shows how these professionals draw on cosmopolitanism to define themselves as ‘non-nationals’. This involves downplaying national affiliations and cultural differences while also marking national identity categories and ‘cultural features’ to maintain the difference they collectively embrace. This however does not imply openness to all otherness. Boundary drawing to demarcate the cosmopolitan ‘us’ in relation to national (mono)culture is equally important. The article argues that cosmopolitan identities are socially accomplished as particular modes of collective belonging that are part of – not beyond – a global discursive sphere of identity politics

Polymorphic transition of tin under shock wave compression: Experimental results

In this work, the β-bct polymorphic transition in tin is investigated by means of plate impact experiments. The Sn target surface is observed in a partially released state obtained thanks to a transparent lithium fluoride (LiF) anvil. We report both measurements of interface velocity and temperature obtained using Photon Doppler Velocimetry and IR optical pyrometer on shock-loaded tin from 8 to 16 GPa. We show that the Mabire Model EOS associated to the SCG plasticity model provides an overall good estimate of the velocity profiles. However, depnding on the shock amplitude, its prediction of the temperature profile may be less satisfactory, hence underlining the need for future improvements in terms of phase transition kinetics description

Shocks Sensing by Fiber Bragg Gratings and a 100 MHz Dynamic Dispersive Interrogator

International audienceA multi-channels high resolution dispersive interrogator with at a high sampling rate has been developed to measure shocks pressure levels by Fiber Bragg Gratings (FBGs). Two FBG orientations are compared numerically and experimentally. The first one is along the cylindrical target axis, thus the grating spectrum is "blue shifted". The second orientation is perpendicular to the target axis and the grating spectrum is "red shifted". The interrogator uses a femtosecond laser source to cover the C+L band spectrum. The source repetition rate (100 MHz) fixes the spectra acquisition rate. The wavelengths are basically converted to time using a long telecom fiber. The time-multiplexed spectra are recorded with 400 points by a fast oscilloscope (40 GSa/s). The experimental setup is a Tin plate impact on a PMMA target performed in a 35-mm single-stage gas gun. An impact at 510 m/s generates a pressure level of 1.69 GPa during 5 µs. The performance of the dynamic interrogator and the wavelength shifts in the two FBG configurations are discussed

Dynamic Dispersive Spectrometer using a Fiber Bragg Grating for High Pressure Measurements

International audienceA new high resolution dispersive spectrometer has been developed to measure high pressure shock profiles every 10 ns using long Fiber Bragg Gratings. The performances are compared with a dynamic AWG-based spectrometer. Two small diameter fibers allow inserting in parallel two 50-mm long gratings into the target. The use of slightly chirped gratings provides the localization of the shock-wave along them. Placed along the target axis, a gratings reflected spectrum is "blue shifted". The FBG's central wavelength are 1605 nm to cover a pressure range of 0-8 GPa. The new spectrometer is based on a femtosecond laser source, a long dispersive fiber and a fast acquisition system with an electrical bandwidth above 30 GHz. The experimental setup was a symmetric impact with 6061T6 aluminum, performed with a 110-mm in diameter single-stage gas gun. An impact velocity of 314 m/s is obtained and generated a sustained level of 2.1 GPa during few microseconds. A resulted Bragg shift of (16 ± 1) nm is measured. The dispersive spectrometer offers much greater resolution than the AWG one which is favorable to retrieve more easily a pressure profile

Dynamic High Pressure Measurements Using a Fiber Bragg Grating Probe and an Arrayed Waveguide Grating Spectrometer

18th Interferometry Conference, San Diego, CA, AUG 30-SEP 01, 2016International audienceHigh pressure shock profiles are monitored using a long Fiber Bragg Grating (FBG). Such thin probe, with a diameter of typically 150 µm, can be inserted directly into targets for shock plate experiments. The shocked FBG's portion is stressed under compression, which increases its optical group index and shortens its grating period. Placed along the 2D symmetrical axis of the cylindrical target, the second effect is stronger and the reflected spectrum shifts towards the shorter wavelengths. The dynamic evolution of FBG spectra is recorded with a customized Arrayed Waveguide Grating (AWG) spectrometer covering the C+L band. The AWG provides 40 channels of 200-GHz spacing with a special flat-top design. The output channels are fiber-connected to photoreceivers (bandwidth: DC - 400 MHz or 10 kHz - 2 GHz). The experimental setup was a symmetric impact, completed in a 110-mm diameter single-stage gas gun with Aluminum (6061T6) impactors and targets. The FBG's central wavelength was 1605 nm to cover the pressure range of 0 - 8 GPa. The FBG was 50-mm long as well as the target's thickness. The 20-mm thick impactor maintains a shock within the target over a distance of 30 mm. For the impact at 522 m/s, the sustained pressure of 3.6 GPa, which resulted in a Bragg shift of (26.2 +/- 1.5) nm, is measured and retrieved with respectively thin-film gauges and the hydrodynamic code Ouranos. The shock sensitivity of the FBG is about 7 nm/GPa, but it decreases with the pressure level. The overall spectra evolution is in good agreement with the numerical simulations

Suivi en temps réel de la pression et de la vitesse de choc par spectrométrie ultra-rapide à l'aide de réseaux de Bragg à périodes variables : sensibilités en pression calculées et expérimentales dans la gamme [0 - 4 GPa]

International audienceFiber Bragg Gratings (FBGs) are gaining acceptance as velocity/pressure gauges in the fields of detonation and shock physics on account of their sensitivity, small size, flexibility, electromagnetic immunity, and wavelength-encoded feature. Chirped FBGs (CFBGs) are investigated as wavelength-to-position discriminators with the purpose of monitoring pressure/velocity profiles over a distance range of typically 100 mm. The use of CFBGs simplifies both sensor deployment and data retrieval and finally improves the accuracy due to the increased number of measurement data. In this paper, the metrological performance of CFBGs used as in situ distributed shock pressure/velocity gauges is investigated both theoretically and experimentally in a planar shock loading configuration with an aluminum-based flyer and target. In the intermediate range for shock stress, i.e., less than the Hugoniot Elastic Limit (HEL) of silica, CFBGs provide simultaneous measurements of both shockwave velocity and stress within the target material. A Bragg wavelength-to-stress model is proposed that takes into account (i) the state-of-stress within the target material, (ii) the stress coupling coefficient due to imperfect impedance matching between the target material and the silica fiber, (iii) the conversion of the state-of-stress into a state-of-strain within the silica fiber, and (iv) the conversion of strain data into observable Bragg wavelength shifts. Finally, the model also takes into account the pressure dependence of constitutive parameters for silica and aluminum. Experiments were performed in planar shock loading using CFBGs as stress gauges, bonded along the target axis with Araldite glue. 6061-T6 aluminum flyers were launched at several velocities by a gas gun onto targets of the same material. A free-space Czerny-Turner (CT) spectrometer and an integrated-optics Arrayed-Waveguide Grating (AWG) were both used as dynamic spectrum analyzers. Experimental Bragg wavelength shifts agree well with theoretical predictions for both elastic and hydrodynamic planar shock loading of 6061-T6 aluminum, opening up large perspectives for shock physics experiments

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Fiber Bragg Grating Dynamic Extensometry on Metallic Samples submitted to High Pulse Power Magnetic Fields

International audienceIsentropic compression of metallic samples under High Pulse Powers (HPPs) are performed at CEA-Gramat. Large strains and high strain rates are obtained under intense magnetic field-driven Laplace forces. On account on electromagnetic immunity, a dedicated Fiber Bragg Grating (FBG) mainframe was designed by CEA LIST. Ring aluminum samples with crossed FBGs bonded onto the external surface were tested on the CYCLOPE HPP facility. Dynamic strain measurements were performed along with Photonic-Doppler Velocimetry (PDV). FBG strain data compare well to strain data derived from PDV displacements, leading the way to direct dynamic extensometry in the purpose of improving Magneto-Hydro-Dynamics (MHD) codes