Ref HAL: hal-03419440_v1
DOI: 10.1007/s10854-021-07037-4
WoS: WOS:000704940000007
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In the design of medium and low voltage equipment such as cable accessories, generator, motor end windings or bushings, issues with electrical field enhancement occur at interfaces between insulators and conductors, resulting in accelerated material ageing. The purpose of this paper is to present a novel dielectric composite material which has the properties to mitigate this local amplification. It is a functional dielectric which resistivity decreases by several orders with electric field from 10(14) to 10(9) ohm m up to 1 kV mm(-1) while the dielectric constant decreases from 15 to 12 in the 10(-2)-10(6) Hz range. This novel material is made with graphite nanoplatelets. It may be used as a resistive or capacitive field grading material in electrical applications.

Ref HAL: hal-02134571_v1
DOI: 10.1103/PhysRevB.99.115431
WoS: 000462895200004
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Polarized optical microscopy and spectroscopy are progressively becoming key methods for the high-throughput characterization of individual carbon nanotubes (CNTs) and other one-dimensional nanostructures, on substrate and in devices. The optical response of CNTs on substrate in cross polarization experiments is usually limited by the polarization conservation of the optical elements in the experimental setup. We developed a theoretical model taking into account the depolarization by the setup and the optical response of the substrate. We show that proper modelization of the experimental data requires to take into account both noncoherent and coherent light depolarization by the optical elements. We also show how the nanotube signal can be decoupled from the complex reflection factor of the antireflection substrate, which is commonly used to enhance the optical contrast. Finally, we describe an experimental protocol to extract the depolarization parameters and the complex nanotube susceptibility, and how it can improve the chirality assignment of individual carbon nanotubes in complex cases.

Ref HAL: hal-01517065_v1
DOI: 10.1111/ijac.12637
WoS: WOS:000397509500020
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1 Citation
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The recycling process toward the elimination of varistor wastes into new electro-active silicon composites has been investigated. We studied the dependence of the E-J characteristics on the aggregate content in the polymer matrix. Formulations with 40 vol.% metal oxide varistor aggregates in the 100-200m range exhibit reliable nonlinear behavior with a switching voltage of 280 +/- 30V/mm. The breakdown voltage of the composite decreases as both filler's diameter and filler's volume fraction increases in the 550-220V/mm and 440-280V/mm range, respectively. This paves the way for the valorization of varistors based zinc oxide (ZnO) ceramics.

Ref HAL: hal-01292652_v1
Ref Arxiv: 1603.06703
DOI: 10.1063/1.4972253
WoS: 000392096800036
Ref. & Cit.: NASA ADS
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10 Citations
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We develop and thoroughly test a stress-controlled, parallel plates shear cell that can be coupled to an optical microscope or a small angle light scattering setup, for simultaneous investigation of the rheological properties and the microscopic structure of soft materials under an imposed shear stress. In order to minimize friction, the cell is based on an air bearing linear stage, the stress is applied through a contactless magnetic actuator, and the strain is measured through optical sensors. We discuss the contributions of inertia and of the small residual friction to the measured signal and demonstrate the performance of our device in both oscillating and step stress experiments on a variety of viscoelastic materials.

Ref HAL: hal-01281406_v1
Ref Arxiv: 1511.07756
DOI: 10.1088/0953-8984/28/7/075201
WoS: 000368793200012
Ref. & Cit.: NASA ADS
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10 Citations
Résumé:

We introduce a temporal scheme for data sampling, based on a variable delay between two successive data acquisitions. The scheme is designed so as to reduce the average data flow rate, while still retaining the information on the data evolution on fast time scales. The practical implementation of the scheme is discussed and demonstrated in light scattering and microscopy experiments that probe the dynamics of colloidal suspensions using CMOS or CCD cameras as detectors.

Commentaires: Published in J. Phys.: Cond. Matter. 11 pages, 5 figures + Supporting Data (Python software to implement the method described in the manuscript)

Ref HAL: hal-00565584_v1
DOI: 10.1039/c0sm00863j
WoS: 000287091600027
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54 Citations
Résumé:

We examine the behavior of spherical silica particles trapped at an air-nematic liquid crystal interface. When a strong normal anchoring is imposed, the beads spontaneously form various structures depending on their area density and the nematic thickness. Using optical tweezers, we determine the pair potential and explain the formation of these patterns. The energy profile is discussed in terms of capillary and elastic interactions. Finally, we detail the mechanisms that control the formation of a hexagonal lattice and analyze the role of gravity for curved interfaces.

Ref HAL: hal-00389881_v1
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