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Ref Arxiv: 2207.07715
DOI: 10.1063/5.0126437
Ref. & Cit.: NASA ADS
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We discuss pressure computations for the hard-disk model performed since 1953 and compare them to the results that we obtain with a powerful event-chain Monte Carlo and a massively parallel Metropolis algorithm. Like other simple models in the sciences, such as the Drosophila model of biology, the hard-disk model has needed monumental efforts to be understood. In particular, we argue that the difficulty of estimating the pressure has not been fully realized in the decades-long controversy over the hard-disk phase-transition scenario. We present the physics of the hard-disk model, the definition of the pressure and its unbiased estimators, several of which are new. We further treat different sampling algorithms and crucial criteria for bounding mixing times in the absence of analytical predictions. Our definite results for the pressure, for up to one million disks, may serve as benchmarks for future sampling algorithms. A synopsis of hard-disk pressure data as well as different versions of the sampling algorithms and pressure estimators are made available in an open-source repository.

Commentaires: 21 pages, 13 figures, open-source repository

Ref HAL: hal-03953404_v1
DOI: 10.1117/12.2632215
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Thanks to their giant nonlinear optical response, liquid crystals support the existence of spatial optical solitons called nematicons. These solitons can be experimentally imaged in a microscope thanks to the fluctuation-induced scattering of the laser beam, but the associated microscope images are generally hard to interpret due to the partially incoherent nature of light scattering. In this contribution, we introduce a theoretical framework allowing to simulate microscope images originating from bulk scattering sources. We apply this framework to the visualization of laser beams and bouncing solitons in the weak nonlinear regime, and show that our framework could be the basis for a novel tomography technique of optical fields.

Ref HAL: hal-03974668_v1
DOI: 10.1142/S1088424622500377
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Nanoparticles made of a substance derived from wood, lignin, are gaining interest as a potential material for use in nanotechnology, including such biological applications as photodynamic antimicrobial chemotherapy (PACT) and photodynamic therapy (PDT), which involve the need for the nanoparticles to contain photosensitizers that absorb and emit in certain wavelength ranges. Among the possible approaches there is one relying on utilizing two-photon absorption in the near infrared region. In this work, we present the linear and non-linear photophysical properties of acetylated lignin nanoparticles which have been loaded with porphyrin, in particular, the femtosecond laser-induced emission which was measured for a single nanoparticle. We demonstrate that these nanoparticles can be excited in the so-called first (NIR-I) and second (NIR-II) optical window in the near-infrared (650–950 nm and 1000–1350 nm, respectively). Because their emission also occurs in the NIR, this presents an advantage for the monitoring of the use of these porphyrin-particle hybrids within PDT and PACT applications.

Ref HAL: hal-03959496_v1
DOI: 10.1016/j.mtchem.2022.101317
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Ref HAL: hal-03939599_v2
DOI: 10.1103/physrevresearch.4.l042042
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Quantum spin Hall insulators (QSHIs) based on HgTe and three-layer InAs/GaSb quantum wells (QWs) have comparable bulk band gaps of about 10-18 meV. The former, however, features a band gap vanishing with temperature, while the gap in InAs/GaSb QSHIs is rather temperature independent. Here, we report on the realization of a large inverted band gap in strained three-layer InAs/GaInSb QWs. By temperature-dependent magnetotransport measurements of gated Hall bar devices, we extract a gap as high as 45 meV. By combining local and nonlocal measurements, we detect edge conductivity at temperatures up to 40 K, possibly of topological origin, with equilibrium lengths of a few micrometers. Our results pave the way for the manipulation of topological edge states at high temperatures in QW heterostructures.

Ref HAL: hal-03951552_v1
DOI: 10.1063/5.0131565
WoS: WOS:000883764300014
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DOI: 10.1122/8.0000506
WoS: WOS:000886063900025
Résumé:

This work focuses on the temperature-dependent structural and rheological characterization of polystyrene-b-poly(n-butyl acrylate)-b-polystyrene triblock copolymers (PS-b-PnBA-b-PS) in the melt and, in particular, on their ability to show a lower disorder-to-order temperature (LDOT). To this aim, copolymers of varying block lengths, but keeping the PnBA block as a major component, were synthesized. Smallangle x-ray scattering revealed that the copolymers with short PS blocks (∼10 kg/mol) approach an LDOT but do not cross it. At room temperature, these copolymers exhibit higher moduli compared to a PnBA homopolymer due to the reinforcing effect of the PS but are flowing at temperatures above the glass transition of the PS. Increasing the PS and PnBA block length, to keep the same PS fraction, induces more profound changes in the structural and viscoelastic behaviors. Such a copolymer crosses the LDOT, leading to a microphase-separated and ordered state at high temperature. Contrary to the copolymers with short PS blocks, the flow regime was not reached, even at temperatures well above the glass transition of the PS. Instead, a low-frequency plateau was observed in rheology, showing the increased lifetime of the microphase-separated PS domains. ABA triblock copolymers exhibiting an LDOT behavior could, thus, be of interest for the design of thermoplastic elastomers or pressure-sensitive adhesives that can resist the flow at high temperatures