Light-Mediated Deep-Tissue Theranostics

This theme issue provides an overview on recent developments of light-mediated imaging and therapy approaches, with an emphasis on those that transcend the shallow tissue penetration dogma

Non-Hermitian topological wall modes in rotating Rayleigh-Benard convection

We show that the rotating Rayleigh-Benard convection, where a rotating fluid is heated from below, exhibits non-Hermitian topological states. Recently, Favier and Knobloch (JFM 2020) hypothesized that the robust wall modes in rapidly rotating convection are topologically protected. We study the linear problem around the conduction profile, and by considering a Berry curvature defined in the complex wavenumber space, particularly, by introducing a complex vertical wavenumber, we find that these modes can be characterized by a non-zero integer Chern number, indicating their topological nature. The eigenvalue problem is intrinsically non-Hermitian, therefore the definition of Berry curvature generalizes that of the stably stratified problem. Moreover, the three-dimensional setup naturally regularizes the eigenvector at the infinite horizontal wavenumber. Under the hydrostatic approximation, it recovers a two-dimensional analogue of the one which explains the topological origin of the equatorial Kelvin and Yanai waves. The existence of the tenacious wall modes relies only on rotation when the fluid is stratified, no matter whether it is stable or unstable. However, the neutrally stratified system does not support a topological edge state. In addition, we define a winding number to visualize the topological nature of the fluid.Comment: 16 pages, 3 figure

Scale dependence of near-inertial wave’s concentration in anticyclones

Near-inertial waves (NIWs), pervasive and dominating the mixing process in the upper ocean, are observed to concentrate in anticyclones. Based on the NIW amplitude equation derived by Young & Ben Jelloul, which captures dispersion and effects of vortical flow’s advection and refraction, this work analytically and numerically studies the influence of scale on the concentration of NIWs. For a sinusoidal background shear flow, the exact solutions expressed as periodic Mathieu functions are approximated by a Gaussian envelope with Hermite polynomial oscillations to determine the distance to the anticyclones. Two dimensionless parameters control NIW’s dynamics: (i) h/Ψ, where h is a constant capturing the strength of wave dispersion and Ψ is the magnitude of the background streamfunction capturing the ratio of dispersion to refraction; (ii) LΨ/LM, the ratio between the spatial scales of background flow and NIWs, where LΨ and LM, respectively, captures the relative strength between advection and refraction. The refraction by the background flow leads to the concentration in the regions with negative vorticity, dispersion controls the variance of the wave packet, and the advection shifts the center of NIWs away from the peak of negative vorticity, which is scale-dependent. When the refraction effect dominates, i. e., small LΨ/LM, NIWs concentrate in anticyclones, and this concentration becomes stronger as h/Ψ decreases; when the advection effect dominates, i.e., large LΨ/LM, the NIW’s concentration is less obvious. Numerical simulations with backgrounds of sinusoidal shear, vortex quadrupoles and random vortices confirm these results. Considering the similarity between the NIW amplitude equation and the Schrödinger equation, we propose a new perspective that the combined effect of uncertainty relation and energy conservation leads to large-scale NIW’s concentration in anticyclones

Spectral condensation in quasi-geostrophic turbulence above small-scale topography

Sea-floor topography is essential for oceanic fluid dynamics in many perspectives, and it is believed to enhance energy dissipation to oceanic flows. This study numerically examines the impact of small-scale topography on the dynamic of quasi-geostrophic barotropic flows and finds that small-amplitude topography enhances upscale energy flux and leads to condensation, which contradicts the common understanding. Topography-induced dissipation only happens when its amplitude is stronger than the first critical value. And there exists a second critical topography magnitude, corresponding to a second-order phase transition. When the topography magnitude lies between the two critical values, energy simultaneously transfers to both large and small scales. When the topography magnitude exceeds the second critical value, energy only transfers downscale. The discovery of counterintuitive topography-enhanced energy flux and the critical phenomenon brings new challenges to topography parameterization in ocean models

Étude sur les propriétés physicochimiques et électrochimiques des liquides ioniques redox et leur application en tant qu’électrolyte dans les supercapaciteurs

Ce mémoire porte sur les recherches et les développements dans le domaine des électrolytes à base de liquide ionique redox. Une nouvelle famille de liquide ionique redox basée sur le ferrocenylsulfonyl(trifluoromethylsulfonyl) (FcNTf) a été développée et étudiée pour la première fois afin de démontrer le potentiel de ces liquides ioniques dans les dispositifs de stockage d’énergie. En premier lieu, les liquides ioniques redox (RILs) composés de l’anion électroactif et du cation d’alkylimidazolium sont synthétisés et caractérisés. L’impact de la variation des chaînes alkyles du cation sur les propriétés physicochimiques et électrochimiques du RIL a été étudié. À une faible concentration en solution, l’impact du cation a peu d’influence sur l’ensemble des propriétés. Cependant, à haute concentration (>50 % massique) et sans électrolyte de support, la formation de films en oxydation a été observée à l'électrode positive. Ce point est intéressant pour les futures recherches et développements dans le domaine, puisque la variation des chaînes alkyles du cation des liquides ioniques redox et la formation de films lors de l’oxydation du FcNTf est peu connue et comprise en littérature. De plus, l’optimisation des conditions de solution d'électrolyte RIL dans les supercapaciteurs est aussi présentée. En deuxième lieu, la mise en application des RILs dans les supercapaciteurs a été testée. La performance énergétique et le mécanisme d’autodécharge ont été ciblés dans cette étude. En présence de l’électrolyte redox, la contribution des réactions faradaiques permet d'accomplir un gain énergique de 287 % versus les systèmes purement capacitifs. À cause de la formation de film à l’électrode, l’électrolyte redox FcNTf joue un rôle primordial dans la prévention de l’autodécharge versus les liquides ioniques qui étaient connus jusqu’à présent. Finalement, ce mémoire a permis de mieux comprendre les effets structure-propriétés relative aux modifications du cation chez les liquides ioniques redox.This thesis is focuses on the development of redox ionic liquid electrolytes for supercapacitors. A new family of redox ionic liquids (RILs) based on ferrocenylsulfonyl(trifluoromethylsulfonyl) (FcNTf) is reported, which show great potential as functional materials for energy storage devices. For the first part, RILs with electro-active anion and alkylimidazolium cations are synthesised and characterized. The impact of the variation of the imidazolium cation alkyl chain on the electrochemical and physicochemical properties is analysed. At lower concentrations of RIL, the cation structure has little impact on the solution properties. However, at higher concentrations, (>50 wt. %) and without supporting electrolyte, formation of a thin film on the electrode surface accompanies the oxidation process. The thin film formation has great impact for the control of deposition of the charged species on the electrode. The influence of the cation structure on the RIL and film deposition during the oxidation reaction is not well understood in the literature so far. In addition, optimisation of RILs as electrolytes for supercapacitors is also presented. In the second part, the RIL electrolyte is tested in supercapacitor cells. With faradaic contribution from the redox electrolyte, an increase of 287% in the energy is observed versus capacitive electrochemical systems. Furthermore, the film layer formation achieved by the use of FcNTf redox ionic liquid is an effective way to prevent the self-discharge of redox-active electrolyte supercapacitor. This thesis has helped to understand the structure-property relationships of redox ionic liquids