ESPCI Paris

Ocean waves can trigger sea ice fractures. This process plays an important role on the evolution of the floe size distributions in the marginal ice zone (MIZ). However, the fracture of sea ice by waves is still poorly constrainted by observations, as it is difficult to precisely forecast, it mostly occurs on short time (minutes) and spatial scales (meters), and are often happening during extreme weather conditions. In order to better understand the fracture of ice by waves, we built on the work of Dumas-Lefebvre et al. [1] and designed an experiment where waves are generated by an icebreaker nearby a continous ice sheet. This experiment was realized in the Saguenay Fjord, Québec, Canada, in February 2024, in the context of the Transforming Climate Action (TCA) program. The continuous 12-cm thick layer of ice that recently formed was fully characterised before the CCGS Amundsen generated wave by sailing at a speed up to 15.8 knots. Wave propagation and ice break-up were recorded by wave buoys placed on the ice surface and by three unmanned aerial vehicles (UAV) in stationary flights overseeing the ice from different angles.Using digital image correlation (DIC), geometric projections and rectifications, we developed a method to recover the three components of the waves velocity field from UAV observations. The accuracy of the method has been tested using the buoy signals as a reference, showing a quantitative agreement with a relative error of about 5%. Thanks to this stereo-DIC method, we obtained the full wave velocity field over a grid of 106x75 meters with a spatial resolution of 0.8 pix/m and a sampling frequency of 30 Hz. This reconstruction method offers a precise, high spatio-temporal sampling needed for future characterization of sea ice fracture, or any other dynamics of textured surfaces.

Visible light photocatalysis has reshaped synthetic organic chemistry by enabling mild and selective radical processes. However, its widespread adoption is still constrained by the reliance on homogeneous photocatalysts, typically precious-metal complexes or organic dyes, which complicate recovery, recyclability, scalability, and integration into telescoped continuous flow processes. Heterogeneous photocatalysts (hPCs) offer a sustainable alternative, and among emerging candidates, π-conjugated polymers (π-CPs) have recently attracted attention as tunable, metal-free semiconductors capable of efficient visible light harvesting. This perspective highlights poly-(arylene-ethynylene)-s (PAEs), a distinctive subclass of π-CPs whose modular, conjugated backbones enable control over morphology, band structure, and excited-state behavior. Historically developed for optoelectronic applications, PAEs are now gaining traction as photocatalysts in synthetic organic chemistry, including in continuous flow reactors. Yet, the absence of systematic structure-reactivity relationships limits rational catalyst design and restricts broader deployment. Here, we examine emerging trends that link PAEs structure to photocatalytic function and articulate guiding principles for designing next-generation polymeric photocatalysts. By integrating concepts from materials science and synthetic methodology, this perspective aims to establish PAEs as robust, recyclable, and versatile platforms for sustainable photocatalysis.

Josephson junctions based on topological insulators are expected to host Majorana-type bound states that promote a 4π-periodic current-phase relationship. One experimental consequence of this periodicity is the absence of odd Shapiro steps in the current-voltage characteristics under microwave radiation. Here, we experimentally study the frequency-dependent amplitude of Shapiro steps in a ballistic Josephson junction involving a 23 nm-thick single nanocrystal of topological insulator Bi2Te2.3Se0.7 connected to two planar Nb-electrodes. We observe a progressive suppression of the first step while decreasing the frequency below 2 GHz. Using the two-channel thermal resistively shunted junction (tRSJ) model, we show that despite a ballistic regime, the overheating phenomena are enough to account for the observed effect. Our results highlight the complex physics of Josephson junctions and underscore that the missing first Shapiro step alone is not a definitive signature of topological superconductivity. Josephson junctions based on topological insulators are expected to host Majorana bound states which are accompanied by the experimental absence of odd Shapiro steps in current-voltage characteristics. Here, the authors investigate Shapiro steps in a ballistic junction with Bi2Te2.3Se0.7, finding that overheating effects, rather than topological superconductivity, are sufficient to explain the suppression of the first step, challenging conventional interpretations.

Reward processes have traditionally been ascribed to dopamine (DA)-associated circuits. While external stimuli, such as food and drugs of abuse, are activators of DA-neuron activity, growing evidence indicates that interoceptive signals also play a critical role. Among these, the gut-brain vagal axis has emerged as a key regulator, although its precise contribution to mesolimbic DA signaling and behavior remains unclear. Here, we combine complementary ex vivo and in vivo approaches across multiple scales to show that gut-brain vagal tone is essential for gating mesolimbic DA system activity and functions, modulating DA-dependent molecular and cellular processes, and scaling both food- and drug-induced reinforcement. These findings challenge the traditional brain-centric view of reward processing, supporting a more integrated model in which vagus-mediated interoceptive signals intrinsically shape motivation and reinforcement. By uncovering the influence of gut-brain vagal communication on DA functions, this work provides insights into the neurobiology of adaptive and maladaptive reward, with broad relevance for eating disorders and addiction.

ABSTRACTImparting broadband transparency and focusing on flexible ultrasound bioelectronics can significantly enhance the capabilities for precise evaluation of tissues and organs as well as treatment of diseases. While existing wearable ultrasound devices, whether rigid or stretchable, often merge rigid ultrasound element arrays with soft materials to achieve a reliable interface on the human skin, they lack controlled artificial microstructures, resulting in compromised ultrasound transparency and challenges in achieving broadband focusing. Here, we report a metapad made of hydrogel metamaterials with high ultrasound transparency and broadband focusing by controlling the hydrogel porosity at a sub-wavelength scale. The hydrogel metapad achieves near-perfect acoustic impedance matching with tissues, low attenuation loss, broadband transmission, and high focusing intensity gain. Ultrasound imaging simulations further show a significant improvement in imaging contrast near the focal region when using the hydrogel metapad. Practical applications demonstrate that it enhances the imaging capabilities of ultrasound probes for vital human organs, including blood vessels and the heart. Our hydrogel metapad holds great potential for advancing soft acoustic functional devices, capable of seamlessly interfacing with both biological tissues and aquatic environments.

We present a practical white-light interferometric method, supported by an open-source Python library optifik for automated spectrum-to-thickness deduction, enabling foam film measurements down to a few nanometers. We describe three typical spectral scenarii encountered in this method: spectra exhibiting numerous interference fringes, spectra with a moderate number of peaks, and spectra with only a few identifiable features, providing illustrative examples for each case. We also discuss the main limitations of the technique, including spectral range constraints, the necessity of knowing the refractive index, and the influence of spectral resolution and signal quality. Finally, we demonstrate the application of the method in a time-resolved study of a TTAB (tetradecyltrimethylammonium bromide) foam film undergoing elongation and thinning. This method can be adapted to measure any thin non-opaque layer.Graphic )