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Abstract Sustained monitoring of marine environments is essential for understanding oceanic processes and maintaining ecological health. Powering distributed sensors in remote ocean settings remains a major challenge. Battery-powered systems are limited by finite operational lifetimes. Small-scale wave energy converters (WECs) offer a promising alternative by harvesting ambient wave-induced motion to enable long-term, autonomous operation of ocean sensing platforms. Among existing WEC architectures, pendulum-based systems embedded within floating structures are attractive for compact deployments. However, their practical implementation is constrained by the ultra-low frequencies characteristic of ocean waves, which require impractically long effective pendulum lengths to achieve resonance in conventional designs. To address this limitation, this work investigates an internal pendulum-based WEC that integrates two complementary frequency-tuning strategies, an adjustable counterweight pendulum and a magnetic negative-stiffness mechanism. The natural resonance frequency of a single pendulum is first studied. The effects of counterweight tuning and magnetic softening can then be evaluated individually, and in combination. The counterweight reduces the effective gravitational restoring torque, while repulsive magnetic interactions near equilibrium further soften the system stiffness, collectively shifting the resonance toward ocean-wave frequencies. As the effective resonance frequency approaches the excitation frequency, the pendulum oscillation amplitude increases, thereby enhancing power delivery to the load. Finite-element magnetostatic simulations in COMSOL Multiphysics demonstrate a tunable negative-stiffness region, achievable through the proposed magnetic configuration. Pendulum structure prototypes are fabricated and evaluated in motor-driven base-excitation experiments. Frequency-sweep measurements of the relative pendulum- frame rotation indicate improved low-frequency response and a broader operating bandwidth for the magnetic-pendulum configuration relative to the conventional single-pendulum and counterweight variants. This study demonstrates that counterweight and magnetic softening mechanisms can enable resonance in compact pendulum-based WECs, advancing their viability for powering autonomous ocean monitoring systems. 

Energy-efficient image acquisition on the edge is crucial for enabling remote sensing applications where the sensor node has weak compute capabilities and must transmit data to a remote server/cloud for processing. To reduce the edge energy consumption, this paper proposes a sensor-algorithm co-designed system called SNAPPIX, which compresses raw pixels in the analog domain inside the sensor. We use coded exposure (CE) as the in-sensor compression strategy as it offers the flexibility to sample, i.e., selectively expose pixels, both spatially and temporally. SNAPPIX has three contributions. First, we propose a task-agnostic strategy to learn the sampling/exposure pattern based on the classic theory of efficient coding. Second, we co- design the downstream vision model with the exposure pattern to address the pixel-level non-uniformity unique to CE-compressed images. Finally, we propose lightweight augmentations to the image sensor hardware to support our in-sensor CE compres- sion. Evaluating on action recognition and video reconstruction, SNAPPIX outperforms state-of-the-art video-based methods at the same speed while reducing the energy by up to 15.4×. We have open-sourced the code at: https://github.com/horizon- research/SnapPix. 

A precise dynamical characterization of quantum impurity models with multiple interacting orbitals is challenging. In quantum Monte Carlo methods, this is embodied by sign problems. A dynamical sign problem makes it exponentially difficult to simulate long times. A multi-orbital sign problem generally results in a prohibitive computational cost for systems with multiple impurity degrees of freedom even in static equilibrium calculations. Here, we present a numerically exact inchworm method that simultaneously alleviates both sign problems, enabling simulation of multi-orbital systems directly in the equilibrium or nonequilibrium steady-state. The method combines ideas from the recently developed steady-state inchworm Monte Carlo framework [Erpenbeck et al., Phys. Rev. Lett. 130, 186301 (2023)] with other ideas from the equilibrium multi-orbital inchworm algorithm [Eidelstein et al., Phys. Rev. Lett. 124, 206405 (2020)]. We verify our method by comparison with analytical limits and numerical results from previous methods. 

Frontal polymerization (FP) is a promising alternative manufacturing method for thermoset-based fiber-reinforced polymer composites (FRP) in comparison with the traditional autoclave/oven-curing method, due to its rapid curing process, low energy consumption, and low cost. Optimizing the weight contents of initiators relative to the resin’s mass is needed to adjust the mechanical properties of FRPs in industrial applications. This study investigates the effect of varying the photo-initiator (PI) weight content on tensile properties and the frontal polymerization characteristics, including the front velocity, front temperature, and degree of cure, in the FP process of the epoxy resin. Specifically, a dual-initiator system, including PI and thermal-initiator (TI), is used to initiate the polymerization process by ultraviolent (UV) light. The weight content of the TI is fixed at 1 w%, and the relative PI concentration is varied from 0.2 w% to 0.5 wt%. Results show that increasing the PI amount from 0.2 wt% to 0.3 wt% significantly improves the front velocity and the degree of cure by about two times. Increasing the PI content from 0.3 wt% to 0.4 wt% results in 15% and 26% higher degree of cure and front velocity, respectively. Moreover, due to the different front velocity in the top and bottom regions of the specimen, the specimens with 0.4 wt% PI exhibited a curved shape. The specimen with 0.5 wt% PI is thermally degraded and foamed. By comparing tensile properties, it is found that increasing the PI concentration from 0.2 wt% to 0.3 wt% improves the tensile strength and Young’s modulus by 3.91% and 7%, respectively, while the tensile strength and the Young’s modulus of frontal polymerized specimens are on average 8% and 14% higher than traditionally oven-cured ones, respectively.