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In this study, the triplet-state properties of BChl a in the Fenna-Matthews-Olson (FMO) light-harvesting complex were interrogated in the absence and presence of PscB, a subunit of the Cba. tepidum reaction center (RC), at room temperature and at 77 K. Application of nanosecond time-resolved transient absorption spectroscopy supports a model in which the pathway of the triplet excitation decay within FMO has two phases, with a fast lifetime of 2.58 μs (0.57 μs at 77 K) and a slow lifetime of 44.8 μs (44.1 μs at 77 K) in the FMO-only sample. Reconstitution of PscB and FMO, however, alters the spectral signatures of BChl a excitons uniquely at 815 nm in the steady-state spectrum at 77 K. Additionally, the triplet-state lifetime of BChl a in the FMO-PscB complex shortens by almost 40% to 28.1 μs at 77 K. The two FMO trimers asymmetrically interfacing with the homodimeric RC wire excitation energy from the chlorosome to the latter. Our data supports that the single central PscB, besides its redox active roles as the electron mediators to ferredoxin, is highly plausibly involved in fine-tuning the asymmetric excitation energy transfer from two branches of FMO to the RC in green sulfur bacteria. 

Membrane-based acoustic metamaterials have been reported to achieve 100% absorption, the acoustic analogue of photonic black-hole. However, the bandwidth is usually very narrow around some local resonance frequency, which limits its practical use. To address this limitation and achieve a broadband absorption, this paper first establishes a theoretical framework for unit cells of air-backed diaphragms, modeled as an equivalent mass-spring-dashpot system. Based on the impedance match principle, three different approaches are numerically investigated by tuning the cavity length, the static pressure in the cavity, and the effective damping of perforated plates. A prototype with polyimide diaphragm and 3D printed substrate is then fabricated and characterized using an acoustic impedance tube. Preliminary experiments show the feasibility to achieve an absorption bandwidth of ∼200 Hz at center frequency of 1.45 kHz. This work pays the way for developing a sub-wavelength light weight broadband acoustic absorber for a variety of applications in noise control. 

An air-backed diaphragm is the key structure of most dynamic pressure sensors and plays a critical role in determining the sensor performance. Our previous analytical model investigated the influence of air cavity length on the sensitivity and bandwidth. The model found that as the cavity length decreases, the static sensitivity monotonically decreases, and the fundamental natural frequency shows a three-stage trend: increasing in the long-cavity-length range, reaching a plateau value in the medium-cavity-length range, and decreasing in the short-cavity-length range, which cannot be captured by the widely used lumped model. In this study, we conducted the first experimental measurements to validate these findings. Pressure sensors with a circular polyimide diaphragm and a backing air cavity with an adjustable length were designed, fabricated, and characterized, from which the static sensitivities and fundamental natural frequencies were obtained as a function of the cavity length. A further parametric study was conducted by changing the in-plane tension in the diaphragm. A finite element model was developed in COMSOL to investigate the effects of thermoviscous damping and provide validation for the experimental study. Along with the analytical model, this study provides a new understanding and important design guidelines for dynamic pressure sensors with air-backed diaphragms. 

Abstract Soft actuators are typically designed to be inherently stress‐free and stable. Relaxing such a design constraint allows exploration of harnessing mechanical prestress and elastic instability to achieve potential high‐performance soft robots. Here, the strategy of prestrain relaxation is leveraged to design pre‐curved soft actuators in 2D and 3D with tunable monostability and bistability that can be implemented for multifunctional soft robotics. By bonding stress‐free active layer with embedded pneumatic channels to a uniaxially or biaxially pre‐stretched elastomeric strip or disk, pre‐curved 2D beam‐like bending actuators and 3D doming actuators are generated after prestrain release, respectively. Such pre‐curved soft actuators exhibit tunable monostable and bistable behavior under actuation by simply manipulating the prestrain and the biased bilayer thickness ratio. Their implications in multifunctional soft robotics are demonstrated in achieving high performance in manipulation and locomotion, including energy‐efficient soft gripper to holding objects through prestress, fast‐speed larva‐like jumping soft crawler with average locomotion speed of 0.65 body‐length s⁻¹(51.4 mm s⁻¹), and fast swimming bistable jellyfish‐like soft robot with an average speed of 53.3 mm s⁻¹.