Mechanical energy conversion technologies such as piezoelectric or triboelectric nanogenerators are able to harvest environmental energy (e.g., vibration, wind, tidal wave) and human body motion for powering electric vehicles, sensor networks, and wearable devices. [1][2][3] Traditional triboelectric nanogenerators (TENGs) may generate high voltage but with extremely low AC current ( J ≈ 0.01-0.1 A m −2 ) density. [1] The performance of TENGs is optimal only at high frequency due to the dielectric displacement current mechanism, while the environmental mechanical sources usually have frequencies lower than 10 Hz. [4] In contrast, the non-equilibrium tribo-tunneling phenomenon, recently discovered in the semiconductor-based Schottky moving contacts, is capable of generating a continuous DC current as high as 100 A m −2 regardless of the motion direction, and not limited by the mechanical source frequency. [3,[5][6][7][8][9][10] The tribo-tunneling transport tip-enhanced current generation, as reported by Liu et al. [3,6] using conductive-atomic force microscope (C-AFM), show that the tribo-tunneling current density ( J) output can be boosted by the nano-sized contact (tip radius R ≈ 30 nm) up to 10 6 A m −2 due to the enhanced electronic excitation and strong localized electric field E. It has been reported that a micro-tip (tip radius R ≈ 30 µm) sliding system produces a current density of 35 A m −2 while larger tip radius (R ≈ 100-300 µm) yields a current density of 10 A m −2 in the test probe sliding system. [5,6] However, scaling up the concept with micro-electromechanical systems (MEMS)-fabricated tip array is time-consuming and costly. The metal micro-tips also cause substrate surface scratching, which impacts the sustainability of the power generation. Moreover, the relatively low open-circuit voltage (V oc , 300-600 mV) of the single metal/Si sliding unit is insufficient for practical applications in electronics. To address those issues, we developed a carbon aerogel-based system in this work, which scales up the DC output and enhances the Voc output by one order via naturally formed Schottky nanocontacts.Carbon aerogel is electrically conductive, synthetic ultralight material composed of 3D network structures of interconnected amorphous carbon nanoparticles. [11] It has been widely used for nanocomposite, electrodes, desalination filters, and heterogeneous catalysis due to its large surface area. [12] In this work, Although tip-enhanced tribo-tunneling in metal/semiconductor point nanocontact is capable of producing DC with high current density, scaling up the process for power harvesting for practical applications is challenging due to the complexity of tip array fabrication and insufficient voltage output. Here, it is demonstrated that mechanical contact between a carbon aerogel and silicon (SiO 2 /Si) interface naturally forms multiple nanocontacts for tribo-tunneling current generation with an open-circuit voltage output (V OC ) reaching 2 V, and short-circuit DC current output (I SC ) of ≈15 µA. It h...

No abstract

Understanding physical mechanisms underlying morphogenesis requires the knowledge of the mechanical properties of embryonic tissue. Despite a long-standing interest in this subject, very few in vivo measurements are currently available. Here, using the early fly embryo as a model, we describe a novel cantilever-based technique for measuring material properties of embryonic tissues. A major advantage of our approach is the ability to exert large (nanonewton-range) forces with subcellular spatial precision: our technique improves signal to noise by approximately an order of magnitude compared to previous methods. This advance allowed us to demonstrate that deformation caused by force applied to a single cell edge spreads across the whole embryo on a time scale of seconds and that the mechanical response is dominated by system-size effects, and not friction between the tissue and its environment. Based on these measurements, we estimate the Young's modulus of the cellular edges in the early embryo.

A shock-preserving finite volume solver with the generalized Lax-Friedrichs splitting flux for Morphing Continuum Theory (MCT) is presented and verified. The numerical MCT solver is showcased in a supersonic turbulent flow with Mach 2.93 over an 8 • compression ramp. The simulation results validated MCT with experiments as an alternative for modeling compressible turbulence. The required size of the smallest mesh cell for the MCT simulation is shown to be almost an order larger than that in a similar DNS study. The comparison shows MCT is a much more computationally friendly theory than the classical NS equations. The dynamics of energy cascade at the length-scale of individual eddies is illuminated through the subscale rotation introduced by MCT. In this regard, MCT provides a statistical averaging procedure for capturing energy transfer in compressible turbulence, not found in classical fluid theories. Analysis of the MCT results show the existence of a statistical coupling of the internal and translational kinetic energy fluctuations with the corresponding eddy rotational energy fluctuations, indicating a multiscale transfer of energy. In conclusion, MCT gives a new characterization of the energy cascade within compressible turbulence without the use of excessive computational resources.