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The leaf-like origami structure was inspired by geometric patterns found in nature, exhibiting unique transitions between open and closed shapes. With a bistable energy landscape, leaf-like origami is able to replicate the autonomous grasping of objects observed in biological systems like the Venus flytrap. We show uniform grasping motions of the leaf-like origami, as well as various non-uniform grasping motions which arise from its multi-transformable nature. Grasping motions can be triggered with high tunability due to the structure's bistable energy landscape. We demonstrate the self-adaptive grasping motion by dropping a target object onto our paper prototype, which does not require an external power source to retain the capture of the object. We also explore the non-uniform grasping motions of the leaf-like structure by selectively controlling the creases, which reveals various unique grasping configurations that can be exploited for versatile, autonomous, and self-adaptive robotic operations.

We investigated the effects of transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) with neurodevelopmental treatment (NDT) on the improvement of motor development and reduction of spasticity in children with cerebral palsy (CP). Twenty-four children with CP were allocated to two groups: the tDCS + NDT group and the only NDT group, done 3 times per week for 5 weeks. The Gross Motor Function Measurement (GMFM-88) and Box and Block Test (BBT) were used to assess changes in motor development, and the Modified Ashworth Scale (MAS) was used to evaluate changes in spasticity. All measurements were carried out at 3 time points: baseline, post-intervention, and 1 month follow-up. We found improvements in the GMFM-88 total scores and in each individual GMFM-88 dimension scores, favoring the tDCS + NDT group over the only NDT group. The BBT scores improved only in the tDCS + NDT group. In addition, the MAS scores reduced in the hemibody with significant motor impairment only in the tDCS + NDT group. The present findings suggest that tDCS combined with NDT can be considered a promising intervention for children with CP, as it can enhance motor development and reduce spasticity in this population.

Origami, the ancient art of paper folding, has shown its potential as a versatile platform to design various reconfigurable structures. The designs of most origami-inspired architected materials rely on a periodic arrangement of identical unit cells repeated throughout the whole system. It is challenging to alter the arrangement once the design is fixed, which may limit the reconfigurable nature of origami-based structures. Inspired by phase transformations in natural materials, here we study origami tessellations that can transform between homogeneous configurations and highly heterogeneous configurations composed of different phases of origami unit cells. We find that extremely localized and reprogrammable heterogeneity can be achieved in our origami tessellation, which enables the control of mechanical stiffness and in-situ tunable locking behavior. To analyze this high reconfigurability and variable stiffness systematically, we employ Shannon information entropy. Our design and analysis strategy can pave the way for designing new types of transformable mechanical devices. Origami-inspired metamaterials are attractive for their programmable shape-shifting properties but are typically characterized by low structural rigidity. Here, 3D heterogeneous origami structures display highly reconfigurable mechanical properties, including finely controllable and reversible stiffness variation.

With the ease of gene sequencing and the technology available to study and manipulate non-model organisms, the need to translate our understanding of model organisms to non-model organisms has become an urgent problem. For example, mining of large coral and their symbiont sequence data is a challenge, but also provides an opportunity for understanding functionality and evolution of these and other non-model organisms. Much more information than for any other eukaryotic species is available for humans, especially related to signal transduction and diseases. However, the coral cnidarian host and human have diverged over 700 million years ago and homologies between proteins are therefore often in the gray zone or undetectable with traditional BLAST searches. We introduce a two-stage approach to identifying putative coral homologues of human proteins. First, through remote homology detection using Hidden Markov Models, we identify candidate human homologues in the cnidarian genome. However, for many proteins, the human genome alone contains multiple family members with similar or even more divergence in sequence. In the second stage, therefore, we filter the remote homology results based on the functional and structural plausibility of each coral candidate, shortlisting the coral proteins likely to be true human homologues. We demonstrate our approach with a pipeline for mapping membrane receptors in humans to membrane receptors in corals, with specific focus on the stony coral, P. damicornis. More than 1000 human membrane receptors mapped to 335 coral receptors, including 151 G protein coupled receptors (GPCRs). To validate specific sub-families, we chose opsin proteins, representative GPCRs that confer light sensitivity, and Toll-like receptors, representative non-GPCRs, which function in the immune response, and their ability to communicate with microorganisms. Through detailed structure-function analysis of their ligand-binding pockets and downstream signaling cascades, we selected those candidate remote homologues likely to carry out related functions in the corals. This pipeline may prove generally useful for other non-model organisms, such as to support the growing field of synthetic biology.

Discontinuous fiber composites (DFCs) made of chopped prepreg tapes have recently drawn the attention of the aerospace and automobile industries thanks to their flexible manufacturing capability. Because of the discontinuity in a form of prepreg tapes, the fibers easily follow the mold contours while maintaining comparable stiffness and strength to continuous quasi-isotropic laminates. Furthermore, the high production rates and part complexities enabled by DFCs make them a competitive alternative to the use of metals in several applications. However, one of the current roadblocks for the use of DFCs is the lack of reliable analysis methods to predict their mechanical behavior, which depends on different parameters such as platelet sizes, aspect ratios, and spatial distribution. In this paper, we first experimentally investigated tensile elastic modulus and strength of unnotched coupons made of two different platelet aspect ratios (square and narrow) for varying coupon thicknesses. From the experiments, the square platelets showed significant thickness effects on both elastic modulus and strength. The narrow platelets also had significant thickness effects on strength but relatively constant modulus with varying thicknesses. In both modulus and strength, the narrow platelets had higher average values with larger deviations. Next, we computationally examined the relationship between the platelet distributions and the corresponding thickness effects. To get a thorough understanding of the effects of the platelet distribution on the mechanical behavior, the analysis was performed in two steps. In the first step, computational models were generated utilizing a uniform platelet distribution. In the second step, the models were generated leveraging platelet orientation tensors obtained from X-ray micro-computed tomography characterization. It was found that the assumption of a uniform orientation distribution condition was sufficient to capture the average modulus and strength with varying thicknesses for both platelet sizes. However, the associated Coefficient of Variation (CoV) of the results were significantly underpredicted, especially in the case of narrow platelets. On the other hand, numerical results using the orientation tensor obtained via micro-CT provided significantly improved predictions of the CoVs with varying thicknesses. These numerical investigations suggest that, for parts manufactured in conditions of limited platelet flow, the average mechanical performance can be accurately predicted by stochastic Finite Element models featuring a uniform platelet orientation distribution. On the other hand, the prediction of the CoV of moduli and strengths urges the use of an accurate representation of the real platelet morphology.

We propose a 3D-printed graded lattice made of hollow elliptical cylinders (HECs) as a new way to design impact mitigation systems. We observe asymmetric dynamics in the graded HEC chains with increasing and decreasing stiffness. Specifically, the increasing stiffness chain shows an acceleration of the propagating waves, while the decreasing stiffness chain shows the opposite. From the standpoint of impact mitigation, the decreasing stiffness chain combined with the strain-softening behavior of HECs results in an order-of-magnitude improvement in force attenuation compared to the increasing stiffness chain. We extend this finding to the graded 2D arrays and demonstrate a similar trend of wave transmission efficiency contrast between the increasing and decreasing stiffness lattices. The 3D-printed HEC lattices shown in this study can lead to the development of a new type of impact mitigating and shock absorbing structures., Comment: 22 pages, 11 figures, 4 appendices

Demonstration of topological boundary modes in elastic systems has attracted a great deal of attention over the past few years due to its unique protection characteristic. Recently, second-order topological insulators have been proposed in manipulating the topologically protected localized states emerging only at corners. Here, we numerically and experimentally study corner states in a two-dimensional phononic crystal, namely a continuous elastic plate with embedded bolts in a hexagonal pattern. We create interfacial corners by adjoining trivial and non-trivial topological configurations. Due to the rich interaction between the bolts and the continuous elastic plate, we find a variety of corner states of and devoid of topological origin. Strikingly, some of the corner states are not only highly-localized but also tunable. Taking advantage of this property, we experimentally demonstrate asymmetric corner localization in a Z-shaped domain wall. This finding could create interest in exploration of tunable corner states for the use of advanced control of wave localization. C.-W.C. and J.Y. are grateful for the support from NSF (CAREER1553202 and EFRI- 1741685). R.C. and G.T. acknowledge support by the project CS.MICRO funded under the program Etoiles Montantes of the Region Pays de la Loire. J.C. acknowledges the support from the European Research Council (ERC) through the Starting Grant 714577 PHONOMETA and from the MINECO through a Ramón y Cajal grant (Grant No. RYC-2015-17156).

This paper proposes a concept of a deployable tubular structure with the Yoshimura pattern based upon a novel folding approach. The developed folding approach is based on the reconfiguration of the Yoshimura tubular structure into the intermediate configurations. All the possible candidates of the intermediate configurations are derived with respect to the design parameters. The structural behavior during the reconfiguration process is analyzed to figure out the driving force for the deployment and the stability of the structure. The deployment of the Yoshimura tubular structure is demonstrated through the prototype with active hinges made with shape memory plastic.

A study has been conducted to evaluate the mechanical performance of various continuous fibers based on 3D printer technology. However, not only mechanical performance but also electromagnetic performance must be considered in aerospace industry. In this study, electromagnetic performance evaluation using a scanning free-space measurement (SFM) system was performed on 3D printed carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) specimens in X-band (8.2 ~ 12.4 GHz). It was possible to measure and analyze the electromagnetic performance of composite specimens made by a 3D printer.

In this research, we aim to combine origami units with vibration-filtering metastructures. By employing the bistable origami structure as resonant unit cells, we propose metastructures with low-frequency vibration isolation ability. The geometrical nonlinearity of the origami building block is harnessed for the adjustable stiffness of the metastructure’s resonant unit. The quantitative relationship between the overall stiffness and geometric parameter of the origami unit is revealed through the potential energy analysis. Both static and dynamic experiments are conducted on the bistable origami cell and the constructed beam-like metastructure to verify the adjustable stiffness and the tunable vibration isolation zone, respectively. Finally, a two-dimensional (2D) plate-like metastructure is designed and numerically studied for the control of different vibration modes. The proposed origami-based metastructures can be potentially useful in various engineering applications where structures with vibration isolation abilities are appreciated.

We examine the role of strong nonlinearity on the topologically-robust edge state in a one-dimensional system. We consider a chain inspired from the Su-Schrieffer-Heeger model, but with a finite-frequency edge state and the dynamics governed by second-order differential equations. We introduce a cubic onsite-nonlinearity and study this nonlinear effect on the edge state's frequency and linear stability. Nonlinear continuation reveals that the edge state loses its typical shape enforced by the chiral symmetry and becomes generally unstable due to various types of instabilities that we analyze using a combination of spectral stability and Krein signature analysis. This results in an initially-excited nonlinear-edge state shedding its energy into the bulk over a long time. However, the stability trends differ both qualitatively and quantitatively when softening and stiffening types of nonlinearity are considered. In the latter, we find a frequency regime where nonlinear edge states can be linearly stable. This enables high-amplitude edge states to remain spatially localized without shedding their energy, a feature that we have confirmed via long-time dynamical simulations. Finally, we examine the robustness of frequency and stability of nonlinear edge states against disorder, and find that those are more robust under a chiral disorder compared to a non-chiral disorder. Moreover, the frequency-regime where high-amplitude edge states were found to be linearly stable remains intact in the presence of small amount of disorder of both types., Comment: 13 pages, 8 figures

Elastic valley metamaterials offer an excellent platform to manipulate elastic waves and have potential applications in energy harvesting and elastography. Here we introduce a series of strategies to realize a topological transition in spiral elastic valley metamaterials by parameter modulations. We show the evolution of the Berry curvature and valley Chern number as a function of inherent parameters of a spiral, which further results in a general scheme to achieve topological valley edge states. Our strategy leverages multiple degrees of freedom in spiral elastic valley metamaterials to provide enhanced opportunities for desired topological states.

We present the first demonstration of a battery-free untethered wirelessly powered sub-gram jumping robot on an insect-scale. In order to operate the insect-sized robot autonomously, the limitation in battery use emphasizes the need for a wireless power transmission system as an onboard power solution. We designed a wireless power transmission system based on inductive coupling to power the Shape Memory Alloy (SMA), which serves as an elastic energy storage element and actuator for the jumping robot. The assembled mechanical structures, onboard power and electronics yield a 2 mm (high) × 24 mm (long) × 12 mm (wide) robot with ∼a weight of 216 mg. The experiments show that our jumping robot wirelessly lift-off up to 5.75 times its body length and repeats the jump around 7 times per minute. To date, out of the several untethered sub-gram insect-scale jumping robots with onboard power, this is the first wirelessly powered robot with the highest jumping performance. The novelty in this work, which addresses the engineering challenges in insect-scale jumping robots, is an untethered wirelessly powered design that achieves dynamic jumping maneuvers, and has self-righting ability.

We investigate the impact behavior of the Triangulated Cylindrical Origami (TCO) architecture to determine if it can effectively protect a payload dropped from a height. The TCO architecture inherently exhibits coupled longitudinal and rotational motions. TCO is highly tunable and can offer monostable or bistable characteristics based on its initial geometric configurations such as the height and rotational angle. When monostable TCO unit cells are combined in a chain, they can exhibit interesting rarefaction behavior under impact. Specifically, if one end of the chain is impacted, the initial compressive wave can be overtaken by a tensile wave, such that the other end of the chain can feel tension instead of compression in a counter-intuitive manner. In this study, we begin by designing monostable TCO unit cells that are numerically shown to exhibit rarefaction behavior when constructed in chains. Then, we fabricate plastic TCO unit cell prototypes and apply static compression to these prototypes to verify their monostability and to determine their mechanical properties. These unit cells are then organized in a chain of multiple unit cells that are connected mechanically. The chain is then tested dynamically by dropping it using a custom-made drop tower apparatus. We measure the impact felt by the TCO system by using accelerometers and digital image correlation systems. We find that this origami-based system offers a tunable way to mitigate impact applied to the proof mass, showing great potential as a novel payload impact mitigation system for space applications.

We investigate the extreme wave event in mechanical metamaterials composed of Triangulated Cylindrical Origami (TCO). Specifically, we focus on the realization of so-called rogue waves by employing a homogeneous one-dimensional chain constructed from the TCO unit cells. Our numerical simulation shows the significant energy focusing in the very limited number of unit cells. The wave localization behavior varies as a function of the geometrical parameters of the TCO, which enables us to manipulate the wave localization. The configurability of the wave localization using the TCO can be leveraged for energy harvesting purposes in engineering applications.

The $\mathrm{spin}\ensuremath{-}1$ Weyl point is formed by three bands touching at a single point in three-dimensional (3D) momentum space, with two of the bands showing conelike dispersion while the third band is flat. Such a triply degenerate point carries a higher topological charge $\ifmmode\pm\else\textpm\fi{}2$ and can be described by a three-band Hamiltonian. We first propose a tight-binding model of a 3D Lieb lattice with chiral interlayer coupling to form the spin-1 Weyl point. Then we design a chiral phononic crystal that carries these $\mathrm{spin}\ensuremath{-}1$ Weyl points and special straight-type acoustic Fermi arcs. We also demonstrate computationally the robust propagation of topologically protected surface states that can travel around a corner or defect without reflection. Our results pave the way to the manipulation of acoustic waves in 3D structures, and they provide a platform for exploring energy transport properties in 3D $\mathrm{spin}\ensuremath{-}1$ Weyl systems.

Coral reef ecosystems support significant biological activities and harbor huge diversity, but they are facing a severe crisis driven by anthropogenic activities and climate change. An important behavioral trait of the coral holobiont is coral motion, which may play an essential role in feeding, competition, reproduction, and thus survival and fitness. Therefore, characterizing coral behavior through motion analysis will aid our understanding of basic biological and physical coral functions. However, tissue motion in the stony scleractinian corals that contribute most to coral reef construction are subtle and may be imperceptible to both the human eye and commonly used imaging techniques. Here we propose and apply a systematic approach to quantify and visualize subtle coral motion across a series of light and dark cycles in the scleractinian coral Montipora capricornis. We use digital image correlation and optical flow techniques to quantify and characterize minute coral motions under different light conditions. In addition, as a visualization tool, motion magnification algorithm magnifies coral motions in different frequencies, which explicitly displays the distinctive dynamic modes of coral movement. Specifically, our assessment of displacement, strain, optical flow, and mode shape quantify coral motion under different light conditions, and they all show that M. capricornis exhibits more active motions at night compared to day. Our approach provides an unprecedented insight into micro-scale coral movement and behavior through macro-scale digital imaging, thus offering a useful empirical toolset for the coral research community.

We studied effects of material anisotropy on impact mitigation in single column woodpile structures. Local vibrations and nonlinear contacts of cylindrical members are key mechanisms of wave modulation in woodpile structures. We numerically obtained wave propagations in single column woodpile structures by changing longitudinal and/or transverse stiffness different from stiffness along the stacking direction. We found that changes in longitudinal and/or transverse stiffness altered wave propagation tendency as well as impact mitigation rate. We observed compact and wide waves propagated through single column woodpile structures with small stiffness ratio, while disintegrated but narrow waves with large stiffness ratio. According to dynamic behavior under impact loadings and frequency responses of woodpiles, bending vibration changed from 3rd to 1st mode and low energy band moved to relatively low frequency region when the single column woodpile structures had small stiffness ratio. This leads to increase impact mitigation characteristics of single column woodpile structures.

In this paper, we present a review of machine health managements for the smart factory. As the Industry 4.0 leads current factory automation and intelligent machines, the machine health management for diagnostic and prognostic purposes are essential, and their importance is getting more significant for the realization of the smart factory in the Industry 4.0. After brief introductions to important concepts and definitions composing smart factory and Industry 4.0, the developments in maintenance strategies towards Prognostics and health management (PHM) of machines are summarized. The review of machine health managements is followed, classifying the references by the monitoring components, types of measurements, as well as PHM tools and algorithms. 94 existing articles are reviewed and summarized in this regard. The implementations of machine health managements within the smart factory are discussed in terms of data connectivity, communications, Cyber-physical system (CPS) and virtual factory, relating them to Internet of things (IoT), cloud computing, and big data management.

Recently, there have been significant efforts to guide mechanical energy in structures by relying on a novel topological framework popularized by the discovery of topological insulators. Here, we propose a topological metamaterial system based on the design of the Stewart Platform, which can not only guide mechanical waves robustly in a desired path, but also can be tuned in situ to change this wave path at will. Without resorting to any active materials, the current system harnesses bistablilty in its unit cells, such that tuning can be performed simply by a dial-in action. Consequently, a topological transition mechanism inspired by the quantum valley Hall effect can be achieved. We show the possibility of tuning in a variety of topological and traditional waveguides in the same system, and numerically investigate key qualitative and quantitative differences between them. We observe that even though both types of waveguides can lead to significant wave transmission for a certain frequency range, topological waveguides are distinctive as they support robust, back scattering immune, one-way wave propagation.

Numerical calculations are performed to examine the interaction of highly nonlinear solitary waves in one-dimensional granular crystals with elastic solids containing a defect in the form of an embedded spherical void. The calculations are based on a coupled numerical model, combining concepts of discrete and finite elements. It is found that the delay and force amplitude of the reflected solitary waves are controlled by the local contact stiffness of the inspected sample, and are strongly affected by the size and depth of the embedded void. Moreover, the predictions show a steady increase of delay of the reflected solitary waves with increasing void radius for a fixed void depth, approaching the pristine case (no void) at sufficiently small void sizes. It is also found that the detectability of voids near the surface generally increases with decreasing sample's elastic modulus, and can be further increased by adjusting the striker velocity. The findings from this study can be used for developing a solitary wave-based diagnostic scheme to inspect elastic solids with void-like defects.