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1. Broadband Frequency and Spatial On-Demand Tailoring of Topological Wave Propagation Harnessing Piezoelectric Metamaterials

   https://doi.org/10.3389/fmats.2020.602996  

   Dorin, Patrick ; Wang, K. W. ( January 2021 , Frontiers in Materials)

   null (Ed.)

   Many engineering applications leverage metamaterials to achieve elastic wave control. To enhance the performance and expand the functionalities of elastic waveguides, the concepts of electronic transport in topological insulators have been applied to elastic metamaterials. Initial studies showed that topologically protected elastic wave transmission in mechanical metamaterials could be realized that is immune to backscattering and undesired localization in the presence of defects or disorder. Recent studies have developed tunable topological elastic metamaterials to maximize performance in the presence of varying external conditions, adapt to changing operating requirements, and enable new functionalities such as a programmable wave path. However, a challenge remains to achieve a tunable topological metamaterial that is comprehensively adaptable in both the frequency and spatial domains and is effective over a broad frequency bandwidth that includes a subwavelength regime. To advance the state of the art, this research presents a piezoelectric metamaterial with the capability to concurrently tailor the frequency, path, and mode shape of topological waves using resonant circuitry. In the research presented in this manuscript, the plane wave expansion method is used to detect a frequency tunable subwavelength Dirac point in the band structure of the periodic unit cell and discover an operating region over which topological wave propagation can exist. Dispersion analyses for a finite strip illuminate how circuit parameters can be utilized to adjust mode shapes corresponding to topological edge states. A further evaluation provides insight into how increased electromechanical coupling and lattice reconfiguration can be exploited to enhance the frequency range for topological wave propagation, increase achievable mode localization, and attain additional edge states. Topological guided wave propagation that is subwavelength in nature and adaptive in path, localization, and frequency is illustrated in numerical simulations of thin plate structures. Outcomes from the presented work indicate that the easily integrable and comprehensively tunable proposed metamaterial could be employed in applications requiring a multitude of functions over a broad frequency bandwidth. 

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2. Analysis of Fault Zone Resonance Modes Recorded by a Dense Seismic Array Across the San Jacinto Fault Zone at Blackburn Saddle

   https://doi.org/10.1029/2020JB019756  

   Qiu, Hongrui ; Allam, Amir A. ; Lin, Fan‐Chi ; Ben‐Zion, Yehuda ( October 2020 , Journal of Geophysical Research: Solid Earth)

   We present observations and modeling of spatial eigen‐functions of resonating waves within fault zone waveguide, using data recorded on a dense seismic array across the San Jacinto Fault Zone (SJFZ) in southern California. The array consists of 5‐Hz geophones that cross the SJFZ with ~10–30 m spacing at the Blackburn Saddle near the Hemet Stepover. Wavefield snapshots after theSwave arrival are consistent for more than 50 near‐fault events, suggesting that this pattern is controlled by the fault zone structure rather than source properties. Data from example event with high signal to noise ratio show three main frequency peaks at ~1.3, ~2.0, and ~2.8 Hz in the amplitude spectra of resonance waves averaged over stations near the fault. The data are modeled with analytical expressions for eigen‐functions of resonance waves in a low‐velocity layer (fault zone) between two quarter‐spaces. Using a grid search‐based method, we investigate the possible width of the waveguide, location within the array, and shear wave velocities of the media that fit well the resonance signal at ~1.3 Hz. The results indicate a ~300 m wide damaged fault zone layer with ~65%Swave velocity reduction compared to the host rock. The SW edge of the low‐velocity zone is near the mapped fault surface trace, indicating that the damage zone is asymmetrically located at the regionally faster NE crustal block. The imaging resolution of the fault zone structure can be improved by modeling fault zone resonance modes and trapped waves together.

    

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3. Feedback Decoupling of Magnetically Coupled Actuators

   https://doi.org/10.1109/AIM46487.2021.9517598  

   Mohammadzadeh, M. ; Shariatmadari, M. R. ; Riahi, N. ; Komaee, A. ( January 2021 , 2021 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM))

   null (Ed.)

   Permanent magnet manipulators provide a unique potential for safe operation of magnetically driven medical tools inside the human body for noninvasive surgical, imaging, and drug targeting procedures. These systems manipulate magnetic objects from a distance without direct contact, by generating a magnetic field using strong permanent magnets, and controlling the shape of this field properly. Control over the magnetic field is gained by displacement of the magnets using independent mechanical actuators for each magnet. However, interactions between the magnets result in a coupling between the actuators, which prevents them from independent and precise operation. This paper develops a multivariate, nonlinear feedback control to cancel the magnetic coupling between the actuators in effect. This feedback control incorporates a complex mathematical model of the magnetic interactions between the actuators, which does not admit a simple analytical form. Instead, this model is constructed numerically using the finite element method. The decoupling performance of the proposed feedback control is verified by numerical simulations. 

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4. Nonlinear localized modes in two-dimensional hexagonally-packed magnetic lattices

   https://doi.org/10.1088/1367-2630/abdb6f  

   Chong, Christopher ; Wang, Yifan ; Maréchal, Donovan ; Charalampidis, Efstathios G. ; Molerón, Miguel ; Martínez, Alejandro J. ; Porter, Mason A. ; Kevrekidis, Panayotis G. ; Daraio, Chiara ( April 2021 , New Journal of Physics)

   We conduct an extensive study of nonlinear localized modes (NLMs), which are temporally periodic and spatially localized structures, in a two-dimensional array of repelling magnets. In our experiments, we arrange a lattice in a hexagonal configuration with a light-mass defect, and we harmonically drive the center of the chain with a tunable excitation frequency, amplitude, and angle. We use a damped, driven variant of a vector Fermi–Pasta–Ulam–Tsingou lattice to model our experimental setup. Despite the idealized nature of this model, we obtain good qualitative agreement between theory and experiments for a variety of dynamical behaviors. We find that the spatial decay is direction-dependent and that drive amplitudes along fundamental displacement axes lead to nonlinear resonant peaks in frequency continuations that are similar to those that occur in one-dimensional damped, driven lattices. However, we observe numerically that driving along other directions results in asymmetric NLMs that bifurcate from the main solution branch, which consists of symmetric NLMs. We also demonstrate both experimentally and numerically that solutions that appear to be time-quasiperiodic bifurcate from the branch of symmetric time-periodic NLMs.

    

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5. Diffusion of volatile organics and water in the epicuticular waxes of petunia petal epidermal cells

   https://doi.org/10.1111/tpj.15693  

   Ray, Shaunak ; Savoie, Brett M. ; Dudareva, Natalia ; Morgan, John A. ( February 2022 , The Plant Journal)

   Plant cuticles are a mixture of crystalline and amorphous waxes that restrict the exchange of molecules between the plant and the atmosphere. The multicomponent nature of cuticular waxes complicates the study of the relationship between the physical and transport properties. Here, a model cuticle based on the epicuticular waxes ofPetunia hybridaflower petals was formulated to test the effect of wax composition on diffusion of water and volatile organic compounds (VOCs). The model cuticle was composed of ann‐tetracosane (C₂₄H₅₀), 1‐docosanol (C₂₂H₄₅OH), and 3‐methylbutyl dodecanoate (C₁₇H₃₄O₂), reflecting the relative chain length, functional groups, molecular arrangements, and crystallinity of the natural waxes. Molecular dynamics simulations were performed to obtain diffusion coefficients for compounds moving through waxes of varying composition. Simulated VOC diffusivities of the model system were found to highly correlate within vitromeasurements in isolated petunia cuticles. VOC diffusivity increased up to 30‐fold in completely amorphous waxes, indicating a significant effect of crystallinity on cuticular permeability. The crystallinity of the waxes was highly dependent on the elongation of the lattice length and decrease in gap width between crystalline unit cells. Diffusion of water and higher molecular weight VOCs were significantly affected by alterations in crystalline spacing and lengths, whereas the low molecular weight VOCs were less affected. Comparison of measured diffusion coefficients from atomistic simulations and emissions from petunia flowers indicates that the role of the plant cuticle in the VOC emission network is attributed to the differential control on mass transfer of individual VOCs by controlling the composition, amount, and dynamics of scent emission.

    

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