bluuebunny/crossref_metadata_2025 huggingface dataset:
Invariant Representation of Wave Propagation Properties for a Mono-Coupled Electro-Mechanical Periodic Structure
Authors: Belloni Edoardo , Braghin Francesco , Cazzulani Gabriele , Cenedese Mattia
Published: November 2016

During the last decades, a growing interest has been devoted to periodic structures and metamaterials. One of the most interesting characteristics of this class of materials is that they present a transmission gap for given frequency ranges. This peculiar characteristic has many potential applications: from optics to seismic isolation, from filtering to wave guiding. In literature, different approaches were developed to study such kind of structures. In this paper, using an approach based on transfer matrices of a single unit cell and its invariants, a way to represent in compact form the behavior of a mono-coupled periodic structure is presented. As a result, the wave propagation properties are shown as being dependent both on the frequency range and on some chosen design parameters. Furthermore, the adding of multiphysics materials (in the case of this paper piezoelectric inserts with dedicated electric circuits) inside the structure allows, through the tuning of both the mechanical and the electrical parameters, to actively control the bandgap position. This approach also allows checking the robustness of parameter choices with respect to desired bandgap frequency ranges. Finally, some applications of this method for active control of wave propagation are presented.
Optimized Parameters for Synthesis of BaTiO3 Films With High Electromechanical Coupling
Authors: Zhou Zhi , Bowland Christopher C. , Patterson Brendan A. , Malakooti Mohammad H. , Sodano Henry A.
Published: November 2016

This research improves upon prior research efforts on the hydrothermal synthesis of barium titanate (BaTiO3) films. It has been established that BaTiO3 can be synthesized using a two-step hydrothermal reaction that first synthesizes TiO2 then converts it to BaTiO3. Past research, however, resulted in relatively low ferroelectric properties using this technique. The research addresses that shortcoming by offering an optimized hydrothermal synthesis process that significantly increase the electromechanical coupling of the BaTiO3 film. Here, it is shown that the d33 achieves a value of 80 pm/V, which is the bulk BaTiO3 value. Additionally, this optimization results in an enhanced dielectric constant of 1600. Therefore, this research reveals that the ferroelectric properties of a hydrothermally synthesized BaTiO3 film can be significantly enhanced through slight modifications in the hydrothermal processing procedure.
Experimental Characterization of the Dynamics of VO2-Based MEMS Mirrors
Authors: Torres David , Wang Tongyu , Zhang Jun , Dooley Sarah , Tan Xiaobo , Sepúlveda Nelson
Published: November 2016

In this work, the time and frequency response of VO2-based MEMS mirrors are characterized across the transition for individual and simultaneous actuation. First, a step input train of increasing amplitude are applied to the device up to the point of transition is reached. Second, the frequency response is measured by applying a small sinusoidal input, where the displacement remained inside the hysteresis of the VO2. The frequency of the input varied from 0.1 to 2000 Hz. The thermal dynamics of the device is found to be the factor limiting the device’s band-width to less than 10 Hz. The average resonant frequency of the present VO2-based MEMS mirror was found to be 412.5 Hz for individual actuation. These results allow for the extraction of the necessary parameters to create a model that can be used to design devices with specific dynamic performance.
Operational Space Control of a Lightweight Robotic Arm Actuated by Shape Memory Alloy (SMA) Wires
Authors: Quintanar-Guzmán Serket , Kannan Somasundar , Olivares-Mendez Miguel A. , Voos Holger
Published: November 2016

This paper presents the design and control of a two link lightweight robotic arm using a couple of antagonistic Shape Memory Alloy (SMA) wires as actuators. A nonlinear robust control law for accurate positioning of the end effector of the two-link SMA based robotic arm is developed to handle the hysteresis behavior present in the system. The model presented consists of two subsystems: firstly the SMA wires model and secondly the dynamics of the robotic arm itself. The control objective is to position the robotic arm’s end effector in a given operational plane position. For this regulation problem a sliding mode control law is applied to the hysteretic system. Finally a Lyapunov analysis is applied to the closed-loop system demonstrating the stability of the system under given conditions. The simulation results demonstrate the accurate and fast response of the control law for position regulation. In addition, the stability of the closed-loop system can be corroborated.
A Performance Prediction for Fe-Ga Magnetostrictive Strain Sensor
Authors: Yoo JinHyeong
Published: November 2016

This study will present a proof-of-concept non-contact strain sensor, utilizing a prototype magnetostrictive (Fe-Ga alloy, Galfenol) strip on a steel plate; coupled mechanical-magnetostrictive equations will be used to evaluate sensor performance prediction. In contrast with typical piezo-ceramic materials, Galfenol is ductile and has an excellent ability to withstand mechanical shock. Galfenol also changes its permeability in response to applied stress. This stress-based permeability change is not time dependent and can measure static loads. The variation of magnetic induction with stress depends strongly on bias magnetic field. Typically, the performance of Galfenol is measured in a compressional load region because it has higher response there. However, in this study, we are aiming to develop a sensor for tensile stress measurement. To achieve a compression load in the sensing element, a Galfenol strip is aligned perpendicular to a tension bar, so that tension in the bar creates compression in the strip, via the Poisson effect.

The experimental setup in this study consists of a polycrystalline Galfenol strip bonded in the horizontal direction of a steel dog-bone shaped tension specimen. Two permanent magnets are attached at both ends of the Galfenol strip to provide a magnetic bias field through the strip. The magnetic flux through the Galfenol strip is measured with a non-contact Hall sensor during the tensile load test. The design reported here aims at low frequency applications, such as static and dynamic tension monitoring.
Electrode Fabrication for Scanning Electrochemical Microscopy and Shear Force Imaging
Authors: Northcutt Robert , Maddox Jacob , Sundaresan Vishnu-Baba
Published: November 2016

The development of novel characterization techniques is critical for understanding the fundamentals of material systems. Bioinspired systems are regularly implemented but poorly defined through quantitative measurement. In an effort to specify the coupling between multiple domains seen in biologically inspired systems, high resolution measurement systems capable of simultaneously measuring various phenomena such as electrical, chemical, mechanical, or optical signals is required. Scanning electrochemical microscopy (SECM) and shear-force (SF) imaging are nanoscale measurement techniques which examine the electrochemical behavior at a liquid-solid or liquid-liquid interface and simultaneously probe morphological features. It is therefore a suitable measurement technique for understanding biological phenomena.

SF imaging is a high resolution technique, allowing for nanoscale measurement of extensional actuation in materials with high signal to noise ratio. The sensing capabilities of SECM-SF techniques are dependent on the characteristics of the micro-scale electrodes (ultramicroelectrodes or UMEs) used to investigate surfaces. Current limitations to this technique are due to the fabrication process which introduces structural damping, reducing the signal produced. Additionally, despite the high cost of materials and processing, contemporary processes only produce a 10% yield. This article demonstrates a UME fabrication process with a 60% yield as well as improved amplitude (250% increase) and sensitivity (210% increase) during SF imaging. This process is expected to improve the signal to noise ratio of SF-based measurement systems. With these improvements, SECM-SF could become a more suitable technique for measuring cell or tissue activity, corrosion of materials, or coupled mechanics of synthetic faradaic materials.
Predicting the Output of a Triboelectric Energy Harvester Undergoing Mechanical Pressure
Authors: Sharifi Kia Danial , Towfighian Shahrzad , Jin Congrui
Published: November 2016

Energy harvesting using a triboelectric nanogenerator (TENG) has been a major area of research in the recent years in order to harvest mechanical energy in different scales. High energy conversion efficiency, broad range of application in different systems and relatively easy fabrication process are among the factors demonstrating essential needs for TENG technology development. Performance of a TENG could be affected by many factors such as the frequency of vibration and the surface charge density. As a key factor in improving the power output of TENGs, surface charge density could be modified by the selection of proper charging materials and by increasing the contact area between the tribo-pairs. Although there have been numerous studies analyzing the performance of different tribo-pairs and different interfacial structures for a TENG, a systematical analysis of the contact phenomena between the interfacial structures in order to investigate the effects of different surface properties and structures such as, surface roughness, dielectric properties or the presence of nanostructures is still not available. In the current study, systematical numerical simulations have been performed on the adhesive contact behavior of the macro/nanostructures at the TENG interface. An interaction potential has been used to represent the adhesive interactions while surface deformations are coupled using half-space Green’s function. Furthermore, effects of the deformation of the interfacial structure on the performance and output of the TENG has been investigated by developing a theoretical model for a vertical-contact-mode TENG using a mass-spring system to represent the motion of the moving electrode. Coupling the theoretical model to the instantaneous deformation of the interfacial structure, real-time output of the TENG in terms of short-circuit voltage and open-circuit current has been studied in response to a predefined pressure input. The results of the current study demonstrate the effects of the deformation of the interfacial structure on the output characteristics of TENGs during the transition between partial-contact to full-contact modes. Numerical simulation results represent acceptable correlations with previously reported experimental data. The simulation package developed in this study is capable of simulating the contact behavior of the interfacial structure and predicting the deformed geometry.
Investigating Secondary Equilibration in Thermoplastic Ionomers Under a Thermo-Electric Field
Authors: Vijayaraghavan Prasant , Sundaresan Vishnu-Baba
Published: November 2016

Ionomers are polymers containing a small fraction of charged groups in their polymer backbone. These ionic groups link together to form ionic aggregates which act as temporary cross-links. On heating over the ionic dissociation temperature, these ionic aggregates become mobile in the melt and reaggregate upon cooling. The structure and dynamic behavior of these ionic aggregates gives rise to interesting mechanical and functional properties of the ionomers. Thermal processing of ionomers leads to secondary equilibration of these ionic aggregates. We study this phenomenon of secondary equilibration on application of a thermo-electric field where an electrostatic field is maintained over the ionomer melt. The end goal is to achieve control over the size and distribution of the ionic aggregates by means of an external electric field. The characterization techniques utilized to study the onset of secondary equilibration are UV-Vis Spectroscopy, Differential Scanning Calorimetry, Fourier Transfer Infrared Spectroscopy and Attenuated Total Reflectance analysis. The results indicate that the phenomenon of secondary equilibration is present under the application of a thermoelectric field as indicated by change in spectral and thermal data. A fundamental understanding of the secondary equilibration phenomenon and eventual prevention of the onset of secondary equilibration will lead to long term control of the ionic aggregates by means of an external electric field which will improve the function and utility of these ionomeric materials.
On the Modeling and Experimental Validation of Multi-Field Polymer-Based Bimorphs
Authors: Erol Anil , Masters Sarah , von Lockette Paris , Ounaies Zoubeida
Published: November 2016

Origami — the Japanese art of folding — has inspired various engineering applications for several decades due to its ability to manipulate complex shapes. In our study, multi-field actuated self-folding Origami structures are developed with the implementation of two classes of smart materials: relaxor ferroelectric polymers and magneto-active elastomers (MAEs). The chosen relaxor ferroelectric is P(VDF-TrFE-CTFE), a P(VDF)-based terpolymer and the MAE is a PDMS substrate with embedded barium hexaferrite particles. At the macroscale, this study involves the modeling of the large deformation of a bimorph comprising the aforementioned magnetically and electrically actuated materials using a 1D analytical model derived from the equilibrium of a differential element. The large deformation is extracted from curvatures solved at each point for the resulting differential equation of the equilibrium state. On the microscale, this study also considers the nonlinear behavior of the smart materials. The nonlinear dielectric response of the relaxor ferroelectric polymer is captured by an electric field-dependent electrostrictive coefficient derived from a microstructure-based energy balance for the electrostriction of the terpolymer. The energy density function is postulated to be composed of an elastic contribution described by the Arruda-Boyce hyperelastic model and an electric contribution based on dipole-dipole interactions. On the other hand, a magnetic field-dependent torque drives the actuation of the MAEs, which is also dependent on the orientation of the material to the field. The integration of the micro and macro components results in an analytical model of a 1D, multi-layered flat structure that can be numerically solved for displacements under combined fields. The model is compared with well-matching experimental results of a unimorph and a bimorph structure as validation. The experiments measured the tip displacement of the beam under combined fields for a quantitative analysis. The study takes the analysis further by optimizing parameters such as geometry, field strengths, and the combination of active layers for relevant target shapes.
Finite Element Model of a Hydrogel-Based Micro-Valve
Authors: Mehner Philipp J. , Haefner Sebastian , Franke Markus , Voigt Andreas , Marschner Uwe , Richter Andreas
Published: November 2016

Micro-valves play an important role in controlling and operating microfluidic systems. Utilizing stimuli-sensitive hydrogels facilitates the construction of smart micro-valves controlled by temperature, concentration (salt, organic solvent) or pH level.

We propose a finite element model which uses the thermal domain as an auxiliary domain for the volume change response of hydrogels. Behaviors like local displacements within the hydrogel are difficult to measure, but can be reproduced with finite elements. For the application of the micro-valve, the hydrogel model is connected to the fluid domain. The hydrogel is placed directly into the fluid flow and opens or closes the flow path. For this, a full iterative cycle with material properties and remeshing in each simulation step is implemented in ANSYS®.

This model concept and the results will help to better understand, predict and visualize the behavior of hydrogels and support the development of highly integrated hydrogel-based microfluidic circuits.
Engineering Design Tools for Shape Memory Alloy Actuators: CASMART Collaborative Best Practices and Case Studies
Authors: Wheeler Robert W. , Benafan Othmane , Gao Xiujie , Calkins Frederick T. , Ghanbari Zahra , Hommer Garrison , Lagoudas Dimitris , Petersen Andrew , Pless Jennifer M. , Stebner Aaron P. , Turner Travis L.
Published: November 2016

The primary goal of the Consortium for the Advancement of Shape Memory Alloy Research and Technology (CASMART) is to enable the design of revolutionary applications based on shape memory alloy (SMA) technology. In order to help realize this goal and reduce the development time and required experience for the fabrication of SMA actuation systems, several modeling tools have been developed for common actuator types and are discussed herein along with case studies, which highlight the capabilities and limitations of these tools. Due to their ability to sustain high stresses and recover large deformations, SMAs have many potential applications as reliable, lightweight, solid-state actuators. Their advantage over classical actuators can also be further improved when the actuator geometry is modified to fit the specific application. In this paper, three common actuator designs are studied: wires, which are lightweight, low-profile, and easily implemented; springs, which offer actuation strokes upwards of 200% at reduced mechanical loads; and torque tubes, which can provide large actuation forces in small volumes and develop a repeatable zero-load actuation response (known as the two-way shape memory effect). The modeling frameworks, which have been implemented in the design tools, are developed for each of these frequently used SMA actuator types. In order to demonstrate the versatility and flexibility of the presented design tools, as well as validate their modeling framework, several design challenges were completed. These case studies include the design and development of an active hinge for the deployment of a solar array or foldable space structure, an adaptive solar array deployment and positioning system, a passive air temperature controller for the regulation of flow temperatures inside of a jet engine, and a redesign of the Corvette active hatch, which allows for pressure equalization of the car interior. For each of the presented case studies, a prototype or proof-of-concept was fabricated and the experimental results and lessons learned are discussed. This analysis presents a collection of CASMART collaborative best practices in order to allow readers to utilize the available design tools and understand their modeling principles. These design tools, which are based on engineering models, can provide first-order optimal designs and are a basic and efficient method for either demonstrating design feasibility or refining design parameters. Although the design and integration of an SMA-based actuation system always requires application- and environment-specific engineering considerations, common modeling tools can significantly reduce the investment required for actuation system development and provide valuable engineering insight.
Heating and Loading Paths to Optimize the Performance of Trained Shape Memory Alloy Torsional Actuators
Authors: Nicholson Douglas E. , Bass Micheal A. , Mabe James H. , Benafan Othmane , Padula Santo A. , Vaidyanathan Raj
Published: November 2016

Near-equiatomic NiTi shape memory alloy (SMA) torsional tube actuators were trained for two-way shape memory effect (TWSME) by repeated thermal cycling under an isobaric load. Performance of the trained actuators was assessed by thermally cycling through a complete phase transformation under a range of isobaric loads that varied from negative to positive and included loads near zero. To assess the actuation performance of the trained SMA components, extended isobaric thermal cycling and cycling under varying loads to constant strain limits was performed. Additionally, isothermal loading was applied in the fully martensitic state prior to and following training.

Results show stable TWSME when cycling under significant isobaric loading in the trained direction, however at low or negative loads (loads applied opposite to the training direction) a degradation of TWSME occurred during thermal cycling. Isothermal loading showed that martensite variant reorientation and detwinning was redistributed in the trained actuator when compared to an untrained actuator. Thermal cycling against constant strain limits was shown to have a negligible effect on the stability of the TWSME and overall performance of the trained actuator. Various combinations of isothermal and isobaric loading were shown to expand the operating range at low and negative loads. Additionally, load paths were identified which limit the degradation of TWSME over extended cycling.

The aforementioned results are discussed in the context of the correlation between uniaxial isobaric and isothermal loading and texture measurements obtained by in-situ neutron diffraction at stress and temperature. These results show various thermomechanical combinations of heating and loading sequences that yield the same final martensite texture in SMA, which highlights the ability to take different paths yet still obtain the desired actuator response while minimizing irrecoverable deformation mechanisms. The implications of extending these uniaxial results to the design and fabrication and ultimately improving the performance of torsional SMA actuators are discussed.
A Bistable Piezoelectric Energy Harvester With an Elastic Magnifier for Applications in Medical Pacemakers
Authors: Galbier Antonio C. , Karami M. Amin
Published: November 2016

Embedded piezoelectric energy harvesting (PEH) systems in medical pacemakers have been an attractive and well visited research area. These systems typically utilize different configurations of beam structures with forcing originating from heart beat oscillations. The goal of these systems is to remove the pacemaker battery, which makes up 60–80% of the device volume, and replace it with a self-reliant power option. With emerging technologies encouraging a push towards leadless pacemakers typical energy harvesting beam structures are becoming inherently coupled with the heart system. The introduction of the nonlinearity resulting from the bistable magnetic interaction of two magnets is known to enhance energy harvesting performance due to its double-well potential behavior. Introducing the elastic magnifier enables large tip oscillations and high energy orbits for the bistable system. A continuous nonlinear model is derived for the bistable system (BPEH) and a one-degree-of-freedom linear mass-spring-damper model is derived for the elastic magnifier. The elastic magnifier (EM) will not consider the damping negligible due to the viscous nature of the heart, unlike most models. For experimental testing a physical model was created for the bistable structure and fashioned to an elastic magnifier. A hydrogel was chosen as the physical model for the EM. Experimental results have shown that the bistable piezoelectric energy harvester coupled with a linear elastic magnifier (BPEH+LEM) produces more power at certain input frequencies and operates a larger bandwidth than a PEH, BPEH, and a standard piezoelectric energy harvester with the elastic magnifier (PEH+LEM). Numerical simulations were validated by these results showing that this system enters high-energy and high orbit oscillations. It has been shown that BPEH systems implemented in medical pacemakers can have enhanced performance if positioned over the myocardial heart wall.
Pore-Spanning PPy(DBS) as a Voltage-Gated Synthetic Membrane Ion Channel
Authors: Hery Travis M. , Sundaresan Vishnu-Baba
Published: November 2016

The transport of monovalent cations across a suspended PPy(DBS) polymer membrane in an aqueous solution as a function of its redox state is investigated. Maximum ion transport is found to occur when PPy(DBS) is in the reduced state, and minimum transport in the oxidized state. No deviation in the dynamics of ion transport based on the direction of the applied electrical field is observed. Additionally, it is found that ion transport rates linearly increased proportional to the state of reduction until a steady state is reached when the polymer is fully reduced. Therefore controlled, bidirectional ion transport is for the first time demonstrated. The effect of aqueous Li+ concentration on ion transport in the fully reduced state of the polymer is studied. It is found that ion transport concentration dependence follows Michaelis-Menten kinetics (which models protein reaction rates, such as those forming ion channels in a cell membrane) with an r2 value of 0.99. For the given PPy(DBS) polymer charge density and applied potential across the membrane, the maximum possible ion transport rate per channel is found to be 738 ions per second and the Michaelis constant, representing the concentration at which half the maximum ion transport rate occurs, is 619.5mM.
Design of Origami Structures With Smooth Folds
Authors: Peraza Hernandez Edwin A. , Hartl Darren J. , Lagoudas Dimitris C.
Published: November 2016

Origami provides inspiration and solutions to the fabrication and functionality of various structures. Origami design methods in the literature are limited to the idealization of the folds as creases of zeroth-order geometric continuity. This idealization is not proper for origami structures having non-negligible fold thickness or maximum curvature at the folds restricted by material or structural limitations. For these structures, the folds are not accurately represented as creases but instead as bent regions of higher-order geometric continuity. These fold regions of arbitrary order of continuity are denoted in this work as smooth folds. A method for the design of a single planar sheet and its associated pattern of smooth folds that morphs into a given three-dimensional goal shape represented as a polygonal mesh is proposed. The parameterization of the planar sheet and the constraints allowing for a valid smooth fold pattern and matching of the goal shape in a folded configuration are presented. The folding deformation of the determined sheet designs is simulated using a previously derived kinematic model for origami with smooth folds. Various testing examples considering diverse goal shapes are presented. The results demonstrate that each considered sheet design matches its corresponding goal shape in a known folded configuration having fold angles determined from the geometry of the goal mesh. The proposed method can be used for the design of origami structures having folds of arbitrary order of geometric continuity such as origami-inspired active structures.
Damage Detection With Guided Waves and Fiber Bragg Grating Sensor Arrays
Authors: Sun Xiaoyi , Tian Zhenhua , Lin Bin , Yu Lingyu
Published: November 2016

This paper presents a damage detection and imaging approach using guided waves and through the use of optical fiber Bragg Grating (FBG) sensors for structural health monitoring (SHM) purpose. An FBG array composed with four linearly aligned FBG sensors for guided wave sensing is designed. It is found that FBG sensors are optimized for sensing guided wave coming along the axial direction yet minimized for those along the normal direction. To overcome this limitation and allow for all directional sensing, a FBG phased array beamforming algorithm is derived based on the commonly used delay-and-sum beamforming algorithm principle. The work continues to evaluate the detection capability of the FBG array through two experimental studies on an aluminum plate: (a) guided wave source localization; (b) surface damage detection. The results indicates that both targets are successfully detected and agree well with their actual locations and thus confirms the capability of using presented FBG phased array for rapidly inspecting a large area with limited access.
Influence of VO2 Thin Film Coatings on the Performance of Integrated MEMS Bridges and Cantilevers
Authors: Cao Yunqi , Torres David , Wang Tongyu , Sepúlveda Nelson
Published: November 2016

Vanadium oxide (VO2) shows a solid-solid phase transition at around 68 °C where its mechanical and electrical properties start to change dramatically. During the phase transition, the large compressive stress generated by the VO2 thin film coating could induce a significant frequency shift in the bimorph structures such as clamped-clamped (C-C) beams and clamed-free (C-F) beams. However, for regions outside the phase transition, the stress produced by the thermal expansion coefficient difference between VO2 and the cantilever or bridge structural material dominates the frequency shift. Therefore, the two ends of the frequency hysteresis curve exhibits a pattern or behavior that can be different than the one shown during the phase transition. It was observed that opposite trends have been found before and after the phase transition region. This phenomena can be explained by the two competing mechanisms present in VO2-based MEMS: frequency shift due to thermal coefficient difference between VO2 and silicon dioxide (SiO2) (the materials in the bimorph), and the frequency change induced by the phase transition of VO2.
A Novel DC Current Sensor Using SMA Controlled Piezoelectric Bimorph Cantilever
Authors: Kaluvan Suresh , Zhang Haifeng
Published: November 2016

A new approach to measure direct current (DC) using shape memory alloy (SMA) tuning piezo cantilever resonant frequency technique is proposed in this work. The proposed current sensor system is designed using an electrically insulated SMA wire surface mounted on the cantilever beam with piezoelectric actuator. The cantilever beam is maintained at resonance using a closed loop piezo resonator circuit and the current ‘I’ to be measured is given to the SMA wire. The current induced temperature change of the SMA wire produces a mechanical shape change and produces a stiffness change to the resonating cantilever beam. The shift in resonant frequency due to the stiffness change is measured, which is related to the input electrical current ‘I’ to the SMA wire. The key enabling concept of this proposed work is to alter the cantilever resonant frequency using the shape changing property of SMA wire with input unknown electric current. The analytical model of the current sensor system is derived and the results are compared with the experimental results. The SMA coupled with piezo actuator based resonant current sensing system is evaluated for the input current range of 0 to 0.5A. The proposed current sensing concept is simple and completely novel and it is found that it has very high sensitivity to current and result is piecewise linear.
Dispersion in Nonlinear Plates: Amplitude Dependent Lamb Waves
Authors: Packo Pawel , Leamy Michael J.
Published: November 2016

This paper presents results from a perturbation-based analysis approach, and accompanying numerical validation, for calculating amplitude-dependent Lamb wave dispersion in nonlinear plates. Nonlinearities considered include those arising from geometric and material nonlinearities. Using a Lindstedt-Poincaré perturbation analysis, nonlinear dispersion relationships are presented in closed form using the partial wave technique. Solvability conditions, based on an operator formalism accompanied by inner product projections against adjoint solutions, yield higher-order dispersion approximations capturing amplitude-dependent Lamb wave propagation. Numerical simulations using a cellular automata approach verify the predicted dispersion shifts for an example nonlinear plate. The analysis and identification of amplitude-dependent, nonlinear Lamb wave dispersion complements recent research focusing on higher harmonic generation and internally resonant waves, which require precise frequency-wavenumber matching, including at large amplitudes.
Adaptive Switch Timing Control Law for Optimal Displacement Reduction via SSDI
Authors: Kelley Christopher R. , Kauffman Jeffrey L.
Published: November 2016

In the conventional implementation of synchronized switch damping (SSD), the switches are intended to occur at every displacement extrema. However, recent work reveals that switching at the vibration peaks is only optimal for displacement reduction under resonance excitation. In general, the optimal switch timing is dependent on the excitation frequency along with the electromechanical coupling and modal damping of the structure. This work seeks to develop a control framework that searches through the possible switch times to find the optimal switch time for synchronized switch damping on an inductor (SSDI) under steady state excitation. The control law does not need any knowledge of the system, only requiring the voltage of the piezo actuator to develop a displacement estimate that is minimized by adjusting the switch timing. Furthermore, the controller naturally senses changes in the excitation and adapts the switch timing to best reduce displacement under the new excitation.
Equivalent Electromechanical Circuit Analysis for Electrical Tuning of Magnetostrictive Unimorph System Dynamics
Authors: Germer M. , Marschner U. , Yoo J. H. , Flatau A. B.
Published: November 2016

Equivalent electromechanical circuit analysis models provide efficient tools for analysis of power flow across multiple physical domains. In this work, we use this tool to develop a model of the power flow through mechanical, magnetic and electrical domains for analysis of magnetostrictive material-based devices. The magnetostrictive unimorph system in this study consists of a magnetostrictive galfenol (Fe-Ga alloy) layer bonded to a non-magnetic flexible metal layer, a pickup coil wound around the bimetallic strip and an electrical load. Permanent magnets are used to set a magnetic bias field and to provide a tip mass load at the free end of the cantilevered unimorph. The electrical load is connected to the pickup coil, such that vibration in the magnetostrictive alloy layer caused by the vibrating structure generates electrical energy that is dissipated by the electrical load, thereby damping the vibrations in the structure. The pickup coil output voltage varies with fluctuation in the magnetic flux density due to vibration of the beam.

The electrical load discussed in this paper includes an inductance and a resistor (work that also includes capacitance is on-going). An electromechanical circuit model of the electrically loaded magnetostrictive unimorph system is used to study system dynamics. For this purpose the circuit description is simplified by a transformation of the electrical and magnetic elements into the mechanical domain. The network model of this system and simulations of its dynamic behavior are presented.
Enhancing the Output Power of a Piezoelectric Energy Harvester by Reducing the Effect of the Internal Capacitance Using Inductance
Authors: Zargarani Anahita , Mahmoodi S. Nima
Published: November 2016

This paper describes an innovative method for enhancing the power output of a piezoelectric energy harvester. The proposed approach is adopting inductance to reduce the effect of the internal capacitance of the piezoelectric harvester to boost the power output. Four electrical circuits for a piezoelectric beam harvester are studied; Simple Resistive Load (SRL), Inductive Load (IL), Standard AC-DC, and Inductive AC-DC circuits. An inductor is added to the SRL and standard AC-DC circuits to build the new IL and Inductive AC-DC circuits respectively. The power outputs of the four circuits are then studied. The results show that the adaptation of inductor enhances the power output. The IL circuit enhances the power output comparing to the SRL circuit. The Inductive AC-DC circuit also avails the standard AC-DC circuit.
Stiffness Tuning of NiTi Implants Through Aging
Authors: Shayesteh Moghaddam Narges , Amerinatanzi Amirhesam , Saedi Soheil , Turabi Ali Sadi , Karaca Haluk , Elahinia Mohammad
Published: November 2016

NiTi alloys are interesting materials for biomedical implants since they offer unique characteristics such as superelastic behavior, low stiffness (I.e., modulus of elasticity) close to that of the cortical bone, and shock absorption. Thermal treatments are the most common and practical ways to improve the superelasticity of these alloys. In addition to the superelastic behavior of the metallic implants, it is important for the implants to have a stiffness similar to that of cortical bone in order to reduce the risk of failure caused by stress shielding. The cortical bone has a stiffness ranging from 12 to 31 GPa for different patients (e.g., sex, age, mechanical behavior of bone) and various bone locations (e.g., jaw implant, hip implant), while the untreated Ni-rich NiTi has the stiffness equal to 41.37 GPa. One recently used technique to lower the stiffness of NiTi implant is to introduce porosity into the implant. The major problem associated with the imposed porosity is stress concentration on the pore walls and the subsequent implant failure. In this work, the purpose is to tune the stiffness via changing the post-heat treatment conditions, i.e., aging time and aging temperature.

In this study, several bulk specimens of Ni-rich NiTi (SLM Ni50.8Ti49.2) were additively manufactured using selective laser melting (SLM) technique. The samples were solution annealed (950 °C, 5.5 h) and subsequently water quenched to provide equilibrium state in the samples. Subsequently, different aging conditions (350 °C and 450 °C for 5 to 18 hours) were applied to the samples. Mechanical testing (compression) was conducted on the samples and the stiffness of each sample was defined to investigate the effect of aging on the stiffness.

Our results indicate that the range of 29.9 to 43.7 GPa for stiffness can be achieved through the implant via different time period and temperatures for aging. The modulus of 43.7 GPa is attributed to 10 hours heat treatment under 450 °C and the modulus of 29.9 GPa is attributed to 18 hours heat treatment under 350 °C.
Biologically Inspired Fluidic Flexible Matrix Composite Pumps for Wave Energy Conversion
Authors: Squibb Carson , Groo LoriAnne , Bialy Adrian , Philen Michael
Published: November 2016

Inspired by the fibrillar network in plant cell walls and the helical fibers found in soft bodied hydrostats (e.g. worms, squid, elephant trunks, and octopus arms), fluidic flexible matrix composites (F2MCs) are composite tubes that consist of multiple layers of oriented, high performance fibers, such as carbon, precisely placed in a flexible matrix resin to form high-mechanical advantage actuators and variable stiffness materials. Unique to the F2MC tube is its ability to generate high pressures and volume change with a small external load as a result of the stiff reinforcement fiber orientation in the wall of the tube and the soft supporting elastomer. When a load is applied to the tubes, the volume of the composite pump is reduced and fluid is forced out of the tube by the reinforcing fibers. The objective of this research is to design, fabricate and characterize F2MCs for use in wave energy conversion where ocean waves provide the axial load to drive fluid through the pumps. F2MCs pumps are tested in a water basin and mechanically cycled between 0 Hz and 2 Hz at up to 17 percent strain. Instantaneous input power is found by measuring the displacement and applied force to the actuators, while output power values are derived from pressure and flow rate measurements at the tube outlet. From these measurements the actuator efficiency is subsequently determined.
Floating Worlds: Cosplay Photo Shoots and the Creation of Imaginary Cosmopolitan Places
Authors: Langsford Claire Margaret
Published: November 2016

Cosplay is a globalised craft and performance practice centred upon the recreation of pre-existing character designs in the form of wearable costumes, performances and photography. Cosplay costumes and performances are typically inspired by science-fiction and fantasy texts, set in places existing outside of contemporary time and space such as Medieval Europe or alien planets. Among Australian cosplayers popular source texts include Western film and television, as well as Japanese anime, manga and videogames.

Photo shoots are a popular activity among cosplayers in Australian communities of practice. Working collaboratively with photographers and other practitioners, cosplayers create staged images of their character costumes posing at especially selected locations. Using images created by cosplayers and the author during fieldwork among Australian communities of practice, this article will explore how visions of deterritorialised, cosmopolitan floating worlds are produced in local, physical spaces; how universities become European castles and parks are transformed into Edo-period Japan.
Love From Afar: Transcending Distance and Difference in Age-Dissimilar Couplings?
Authors: McKenzie Lara
Published: November 2016

When undertaking research into heterosexual, age-dissimilar relationships in Australia, I was surprised by the high proportion of couples who had begun or developed their relationships from a distance, or were living in distance relationships. These couples’ circumstances varied: some were in inter-cultural couplings, often involving older, white Australian men and younger, Southeast Asian women; some had met while travelling overseas; and others lived in different locations across Australia. Based on interviews, this paper explores couples’ shared understandings of their relationships, focusing on the dimensions of age, nation, and distance. Interviewees spoke of their relationships as transcending—as well as simultaneously constructing—distance and (age and national) difference. Yet while anthropological analyses of cosmopolitanism have frequently explored distance and difference, the notion of transcendence has received little attention. I argue that transcendence is and should be considered central to analyses of cosmopolitan coupledom, as well as to the anthropology of love.
Multiple Peripherals One Cosmopolitanism: Rights Based Feminism and The Globe Trotting Pick Up Artist
Authors: Lewis Brigitte
Published: November 2016

A critical reading of Nigel Rapport’s work on cosmopolitan theory in anthropology, specifically the book Anyone: The Cosmopolitan Subject of Anthropology (Rapport 2012). Reading Rapport’s work ‘against the grain’, I explore the androgynous quality of his notion of an anthropological cosmopolitanism. I then argue for a feminist methodological framework to be used in cosmopolitanism's place.
Monte Carlo simulations of atomic layer deposition on 3D large surface area structures: Required precursor exposure for pillar- versus hole-type structures
Authors: Cremers Véronique , Geenen Filip , Detavernier Christophe , Dendooven Jolien
Published: November 2016

Due to its excellent conformality, atomic layer deposition (ALD) has become a key method for coating and functionalizing three dimensional (3D) large surface area structures such as anodized alumina (AAO), silicon pillars, nanowires, and carbon nanotubes. Large surface area substrates often consist of arrays of quasi-one-dimensional holes (into which the precursor gas needs to penetrate, e.g., for AAO), or “forests” of pillars (where the precursor gas can reach the surface through the empty 3D space surrounding the pillars). Using a full 3D Monte Carlo model, the authors compared deposition onto an infinite array of holes versus an infinite array of pillars. As expected, the authors observed that the required exposure to conformally coat an array of holes is determined by the height to width ratio of the individual holes, and is independent of their spacing in the array. For the pillars, the required exposure increases with decreasing center-to-center distance and converges in the limit to the exposure of an array of holes. Our simulations show that, when targeting a specific surface area enhancement factor in the range 20–100, a well-spaced pillar geometry requires a 2–30 times smaller precursor exposure than a hole geometry and is therefore more ALD friendly. The difference in required exposure is shown to depend on the initial sticking probability and structural dimensions.
Effects of contact states on polymer pattern deformation during demolding process in nanoimprint lithography
Authors: Ma Lijun , Wang Qing , Zhang Rui , Zheng Xu , Zheng Tong
Published: November 2016

The effects of contact states on polymer pattern deformation during demolding are investigated using a numerical simulation approach considering the relationship between the demolding force and demolding displacement. According to the difference of the contact states between the mold and polymer, the demolding model is divided into three kinds of contact types. It is shown that tearing of the residual layer and breaking of the polymer embossment have direct relations with the adhesion states of the contact surfaces at different positions. Among the three kinds of contact types, the sufficient contact type has the highest resolution, but it also has a large probability of defects. The incomplete contact type has the lowest defect rate, but it has a poor resolution. For the complete contact type, both the probability of defects and the resolution are better of the three kinds of contact types.
Reactive oxygen species induce virus-independent MAVS oligomerization in systemic lupus erythematosus
Authors: Buskiewicz Iwona A. , Montgomery Theresa , Yasewicz Elizabeth C. , Huber Sally A. , Murphy Michael P. , Hartley Richard C. , Kelly Ryan , Crow Mary K. , Perl Andras , Budd Ralph C. , Koenig Andreas
Published: November 2016

Oxidative stress oligomerizes an outer mitochondrial membrane protein to trigger an antiviral response in the absence of infection.
Science Signaling
Podcast for 29 November 2016: Pre-B cell receptor signaling in leukemia
Authors: Wilson Bridget S. , VanHook Annalisa M.
Published: November 2016

Transient homotypic interactions between pre–B cell receptors promote survival of acute lymphoblastic leukemia cells (Erasmus
et al
., in 29 November 2016 issue).
ERK blocks pre-miRNA export
Authors: Ferrarelli Leslie K.
Published: November 2016

Blocking the ERK-dependent suppression of miRNA biogenesis may alleviate chemotherapeutic resistance in patients with liver cancer.
Papers of note in
Science Translational Medicine
Authors: Ferrarelli Leslie K.
Published: November 2016

This week’s papers describe a nanobody targeting an inflammation-associated ion channel and insights into the development of BMP signaling–driven heterotopic ossification.
Harmonizing ribosomal proteins and rRNA
Authors: Mushegian Alexandra A.
Published: November 2016

An rRNA processing protein has an additional role in regulating the transcription of ribosomal proteins.