bluuebunny/crossref_metadata_2025 huggingface dataset:
Short‐term effects of in‐row subsoiling and simultaneous admixing of organic material on growth of spring barley (H. vulgare)
Authors: Jakobs I. , Schmittmann O. , Schulze Lammers P.
Published: November 2017

Previous studies have shown that deep tillage, so‐called subsoiling, is beneficial for yield development, and that tillage of deeper soil layers can promote water and nutrient availability during dry periods. The application of composts to the topsoil has been widely studied and evaluated, and it has been shown to improve soil stability and plant N uptake. These effects can differ over time depending on the compost type. Since dry periods have become more frequent, sustainable soil tillage and fertilizer practices must be developed. A combination of deep soil tillage and compost application might be a way to ensure proper plant supply during dry periods. Therefore, a field experiment on spring barley growth was carried out to evaluate the short‐term effects of in‐row subsoiling with simultaneous admixing of compost. Two types of composts and one organic fertilizer (Bio: decomposed organic waste, Green: decomposed green cuttings and CM: cattle manure) were admixed into the subsoil, and a control treatment received single deep loosening (DL) to a depth of 0.6 m. Yield development, yield parameters and grain quality were analysed and showed that the DL and Bio treatments resulted in the highest yields, and a significantly increased ear density and number of kernels. The TKW (100‐kernel weight) of the CM treatment was significantly lower than the other treatments. In all treatments, a clear trend of decreasing yields with increasing distance from the subsoil tillage was observed. Thus a subsoil tillage every meter can increase overall yield development and offers a new perspective for sustainable crop production.
Thermochronological insights into the structural contact between the Tian Shan and Pamirs, Tajikistan
Authors: Jepson Gilby , Glorie Stijn , Konopelko Dmitry , Gillespie Jack , Danišík Martin , Evans Noreen J. , Mamadjanov Yunus , Collins Alan S.
Published: November 2017

Multi‐method thermochronology along the Vakhsh‐Surkhob fault zone reveals the thermotectonic history of the South Tian Shan–Pamirs boundary. Apatite U/Pb analyses yield a consistent age of 251 ± 2 Ma, corresponding to cooling below ~550–350°C, related to the final closure of the Palaeo‐Asian Ocean and contemporaneous magmatism in the South Tian Shan. Zircon (U–Th–Sm)/He ages constrain cooling below ~180°C to the end of the Triassic (~200 Ma), likely related either to deformation induced by the Qiangtang collision or to the closure of the Rushan Ocean. Apatite fission track thermochronology reveals two low‐temperature (<120°C) thermal events at ~25 Ma and ~10 Ma, which may be correlated with tectonic activity at the distant southern Eurasian margin. The late Miocene cooling is confirmed by apatite (U–Th–Sm)/He data and marks the onset of mountain building within the South Tian Shan that is ongoing today.
Using an R shiny to enhance the learning experience of confidence intervals
Authors: Williams Immanuel James , Williams Kelley Kim
Published: November 2017

Many students find understanding confidence intervals difficult, especially because of the amalgamation of concepts such as confidence levels, standard error, point estimates and sample sizes. An R Shiny application was created to assist the learning process of confidence intervals using graphics and data from the US National Basketball Association.
Temperature cycling during platelet cold storage improves in vivo recovery and survival in healthy volunteers
Authors: Vostal Jaroslav G. , Gelderman Monique P. , Skripchenko Andrey , Xu Fei , Li Ying , Ryan Johannah , Cheng Chunrong , Whitley Pam , Wellington Michael , Sawyer Sherrie , Hanley Shalene , Wagner Stephen J.
Published: November 2017

BACKGROUND

Room temperature (RT) storage of platelets (PLTs) can support bacterial proliferation in contaminated units, which can lead to transfusion‐transmitted septic reactions. Cold temperature storage of PLTs could reduce bacterial proliferation but cold exposure produces activation‐like changes in PLTs and leads to their rapid clearance from circulation. Cold‐induced changes are reversible by warming and periodic rewarming during cold storage (temperature cycling [TC]) has been proposed to alleviate cold‐induced reduction in PLT circulation.

STUDY DESIGN AND METHODS

A clinical trial in healthy human volunteers was designed to compare in vivo recovery, survival, and area under the curve (AUC) of radiolabeled autologous apheresis PLTs stored for 7 days at RT or under TC or cold conditions. Paired comparisons of RT versus TC and TC versus cold PLTs were conducted.

RESULTS

Room temperature PLTs had in vivo recovery of 55.7 ± 13.9%, survival of 161.3 ± 28.8 hours, and AUC of 5031.2 ± 1643.3. TC PLTs had recovery of 42.6 ± 16.4%, survival of 48.1 ± 14.4% hours, and AUC of 1331.3 ± 910.2 (n = 12, p < 0.05). In a separate paired comparison, cold PLTs had recovery of 23.1 ± 8.8%, survival of 33.7 ± 14.7 hours, and AUC of 540.2 ± 229.6 while TC PLTs had recovery of 36.5 ± 12.9%, survival of 49.0 ± 17.3 hours, and AUC of 1164.3 ± 622.2 (n = 4, AUC had p < 0.05).

CONCLUSION

TC storage for 7 days produced PLTs with better in vivo circulation kinetics than cold storage but is not equivalent to RT storage.
Unchanged mitochondrial phenotype, but accumulation of lipids in the myometrium in obese pregnant women
Authors: Gam Christiane Marie Bourgin Folke , Larsen Lea Hüche , Mortensen Ole Hartvig , Engelbrechtsen Line , Poulsen Steen Seier , Qvortrup Klaus , Mathiesen Elisabeth Reinhart , Damm Peter , Quistorff Bjørn
Published: November 2017

Key points

Obesity during pregnancy and childbirth is associated with labour dystocia leading to instrumental or operative delivery, but the underlying pathophysiological mechanisms remain unclear and insufficient uterine contractility has been suggested.

This study examined whether reduced myometrial mitochondrial capacity or quantity could contribute as a pathophysiological mechanism to labour dystocia.

Data did not support reduced myometrial mitochondrial capacity or quantity in the myometrium at term in obese women, but a reduced myocyte density with increased triglyceride content was demonstrated, which could lead to poorer uterine contractility.

These results add to the understanding of systemic effects of obesity, placing also the myometrium at term as an affected non‐adipose tissue.

Obesity is known to increase the risk of labour dystocia and insufficient energy supply, due to reduced mitochondrial capacity or quantity, could be a possible mechanism leading to reduced efficiency of uterine contractility during labour. In the present study of 36 women having an elective Caesarean section at term, obesity did not change mitochondrial phenotype in the myometrial myocyte obtained from uterine biopsies taken at delivery. Respiration rates in isolated mitochondria were unaffected by obesity. No indication of reduced content, investigated by quantification of the complexes of the respiratory chain, or altered regulation, examined by myometrial mRNA levels of genes related to mitochondrial biogenesis and inflammation, was detected. Yet we found increased myometrial triglyceride content in the obese group (2.39 ± 0.26 vs. 1.56 ± 0.20 mm, P = 0.024), while protein content and citrate synthase activity per gram wet weight myometrium were significantly lower in the obese (109.2 ± 7.2 vs. 139.4 ± 5.6 mg g−1, P = 0.002, and 24.8 ± 1.0 vs. 29.6 ± 1.4 U g−1 wet wt, P = 0.008, respectively). These differences were substantiated by our histological findings where staining for nuclei, cytoplasm, glycogen and collagen supported the idea of a smaller muscle content in the myometrium in obese women. In conclusion no indication of myometrial mitochondrial dysfunction in the isolated state was found, but the observed increase of lipid content might play a role in the pathophysiological mechanisms behind labour dystocia in obese women.
Blast Wave-Induced Mixing in a Laser Ignited Hypersonic Flow
Authors: Gibbons Nicholas , Gehre Rolf , Brieschenk Stefan , Wheatley Vincent
Published: November 2017

A laser ignition system suitable for a hypersonic scramjet engine is considered. Wall-modeled large eddy simulation (LES) is used to study a scramjet-like geometry with a single hydrogen injector on the inlet, at a Mach 8 flight condition with a total enthalpy of 2.5 MJ. Detailed chemical kinetics and high fidelity turbulence modeling are used. The laser forms a kernel of high temperature plasma inside the fuel plume that briefly ignites the flow and leads to massive disruption of the flow structures around the jet, due to the expanding plasma kernel driving a blast wave that collides with the surrounding flow. The blast wave produces vorticity as it passes through the fuel–air interface, but comparably less than that produced by the jetting of the hot gas affected by the laser as it expands outward into the crossflow. The remnant of the plasma rolls up into a powerful vortex ring and noticeably increases the fuel plume area and the volume of well mixed reactants present in the simulation. These results indicate that the laser ignition system does more than just supply the energy to ignite the flow; it also substantially alters the flow structure and the mixing process.
High-Order Eulerian Simulations of Multimaterial Elastic–Plastic Flow
Authors: Subramaniam Akshay , Ghaisas Niranjan S. , Lele Sanjiva K.
Published: November 2017

We develop a new high-order numerical method for continuum simulations of multimaterial phenomena in solids exhibiting elastic–plastic behavior using the diffuse interface numerical approximation. This numerical method extends an earlier single material high-order formulation that uses a tenth-order high-resolution compact finite difference scheme in conjunction with a localized artificial diffusivity (LAD) method for shock and contact discontinuity capturing. The LAD method is extended here to the multimaterial formulation and is shown to perform well for problems involving shock waves, material interfaces and interactions between the two. Accuracy of the proposed approach in terms of formal order (eighth-order) and numerical resolution is demonstrated using a suite of test problems containing smooth solutions. Finally, the Richtmyer–Meshkov (RM) instability between copper and aluminum is simulated in two-dimensional (2D) and a parametric study is performed to assess the effect of initial perturbation amplitude and yield stress.
Properties of the Turbulent Mixing Layer in a Spherical Implosion
Authors: Boureima Ismael , Ramaprabhu Praveen , Attal Nitesh
Published: November 2017

We describe the behavior of a multimode interface that degenerates into a turbulent mixing layer when subjected to a spherical implosion. Results are presented from three-dimensional (3D) numerical simulations performed using the astrophysical flash code, while the underlying problem description is adopted from Youngs and Williams (YW). During the implosion, perturbations at the interface are subjected to growth due to the Richtmyer–Meshkov (RM) instability, the Rayleigh–Taylor (RT) instability, as well as the Bell–Plesset (BP) effects. We report on several quantities of interest to the turbulence modeling community, including the turbulent kinetic energy (TKE), components of the anisotropy tensor, density self-correlation, and atomic mixing, among others.
Beam Array Designs for a Cochlea-Inspired Accelerometer for Impact Measurements
Authors: Joyce Bryan , Dodson Jacob , Wolfson Janet
Published: November 2017

Limitations on neuron firing rates restrict the frequency bandwidth of many biological sensory systems. The cochlea overcomes these limitations to hear high frequency sounds through its tonotopic structure and non-synchronous sampling. The cochlea’s tapering basilar membrane serves as a filter bank decomposing an applied sound into its frequency components. Auditory hair cells produce neural impulses at the peaks in the local basilar membrane oscillations resulting in an event-driven, sub-Nyquist rate sampling strategy. These two effects extend the human hearing range to about 20 kHz despite maximum neuron firing rates of just a few hundred hertz. Inspired by this, this paper presents a concept demonstration of an accelerometer and signal compression strategy for high-rate impact events using a similar filter bank approach. A series of clamped-clamped beams will serve as analog analysis filters much like the cochlea’s basilar membrane. This paper focuses on the design and simulation of such a beam array and how the natural frequencies and damping ratios of the beams’ first modes affect measuring a broadband impact excitation.
A Stabilization of Fixed Gain Controlled Infinite Dimensional Systems by Augmentation With Direct Adaptive Control
Authors: Balas Mark J. , Frost Susan A.
Published: November 2017

Linear infinite dimensional systems are described by a closed, densely defined linear operator that generates a continuous semigroup of bounded operators on a general Hilbert space of states and are controlled via a finite number of actuators and sensors. Many distributed applications are included in this formulation, such as large flexible aerospace structures, adaptive optics, diffusion reactions, smart electric power grids, and quantum information systems. We have developed the following stability result: an infinite dimensional linear system is Almost Strictly Dissipative (ASD) if and only if its high frequency gain CB is symmetric and positive definite and the open loop system is minimum phase, i.e. its transmission zeros are all exponentially stable.

In this paper, we focus on infinite dimensional linear systems for which a fixed gain linear infinite or finite dimensional controller is already in place. It is usually true that fixed gain controllers are designed for particular applications but these controllers may not be able to stabilize the plant under all variations in the operating domain. Therefore we propose to augment this fixed gain controller with a relatively simple direct adaptive controller that will maintain stability of the full closed loop system over a much larger domain of operation. This can ensure that a flexible structure controller based on a reduced order model will still maintain closed-loop stability in the presence of unmodeled system dynamics. The augmentation approach is also valuable to reduce risk in loss of control situations.

First we show that the transmission zeros of the augmented infinite dimensional system are the open loop plant transmission zeros and the eigenvalues (or poles) of the fixed gain controller. So when the open-loop plant transmission zeros are exponentially stable, the addition of any stable fixed gain controller does not alter the stability of the transmission zeros. Therefore the combined plant plus controller is ASD and the closed loop stability when the direct adaptive controller augments this combined system is retained. Consequently direct adaptive augmentation of controlled linear infinite dimensional systems can produce robust stabilization even when the fixed gain controller is based on approximation of the original system. These results are illustrated by application to a general infinite dimensional model described by nuclear operators with compact resolvent which are representative of distributed parameter models of mechanically flexible structures. with a reduced order model based controller and adaptive augmentation.
Nonlinearities in Experimental System Identification of a Piezocomposite Beam Model
Authors: Heaney Patrick S. , Bilgen Onur
Published: November 2017

Piezocomposite beams are often modeled using linear constitutive equations describing the electromechanical coupling of the material. In nearly all experimental identification processes, nonlinearities in these equations are ignored, which can lead to significant errors in the identified models. Following a common practice in the literature, a piezocomposite cantilever beam is modeled as a single degree of freedom system, with strain induced harmonic excitation governed by linear piezoelectric constitutive relationships. The validity of the linear property assumptions is investigated. It is experimentally demonstrated that the relationship between input and response of the beam is significantly nonlinear. The impact of this nonlinear behavior on the parameter identification of the system is shown for three different testing methods, (1) Open Loop Excitation, (2) Constant Input, and (3) Constant Response. For each method, the command amplitude is varied which yields different parameter estimates for the single degree of freedom beam model. These results demonstrate that the assumed linear constitutive relationships lead to parameter estimates which are only accurate for the specific testing method and the specific commanded input or response amplitude, even under highly controlled testing procedures. The paper concludes with comments on the system identification of a single degree of freedom model given this nonlinear system behavior.
Experimental Mode Shape Identification for a Cantilever Beam Using Optical Fiber Bragg Gratings
Authors: Heaney Patrick S. , Bilgen Onur
Published: November 2017

Parameter estimation of a cantilever beam model typically involves estimating the effective parameters of the system for an assumed mode shape. This shape assumption, which is difficult to verify with traditional single-point sensors, can be validated through the distributed strain measurements available from optical Fiber Bragg Grating sensors. In this paper, the experimental mode shapes of a cantilever beam acquired from Fiber Bragg Grating sensors are compared with the analytical predictions of classical beam theory for the first two bending modes. A single degree of freedom model is also analyzed for the first bending mode and compared to the distributed parameter model and experimental data. It is shown that the distributed parameter model provides a good estimate of the strain profile at the first two natural frequencies, and that the single degree of freedom and distributed parameter models are in close agreement at the first natural frequency.
A Heat Transfer System Identification Method for Shape Memory Alloy Wires
Authors: Wright Cody , Bilgen Onur
Published: November 2017

The thermo-mechanical coupling of shape memory alloys has been modeled comprehensively using energy based constitutive models. These constitutive models describe the relationship of temperature, stress and strain in material and propose a solid methodology for system identification of model parameters. Equally important in the dynamics of shape memory alloy applications is the heat transfer model. Heat transfer models have been proposed but a complete resource for system identification of the model parameters is missing in the literature. Therefore, in this paper, the parameters for a low-order heat transfer model are identified experimentally. It is shown that for all parameters the measured parameters accurately model the system leading to the necessary values for use in predictive models. Furthermore, it is shown that using nominal values will produce inaccuracies in the predicted system response.
Parametric Analysis of a Compliant Hinge Mechanism for a Shape Memory Alloy Actuated Arm
Authors: Wright Cody , Bilgen Onur
Published: November 2017

A compliant hinge is proposed to replace conventional revolute joints for a shape memory alloy actuated arm-like mechanism. The arm-like mechanism is designed to replicate the articulation of the elbow joint, linking the humerus and radius, while being able to lift a dead load using a shape memory alloy wire as the biceps muscle. A parametric analysis on hinge geometry and Young’s modulus is performed to determine if a feasible geometric and material solution exists based on the application requirements. The results indicate optimum solutions are logarithmically correlated between modulus of elasticity and width-to-thickness ratio. Overlaying the results of the parametric study onto an Ashby chart indicates that large hinge widths are necessary. These results indicate more complex geometries are needed for arm-like manipulator applications.
Sensitivity Analysis and Design of an Open-Loop Active Normal Force for Dry Friction Dampers
Authors: Wu Yaguang , Fan Yu , Li Lin , Liu Jiuzhou
Published: November 2017

In this paper we design an open-loop active normal force for dry friction dampers, aiming to enhance the damping effect. The active normal force is composed of a constant term plus a time-varying term with zero mean value. The constant term is the best constant normal force that minimizes the forced response in the resonant frequency band. The time-varying force can be expressed by the Fourier Series and here we assume that it is composed of four harmonics with respect to the excitation frequency. Overall eight unknown parameters are therefore to be determined, namely the combination coefficients of the fours harmonics and phase differences between them. First, the global sensitivity of these parameters with respect to the forced response are analysed, in order to select the most significant parameters and to eliminate the unimportant ones. To do that the Fourier Amplitude Sensitivity Test (FAST) is performed based on the Lumped Parameter Model, where the forced response of is calculated by the Multi-Harmonic Balance Method (MHBM) combined with Alternating Frequency/Time domain (AFT). The arc-length continuation technique is used to improve the convergence. We found that the interaction between the amplitude and phase of the second harmonic significantly impacts the forced response around resonance frequencies. Then only these two parameters are considered to minimize the forced response in the frequency band, rather than considering all eight parameters. Results show that a further 25% reduction of the response peak can be achieved by the designed time-varying normal force in comparison with the best constant normal force. The proposed design process is applicable for any dry friction dampers if it is possible to impose an open-loop active normal force.
Modeling of a Bio-Inspired Canal-Type Lateral Line System
Authors: Sharif Montassar Aidi , McHenry Matthew J. , Tan Xiaobo
Published: November 2017

It is of interest to exploit the insight from the lateral line system of fish for flow sensing applications. The lateral line consists of arrays of flow sensors, known as neuromasts, with hair cells encased within a gel-like structure called cupula. There are two types of neuromasts, superficial neuromasts, which reside on the surface, and canal neuromasts, which are recessed within a channel with its ends open at the body’s surface. In this work we investigate the modeling of a canal-type artificial lateral line system. The canal is filled with viscous fluid to emulate its biological counterpart. The artificial neuromast consists of an ionic polymer-metal composite (IPMC) sensor embedded within a soft molded cupula structure. The displacement of the cupula structure and the resulting short-circuit current of the IPMC sensor under an oscillatory flow are modeled and solved with finite-element methods. The Poisson-Nernst-Planck (PNP) model is used to describe the fundamental physics within the IPMC, where the bending stimulus due to the cupula displacement is coupled to the PNP model through the cation convective flux term. Comparison of the numerically computed cupula displacement with an analytical approximation is conducted. The effects of material stiffness and and device size on the device sensitivity are further explored.
Modeling and Simulation of Architectured Iron-Based SMA Materials
Authors: Zaki Wael , Cissé Cheikh , Ben Zineb Tarak
Published: November 2017

The paper presents results of finite element analysis of architectured iron-based shape memory alloy (SMA) samples consisting of bulk SMA and void combined to different proportions and according to different geometric patterns. The finite element simulation uses a constitutive model for iron-based SMAs that was recently developed by the authors in order to account for the behavior of the bulk material. The simulation of the architectured SMA is then carried out using a unit cell method to simplify calculations and reduce computation time. For each unit cell, periodic boundary conditions are assumed and enforced. The validity of this assumption is demonstrated by comparing the average behavior of one unit cell to that of a considerably larger sample comprising multiple such cells. The averaging procedure used is implemented numerically, by calculating volume averages of mechanical fields such as stress and strain over each finite element model considered as a combination of mesh elements.
Analytical Model for a Superelastic SMA Beam
Authors: Viet N. V. , Zaki Wael , Umer Rehan
Published: November 2017

We propose an analytical model for a superelastic shape memory alloy (SMA) beam. The model considers reversible phase transformation between austenite and a single martensite variant driven by mechanical loading/unloading. In particular, we consider a cantilever beam subjected to a concentrated transverse force acting at the tip. The force is gradually increased from zero to a maximum value sufficient to cause complete transformation of the initially austenitic phase into martensite away from the beam core. The force is then gradually removed, resulting in complete strain recovery. In each stage of the loading/unloading process, an analytical relation is established between bending moment and curvature in terms of position along the axis of the beam. The model is compared to a uniaxial numerical beam model and to finite element analysis (FEA) results for the same beam in 3D, with very good agreement in each case. The moment-curvature relation is then integrated to obtain a nonlinear expression for the deflection and stress distribution in terms of position along the length of the beam. The expression is validated against 3D simulation results.
Numerical Verification of the Tuned Inertial Mass Effect of a Wave Energy Converter
Authors: Haraguchi Ruriko , Asai Takehiko
Published: November 2017

This paper introduces the mechanism of a buoy-type wave energy converter (WEC) with a tuned inertial mass (TIM) mechanism. The TIM mechanism consists of a rotational mass and motor connected in series with a tuning spring. While it is common to control the current of the power take-off system, the stiffness of the spring is tuned in addition so that the inertial mass part resonates with the dominant frequency of the wave motion. The method to design the parameters to maximize the power generation capability is introduced and numerical studies for both narrowband and broadband sea states are carried out. It is shown that the proposed device demonstrates better energy harvesting performance compared to the WEC without the TIM mechanism to band-limited stationary random vibration.
Unusual Dynamic Behaviors Induced by Time-Space Modulated Structures
Authors: Yi Kaijun , Collet Manuel , Karkar Sami
Published: November 2017

Time-space modulated structures (or dynamic structures) possess properties modulated both in time and space. They have been extensively studied in diverse areas. This presented work theoretically studies the unusual wave propagation phenomena induced by elastic waves incident on time-space modulated beams. The scattering matrix is developed to predict the characteristics of the reflected and transmitted waves. It is shown that the scattering matrix directly indicates the non-reciprocal wave transmission and frequency splitting phenomena caused by the dynamic beam, it also reveals a frequency conversion phenomenon, which is rarely noticed by researchers but has very significant influence on the application of dynamic structures.
Experimental Investigation of High-Speed/High-Voltage SMA Actuation
Authors: Motzki Paul , Gorges Tom , Würtz Thomas , Seelecke Stefan
Published: November 2017

The thermal shape memory effect describes the ability of a deformed material to return to its original shape when heated. This effect is found in shape memory alloys (SMAs) such as nickel-titanium (NiTi). SMA actuator wire is known for its high energy density and allows for the construction of compact systems. An additional advantage is the so-called “self-sensing” effect, which can be used for sensor tasks within an actuator-sensor-system.

In most applications, a current is used to heat the SMA wires through joule heating. Usually a current between zero and four ampere is recommended by the SMA wire manufacturers depending on the wire diameter. Therefore, supply voltage is adjusted to the SMA wire’s electrical resistance to reach the recommended current.

The focus of this work is to use supply voltages of magnitudes higher than the recommended supply voltages on SMA actuator wires. This actuation method has the advantage of being able to use industry standard voltage supplies for SMA actuators. Additionally, depending on the application, faster actuation and higher strokes can be achieved.

The high voltage results in a high current in the SMA wire. To prevent the wire from being destroyed by the high current, short pulses in the micro- and millisecond range are used.

As part of the presented work, a test setup has been constructed to examine the effects of the crucial parameters such as supply voltage amplitude, pulse duration, wire diameter and wire pre-tension. The monitored parameters in this setup are the wire displacement, wire current and force generated by the SMA wire. All sensors in this setup and their timing is validated through several experiments. Additionally, a highspeed optical camera system is used to record qualitative videos of the SMA wire’s behavior under there extreme conditions. This optical feedback is necessary to fully understand and interpret the measured force and displacement signals.
Development of a Reconfigurable End-Effector Prototype
Authors: Khelfa Frank , Zimmer Lukas , Motzki Paul , Seelecke Stefan
Published: November 2017

Material handling is a crucial part of manufacturing and assembly in industry. In state-of-the-art handling systems, robots use various end-effectors to grip and transport different shapes of workpieces. The exchange process of fitted end-effectors to appropriate workpieces, often requires to interrupt the manufacturing process. From the prospective of economic efficiency, there is an inherent benefit creating a reconfigurable end-effector that is able to adjust automatically to different workpiece geometries. In this work a novel end-effector prototype based on shape memory alloys (SMA’s) is developed and experimentally validated. The end-effector prototype has four arms with two SMA driven reconfigurable degrees of freedom (DOF’s) to allow gripping of different workpiece shapes and geometries. Each arm is rotatable by 90 degrees (1. DOF) and uses a counterweight to relieve the SMA wire. The tip of the arm is driven by a separate SMA in a 20 degree range and it has a special locking mechanism to hold different positions without any flowing current. The designs of the actuator constructions are presented and a prototype is produced via rapid-prototyping. Future work will include the characterization of the second DOF and controlling the positions of both DOF’s by using a PID controller based on the SMA self-sensing ability.
Self-Start Piezoelectric Energy Harvesting Circuit With Adjustable UVLO Converter for Wireless Sensor Network
Authors: Jung Hyun Jun , Lee Soobum , Jabbar Hamid , Jeong Se Yeong , Sung Tae Hyun
Published: November 2017

This paper proposes a self-start piezoelectric energy harvesting circuit with an undervoltage-lockout (UVLO) converter for a wireless sensor network (WSN). First, a self-start circuit with mini piezoelectric energy harvester (PEH) is designed to supply the power for operation of the oscillator without battery. The experimental results show that a batteryless self-start circuit successfully operates the oscillator with mini-PEH, and self-starting time is 0.45 s. Second, this paper proposes an adjustable UVLO converter that can supply the power even if a power consumption of a wireless sensor node is higher than generated power from PEH. The experimental result shows the adjustable UVLO converter supplies 45 mW for 0.12 s after charging the output power of an impedance matching circuit (1.7 mW) for 10 s. This paper shows that the proposed circuit successfully overcomes challenging issues — self-start and lower power generation — for powering WSN.
Nonreciprocal Acoustics Using Programmable Boundary Conditions: From Boundary Control and Active Metamaterials to the Acoustic Diode
Authors: Karkar Sami , Collet Manuel
Published: November 2017

In this communication, we first introduce the concept of programmable boundary conditions, and then use it to design a nonreciprocal acoustic device: an effective, broadband, acoustic diode.

Previous works showed that, using sufficiently small transducers, an active acoustic metasurface can be realized: a smart active acoustic skin with tunable acoustic properties. Using distributed control, these properties can be adapted or reconfigured in real-time. Or, it can even depend on the acoustic field itself, allowing for a programming of the (meta)surface properties: a programmable boundary condition. For instance, a partial derivative equation depending on the acoustic quantities can be imposed, in a discretized form, at the surface of such a programmable boundary. This type of non-standard boundary conditions have been shown to provide the necessary basis for nonreciprocal propagation for a plane wave interacting with a boundary with non grazing incidence, ie. for wavevectors that possess a component normal to the boundary. This restriction may appear problematic when the wavevector is then parallel to the boundary, e.g. when dealing with plane waves in a 1D waveguide, as in an acoustic diode.

An acoustic diode, or acoustic isolator, is a nonreciprocal device that let acoustic power pass only in one direction, hence breaking the reciprocity of normal acoustic propagation. We propose a new model of acoustic diode, based on active components: a continuous, distributed source inside the domain. However, based on the modeling of parietal sources in ducts, in the low frequency range, we show that the boundary control approach and the distributed domain sources are equivalent. The only difference is that, in the case of the programmable boundary condition, the near-field of the boundary also contains a component normal to the boundary. Hence our acoustic diode can be realized in practice using programmable boundary conditions. Moreover, the acoustic diode is effective on a broad frequency range, since it can work both on the fundamental mode (plane waves) and on higher-order mode of the waveguide.
Exploiting the Subharmonic Parametric Resonance of a Bi-Stable Beam for Energy Harvesting
Authors: Emam Samir A. , Panyam Meghashyam , Daqaq Mohammed F.
Published: November 2017

We investigate the potential of harvesting vibration energy via a bi-stable beam subjected to subharmonic parametric excitations. The vibrating structure is a buckled beam with two stable equilibria separated by a potential barrier. The beam is subjected to a superposition of a static axial load beyond its critical buckling load and a harmonic axial excitation which frequency is around twice the frequency of the first vibration mode. A micro-fiber composite (MFC) is attached to one side of the beam to convert the strain energy resulting from the beams oscillation into electricity. The study considers two regimes of excitations: an amplitude sweep and a frequency sweep. In the first regime, the amplitude of excitation is varied while the excitation frequency is tuned at twice the natural frequency of the first vibration mode. In the second regime, the excitation frequency is swept forward and backward around the subharmonic resonant frequency while the amplitude of excitation is kept constant. A theoretical model which governs the electromechanical coupling of the transverse vibrations of the beam and the output voltage is used to monitor the response as the excitation parameters are changed. An experimental setup is built and a series of tests is performed. The theoretical results are in good agreement with their experimental counterparts. The experiment also shows that this type of bi-stable energy harvesters exhibits a broadband frequency response as compared to the classical linear harvesters.
Exploring the Dynamic Characteristics of Degree-4 Vertex Origami Metamaterials
Authors: Xia Yutong , Fang Hongbin , Wang K. W.
Published: November 2017

Origami-inspired mechanical metamaterials could exhibit extraordinary properties that originate almost exclusively from the intrinsic geometry of the constituent folds. While most of current state of the art efforts have focused on the origami’s static and quasi-static scenarios, this research explores the dynamic characteristics of degree-4 vertex (4-vertex) origami folding. Here we characterize the mechanics and dynamics of two 4-vertex origami structures, one is a stacked Miura-ori (SMO) structure with structural bistability, and the other is a stacked single-collinear origami (SSCO) structure with locking-induced stiffness jump; they are the constituent units of the corresponding origami metamaterials. In this research, we theoretically model and numerically analyze their dynamic responses under harmonic base excitations. For the SMO structure, we use a third-order polynomial to approximate the bistable stiffness profile, and numerical simulations reveal rich phenomena including small-amplitude intrawell, large-amplitude interwell, and chaotic oscillations. Spectrum analyses reveal that the quadratic and cubic nonlinearities dominate the intrawell oscillations and interwell oscillations, respectively. For the SSCO structure, we use a piecewise constant function to describe the stiffness jump, which gives rise to a frequency-amplitude response with hardening nonlinearity characteristics. Mainly two types of oscillations are observed, one with small amplitude that coincides with the linear scenario because locking is not triggered, and the other with large amplitude and significant nonlinear characteristics. The method of averaging is adopted to analytically predict the piecewise stiffness dynamics. Overall, this research bridges the gap between the origami quasi-static mechanics and origami folding dynamics, and paves the way for further dynamic applications of origami-based structures and metamaterials.
Design, Development, and Structural Testing of a Camber-Morphing Flying Wing Airplane
Authors: Keidel D. , Fasel U. , Molinari G. , Ermanni P.
Published: November 2017

This work presents the design, optimization, manufacturing, and experimental characterization of a swept, camber-morphing, flying wing. By virtue of a novel actuation concept, combined with a compliant structural concept, camber deflections of sufficient amplitude to achieve controllability in roll and pitch are attained. The optimization, which accounts for aeroelastic interactions in the assessment of the wing behaviour, concurrently optimizes the variables describing the aerodynamic shape, the inner structure, and the actuation strategy. The aerodynamic shape is optimized for a longitudinally stable flying wing, which solely relies on morphing deflections to control its attitude. The morphing deflection can be varied along the span, enabling to attain optimized deformed shapes for any flight condition. To validate the concept and assess its structural characteristics and actuation capabilities, an experimental demonstrator was fabricated. The wing has a total span of 3.2m and a maximum chord length of 23cm. Its structural integrity was assessed through a wing up-bending test, permitting to both characterize its load-carrying capacity and validate the structural model. The actuation capability was assessed by measuring the deformed shapes through a digital image correlation system, enabling to successfully confirm the predictions obtained through a detailed FE model.
Development of Multi-Dimensional 3D Printed Vascular Networks for Self-Healing Materials
Authors: Qamar Isabel P. S. , Trask Richard S.
Published: November 2017

Self-healing materials have emerged as an alternative solution to the repair of damage in fibre-reinforced composites. Recent developments have largely focused on a vascular approach, due to the ability to transport healing agents over long distances and continually replenish from an external source. However fracture of the vascular network is required to enable the healing agents to infiltrate the crack plane, ceasing its primary function in transporting fluid and preventing the repair of any further damage events. Here we present a novel approach to vascular self-healing through the development and integration of 3D printed, porous, thermoplastic networks into a thermoset matrix. This concept exploits the inherently low surface chemistry of thermoplastic materials, which results in adhesive failure between the thermoplastic network and thermoset matrix on arrival of a propagating crack, thus exposing the radial pores of the network and allowing the healing agents to flow into the damage site. We investigate the potential of two additive manufacturing techniques, fused deposition modeling (FDM) and stereolithography, to fabricate free-standing, self-healing networks. Furthermore, we assess the interaction of a crack with branched network structures under static indentation in order to establish the feasibility of additive manufacture for multi-dimensional 3D printed self-healing networks.
Ultrasound Actuation of Shape-Memory Polymer Filaments: Acoustic-Thermoelastic Modeling and Testing
Authors: Bhargava Aarushi , Peng Kaiyuan , Stieg Jerry , Mirzaeifar Reza , Shahab Shima
Published: November 2017

Controlled drug delivery (CDD) technology has received extensive attention in the past three decades due to numerous advantages of this technology when compared to the conventional methods. Despite recent efforts and substantial achievements, controlled drug releasing systems still face major challenges in practice, including chemical issues with synthesizing biocompatible drug containers and releasing the pharmaceutical compounds at the targeted location with a controlled time rate. In this work, we present experimentally-validated acoustic-thermoelastic mathematical modeling to show the feasibility of using shape memory polymers (SMPs) and focused ultrasound (FU) technology for designing a novel drug-delivery system. SMPs represent a new class of materials that have the ability of storing a temporary shape and returning to their permanent or original shape when subjected to external stimuli such as heat. FU is used as a trigger for noninvasively stimulating SMP-based drug capsules. FU has a superior capability to localize the heating effect, thus initiating the shape recovery process only in selected parts of the polymer. A multiphysics model is developed, which optimizes the design of a SMP-based CDD system using acoustic-thermoelastic analysis of a filament as the constituting base structure and quantifies its activation through FU. The analytical and numerical models are divided into three parts. The first part studies the acoustic behavior of SMPs using Khokhlov-Zabolotskaya-Kuznetsov (KZK) model. The equation solves for acoustic pressure field in a hybrid time-frequency domain using operator-splitting method and examines the effects of absorption, diffraction and nonlinear distortion on the propagating wave in the medium. The second part provides a numerical model based on Penne’s Bioheat equation to estimate the thermal field developed in SMPs as a result of focused acoustic pressure field. The third part provides a numerical framework to predict the mechanical stresses developed in SMPs under FU and consequent shape recovery. The mechanical model is formulated by a compressible neo-Hookean constitutive equation, which assumes the SMPs behave as a thermoelastic material and predicts the shape memory effect under FU. Experimental validation is performed using a FU transducer in a water tank. The recovery of thermally responsive SMPs under FU predicted by our model shows a good accordance with the experiments. The modeling results are used to optimize parameters such as nonlinear properties, input frequency, source power and dimensional effects to achieve maximum shape recovery.
Design and Evaluation of Advanced Smart Needles for Brain Biopsy
Authors: Sahlabadi Mohammad , Khodaei Seyedvahid , Hutapea Parsaoran
Published: November 2017

Biopsy involves removing a piece of tissues for further medical examination. Brain biopsy is generally performed using different techniques, such as open biopsy, stereotactic core biopsy, and needle biopsy. Open biopsy is the most common and the most invasive form of the brain biopsy. During the procedure, a piece of the skull is removed and the brain is exposed. Stereotactic core and needle biopsies are minimally invasive. In these procedures, a hole is usually drilled into the skull and a needle is inserted through the hole to extract the tissue. Brain biopsy has its risks and complications due to the vulnerability of the brain tissue. Although using needle or stereotactic biopsies reduce the risks, brain biopsy may cause swelling or bleeding in the brain, and in some cases, can result in infection, stroke, seizure or even coma. A needle biopsy with conventional needles involves pulling or pushing the cutting stylet inside the needle hollow body (cannula). The manual pulling and pushing procedure induces lateral movement of the needle, which increases the damage in brain tissue. The goal here is to completely remove the needle harmful lateral movement. In this work, design of smart biopsy needles is proposed and demonstrated by incorporating nitinol wires and springs to control the lateral movement of the cutting stylet. The first design comprises of two parts. The first part of the needle is a 360° tissue cutting stylet, and the second part is the cannula. The cutting stylet can slide inside the cannula and a nitinol wire is embedded at the end of the stylet and the end of the cannula. As the electric current is applied on the nitinol wire, it shrinks and pulls the cutting stylet. The second design is almost similar to the first design, but it has a 180° tissue cutting stylet with a similar actuating mechanism. The last design uses a nitinol torsion spring that is attached to the cutting stylet. It cuts tissue samples by activating the nitinol spring to rotate the cutting stylet.