bluuebunny/crossref_metadata_2025 huggingface dataset:
Recognition and significance of bayhead delta deposits in the rock record: A comparison of modern and ancient systems
Authors: Aschoff Jennifer L. , Olariu Cornel , Steel Ronald J.
Published: November 2016

Despite advances in estuarine facies models, ancient bayhead delta deposits are not widely recognized or utilized, and their facies characteristics are poorly documented. Sedimentology of three well‐exposed, bayhead delta deposits within the well‐known stratigraphic framework of the Book Cliffs, Utah, and comparison to modern bayhead deltas provide insight into their variability, and a model for reservoir prediction. Bayhead deltas develop at the innermost part of bays within wave‐dominated and mixed‐energy estuaries on transgressive coastlines. The deposits of these deltas are valuable because they record the high‐frequency turnaround from transgression to regression; in turn, this delineates the long‐term transgression trajectory and informs reservoir prediction. This study uses outcrop data and synthesis of modern bayhead delta characteristics to define criteria for bayhead delta recognition, develop a detailed facies model and highlight their utility in a regional context. The following criteria for bayhead delta identification are proposed herein: (i) overall coarsening‐up pattern; (ii) small‐scale clinoform (5 to 15 m height; 100 to 1000 m length) showing a down‐clinoform decrease in grain size and palaeocurrent energy; (iii) increasing abundance of mud interbeds towards the clinoform toe; (iv) basinward‐directed palaeocurrents generated mainly by fluvial input with strong tidal overprint; (v) greatest tidal influence in the intertidal zone of the inactive delta front and better preservation of turbidites at clinoform toes; (vi) brackish trace and body fossils; and (vii) position within an overall backstepping stratigraphic succession. Ancient bayhead deltas described in this study are situated within a moderately rising to flatly rising transgressive interval over a 300 km transect. Steeply rising transgressive trajectories sequester sandy, thicker, better connected transgressive deposits in the inner part of the estuary where bayhead deltas tend to stack vertically. Flatter transgressive trajectories sequester sand in disparate, disconnected estuarine sandstone bodies with partial preservation of bayhead deltas. Proposed criteria aid recognition of bayhead delta deposits in other basins to reconstruct transgressive shoreline trajectories that inform reservoir models and volumetrics.
Immunomodulatory and Immunosuppressive Roles of 1α,25(OH)2D3 in Autoimmune Diseases
Authors: Alhassan Mohammed H. , Saboor‐Yaraghi A. A. , Mirshafiey A. , Vahedi H. , Shiri‐Shahsavar M. R. , Mousavi Nasl Khameneh A.
Published: November 2016

Autoimmune diseases are pathological conditions characterized by abnormal responses, accompanied by autoantibodies to self‐molecules. The role of vitamin D in autoimmune diseases has increased significantly in the recent past from its functions in calcium and phosphate homoeostasis, and it is now involved in the regulations and proliferations of Th1 and Th17 lymphocyte. 1α,25(OH)2D3 is very important in ameliorations of inflammatory disorders arising from autoimmune diseases, but the mechanism by which this is performed is still a bone of contentions. This review aimed to highlight the existing facts about the roles of Vitamin D in the treatment and management of autoimmune diseases. An extensive online literature search was conducted using PubMed, MEDLINE and Scopus. Accumulated bodies of research evidence are available which demonstrates that Vitamin D has a very important part to play in the regulation of immune responses in autoimmune diseases. Some of the authors suggested that Vitamin D3 carry‐out its immunosuppressive and immune modulatory action, through its actions on antigen‐presenting cells and activated T and B cells with the help of Vitamin D receptors present on the each of these cells. Vitamin D supplementation assists in autoimmune disorders by making qualitative and quantitative changes in the immune system (downregulation of Th1 and upregulations of Th2 cells). This resulted in the body to be more tolerant of self and less likely to mount autoimmune responses.
Medically Documented Suicide Ideation Among U.S. Army Soldiers
Authors: Ursano Robert J. , Kessler Ronald C. , Stein Murray B. , Naifeh James A. , Nock Matthew K. , Aliaga Pablo A. , Fullerton Carol S. , Wynn Gary H. , Ng Tsz Hin Hinz , Dinh Hieu M. , Sampson Nancy A. , Kao Tzu‐Cheg , Schoenbaum Michael , McCarroll James E. , Cox Kenneth L. , Heeringa Steven G. ,   the Army STARRS collaborators
Published: November 2016

We used administrative data to examine predictors of medically documented suicide ideation (SI) among Regular Army soldiers from 2006 through 2009 (N = 10,466 ideators, 124,959 control person‐months). Enlisted ideators (97.8% of all cases) were more likely than controls to be female, younger, older when entering service, less educated, never or previously deployed, and have a recent mental health diagnosis. Officer ideators were more likely than controls to be female, younger, younger when entering service, never married, and have a recent mental health diagnosis. Risk among enlisted soldiers peaked in the second month of service and declined steadily, whereas risk among officers remained relatively stable over time. Risk of SI is highest among enlisted soldiers early in Army service, females, and those with a recent mental health diagnosis.
The Rise and Fall of Iraq in the Social Sciences*
Authors: Ahram Ariel I.
Published: November 2016

Objective

This article analyzes how the extremely authoritarian nature of the Iraqi regime affected scholarship of Iraq and shows how regime opacity and brutality constrain social science research.

Methods

The article examines scholarly output on Iraq using qualitative and quantitative metrics from the Saddam Hussein era and the post‐2003 period after his removal from power.

Results

The article finds a dramatic increase in the quantity of publications on Iraq after 2003 and a shift toward more nomothetic, theory‐building research involving Iraq. New forms of research on Iraq, including field research, embedded observation, interviews, surveys, and archival research, also became prevalent after 2003.

Conclusion

The progress of social science research depends both on regime transparency and regime stability. Researchers can adjust techniques to address the absence of transparency or stability, but without the combination of both, the overall venture suffers.
Paranoia and Perspective, or How I Learned to Stop Worrying and Start Loving Research in the Islamic Republic of Iran*
Authors: Malekzadeh Shervin
Published: November 2016

Objectives

To demonstrate that qualitative research is both possible and desirable in closed, nondemocratic settings such as Iran, research sites seemingly hostile to the outside investigator.

Methods

Using an ethnographical approach consisting of document analysis, semi‐structured interviews, and participant observation, the project documents the development of postrevolutionary schooling in Iran by mapping ruptures within the pedagogical state's project following the 1979 Revolution as well as gaps between the state's formal goals and the private use and appropriation of the public school system by ordinary families from below.

Results

A willingness to embrace contingency and flexibility in the field yielded an original and empirically rich data set that in turn inspired four general rules for research in authoritarian and nonauthoritarian countries: do not panic; make it boring; self‐reflect; and panic, if just a little.

Conclusions

By engaging in research in authoritarian and nonauthoritarian settings, researchers demonstrate a commitment to drawing out local complexity and agency, producing findings that are likely to unsettle and disrupt existing literatures drenched with the weight of tropes and unexamined assumptions, incrementally leading to analysis that is restorative of “the local” even as it informs nonlocal audiences outside of the case.
Scientific Closure and Research Strategies in Uzbekistan*
Authors: Markowitz Lawrence P.
Published: November 2016

Objectives

Using the example of Uzbekistan, this article examines the challenges and opportunities for conducting field research in a context of tightened scientific closure in those countries with highly autocratic regimes.

Methods

Drawing on the author's own field experience conducting elite interviews in Uzbekistan in 2002 and 2003 (as well as many subsequent visits), it examines three strategies of field research that emerged in this context of tightening scientific closure.

Results

The article outlines several essential features of authoritarianism in Uzbekistan and tracks the regime's shift toward scientific closure over three distinct phases, tracing out the implications of this shift for those carrying out systematic field research.

Conclusions

Uzbekistan illustrates the challenges and opportunities facing researchers under conditions of scientific closure in the 20–30 other countries ruled by hard authoritarian regimes.
Overcoming Research Obstacles in Hybrid Regimes: Lessons from Rwanda*
Authors: Loyle Cyanne E.
Published: November 2016

Objective

This article discusses the challenges of conducting research in hybrid regimes. Under these conditions, governments proscribe the types of questions researchers can ask and self‐preservation on the part of the researcher induces further self‐censorship. This ultimately impacts the type of research we conduct and the outputs of that research.

Methods

Experiences conducting research in Rwanda are used to explore these challenges.

Results

Research restrictions and monitoring in hybrid regimes is found to limit the types of research questions that scholars can ask as well as the questions that they do ask.

Conclusions

In this article, I suggest that being knowledgeable of the context, exercising creativity when needed, and demonstrating respect for research participants are essential skills for navigating the obstacles of conducting research in a hybrid regime.
Soil carbon as affected by cover crops under no‐till under tropical climate
Authors: Rosolem C. A. , Li Y. , Garcia R. A.
Published: November 2016

In tropical, low‐fertility soils, crop yields are dependent on soil carbon, and cropping systems under no‐till can increase soil C stocks. Plant residues supplied by cover crops in no‐till systems may improve aggregate stability and soil carbon, which may be further increased with the introduction of a legume in the cropping system. This research studied the effects of cover crops in rotation with soybean under no‐till on soil carbon and nitrogen, in Botucatu, Brazil, for 3 yr. The cover crops were millet (Penninsetum americanum Leek), cober crop (Sorghum bicolor × Sorghum sudanense) and sunn hemp (Crotalaria juncea L.), grown in the spring. Fallow without cover crops was used as a control. Grain sorghum (Sorghum bicolor L. Moench) and soybean (Glycine max (L.) Merril) were grown in fall–winter and summer, respectively. Generally, cover crops increased soil carbon contents, but soil N was only increased by sunn hemp in the particulate organic C fraction. An increase in the labile carbon fraction in the topsoil layers was closely related to cover crop root development. Fallow in spring should not be recommended in degraded soils with lowcarbon stock. Labile‐fractioned soil organic carbon and total carbon levels are more efficiently increased by grasses than by legumes in the short term, and grasses cropped in spring increase soil C/N ratio. Conversely, the introduction of a legume (sunn hemp) maintained a more stable C/N ratio, that is around 10, which would be more effective in increasing soil C in the long term.
Damage Precursors in Individual Microfibers
Authors: Cole Daniel P. , Henry Todd C. , Gardea Frank , Haynes Robert
Published: November 2016

Structural health monitoring of composite materials is limited by the lack of fundamental understanding of early stage damage at the local material level. This includes damage precursor formation on fiber surfaces, within the matrix, and at the fiber-matrix interface/interphase. In this effort, we present a micro-/nano-scale technique for characterizing damage precursor formation on individual carbon fibers exposed to cyclic tensile loads. Nanoindentation and atomic force microscopy (AFM) were used to study the local properties of the individual microfibers before and after global loading events. An AFM image analysis was used to track evolution of topography on the fiber surfaces. The work is a first step toward understanding damage precursor formation in individual microfibers; the work is expected to enable multiscale composites modeling efforts as well as enable the development of future self-sensing materials.
Modeling of Smart Heat Pump Using Thermoelectric and Electrocaloric Materials
Authors: Feng Dudong , Yao Shi-chune , Zhang Tian , Zhang Qiming
Published: November 2016

In this study, a smart heat pump, which could be used for the cooling of electronics, made of the laminated structure of thermoelectric (TE) and electrocaloric (EC) materials is studied. A simple arrangement of two TE layers sandwiched with one EC layer is modeled. This smart heat pump utilized the newly developed EC materials of giant adiabatic temperature change and the TE materials of high figure of merit, which has the advantages of no moving parts, made of solid state, operable over large working temperature difference, and can be formed into very small size. The operation of the device is numerically modelled considering the three major parametric effects: EC operation as function of time, electric current applied on TE, and temperature difference between the hot and cold sinks. The results on Coefficient of Performance (COP) and heat flow per unit area are discussed. This study validates the feasibility of TE-EC-TE laminated structure heat pump, and extends the understanding by further discussing the performance of structures with more laminated layers.
Power Generation From Human Motion Through Magnetic Spring System
Authors: Wang Wei , Zhang Nan , Cao Junyi , Lin Jing
Published: November 2016

A magnetic-spring electromagnetic energy harvester which consists of a hollow tube with two magnets fixed to the end and an attracting magnetic stack moving inside it is presented in this paper to harvest energy from human motion. The dynamic model of the electromagnetic generator is derived according to Newton’s law and Ansoft Maxwell software is used to calculate the repulsive force between middle and end magnets. Experimental results under frequency-sweep excitation and constant frequency excitation with different acceleration levels show that the generator has the potential to generate electricity for a broadband frequency range and ability to light up a LED. In the experiments considering human motion, the voltage response caused by the impact between shoes and ground are investigated. Under that condition, the influence of equivalent mass of moving magnetic stack and speeds of motion on the energy harvesting efficiency is analyzed. Results show that larger equivalent mass could obviously improve the performance of the generator and the obtained maximum output power reaches 2.11 mW.
Predicting Non-Stationary and Stochastic Activation of Saddle-Node Bifurcation
Authors: Kim Jinki , Harne R. L. , Wang K. W.
Published: November 2016

Accurately predicting the onset of large behavioral deviations associated with saddle-node bifurcations is imperative in a broad range of sciences and for a wide variety of purposes, including ecological assessment, signal amplification, and adaptive material/structure applications such as structural health monitoring and piezoelectric energy harvesting. In many such practices, noise and non-stationarity are unavoidable and ever-present influences. As a result, it is critical to simultaneously account for these two factors towards the estimation of parameters that may induce sudden bifurcations. Here, a new analytical formulation is presented to accurately determine the probable time at which a system undergoes an escape event as governing parameters are swept towards a saddle-node bifurcation point in the presence of noise. The double-well Duffing oscillator serves as the archetype system of interest since it possesses a dynamic saddle-node bifurcation. Using this archetype example, the stochastic normal form of the saddle-node bifurcation is derived from which expressions of the escape statistics are formulated. Non-stationarity is accounted for using a time dependent bifurcation parameter in the stochastic normal form. Then, the mean escape time is approximated from the probability density function to yield a straightforward means to estimate the point of bifurcation. Experiments conducted using a double-well Duffing analog circuit verify that the analytical approximations provide faithful estimation of the critical parameters that lead to the non-stationary and noise-activated saddle-node bifurcation.
Conformal Growth of Textured Barium Titanate Films on Patterned Silicon Wafer
Authors: Zhou Zhi , Patterson Brendan A. , Bowland Christopher C. , Malakooti Mohammad H. , Sodano Henry A.
Published: November 2016

This work presents a fabrication process for the conformal growth of vertically aligned BaTiO3 films on 3-dimensionally patterned silicon waters. The conformal growth is performed through a two-step hydrothermal reaction that enables the direct growth of piezoelectric films on nonplanar architectures while utilizing relatively low synthesis temperatures. Scanning electron microscopy (SEM) is used to show the controllable conversion of TiO2 nanowires to BaTiO3 films and x-ray diffraction (XRD) is used to validate the crystal structures. Tested by a refined piezoresponse force microscopy (PFM) method, the conformal films exhibited a piezoelectric coupling coefficient as high as 100 pm/V. With superior piezoelectric properties and the capability to grow on design specific surfaces, the BaTiO3 conformal films demonstrate high potential for sensors, random access memory, and other micro-electromechanical systems.
Experimental Validation of Compliant Joints in a Dynamic Spar Numerical Model
Authors: Calogero Joseph , Frecker Mary , Hasnain Zohaib , Hubbard James E.
Published: November 2016

A dynamic spar numerical model for passive shape change is validated for a single degree of freedom contact-aided compliant mechanism (CCM) in a flapping spar. CCMs are modeled as compliant joints: spherical joints with distributed mass and three axis nonlinear torsional spring-dampers. Several assumptions were made in the original formulation of the model, such as assuming the spars were rigid and a simple damping model for the compliant joints. An experiment was performed to validate the assumptions and tune the model. Four configurations of the leading edge spar were tested: a solid spar, a previously designed CCM at two spatial locations, and a modified version of the CCM. Reflective markers were placed on each configuration, then the spars were inserted into the wing roots of a clamped ornithopter. An array of computer vision cameras was used to track the spar and CCM kinematics as they were flapped. First, a flapping angle function was extracted using a moving average of the flapping cycles. Then, a genetic algorithm was implemented to tune the stiffness and damping parameters for each of the configuration, minimizing the root mean square error between the model and experimental marker kinematics. The model was able to capture the deflection amplitude and harmonics of the CCMs with very good agreement and minimal to no phase shift.
Bio-Inspired Coupling of Camber and Sweep in Morphing Wings
Authors: Moosavian Amin , Gamble Lawren L. , Pankonien Alexander M. , Inman Daniel J.
Published: November 2016

This work aims to investigate how bio-inspired morphing wings built with state-of-the-art materials affect the aerodynamics and extend the range of flight conditions. In particular, this study investigates the aerodynamic effects of coupled airfoil and planform sweep morphing. The morphed geometries were chosen to resemble a current morphing design that uses Macro Fiber Composites (MFCs) and Shape Memory Alloy (SMA) wires. The primary mode of camber actuation is achieved using the MFCs which are supplemented using antagonistic SMA wires, forming a hinge ahead of the MFCs. The SMA hinge also allows for bi-directional actuation, resulting in a reflexed airfoil. Numerical simulations were conducted using a Reynolds-averaged-Navier-Stokes (RANS) turbulence model for low-Reynolds-number flow, in addition to wind tunnel experiments. Nine different wing configurations were considered consisting of combinations of 3 sweep angles and 3 airfoil profiles, including unactuated (baseline), monotonic camber actuation, and reflex actuation. These geometries were 3D printed on a high resolution printer. Tests were conducted in a 2 ft. × 2 ft. wind tunnel at the University of Michigan at a flow speed of 10 m/s, consistent with the flow regime expected for this scale of aircraft. The preliminary results suggest a definite improvement in flight performance associated with the proposed coupling.
Self-Clearing of Metalized Electrodes and its Impact on Electroactive Polymer (EAP) Based Actuators
Authors: Ahmed Saad , Ounaies Zoubeida
Published: November 2016

EAP based actuator technologies are extensively studied to design smart/intelligent systems ranging from deployable space structures, morphing wings, to medical devices and artificial muscles. Despite the extensive research on electroactive polymers (EAP), practical implementation of this technology is slow because of low induced forces and defect-driven premature electrical breakdown. Multilayered or stacked configuration can address the low induced force issue. However, construction procedure of multilayered sample is susceptible to more defects, which can further aggravate defect-driven premature breakdown of EAP actuators. Reducing the number of defects using self-clearing concept can improve the EAP actuators’ ability to withstand high electric fields. Self-clearing refers to the partial local breakdown of dielectric medium due to the presence of impurities, which in turn results in the evaporation of some of the metalized electrodes. After this evaporation, the impurity is cleared and any current path would be safely cut off, which means the actuator continues to perform, albeit with a reduced actuation area due to electrode evaporation. In this paper we study the impact of self-clearing metalized silver electrodes on the electrical and electromechanical behavior of EAPs, more specifically P(VDF-TrFE-CTFE) terpolymer. First, we use Weibull statistics to systematically estimate the self-clearing/preconditioning field needed to clear the defects. Then electrical breakdown experiments are conducted with and without preconditioning the samples to investigate their effects on the breakdown strength of the EAP. Finally, we implement this self-clearing/preconditioning field on single and multilayered P (VDF-TrFE-CTFE) unimorph actuators and investigate the resulting electromechanical performance. Due to preconditioning of the actuators using self-clearing concept, the actuators endure higher electric fields compared to a control sample. Loss of capacitance occurs during self-clearing, which in turn affects the electromechanical performance of the actuator. For that reason, we also report on the blocked force of preconditioned and controlled actuators to evaluate and compare their electromechanical performance.
Equivalent Circuit of the Concentration Transport in a Fluidic Channel
Authors: Marschner U. , Páez Chávez J. , Voigt A. , Richter Andreas
Published: November 2016

A new equivalent circuit is presented, which describes the transport of a chemical solution with a certain concentration in a fluidic channel. Channels are basic parts of a microfluidic systems and the concentration of the chemical solution can control the opening and closing of valves based on smart hydrogels. This type of microfluidic systems facilitates the autonomous control of fluid flow, e.g. in chemo-fluidic oscillators. Through this channel, the solution is transported at a velocity determined by the flow rate through the channel and its cross section. While the volumetric flow is not delayed in an ideal channel, the channel acts as delay line for the particles and thus for a certain concentration transport through the channel.

In this setting, the transport of the dissolved chemical by water traveling along the delay channel can be described by the one-dimensional transport equation. In order to derive the equivalent circuit, the transport equation is numerically approximated based on the well-known Method of Lines. This method consists in approximating the original PDE via a large system of ODEs. The ODEs are obtained by discretizing the PDE in space, in such a way that each component of the resulting system of ODEs approximates the solution of the PDE at some grid point along the spatial interval. Once the system of ODEs has been constructed, a flow and a difference quantity can be defined and the ODEs interpreted as finite network elements. Since the equations are isomorphic to electrical ODEs of electrical network elements, the fluidic channel can be expressed by an equivalent circuit. Thus the transient behavior of the transport mechanism can be calculated using a circuit simulator as part of a design automation. Simulation results are presented.
On the Development of an SMA Based Rear Mirror Folding Actuator
Authors: Czechowicz Alexander , Hoffmann Fabian , Langbein Sven , Dültgen Peter , Wieczorek Romeo
Published: November 2016

Nowadays electric motors are used for various applications in the automotive industry which affects the automobiles’ mass significantly. Small and medium sized electromotors are mainly used for comfort applications like locking systems or mirror folding drives. On the other hand, electromotor drives use often a reduction of a high speed rotation to a slow and powerful movement by the usage of gears. Due to the multistage gear ratio principle, such drives emit a noise level up which can be an inferiority attribute of an automotive system. Nevertheless, comfort applications are mainly driven by electromotor actuators in automobiles. Figure 1 shows a cut through a schematic side mirror of a car with two major electromotor drives comparable to the state of the art. The motor for mirror folding consists mainly of the complex gear box which has to fulfill a mirror movement of more than 65° in less than 5 seconds. To move the mirror with the motor has to have enough mechanical power to overcome this force and to move the mirror with a torque of more than 5 Nm.
Preliminary Design of Flapping Wing Micro Aerial Vehicle at Low Reynolds Numbers
Authors: Altememe Abduljaleel , Anderson Stanley , Myers Oliver J. , Hall Asha J.
Published: November 2016

This research discusses preliminary design of a Flapping Wing Micro Aerial Vehicle (FWMAV). One approach is to develop a biologically-inspired flapping wing MAV that can maneuver into confined areas and possess hover capabilities. This platform can potentially be equipped with microphones, cameras, and gas detectors, but one major challenge is the low Reynolds number aerodynamics. The critical components for successful flight include size, weight, and energy efficiency. Preliminary efforts include mechanical designs for payload, biologically inspired chassis, wing and tail.
Droop Nose With Elastic Skin
Authors: Riemenschneider Johannes , Radestock Martin , Vasista Srinivas , Huxdorf Oliver , Monner Hans Peter
Published: November 2016

Morphing is a technology with high potential to reduce emissions in aviation by adapting the shape of the wings to varying external operating conditions. This paper is presenting results from the EU FP7 funded CHANGE project, where different concepts to adapt a UAV wing airfoil to different demands were investigated. The paper is concentrating on the design and experimental testing of a droop nose, which transforms the leading edge part of the 60 cm chord airfoil from a NACA 6510 shape for loiter and low speed to a NACA 2510 shape for a high speed mission. This paper is presenting the use of an especially soft skin, which reduces the needed force for morphing. That way the requirements for the servos driving the droop nose could be reduced significantly. This paper is showing the implications of such a soft design on the accuracy of the shape generated. For such a skin design, the driving mechanism of the system is designed as a compliant mechanism, which was generated by topology optimization, taking into account aerodynamic loads. For easy manufacturing reasons, thermoplastic polylactic acid (PLA) with zero warp property was used for the manufacturing of this compliant mechanism.

Finally deformation measurements of the morphing skin were carried out in a series of lab tests. The match between measured and numerically derived section is quite good, especially in the root region of the wing.

Finally an example of an alternative concept to the soft approach is presented. It is the metal based compliant mechanism with a rather stiff GFRP skin. A discussion on the use of different materials and the way forward towards 3D skin optimization is wrapping up the paper.
Characterization of Ni-Mn-Ga Shape Memory Single Crystals for Magnetic Properties and Magnetic Field Induced Shear and Normal Strains
Authors: Kiang Jademond , Tong Liyong
Published: November 2016

This paper presents a novel experimental apparatus and a test method for measuring simultaneously quasi-static average longitudinal and shear magnetic-field-induced strain (MFIS) of Ni-Mn-Ga single crystals. The apparatus consists of an aluminum casing, a weight-controlled plunger, two displacement probes (one vertical and one lateral), and a torsion guide etc. Three Ni-Mn-Ga square prism samples were tested. Twin boundary bands were clearly visible after the application of magnetic field. A range of material properties were measured. These include: (a) magnetic anisotropy constant; (b) single variant magnetization curves for the easy and hard axes; (c) nonlinear compressive stress-strain curves for all three samples at room temperature; and (d) average longitudinal and shear MFIS curves versus magnetic field strength for three prism samples subject to various compressive external stresses.
Chain Failure Events in Microfluidic Membrane Networks
Authors: Makhoul-Mansour Michelle , Challita Elio J. , Freeman Eric C.
Published: November 2016

Multiple lipid encased water droplets may be linked together in oil to form large networks of droplet interface bilayers thus creating a new class of stimuli-responsive materials for applications in sensing, actuation, drug delivery, and tissue engineering. While single droplet interface bilayers have been extensively studied, comparatively little is known about their interaction in large networks. One particular problem of interest is understanding the impact of the coalescence of two neighboring droplets on the overall structural integrity of the network. Here, we propose a computational modeling scheme that predicts and characterizes the mechanical properties of the multiple lipid bilayer interfaces within the droplet network upon intentional coalescence of adjacent droplets. Droplet networks with tailored architectures are synthesized with the aid of magnetic motor droplets containing a biocompatible ferrofluid. The equilibrium configuration of the droplet networks is compared to computational prediction which defines the overall stability by summing the interfacial energies. Once the networks are completed, failure in selected membranes is induced. As the targeted droplets coalesce together, the equilibrium structure of the network is altered and the remaining droplets may shift to new configurations dictated by their minimized mechanical energies.
Optimized Modal Synchronized Switching Control for Flexible Structures
Authors: Cazzulani G. , Braghin F. , Mazzocchi F.
Published: November 2016

This paper focuses on the Synchronized Switching Damping (SSD) control, a semi-active vibration suppression technique based on the coupling between a mechanical structure and piezoelectric actuators. This control family is optimized for structures subjected to mono-harmonic excitation. Anyway, in the last years, different solutions to address multi-harmonic and multi-modal excitation have been developed. One of them is the so-called Modal SSD, where the switches of the shunting circuit are governed by the behavior of the modal coordinates of the structure. Although the control performance is good, this paper shows that there are still some issues to be solved. For this reason, the paper proposes a modified version of this control strategy able to improve the control performance without increasing the circuit complexity. The proposed solution is firstly described in detail and then tested and compared with the existing ones on the numerical model of a cantilever beam.
Measurement of Flapping Wing Deformation Using Piezoelectric Modal Sensors
Authors: Tran Jason , Cameron Christopher G. , Sirohi Jayant
Published: November 2016

An experimental investigation was conducted to measure the deformation of flapping wings with distributed piezoelectric modal sensors. The sensors are bonded to the surface of a wing and shaped to extract a specific modal co-ordinate. The experimental setup consisted of a carbon fiber beam with shaped sensors designed to extract the 1st and 2nd modal co-ordinates. The beam was mounted to two different excitation devices (shaker or servomotor) that allowed the beam to be excited at a desired frequency and motion. The resulting electrical signals from the strained modal sensors are calibrated to modal co-ordinate measurements. In order to validate modal sensor measurements, the Digital Image Correlation (DIC) technique is used to obtain full field deformation measurements of the beam. The measured deformation from DIC is then used in conjunction with operational modal analysis to extract modal co-ordinates. Comparison of the modal co-ordinates obtained via modal sensors against DIC measurements show good agreement. Furthermore, a sensitivity analysis was performed to gauge the robustness of modal sensors against construction errors. The results obtained show that modal sensors are a simple and accurate method of obtaining the deformation of a flapping wing.
Novel Chiral Structure With Tailored Mechanical Response Exploiting Elastic Instabilities
Authors: Runkel Falk , Molinari Giulio , Arrieta Andres F. , Ermanni Paolo
Published: November 2016

This paper presents a structural concept that exploits elastic instabilities in novel periodic lattice structures for shape adaptation purposes. The nonlinear behaviour resulting from the occurrence of local buckling is utilised to achieve significant variations in the global structural response of the lattice. For the proposed structural concept, a unit cell is identified and utilised to investigate the mechanical characteristics for the load cases of uniaxial compression, shear, and rotation, conducting nonlinear finite element simulations. The results of the unit cell characterization are compared to the mechanical response of lattice structures under equivalent loading and convergence is achieved for all considered load cases. This paper therefore introduces a novel design concept to achieve selective compliance, especially beneficial for shape adaptation of wing structures.
High-Cycle Fatigue Criterion for Shape Memory Alloys Based on Shakedown Theory
Authors: Zaki Wael , Gu Xiaojun , Moumni Ziad , Zhang Weihong
Published: November 2016

Based on a recently developed shakedown theory for non-smooth nonlinear materials, we derive a criterion for high-cycle fatigue in shape memory alloys (SMAs). The fatigue criterion takes into account phase transformation as well as reorientation of martensite variants as the source of fatigue damage. The mathematical derivation of the criterion is based on the requirement of elastic shakedown for a given structure to achieve unlimited fatigue endurance. Elastic shakedown is defined as an asymptotic state in which damage due to time-varying load becomes confined at the mesoscopic scale, or the scale of the grain, with no discernable inelasticity at the macroscopic scale. From an energy standpoint, elastic shakedown corresponds to a situation where energy dissipation becomes bounded and the response elastic after a certain number of loading cycles. A sufficient condition to achieve this state was established by Melan (1936) [1] and Koiter (1960) [2] for elastoplastic materials and later generalized to hardening plasticity by Nguyen (2003) and to non-smooth non-linear materials by Peigney (2014). The latter formulation is applicable to SMAs obeying the ZM constitutive model (Zaki & Moumni, 2007) and is shown here to allow the derivation of a high-cycle fatigue criterion analogous to the one proposed by Dang Van (1973) for elastoplastic materials. The criterion allows establishing a safe domain in stress deviator space at the mesoscopic scale consisting of a hypercylinder with axis parallel to the direction of martensite orientation. The hypercylinder is delimited along its axis by two transverse hyperplanes representing bounds on admissible stress states consistent with the loading conditions for phase transformation. Safety with regard to high-cycle fatigue, upon elastic shakedown, is conditioned by the persistence of the macroscopic stress path, as the load varies and at every material point, strictly within the hypercylinder. The size of the hypercylinder is shown to strongly depend on the relative amount of martensite present in the SMA.
Nonlinear Piezoelectric Material Properties and Non-Uniform Poling in a Flexible Electro-Active Composite Finite Element Model
Authors: Calogero Joseph , Ben Atitallah Hassene , Wyckoff Nicholas , Ounaies Zoubeida , Frecker Mary
Published: November 2016

Active Fiber Composites (AFCs) are piezoelectric devices comprised of long cylindrical fibers, typically made of ceramic lead zirconate titanate (PZT), embedded in an epoxy polymer. AFCs use interdigitated electrodes to produce electric field lines parallel to the fibers (33-mode) rather than across the diameter, exploiting the stronger out-of-plane electromechanical coupling. Nonlinear piezoelectric and dielectric terms and non-uniform poling are often neglected in modeling AFCs due to the added complexity, however including the terms improves accuracy for strong electric fields and where the electrode geometry causes non-uniform electric fields. For that reason, a new finite element model of the AFC is developed which includes the effect of nonlinearities in piezoelectric strain constants and electric permittivity due to a non-uniform applied electric field resulting from two sets of interdigitated electrodes. The methods used to apply the nonlinear constitutive equations and poling are described. A comparison of the AFC response with linear and nonlinear material properties, with non-uniform poling, is shown for increasing applied electric fields. The difference in AFC response illustrates the necessity to include Rayleigh Law terms and non-uniform poling in the model.
Investigation of Ion Transport in Polypyrrole Modified Ultra-Microelectrodes During Scanning Electrochemical Microscopy
Authors: Venugopal Vinithra , Venkatesh Vijay , Sundaresan Vishnu Baba
Published: November 2016

Scanning electrochemical microscopy (SECM) is an electrochemical technique used to measure faradaic current changes local to the surface of a sample. The incorporation of shear force (SF) feedback in SECM enables the concurrent acquisition of topographical data of substrates along with electrochemical measurements. Contemporary SECM measurements require a redox mediator such as ferrocene methanol (FcMeOH) for electrochemical measurements; however, this could prove detrimental in the imaging of biological cells. In this article, nanoscale polypyrrole membranes doped with dodecylbenzene sulfonate (PPy(DBS)) are deposited at the tip of an ultra-microelectrode (UME) to demonstrate a novel modification of the contemporary SECM-SF imaging technique that operates in the absence of a redox mediator. The effect of distance from an insulating substrate and bulk electrolyte concentration on sensor response are examined to validate this technique as a tool for correlated topographical imaging and cation flux mapping. Varying the distance of the PPy(DBS) tipped probe from the substrate in a solution containing NaCl causes a localized change in cation concentration within the vicinity of the membrane due to hindered diffusion of ions from the bulk solution to the diffusion field. The cation transport into the membrane in close proximity to the substrate is low as compared to that in the electrolyte bulk and asymptotically approaches the bulk value at the sense length. At a constant height from the base, changing the bulk NaCl concentration from 5 mM to 10 mM increases the filling efficiency from 35% to 70%. Further, the sense length of this modified electrode in NaCl is about 440 nm which is significantly lower as compared to that of a bare electrode in ferrocene methanol (5–20 μm). It is postulated that this novel technique will be capable of producing high resolution maps of surface cation concentrations, thus having a significant impact in the field of biological imaging.
Noise Reduction in a High Lift Wing Using SMAs: Computational Fluid-Structural Analysis
Authors: Scholten William , Patterson Ryan , Hartl Darren , Strganac Thomas , Volpi Jeff , Chapelon Quentin , Turner Travis
Published: November 2016

The leading-edge-slat on an aircraft is a significant contributor to the airframe noise during the low speed maneuvers of approach and landing. It has been shown in previous work that the slat noise may be reduced with a slat-cove filler (SCF). The objective of this current work is to determine how the SMA SCF behaves under steady flow using finite element structural models and finite volume (FV) fluid models based on a scaled wind tunnel model of a newly considered multi-element wing with a SCF. Computational fluid dynamics (CFD) analysis of the wing is conducted at multiple angles of attack, different flow speeds and high lift device deployment states. The FV fluid models make use of overset meshes, which overlap a slave mesh (that can undergo movement and deformation) unto a fixed master mesh, allowing for retraction and deployment of the slat and flap in the CFD analysis. The structural and fluid models are linked using a previously developed framework that permits the use of custom user material subroutines (for superelastic response of the SMA material) in the structural model, allowing for the performance of fluid-structure interaction (FSI) analysis. The fluid and structural solvers are weakly coupled such that the fluid solver transfers pressure data and the structural solver transfers displacements, but the physical quantities of each program are solved independently. FSI results are shown for the cases of the slat/SCF in the fully-deployed configuration as well as for the case of the slat/SCF undergoing retraction in flow.
Realization of Origami-Inspired Smart Structures Using Electroactive Polymer (EAP)
Authors: Ahmed Saad , Arrojado Erika , Ounaies Zoubeida
Published: November 2016

Robert Lang has brought functionality to origami, the art of paper folding, by developing an extensive series of “action origami” figures. As the name suggests, these figures can perform actions and produce an output motion with the help of manual actuation, unlike traditional origami. For instance, different figures can bite, row, and fly. The goal of this research study is to adapt a few of these action origami figures put forth by Robert Lang to create ‘active’ action origami; these systems, instead of relying on manual actuation for motion, will rely on electro-mechanical actuation. This electro-mechanical actuation will be achieved through the judicious use of an electroactive polymer known as P (VDF-TrFE-CTFE) terpolymer. The terpolymer’s in-plane motion in response to an electric field is converted into bending using a unimorph configuration. This bending motion is exploited to actuate three so-called “action origami” structures: the flapping butterfly, the catapult, and the barking dog. Based on knowledge of the kinematics of the origami structures, multilayered terpolymer actuator is placed strategically on the origami figures with an aim to maximize the resulting actuation motion. In order to understand the behavior, capabilities, and limitations of the terpolymer as an active material, both qualitative and quantitative data are collected from the actuation of these three different action origami structures as a function of number of terpolymer layers, applied electric field and frequency of the applied field. The goal is to find the suitable shapes and crease patterns of the structures as well as the configurations with the terpolymer film to maximize the actuation. These three structures are tested and results show that PVDF-terpolymer is an effective actuator with ability to deform a substrate to a desired shape in the presence of an electric field: the butterfly was able to flap, the mouth of the dog was able to “bark,” and the catapult was able to launch a small ball of paper. Through experimentation, it was determined what parameters affect actuation and furthermore what values of those parameters will maximize the actuation.
Application of Auxetic Polymeric Structures for Body Protection
Authors: Yang Chulho , Vora Hitesh D. , Chang Young B.
Published: November 2016

Negative Poisson’s ratio (NPR) materials, also known as auxetic materials, have many promising application areas. In recent years, various auxetic material structures have been designed and fabricated for diverse applications that utilized normal materials which follow Hooke’s law but still show the properties of negative Poisson’s ratios.

In light of this, efforts are made to apply auxetic material structures to body protection pads that are comfortable to wear and effective in protecting body parts by reducing impact force and preventing injuries in high-risk individuals such as elderly people, industry workers, law enforcement and military personnel, and sport players. For those people, blunt impacts such as falls, bullets, and blast wave may reduce quality of life, increase the possibility of early death and generate an extremely high medical costs. Therefore, it is important to develop new body protectors that best combine each individual’s requirements of wearing comfort (flexible, light weight), ease of fitting (customized), ensured protection, and cost-effectiveness. The developed protection pad would be made from multilayer materials with an adaptive structure to achieve a unique multifunctional properties such as high hardness, impact toughness, light weight, excellent shock absorption, self-assembly suitable for the needs.

Particularly, an integrated computational (finite element analysis) approach is used to investigate the effect of three material structures (honeycomb or flexin structure, re-entrant hexagonal cells or reflexin structure, and arrowhead structure) in combination with three polymeric materials (Polylactic acid (PLA) and two thermoplastic polyurethane (TPU) materials). Efforts are made to relate the individual and/or combined effect of auxetic structure and materials to the overall stiffness and shock-absorption performance of the body protection pads.

Initially, parametric 3D CAD models of auxetic polymeric structures are developed. Later, key structural characteristics of protectors are evaluated through static analyses of FEA models. Impact/shock analyses are conducted to validate the results obtained from the static analyses. The mechanism for ideal input force distribution or shunting is suggested for designing protectors using various shapes, thicknesses, and materials of auxetic materials to reduce the risk of injury. The results show that the auxetic material can be considered as an effective material structure for body protection pads.