bluuebunny/crossref_metadata_2025 huggingface dataset:
About time: age, period, and cohort effects on support for Quebec sovereignty
Authors: Vallée‐Dubois Florence , Dassonneville Ruth , Godbout Jean‐François
Published: November 2017

Can age, period and cohort effects help explain support for Quebec sovereignty? Previous work on this question has focused mostly on the effects of age and cohort. We contribute to this debate by adding a period perspective. As such, our study is the first to investigate the impact of age, cohort and period effects in a single study of opinion towards sovereignty in Quebec. We take advantage of an original dataset that includes survey data collected between 1985 and 2012. We use these data to examine the impact of age, birth year and survey year on support for this constitutional option among francophone Quebeckers. Our results are in line with previous work: we show that younger Quebeckers are more likely to support sovereignty, and that some cohorts – namely, respondents born between 1945 and 1959 – are also more likely to favour this option. Perhaps more surprisingly, we find that specific events are comparatively the most important factor to explain fluctuations in Quebeckers' attitudes towards sovereignty.
Gastric accommodation in healthy subjects studied by ultrasound, manometry, and impedancemetry
Authors: Storlid E. L. , Hausken T. , Lied G. A. , Gilja O. H. , Hatlebakk J. G.
Published: November 2017

Background

Gastric accommodation to a meal may be important in the pathogenesis of upper gastrointestinal disorders, but has been difficult to investigate in a minimally invasive fashion.

Methods

We studied gastric and lower esophageal physiology during food intake, combining transabdominal ultrasound, multichannel high‐resolution impedance‐manometry (HRIM) and a symptom questionnaire. A HRIM catheter was distally positioned at incisura angularis and 300 mL saline with 75 g glucose was ingested. Target variables were recorded for 30 min after fluid intake.

Key Results

Fifteen healthy subjects’ participated (11W/4M, median age 23.8 y) and all accepted the meal with few symptoms. At incisura angularis maximum change in pressure from pre‐intake values was −7.4 mmHg after 60 s (P < .0001), rising to pre‐intake values within 20 min. The corresponding area increased significantly from pre‐intake values of 8.0 cm2 to 14.1 cm2 shortly after intake (P = .0012), peaked at 5 min and slowly decreased towards 30 min. The corresponding maximum change in stress from pre‐intake pressure values was −59.2 mmHg shortly after (P < .0001), reaching pre‐intake values within 20 min. Strain rose from 0 shortly before to 0.36 shortly after (P < .0001), peaking at 5 min. At incisura angularis, fullness was positively correlated with area and to strain, while fullness, area, and stress were negatively correlated with pressure.

Conclusions & Inferences

The multimodal method enabled assessment of the gastric accommodation reflex, stress and strain in the stomach. It triggered few symptoms in healthy volunteers. We propose it to be a more physiological replacement of the barostat technique.
Insights on efficacious doses of PAMORAs for patients on chronic opioid therapy or opioid‐naïve patients
Authors: van Malderen K. , Halawi H. , Camilleri M.
Published: November 2017

Background

Opioid‐induced constipation (OIC) is a major side effect of opioid use. Centrally acting antagonists result in opioid withdrawal or worsening of pain and lead to use of peripherally acting mu‐opioid receptor antagonists (PAMORAs). The required doses of the PAMORAs, methylnaltrexone and naloxegol, in the treatment of OIC are well established in chronic opioid users. OIC may occur after short duration of opioid treatment; the required doses of naloxone, naltrexone, and PAMORAs in opioid‐naïve subjects (with no opioid use for at least 3 months) are unclear. The aim of this review was to evaluate the PAMORA dose required for opioid‐naïve subjects to achieve similar beneficial effects on symptoms or valid surrogates to those observed in chronic opioid users.

Methods

A PubMed search of μ‐opioid antagonists to counter μ‐opioid effects included terms: naloxone, naltrexone, methylnaltrexone, alvimopan, and naloxegol, as well as OIC and colonic transit.

Key Results

The approved dose of methylnaltrexone in chronic opioid users, 0.3 mg/kg subcutaneous (SQ), did not affect motility in opioid‐naïve subjects. Trials investigating the required dose of alvimopan showed 0.5‐1 mg dose was efficacious in treating OIC; a 10‐fold higher dose (12 mg) of alvimopan is needed to block effects of codeine on small bowel and colonic transit in opioid‐naïve subjects compared to chronic opioid users. Opioid‐naïve users need 125 mg of naloxegol to reverse the effects of opioids on transit; this is in contrast to the 12.5 to 25 mg needed to treat OIC in chronic opioid users.

Conclusions & Inferences

Opioid‐naïve subjects require a higher dose of PAMORA than chronic opioid users to achieve μ‐opioid antagonist effect.
Decreased 5‐HT2cR and GHSR1a interaction in antipsychotic drug‐induced obesity
Authors: Huang X.‐F. , Weston‐Green K. , Yu Y.
Published: November 2017

Second generation antipsychotics (SGAs), notably atypical antipsychotics including olanzapine, clozapine and risperidone, can cause weight gain and obesity side effects. Antagonism of serotonin 2c receptors (5‐HT2cR) and activation of ghrelin receptor type 1a (GHSR1a) signalling have been identified as a main cause of SGA induced obesity. Here we review the pivotal regulatory role of the 5‐HT2cR in ghrelin‐mediated appetite signalling. The 5‐HT2cR dimerizes with GHSR1a to inhibit orexigenic signalling, while 5‐HT2cR antagonism reduces dimerization and increases GHSR1a‐induced food intake. Dimerization is specific to the unedited 5‐HT2cR isoform. 5‐HT2cR antagonism by SGAs may disrupt the normal inhibitory tone on the GHSR1a, increasing orexigenic signalling. The 5‐HT2cR and its interaction with the GHSR1a could serve as the basis for discovering novel approaches to preventing and treating SGA‐induced obesity.
Orthopedic complications of linear morphea: Implications for early interdisciplinary care
Authors: Schoch Jennifer J. , Schoch Bradley S. , Werthel Jean David , McIntosh Amy L. , Davis Dawn M. R.
Published: November 2017

Linear morphea of the limb primarily affects children, and extracutaneous manifestations are common. Orthopedic surgeons are often essential in the care of patients with linear morphea, yet there are few reports outlining specific orthopedic complications in this population. We sought to improve the understanding of orthopedic complications in linear morphea of the limb. Between 1999 and 2014, 51 children were evaluated for linear morphea of an extremity. Twenty‐six (51%) had documented orthopedic manifestations. Outcome measures included limb length discrepancy, angular malalignment, limb atrophy, and orthopedic surgical intervention. Joint contractures were most common, affecting 88% of patients, followed by limb atrophy, angular deformity, and limb length discrepancy; 14% required surgical intervention. Despite the use of systemic immunosuppressive therapy in many patients, approximately half of patients with linear morphea of an extremity have orthopedic disease. Early orthopedist involvement is crucial to improve limb alignment and preserve function.
Social aggregation of the marine isopodCirolana harfordidoes not rely on the availability of light‐reducing shelters
Authors: Salma Umme , Thomson Murray
Published: November 2017

Social aggregation under shelters can afford benefits to animals such as protection from predators. Many isopods and insects are negatively phototactic and this may help them gravitate towards shelter. Previous studies show that, when placed in an arena with two red shelters, specimens of the marine isopodCirolana harfordiand the terrestrial isopodPorcelio scaberpick one of the two shelters at random and aggregate under it, demonstrating social aggregation under light‐reducing shelters. In the present study, an arena with two clear shelters was used to determine whether group sizes of 4, 8, 12 and 16C. harfordispecimens display social aggregation when the shelters do not accommodate negative phototaxis. In all group sizes,C. harfordispecimens picked one of the shelters at random and significantly more animals aggregated under this shelter compared with the other.Cirolana harfordialso displayed aggregation in an arena with no shelters. Accordingly,C. harfordispecimens do not require shelters that reduce light to display social aggregation. The ability to locate suitable shelter under which there is no substantial reduction in light could benefit the animal in a natural environment comprising heavily shaded areas, as well as at night.
Territorial Conflicts and Japanese Attitudes Towards East Asian Countries: Natural Experiments with Foreigners' Landings on Disputed Islands
Authors: Igarashi Akira
Published: November 2017

Japan disputes the sovereignty of two islands: Senkaku/Diaoyu with China and Takeshima/Dokdo with South Korea. These disputes have triggered political performances. In August 2012, Chinese activists landed on Senkaku/Diaoyu, and South Korean politicians landed on Takeshima/Dokdo. The group threat theory suggests that these events constitute threats to Japanese citizens, which lead to negative attitudes towards these countries. The theory also expects personal variations in the reactions to the threats, and the empirical findings of the theory predict an improvement in the worsened attitudes immediately after the event. Drawing on a Japanese social survey that was conducted every month for the two years during which these landing events occurred, I tested the effect of the events on Japanese attitudes towards China and South Korea in a natural experimental framework. The results show that the events negatively impacted Japanese attitudes towards both countries. However, contrary to the expectations of the group threat theory, individual variations (i.e., socioeconomic status, media exposure, and political orientation) in the responses to the events are not supported. Additionally, the attitudes do not return to preevent levels for one year. The contradictions between previous studies and this study potentially originate from the importance of the territories.
Restoration of contaminated ecosystems: adaptive management in a changing climate
Authors: Farag Aïda M. , Larson Diane L. , Stauber Jenny , Stahl Ralph , Isanhart John , McAbee Kevin , Walsh Christopher J.
Published: November 2017

Three case studies illustrate how adaptive management (AM) has been used in ecological restorations that involve contaminants. Contaminants addressed include mercury, selenium, and contaminants and physical disturbances delivered to streams by urban stormwater runoff. All three cases emphasize the importance of broad stakeholder input early and consistently throughout decision analysis for AM. Risk of contaminant exposure provided input to the decision analyses (e.g. selenium exposure to endangered razorback suckers, Stewart Lake; multiple contaminants in urban stormwater runoff, Melbourne) and was balanced with the protection of resources critical for a desired future state (e.g. preservation old growth trees, South River). Monitoring also played a critical role in the ability to conduct the decision analyses necessary for AM plans. For example, newer technologies in the Melbourne case provided a testable situation where contaminant concentrations and flow disturbance were reduced to support a return to good ecological condition. In at least one case (Stewart Lake), long‐term monitoring data are being used to document the potential effects of climate change on a restoration trajectory. Decision analysis formalized the process by which stakeholders arrived at the priorities for the sites, which together constituted the desired future condition towards which each restoration is aimed. Alternative models were developed that described in mechanistic terms how restoration can influence the system towards the desired future condition. Including known and anticipated effects of future climate scenarios in these models will make them robust to the long‐term exposure and effects of contaminants in restored ecosystems.
Viraemia before, during and after pregnancy in HIV‐infected women on antiretroviral therapy in rural KwaZulu‐Natal, South Africa, 2010–2015
Authors: Chetty Terusha , Newell Marie‐Louise , Thorne Claire , Coutsoudis Anna
Published: November 2017

Objectives

Pregnancy and post‐partum viral load suppression is critical to prevent mother‐to‐child HIV transmission and ensure maternal health. We measured viraemia risk before, during and after pregnancy in HIV‐infected women.

Methods

Between 2010 and 2015, 1425 HIV‐infected pregnant women on lifelong antiretroviral therapy (ART) for at least six months pre‐pregnancy were enrolled in a cohort study in rural KwaZulu‐Natal, South Africa. Odds ratios were estimated in multilevel logistic regression, with pregnancy period time‐varying.

Results

Over half of 1425 women received tenofovir‐based regimens (n = 791). Median pre‐pregnancy ART duration was 2.1 years. Of 988 women (69.3%) with pre‐pregnancy viral loads, 82.0%, 6.8% and 11.2% had VL <50, 50‐999 and ≥1000 copies/ml, respectively. During pregnancy and at six, 12 and 24 months, viral load was ≥1000 copies/ml in 15.2%, 15.7%, 17.8% and 16.6% respectively; viral load <50 was 76.9%, 77%, 75.5% and 75.8%, respectively. Adjusting for age, clinical and pregnancy factors, viraemia risk (viral load ≥50 copies/ml) was not significantly associated with pregnancy [adjusted OR (aOR) 1.31; 95% CI 0.90‐1.92], six months (aOR 1.30; 95% CI 0.83‐2.04), 12 months (aOR 0.96; 95% CI 0.58‐1.58) and 24 months (aOR 1.40; 95% CI 0.89‐2.22) post‐partum. Adjusting for ART duration–pregnancy period interaction, viraemia risk was 1.8 during pregnancy and twofold higher post‐partum.

Conclusions

While undetectable viral load before pregnancy through post‐partum was common, the UNAIDS goal to suppress viraemia in 90% of women was not met. Women on preconception ART remain vulnerable to viraemia; additional support is required to prevent mother‐to‐child HIV transmission and maintain maternal health.
Malaria exacerbates inflammation‐associated elevation in ferritin and soluble transferrin receptor with only modest effects on iron deficiency and iron deficiency anaemia among rural Zambian children
Authors: Barffour Maxwell A. , Schulze Kerry J. , Coles Christian L. , Chileshe Justin , Kalungwana Ng'andwe , Siamusantu Ward , Arguello Margia , Moss William J. , West Keith P. , Palmer Amanda C.
Published: November 2017

Objective

In 4‐ to 8‐year‐old Zambian children (n = 744), we evaluated the effects of adjusting for inflammation (α1‐acid glycoprotein >1 g/l), with or without additional adjustment for malaria, on prevalence estimates of iron deficiency (ID) and iron deficiency anaemia (IDA) during low malaria (LowM) and high malaria (HighM) transmission seasons.

Methods

To estimate adjustment factors, children were classified as: (i) reference (malaria negative without inflammation), (ii) inflammation without malaria (I), (iii) malaria without inflammation (M) and (iv) inflammation with malaria (IM). We estimated the unadjusted ID or IDA prevalence, and then adjusted for inflammation alone (IDI or IDAI) or inflammation and malaria (IDIM or IDAIM).

Results

Mean ferritin was 38 (reference), 45 (I), 43 (M) and 54 μg/l (IM) in LowM, increasing to 44, 56, 96 and 167 μg/l, respectively, in HighM. Corresponding mean sTfR was 6.4, 6.9, 7.9 and 8.4 mg/l in LowM, increasing to 8.2, 9.2. 8.7 and 9.7 mg/l in HighM. Ferritin‐based ID, IDI and IDIM were 7.8%, 8.7% or 9.1%, respectively, in LowM and 4.6%, 10.0% or 11.7%, respectively, in HighM. Corresponding soluble transferrin receptor (sTfR)‐based estimates were 27.0%, 24.1% and 19.1%, respectively, in LowM, increasing to 53.6%, 46.5% and 45.3%, respectively, in HighM. Additional adjustment for malaria resulted in a ~1‐ to 2‐percentage point change in IDA, depending on biomarker and season.

Conclusions

In this population, malaria substantially increased ferritin and sTfR concentrations, with modest effects on ID and IDA prevalence estimates.
In vitro chemosensitivity of feline injection site‐associated sarcoma cell lines to carboplatin
Authors: Maxwell Elizabeth A. , Phillips Heidi , Schaeffer David J. , Fan Timothy M.
Published: November 2017

Objective

To determine the in vitro chemosensitivity of feline injection site‐associated sarcoma (FISAS) cells to carboplatin concentrations generated by elution of carboplatin‐impregnated calcium sulfate hemihydrate (CI‐CSH) beads.

Study design

In vitro study.

Sample

Five immortalized cell lines from histologically confirmed, primary FISASs.

Methods

For each cell line, one 96‐well microplate was used for each time point (24, 48, 72 hours). In each microplate, 3 wells were seeded with ∼7.5 × 103cells per well for every carboplatin treatment added, ranging from 5 to 450 µM. Microculture plates were incubated for 24, 48, or 72 hours. Drug efficacy was assessed via a bioreductive fluorometric assay. For apoptosis analysis, 3 wells were seeded with ∼5 × 104cells per well for every carboplatin treatment added, ranging from 5 to 450 µM. Flow cytometry was performed and the relative percentages of viable, apoptotic, and late apoptotic/necrotic cells were reported. All experiments were run in triplicates.

Results

Carboplatin exerted dose‐dependent and time‐dependent effects on FISAS cell viability. The IC50values were within the range of carboplatin concentrations eluted from CI‐CSH beads.

Conclusion

Elution of carboplatin from CI‐CSH beads generate concentrations sufficient to result in 50% growth inhibition of FISAS cells in vitro. Local tumor control might be achieved by implantation of CI‐CSH beads immediately following radical or marginal excision of the primary tumor or by implantation without tumor resection.
Effects of leaf position on reflectance, transmittance and absorption of red and far‐red light in tomato, Chenopodium album and Amaranthus retroflexus leaves
Authors: Ma L , Upadhyaya M K
Published: November 2017

Leaf optical properties can play an important role in determining the red/far‐red light ratio, a signal of impending competition, in plant canopies. Knowledge of leaf optical properties and factors affecting them is important in understanding of the impacts of red/far‐red ratio in agroecosystems. Effects of leaf position on the plant stem on their optical properties at 660 and 730 nm were studied in tomato and two weeds Chenopodium album and Amaranthus retroflexus. Leaf position on stem strongly influenced leaf optical properties. Reflectance and transmittance were generally lower for the C. album and A. retroflexus leaves at higher positions on the stem, except for reflectance at 730 nm in C. album, which did not change. Reflectance was not affected in tomato. Transmittance generally decreased for leaves at higher positions. Red/far‐red ratios of reflected (Rratio) and transmitted (Tratio) light generally decreased in all species, except Rratio in tomato, where it increased slightly at higher positions. These effects were greater in A. retroflexus compared with C. album and tomato. Changes in these ratios were partly explained by chlorophyll content and leaf mass per area. The results show that leaf position on plant stem influences leaf optical properties in tomato and two weeds and this effect differed between species. These influences and the differences among species could modify red/far‐red ratios in canopies comprising these species, which could influence their growth and inter‐plant interactions.
Flow Mechanism and Characteristics of Pressure-Equalizing Film Along the Surface of a Moving Underwater Vehicle
Authors: Ma Guihui , Chen Fu , Yu Jianyang , Liu Huaping
Published: November 2017

Pressure-equalizing film is a slice of air layer attached to vehicle exterior with nearly uniform inside pressure, similar to ventilated cavity in composition; it is generated through exhaust process of the inside air chamber as vehicle emerges from deep water, and can reduce the lateral force and pitching moment that vertical launched underwater vehicle suffered. In this work, the emerging process of vehicle from water with pressure-equalizing exhaust was numerically calculated to investigate the evolution and flow characteristics of the generated pressure-equalizing film along its surface. Results indicated that during the whole exhaust process, the film can be obviously classified into different sections according to the distribution of phase volume fraction or pressure. The exhaust velocity ratio and flow rate from vehicle interior chamber were also found to increase as vehicle moves. In the analysis of flow structures, vortex structures such as the horseshoe vortex, “detour-separation” vortex, and counter-rotating vortex pair (CVP) can be figured out in the region of the exhaust hole. Under the effect of re-entrant jet, water around the film tail would be entrained upstream then enter the surface film to mix with the pressure-equalizing air. It leads to the happening of the three-dimensional (3D) wall vortex in the flow field.
Hydrodynamic Study on Water Column Oscillation of Varying Cross-Sectional Moonpool and Its Effect on Resistance of a Drill Ship
Authors: Ponnappan Sivabalan , Sankunny Surendran
Published: November 2017

A moonpool is meant for access to the underwater part of the ship from onboard. It is a vertical opening along the depth having an effect on the performance of the floating platform. Inside the moonpool, water motions in horizontal plane is called sloshing and in vertical planes it is called piston mode. Moonpool causes deck wetness and sometimes results in the downtime of the platform. It is the necessity of the operator to be at the safe conditions of platform facing varied environmental conditions. In the present study, vessel response in the region of moonpool resonance was investigated with different shapes of moonpool and comparison is made with Molin's (2001, “On the Piston and Sloshing Modes in Moonpools,” J. Fluid Mech., 430, pp. 27–50.) theoretical and Fukuda's (1977, “Behavior of Water in Vertical Well With Bottom Opening of Ship and Its Effects on Ship-Motion,” J. Soc. Nav. Archit. Jpn., 1977(141), pp. 107–122.) empirical formulas. It is seen that there is a shift in the frequency of resonance based on moonpool shapes. The effect of moonpool on the ship motion with forward speed is also attempted in this paper. Proven packages are used to calculate the calm water resistance of the ship with moonpool of various cross section. Wave making coefficient of the ship is modified due to opening to accommodate the moonpool. The openings to accommodate moonpool causes further entry of water both zero and nonzero Froude number especially in the presence of waves.
Density Ratio and Entrainment Effects on Asymptotic Rayleigh–Taylor Instability
Authors: Shimony Assaf , Malamud Guy , Shvarts Dov
Published: November 2017

A comprehensive numerical study was performed in order to examine the effect of density ratio on the mixing process inside the mixing zone formed by Rayleigh–Taylor instability (RTI). This effect exhibits itself in the mixing parameters and increase of the density of the bubbles. The motivation of this work is to relate the density of the bubbles to the growth parameter for the self-similar evolution, α, we suggest an effective Atwood formulation, found to be approximately half of the original Atwood number. We also examine the sensitivity of the parameters above to the dimensionality (two-dimensional (2D)/three-dimensional (3D)) and to numerical miscibility.
Evaluating and Modeling Force Sensing Resistors for Low Force Applications
Authors: Saadeh Mohammad Y. , Carambat Timothy D. , Arrieta Alejandro M.
Published: November 2017

There has been an increasing demand for force measurement in applications that are portable, wearable, have limited space, low power, or low cost requirements. Such applications cannot support the power and computing requirements of the load cells. Force sensing resistor (FSR) is a passive component that is composed of polymer thick films that change resistance between its terminals due to force applied at its surface. An FSR can provide a suitable alternative to the bulky load cell. However, it inherently exhibits many nonlinear behaviors. This paper evaluates five different FSR sensors (IEE FSR 151 NS, Interlink FSR 402, Sensitronics ShuntMode FSR. FlexiForce A201 FSR, and Sensitorincs ThruMode FSR). The FSRs were evaluated for sensitivity, minimum measurable force, repeatability, creep, and hysteresis. In addition, system identification techniques were used to model each FSR behavior so they can be used as calibrated standalone force sensors. Results show that the Sensitronics ThruMode FSR had the best repeatability and the least hysteresis, while the FlexiForce A201 had the lowest creep, and the Interlinks 402 FSR had the lowest threshold force.
Active Vortex Generator Deployed on Demand by Active Hybrid Composites From Shape Memory Alloys and Fiber Reinforced Polymers
Authors: Gurka Martin , Nissle Sebastian , Hübler Moritz , Kaiser Max
Published: November 2017

High performance airfoils with laminar airflow exhibit minimum drag and maximum lift, but tend to sudden stall due to flow separation at low air speed. This requires an increased approach speed of the aircraft, resulting in less steep approaches and a higher noise exposure of the surroundings. New active vortex generators, deployed only on demand at low speed, energizing the boundary layer of air flow and reducing flow separation, can help to overcome this critical situation. Active hybrid composites, combining the actuation capability of shape memory alloys (SMA) with the possibility of tailoring the compliance of fiber reinforced polymers (FRP) on the materials level, provide an active aerodynamic system with high lightweight potential and small space requirements. Being one of the first applications of active hybrid structures from SMA and FRP we will demonstrate the potential of this new technology with an integrated system of active vortex generators for a glider. In this contribution we present - the design process, based on a FE-model and careful characterization of the actuating SMA and the composite material - manufacturing relevant aspects for reliable series production - the testing of single vortex generators in lab scale under aerodynamic load - and an overview of the whole system.
3D Printed Magnetorheological Elastomers
Authors: Bastola Anil K. , Paudel Milan , Li Lin
Published: November 2017

In this study, 3D printed magnetorheological (MR) elastomer has been characterized through a force vibration testing. The 3D printed MR elastomer is a composite consisting three different materials, magnetic particles and two different elastomers. The MR elastomers were printed layer-by-layer by encapsulating MR fluid within the polymeric elastomer and then allowed to cure at room temperature. The 3D printing allowed to print various patterns of magnetic particles within the elastomeric matrix. In the presence of an external magnetic field, both elastic and damping properties of the 3D printed MR elastomers were changed. Natural frequency, stiffness, damping ratio, damping coefficient, and shear modulus were increased with increasing magnetic field. For the single degree-of-freedoms system, shear mode MR elastomers suppressed the transmitted vibration amplitude up to 31.4% when the magnetic field was 550 mT. The results showed that the 3D printed MR elastomer could be used as a tunable spring element for vibration absorption or isolation applications. However, further optimization of the magnetic particles’ configurations should be performed to obtain the higher MR effect.
Induced Strain Actuation for Solid-State Ornithopters: Pitch and Heave Coupling
Authors: Hauris Francis , Bilgen Onur
Published: November 2017

This paper investigates the heaving and pitching of a wing-like parameterized cantilevered plate with a leading edge stiffener and clamp variation when actuated with a surface-bonded piezoelectric actuator. The response is analyzed using a finite element model that is validated by comparison with known analytical solutions. The validated finite-element model is subjected to a harmonic excitation parametric analysis. The parameters varied in the model are the root clamped percentage, leading edge stiffener thickness, and the aspect ratio of the plate. The model is examined at the first two Eigen frequencies. Metrics of heaving and pitching are developed using surface fitting methods and their amplitudes and phases are reported throughout the parameter space. Emphasis is placed on the interaction and coupling of the first two modes of vibration with respect to the parameters. A piezo-composite wing prototype is fabricated and actuated harmonically with a Macro-Fiber Composite actuator while leading edge stiffener thickness and root clamped percentage is varied. The resulting experimental data is used to further validate the theoretical models.
Non-Chaotic Cross-Well State Transfer of Duffing-Holmes Type Bistable Systems
Authors: Simsek Mehmet R. , Bilgen Onur
Published: November 2017

A control strategy called hybrid position feedback control is applied to a bistable system to prevent multiple crossovers during actuation from one stable equilibrium to the other. The hybrid controller is based on a conventional positive position feedback controller. The controller uses the inertial properties of the structure around the stable positions to achieve large displacements by destabilizing a positive position feedback controller. Once the unstable equilibrium is reached, the controller is stabilized to converge to the target stable equilibrium.

The bistable system under harmonic excitation and hybrid controller are investigated for its behavior. In addition, energy analysis of the system controlled by the hybrid controller is investigated using numerical time domain methods. The energy variance by parameters and the comparison between the open-loop system with harmonic excitation and the controlled system is investigated.
Harnessing the Quasi-Zero Stiffness From Fluidic Origami for Low Frequency Vibration Isolation
Authors: Sadeghi Sahand , Li Suyi
Published: November 2017

This research investigates a quasi-zero stiffness (QZS) property from the pressurized fluidic origami cellular solid, and examines how this QZS property can be harnessed for low-frequency base excitation isolation. The QZS property originates from the nonlinear geometric relations between folding and internal volume change, and it is directly correlated to the design parameters of the constituent Miura-Ori sheets. Two different structures are studied to obtain a design guideline for achieving QZS: one is identical stacked Miura-Ori sheets (ismo) and the other is non-identical stacked Miura-Ori sheets (nismo). Further dynamic analyses based on numerical simulation and harmonic balance method, indicate that the QZS from pressurized fluidic origami can achieve effective base excitation isolation at low frequencies. Results of this study can become the foundation of origami-inspired metamaterials and metastructures with embedded dynamic functionalities.
Crashworthiness Study of Helicopter Skid Landing Gear System Equipped With a Magnetorheological Energy Absorber
Authors: Saleh Muftah , Sedaghati Ramin , Bhat Rama
Published: November 2017

The present study concerns with the performance of a skid landing gear (SLG) system of a rotorcraft impacting the ground at a vertical sink rate of 5.0 m/s. The impact attitude is per chapter 527 of the Airworthiness Manual (AWM) of Transport Canada Civil Aviation and FAR Part 27 of the U.S. Federal Aviation Regulation. A single degree of freedom helicopter model is investigated under two rotor lift factors 0.67 and 1.0. Three Configurations are evaluated: a) A conventional SLG; b) SLG equipped with a passive viscous damper and c) SLG incorporated with a magnetorheological energy absorber. The non-dimensional solutions of the helicopter model show that the passive damper system could reduce the maximum acceleration experienced by the helicopter occupants by 21% and 19.8% in comparison to the undamped system for the above rotor lift factors, respectively. However, the passive damper fails to constrain the non-dimensional energy absorption stroke of the damper within the given 18 cm maximum stroke and a bottoming out of the damper piston was noticed. Therefore, the alternative and successful choice was to employ a magnetorheological energy absorber (MREA). To improve the MREA controllability and to resettle the payload with no oscillations, i.e. in one cycle, two different Bingham numbers for compression stroke and rebound stroke were defined in the non-dimensional solution. Several simulations were conducted for different values of Bingham numbers. Among these numerical simulation results, the solution that implemented the optimum Bingham numbers was found to be the only one feasible solution. In this case the MREA with optimum Bingham number for compression could utilize the full energy absorption stroke to attain soft landing. In the rebound stroke, the generated optimal on-state damping force successfully controls the bounce of the payload until the payload settles down to its original equilibrium position with no oscillations.
Variable Thermal Conductance Metamaterials for Passive or Active Thermal Management
Authors: Phoenix Austin A. , Wilson Evan
Published: November 2017

To continue to meet spacecraft systems ever increasing thermal management requirements, new control methods need to be developed. While advances in metamaterials have provided the ability to generate materials with a broad range of material properties, relatively little advancement has been made in the development of adaptive metamaterials. This paper is focused on the development of a thermal management metamaterial that enables the active and passive control of a metamaterial’s thermal conductance. This variable conductivity is achieved through the application of internally or externally applied loads that induce internal contact resulting in changes in the conductive path length and the effective conductive area. This capability enables active or passive control of a metamaterial’s effective thermal conduction through the application of mechanical and thermal strain. Passively applied thermal strains can be used to design a highly nonlinear material thermal conductivity as a function of temperature. Actively, this can be used to precisely control the temperature of an interface through dynamically changing the instantaneous heat flux through the metamaterial. This work expands on the field of thermal switches by enabling a non-binary configuration where the initial air gap is slowly closed as contact sequentially introduced into the metamaterial. As internally or externally developed loading is applied, contact is introduced with an increasing contact area until full contact is achieved. This intermediate step of partial contact enables unique design capabilities that enable highly nonlinear thermal conductivity as a function of temperature as well as stability regions that allow passive thermal control. An example metamaterial was developed and evaluated to quantify the potential of this concept. The specific metamaterial configuration assessed in this paper uses offset flat and curved copper plates that are connected at the edges of the plate using a low conductivity epoxy. To evaluate the metamaterial performance, the stiffness and thermal conductivity are calculated as a function of the resulting contact area and the required applied loading. This work is focused on determining the potential of this metamaterial concept by evaluating this initial concept confirmation to establish the magnitude of the thermal conductance change, and the design of the conductivity change a function of applied loading.
Coupling of Two Resonant Modes for Insect Wing Mimicking in a Flexible-Wing NAV and Generate Lift
Authors: Faux Damien , Cattan Eric , Grondel Sebastien , Thomas Olivier
Published: November 2017

This work is based on the original concept of coupling two resonant vibration modes to reproduce insect wing kinematics and generate lift. The key issue is designing the geometry and the elastic properties of the artificial wings to achieve quadrature coupling of the bending and twisting motions using only one actuator. Qualitatively, this implies bringing the frequency of the two resonant modes closer. In the light of this challenge, an optimal wing configuration was determined for a micromachined polymer prototype three centimeters wide and validated through experimental modal analyses to illustrate the proximity of the frequencies of the bending and twisting modes. Then, a dedicated lift force measurement bench was developed and used to demonstrate a lift force equivalent to 110% of the prototype weight. For the first time, high-speed camera measurements of the wing motion confirmed that maximum lift was obtained as expected for bending and twisting motions in phase quadrature with a fully resonant motion of the wings using a single actuator.
Shape Adaptive Structures by 4D Printing
Authors: Hu G. F. , Damanpack A. R. , Bodaghi M. , Liao W. H.
Published: November 2017

This paper introduces a 4D printing method to program shape memory polymers (SMPs) during fabrication process. Fused deposition modeling is employed to program SMPs during depositing the material. This approach is implemented to fabricate complicated polymeric structures by self-bending features without need of any post-programming. Experiments are conducted to demonstrate feasibility of one-dimensional (1D)-to 2D and 2D-to-3D self-bending. It is shown that 4D printed plate structures can transform into 3D curved shell structures by simply heating. A 3D macroscopic constitutive model is developed to predict thermo-mechanical behaviors of the printed SMPs. Governing equations are also established to simulate programming mechanism during printing process and shape change of self-bending structures. In this respect, a finite element formulation is developed considering von-Kármán geometric non-linearity and solved by implementing iterative Newton-Raphson scheme. The accuracy of the computational approach is checked with experimental results. It is shown that the structural-material model is capable of replicating the main features observed in the experiments.
Tapered Test Specimen for Rapid Damage Precursor Identification
Authors: Henry Todd C. , Haynes Robert A. , Cole Daniel P. , Haile Mulugeta A. , Coatney Michael D. , Weiss Volker
Published: November 2017

Traditionally, most mechanical testing is conducted on specimens of uniform cross-section and stress magnitude, or only a single position along the specimen length is of interest. Investigations of various stress levels therefore requires separate tests with a unique specimen at each stress level of interest. The impetus of the current work was to develop a method for the design and monitoring of a specimen that simultaneously experiences a continuum of stress magnitudes across various positions. A linearly-tapered specimen was developed and subjected to sinusoidal tension-tension fatigue until specimen failure, with the expectation that a record of damage exists along the length of the specimen due to the varying level of induced stress. Baseline and post-failure scans of x-ray diffraction, electrical resistance via four point probe, nano-indentation, eddy current, and geometric changes were compared. Attempts were made to characterize the pre- and post-test property behaviors as a function of the applied stress, which varied linearly along the specimen, and as a function of fatigue cycles, which were the same along the length of the specimen. The mechanisms of specimen damage due to fatigue cycling were investigated and analyzed to improve durability and damage tolerance understanding.
Characterization of a 3D-Printed Conductive PLA Material With Electrically Controlled Stiffness
Authors: Al-Rubaiai Mohammed , Pinto Thassyo , Torres David , Sepulveda Nelson , Tan Xiaobo
Published: November 2017

In this paper, we present characterization results for thermal, mechanical, and electrical properties of a 3D-printed conductive polylactic acid (PLA) composite material. The material exhibits electrically controllable stiffness, allowing for the fabrication of novel robotic and biomedical devices. In particular, an applied voltage induces a Joule heating effect, which modulates the material stiffness. Dumbbell samples are 3D-printed and loaded into a universal testing machine (UTM) to measure their Young’s moduli at different temperatures. The conductive PLA composite shows 98.6% reduction of Young’s modulus, from 1 GPa at room temperature to 13.6 MPa at 80 °C, which is fully recovered when cooled down to its initial temperature. Measurements with differential scanning calorimeter (DSC) and thermal diffusivity analyzer are conducted to investigate the thermal behavior of this material. Electrical conductivity of the material is measured under different temperatures, where the resistivity increases about 60% from 30 °C to 100 °C and hysteresis between the resistivity and the temperature is observed. These tests have shown that the conductive PLA composite has a glass transition temperature (Tg) of 56.7 °C, melting point (Tm) of 153.8 °C, and thermal conductivity of 0.366 W/(mK). The obtained results can be used as design parameters in finite element models and computational tools to rapidly simulate multi-material components for several applications such as object manipulation, grasping, and flow sensing.
A Novel Biomimetic Torsional Actuator Design Using Twisted Polymer Actuators
Authors: Shafer Michael W. , Feigenbaum Heidi P. , Higueras Ruiz Diego Ricardo
Published: November 2017

Artificial muscle systems have the potential to impact many technologies ranging from advanced prosthesis to miniature robotics. Recently, it has been shown that twisting drawn polymer monofilaments, such as nylon fishing line or sewing thread, can result in a biomimetic thermally activated torsional actuator. The actuation phenomenon in these twisted polymer actuators (TPAs) is thought to be a result of an untwisting that occurs about the fiber’s axis due to an anisotropic thermal expansion. Before being twisted, the precursor fibers are comprised of polymer chains that are aligned axially. During fabrication of TPAs, the polymer chains reorient as the precursor fiber is twisted about the central axis of the monofilament. At the end of the fabrication process, the TPA is annealed in order to relieve internal stresses and to keep the fiber in the twisted configuration. The mechanism of untwisting actuation is generally thought to be a result of radial expansion and axial contraction. After being twisted, these radial and axial expansion relationships remain relatively unchanged, but the polymer chain direction is no longer axially aligned. Thus, upon heating the twisted fibers of the TPA, the fibers untwist and torsional actuation occurs. This actuation phenomenon has been used in the past to create linear actuators, but can also be use directly as a torsional actuator. Compared to other torsional actuators TPAs are low cost, lightweight, and can actuate reasonably high torques per unit volume. However, because TPAs are thermally activated, they may not be suitable for all applications. In this work, we present a novel TPA design for use as a torsional actuator for miniature actuation and artificial muscle applications. Our design bundles twisted monofilaments to increase the torque. Both fabrication and testing methods of the new design are presented. Results for temperature versus torsional displacement under various loads give insights as to how these actuators may be used and the reversibility of the actuation process under different fabrication loads. Additionally, comparisons are made between these bundled actuators and similarly loaded single TPA monofilament actuation.
Resonant Frequency Tuning Strategies for Vibration-Based Energy Harvesters
Authors: Dong Lin , Fisher Frank T.
Published: November 2017

Vibration-based energy harvesting has been widely investigated to as a means to generate low levels of electrical energy for applications such as wireless sensor networks. However, due to the fact that vibration from the environment is typically random and varies with different magnitudes and frequencies, it is a challenge to implement frequency matching in order to maximize the power output of the energy harvester with a wider frequency bandwidth for applications where there is a time-dependent, varying source frequency. Possible solutions of frequency matching include widening the bandwidth of the energy harvesters themselves in order to implement frequency matching and to perform resonance-based tuning approach, the latter of which shows the most promise to implement a frequency matching design. Here three tuning strategies are discussed. First a two-dimensional resonant frequency tuning technique for the cantilever-geometry energy harvesting device which extended previous 1D tuning approaches was developed. This 2D approach could be used in applications where space constraints impact the available design space of the energy harvester. In addition, two novel resonant frequency tuning approaches (tuning via mechanical stretch and tuning via applied bias voltage, respectively) for electroactive polymer (EAP) membrane-based geometry energy harvesters was proposed, such that the resulting changes in membrane tension were used to tune the device for applications targeting variable ambient frequency environments.
Soft Photochemical Actuation Systems: Tuning Performance Through Solvent Selection
Authors: Dicker Michael P. M. , Baker Anna B. , Bond Ian P. , Faul Charl F. J. , Rossiter Jonathan M. , Weaver Paul M.
Published: November 2017

Photochemical actuation systems, those that employ coupled photo-stimuli and chemical reactions to power and control mechanical motion, have the potential to combine the benefits of precise light driven control with chemical energy storage. Furthermore, these systems are inherently soft, making them ideal for use in the emerging field of soft robotics. However, such systems have received comparatively little attention, perhaps due to the poor cycle life and limited activation time of past systems. Here we address these two challenges by switching from the technique of past systems, that of aqueous photoacid solutions and pH-responsive hydrogel actuators, to one employing organic solvents instead. While this switch of solvents successfully eliminates cycle life constraints and allows for tuning of the activation recovery time it also shifts the relative activation point of the hydrogel actuator in such a way that actuation is no longer observed. Several options for addressing this are discussed, with the prospect of using the lessons learned within to make a more informed selection of a different photoacid compound considered the most feasible. While the exploration of photochemical actuation systems is still in a nascent stage, we have great hope for such systems to form the basis of future smart machines with unique functionality.