bluuebunny/crossref_metadata_2025_split huggingface dataset:
First evidence that intrinsic fetal heart rate variability exists and is affected by hypoxic pregnancy
Authors: Frasch Martin G. , Herry Christophe L. , Niu Youguo , Giussani Dino A. 
Published: December 2019

Key points
We introduce a technique to test whether intrinsic fetal heart rate variability (iFHRV) exists and we show the utility of the technique by testing the hypothesis that iFHRV is affected by chronic fetal hypoxia, one of the most common adverse outcomes of human pregnancy complicated by fetal growth restriction.
Using an established late gestation ovine model of fetal development under chronic hypoxic conditions, we identify iFHRV in isolated fetal hearts and show that it is markedly affected by hypoxic pregnancy.
Therefore, the isolated fetal heart has intrinsic variability and carries a memory of adverse intrauterine conditions experienced during the last third of pregnancy.
AbstractFetal heart rate variability (FHRV) emerges from influences of the autonomic nervous system, fetal body and breathing movements, and from baroreflex and circadian processes. We tested whether intrinsic heart rate variability (iHRV), devoid of any external influences, exists in the fetal period and whether it is affected by chronic fetal hypoxia. Chronically catheterized ewes carrying male singleton fetuses were exposed to normoxia (n = 6) or hypoxia (10% inspired O2, n = 9) for the last third of gestation (105–138 days of gestation (dG); term ∼145 dG) in isobaric chambers. At 138 dG, isolated hearts were studied using a Langendorff preparation. We calculated basal intrinsic FHRV (iFHRV) indices reflecting iFHRV's variability, predictability, temporal symmetry, fractality and chaotic behaviour, from the systolic peaks within 15 min segments in each heart. Significance was assumed at P < 0.05. Hearts of fetuses isolated from hypoxic pregnancy showed approximately 4‐fold increases in the Grid transformation as well as the AND similarity index (sgridAND) and a 4‐fold reduction in the scale‐dependent Lyapunov exponent slope. We also detected a 2‐fold reduction in the Recurrence quantification analysis, percentage of laminarity (pL) and recurrences, maximum and average diagonal line (dlmax, dlmean) and the Multiscale time irreversibility asymmetry index. The iHRV measures dlmax, dlmean, pL and sgridAND correlated with left ventricular end‐diastolic pressure across both groups (average R2 = 0.38 ± 0.03). This is the first evidence that iHRV originates in fetal life and that chronic fetal hypoxia significantly alters it. Isolated fetal hearts from hypoxic pregnancy exhibit a time scale‐dependent higher complexity in iFHRV.
Kinetics Modeling on NOx Emissions of a Syngas Turbine Combustor Using Rich-Burn, Quick-Mix, Lean-Burn Combustion Method
Authors: Liu Haoyang , Qian Wenkai , Zhu Min , Li Suhui 
Published: December 2019

Abstract
To avoid flashback issues of the high-H2 syngas fuel, current syngas turbines usually use nonpremixed combustors, which have high NOx emissions. A promising solution to this dilemma is rich-burn, quick-mix, lean-burn (RQL) combustion, which not only reduces NOx emissions but also mitigates flashback. This paper presents a kinetics modeling study on NOx emissions of a syngas–fueled gas turbine combustor using RQL architecture. The combustor was simulated with a chemical reactor network (CRN) model in chemkin-pro software. The combustion and NOx formation reactions were modeled using a detailed kinetics mechanism that was developed for syngas. Impacts of combustor design/operating parameters on NOx emissions were systematically investigated, including combustor outlet temperature, rich/lean air flow split, and residence time split. The mixing effects in both the rich-burn zone and the quick-mix zone were also investigated. Results show that for an RQL combustor, the NOx emissions initially decrease and then increase with combustor outlet temperature. The leading parameters for NOx control are temperature-dependent. At typical modern gas turbine combustor operating temperatures (e.g., &lt;1890 K), the air flow split is the most effective parameter for NOx control, followed by the mixing at the rich-burn zone. However, as the combustor outlet temperature increases, the impacts of air flow split and mixing in the rich-burn zone on NOx reduction become less pronounced, whereas both the residence time split and the mixing in the quick-mix zone become important.
Effects of Surface Tension and Yield Stress on Mucus Plug Rupture: A Numerical Study
Authors: Hu Yingying , Romanò Francesco , Grotberg James B. 
Published: December 2019

Abstract
We study the effects of surface tension and yield stress on mucus plug rupture. A three-dimensional simplified configuration is employed to simulate mucus plug rupture in a collapsed lung airway of the tenth generation. The Herschel–Bulkley model is used to take into account the non-Newtonian viscoplastic fluid properties of mucus. Results show that the maximum wall shear stress greatly changes right prior to the rupture of the mucus plug. The surface tension influences mainly the late stage of the rupture process when the plug deforms greatly and the curvature of the mucus–air interface becomes significant. High surface tension increases the wall shear stress and the time needed to rupture since it produces a resistance to the rupture, as well as strong stress and velocity gradients across the mucus–air interface. The yield stress effects are pronounced mainly at the beginning. High yield stress makes the plug take a long time to yield and slows down the whole rupture process. When the effects induced by the surface tension and yield forces are comparable, dynamical quantities strongly depend on the ratio of the two forces. The pressure difference (the only driving in the study) contributes to wall shear stress much more than yield stress and surface tension per unit length. Wall shear stress is less sensitive to the variation in yield stress than that in surface tension. In general, wall shear stress can be effectively reduced by the smaller pressure difference and surface tension.
Integration of Normative Decision-Making and Batch Sampling for Global Metamodeling
Authors: van Beek Anton , Tao Siyu , Plumlee Matthew , Apley Daniel W. , Chen Wei 
Published: December 2019

Abstract
The cost of adaptive sampling for global metamodeling depends on the total number of costly function evaluations and to which degree these evaluations are performed in parallel. Conventionally, samples are taken through a greedy sampling strategy that is optimal for either a single sample or a handful of samples. The limitation of such an approach is that they compromise optimality when more samples are taken. In this paper, we propose a thrifty adaptive batch sampling (TABS) approach that maximizes a multistage reward function to find an optimal sampling policy containing the total number of sampling stages, the number of samples per stage, and the spatial location of each sample. Consequently, the first batch identified by TABS is optimal with respect to all potential future samples, the available resources, and is consistent with a modeler’s preference and risk attitude. Moreover, we propose two heuristic-based strategies that reduce numerical complexity with a minimal reduction in optimality. Through numerical examples, we show that TABS outperforms or is comparable with greedy sampling strategies. In short, TABS provides modelers with a flexible adaptive sampling tool for global metamodeling that effectively reduces sampling costs while maintaining prediction accuracy.
Descriptive Models of Sequential Decisions in Engineering Design: An Experimental Study
Authors: Chaudhari Ashish M. , Bilionis Ilias , Panchal Jitesh H. 
Published: December 2019

Abstract
Engineering design involves information acquisition decisions such as selecting designs in the design space for testing, selecting information sources, and deciding when to stop design exploration. Existing literature has established normative models for these decisions, but there is lack of knowledge about how human designers make these decisions and which strategies they use. This knowledge is important for accurately modeling design decisions, identifying sources of inefficiencies, and improving the design process. Therefore, the primary objective in this study is to identify models that provide the best description of a designer’s information acquisition decisions when multiple information sources are present and the total budget is limited. We conduct a controlled human subject experiment with two independent variables: the amount of fixed budget and the monetary incentive proportional to the saved budget. By using the experimental observations, we perform Bayesian model comparison on various simple heuristic models and expected utility (EU)-based models. As expected, the subjects’ decisions are better represented by the heuristic models than the EU-based models. While the EU-based models result in better net payoff, the heuristic models used by the subjects generate better design performance. The net payoff using heuristic models is closer to the EU-based models in experimental treatments where the budget is low and there is incentive for saving the budget. This indicates the potential for nudging designers’ decisions toward maximizing the net payoff by setting the fixed budget at low values and providing monetary incentives proportional to saved budget.
Feedback Control of SMA-Wires for Position Determination: A Comparison of the Behavior Under Vacuum and Standard Conditions
Authors: Roj Robin , Dültgen Peter , Schummer Florian , Langbein Sven 
Published: December 2019

Abstract
The possibilities of a technical application of the shape memory effect are comprehensive and widespread. Besides the usage of arbitrary geometries, e.g. in the medical sector, especially wires are of great interest for unlocking mechanisms or other kinds of actuators. One of the challenges of the application of shape memory alloys (SMA) is the small deformation factor that prevents actuations with large travels. A second property that is usually seen as a disadvantage is the thermal dependence of the position. It leads to the necessity of comparably high electrical power for holding a location, as the cooling has to be compensated constantly. Therefore, SMA are usually not in use for such applications. For special environments, this effect can still be an advantage. By using an SMA driven positioning actuator in vacuum, the low loss of heat leads to a very precise and low power consuming alignment. Such actuators can be used for example in satellites. This paper presents an analysis of the properties under atmospheric conditions in comparison to the behavior in vacuum. Along with a comprehensive interpretation of the experimental results, further characteristics, like the functional and structural fatigue, are presented in detail.
Numerical Analysis and Experimental Verification of Synchronized Switching Damping Systems
Authors: Zhang Fengling , Li Lin , Fan Yu , Liu Jiuzhou 
Published: December 2019

Abstract
Synchronized switch damping (SSD) technique utilizing piezoelectric elements is one of good methods of vibration control. This work develops numerical tools for dynamic analysis of structures with SSD dampers, and conducts experiments to verify the effectiveness. A cantilevered beam bonded with piezoelectric patches is considered as the host structure. Two types of SSD circuits are considered, one with no subsequent electric element (SSDS) and another with inductance (SSDI). Firstly, a lumped parameter electromechanical coupling model is employed, with parameters determined experimentally. Then, the frequency response curves of the nonlinear vibration systems are analyzed by the multi-harmonic balance method combined with alternating frequency-time techniques (MHBM/AFT). In order to verify the proposed method, an experimental study is performed. In the experiment SSD circuit is realized by an enhanced analog circuit which is more complex but also more stable than the original SSD circuits. The measured results are compared with those obtained by proposed numerical tools with good agreements. It is also shown that the modal frequencies and modal shapes of SSD systems are almost unchanged with the vibration amplitudes, which indicates that the nonlinear force generated by SSD has little influence on the characteristics of linear structure. It is verified both numerically and experimentally that SSDI damper can produce significant damping for multiple modes.
4D Printed Shape Memory Polymer Composite Structures for Deployable Small Spacecrafts
Authors: Herath Madhubhashitha , Islam Mainul , Epaarachchi Jayantha , Zhang Fenghua , Leng Jinsong 
Published: December 2019

Abstract
Four dimensional (4D) printing is the convergence of three dimensional (3D) printing, which is an emerging additive manufacturing technology for smart materials. 4D printing is referred to the capability of changing the shape, property, or functionality of a 3D printed structure under a particular external stimulus. This paper presents the structural performance, shape memory behavior and photothermal effect of 4D printed pristine shape memory polymer (SMP) and it’s composite (SMPC) with multi-walled carbon nanotubes (MWCNTs). Both materials have demonstrated the ability to retain a temporary shape and then recover their original. It is revealed that the incorporation of MWCNTs into the SMP matrix has enhanced the light stimulus shape recovery capabilities. Light stimulus shape transformation of 4D printed SMPC is advantageous for space engineering applications as light can be focused onto a particular area at a long distance. Subsequently, a model 4D printed deployable boom, which is applicable for small spacecrafts is presented. The shape fixity and recovery behaviors of the proposed boom have been investigated. Notably, the model boom structure has demonstrated ∼86 % shape recovery ratio. The proposed innovative approach of additive manufacturing based deployable composite structures will shape up the future space technologies.
Design, Fabrication, and Testing of Optimized Flexible Cylinders
Authors: Seifert David Ryan , Chapkin Wesley A. , Frank Geoffrey , Baur Jeffrey 
Published: December 2019

Abstract
This article presents the design, fabrication, and testing of multimaterial articulating cylinders with optimized periodic substructures. Genetic Optimization (NSGA-II) is used to obtain promising archetypes, which are rapidly post-processed, additively manufactured, and tested for bending and torsional rigidity. Objectives are set as structural stiffness in torsion and bending, subject to stress and maximum radial displacement constraints. A multimaterial printer allows for two material (stiff and compliant) design. Pareto Optimal structures are down selected and post processed into manufacturable designs, which are then printed. Bending and torsional rigidities are obtained via a series of static load tests, in which a known load is applied and a bending or twisting angle is measured. Design archetypes are compared via load-rotation curves. Performance in both loading environments is related back to the characteristic substructure.
Description of a Hydrogel-Based Micro-Valve As a Library Element for Matlab Simulink
Authors: Mehner Philipp J. , Beck Anthony , Busek Mathias , Voigt Andreas , Marschner Uwe , Richter Andreas 
Published: December 2019

Abstract
We propose a planar hydrogel-based micro-valve design which is modeled as a library element for Matlab Simulink. For this test case, a pressure pump (voltage source) in series with a micro-valve model (variable fluidic resistance) is built up. The micro-valve subsystem is separated in four main parts. Based on the applied temperature stimulus, the equilibrium length is determined according to an experimentally verified fit function. Furthermore, the equilibrium length considers a static hysteresis effect which is modeled in analogy to the saturation of magnetization in electric transformers. In a second step, the transient behavior follows a first order differential equation, but the cooperate diffusion coefficient is size dependent affecting the rise time of the system. This causes a faster swelling than deswelling of the hydrogel. In the third section, the stiffness property is implemented to calculate the maximum sealing pressure and the resulting gap between the hydrogel and the wall. The fluidic resistance of the micro-valve considers a three-dimensional geometry and is calculated based on a look-up table, extracted from a fluid-structure-interaction (FSI) model generated from a finite element structure.
The proposed model allows a full description of the fluidic hydrogel-based micro-valve and is part of an upcoming microfluidic toolbox for Matlab Simulink containing passive elements and optional chemical reactions like mixing fluids and enzyme reactions for future applications.
Experimental Investigation on the Cyclic Compression Behavior of Superelastic NiTi SMA Bars
Authors: Asfaw Amedebrhan M. , Xing Guohua , Ozbulut Osman E. 
Published: December 2019

Abstract
Over the past decade, shape memory alloy (SMA) in the form of wires and cables have been extensively studied for various structural engineering applications. There are numerous application areas where pure compression (or coupled with tension) is the primary load bearing scenario, which requires larger size SMA bars. However, the compression behavior of SMA bars is not well known, and little is reported in the literature. In that perspective, this paper presents an experimental study on large diameter superelastic Nickel-Titanium (NiTi) bars subjected to a cyclic compression load. A total of nine SMA bars having slenderness ratios ranging from 60 to 90 were tested. Hysteretic stress-strain responses are plotted and critical buckling load, energy dissipation and residual strain of SMA bars with different slenderness ratios are presented.
Dynamic Response of an Electrospun PVDF-Fe3O4 Piezoelectric Composite Microfiber
Authors: Chinnam Krishna Chytanya , Casalotti Arnaldo , Lanzara Giulia 
Published: December 2019

Abstract
In this paper the dynamic response of an electrospun nanocomposite piezoelectric microfiber is investigated. The microfiber is formed by magnetic nanoparticles dispersed in Polyvinylidene (PVDF) matrix. Focus is given on the influence of an AC electric field on the dynamic response of the microfiber. In particular, the resonance frequency of the fiber was assessed under an increasing AC electric field at a wide range of frequencies. The electromechanical test results show that the resonance frequency of the fiber is influenced by the applied voltage and, for this case study, it decreases with increasing voltage. The results reported in this paper suggest that, once the mechanism behind such response is fully understood, composite piezoelectric microfibers can be used to fine-tune the resonance frequency of hosting devices.
Acoustical Behaviour of Buckling Dielectric Elastomer Actuators
Authors: Gareis Michael , Maas Jürgen 
Published: December 2019

Abstract
Dielectric elastomers (DE) are regarded as a potential alternative to conventional actuator technologies. They feature low weight, high strains and low material costs. Their scope of application ranges from sensors, energy generators, smart textiles to biomimetic robots and much more. A few concepts of loudspeakers using DE have been demonstrated by the research community. One of the disadvantages of previously concepts was the need for mechanical bias (e.g. by air pressure). This work proposes a new concept of loudspeaker, which does not need prestretch or other means of mechanical bias. Buckling dielectric elastomer transducers (BDET) use the area expansion of actuated DE to buckle up. This mechanism is used to construct a millimeter-scale loudspeaker with good frequency response in the upper frequency range. The concept is implemented using automatically fabricated multi-layer membranes. The multilayer structure allows to generate more force and has higher flexural rigidity than a single-layer setup. Samples with different amount of layers are fabricated and an analytical model is derived. Measurements of the static deflection, the frequency response and the total harmonic distortion validate the model. The small scale of the speaker allows it to be installed in large arrays and thus might offer a hardware platform for high-resolution beam forming or wave field synthesis.
Conglomerate recycling in the Himalayan foreland basin: Implications for grain size and provenance
Authors: Quick Laura , Sinclair H.D. , Attal M. , Singh V. 
Published: December 2019

Abstract
The nature of coarse sediment in rivers emerging from mountain ranges determines rates of downstream fining, the position of the gravel-sand transition, sediment entrainment thresholds, and channel morphologies. Additionally, in the stratigraphic record, clast size distributions and lithologies are used to reconstruct paleo-hydraulic conditions and source area provenance. Using Himalayan rivers, we demonstrate that the signal of first-generation clasts derived from the hinterland of a mountain range can be significantly altered by recycling older, structurally exhumed foreland deposits. The Siwalik foothills of the Himalaya comprise Neogene fluvial sandstones and quartzite-rich conglomerates with well-rounded clasts that were deposited in the Indo-Gangetic foreland basin and later exhumed by erosion, following uplift along the Himalayan mountain front. Mass balance calculations reveal that the Upper Siwalik conglomerate may contribute a significant proportion of the total gravel flux exported from the main Himalayan catchments (up to 100%) despite forming &lt;1% of the catchment geology. Three end-member catchments with variable proportions of gravel flux from Siwalik conglomerates are analyzed to test for the effects of conglomerate recycling. Catchments that recycle the most Upper Siwalik conglomerate form quartzite-rich gravel bars comprising well-rounded pebbles and a narrow grain size distribution, mimicking the characteristics of the Upper Siwalik conglomerate. Conversely, catchments that recycle the least Upper Siwalik conglomerate form gravel bars with a range of Himalayan lithologies, angular quartzite pebbles and a wider grain size distribution. This study highlights that recycling of quartzite-rich conglomerate can dramatically modify the flux, lithology, grain size, and shape of gravel entering the Indo-Gangetic Plain.