Swarming Microdroplets to a Dexterous Micromanipulator

Many astonishing biological collective behaviors exist in nature, and artificial microrobotic swarms have been developed by emulating these scenarios. However, these microswarms typically have single structures and lack the adaptability that many biological swarms exhibit to thrive in complex environments. Inspired by viscoelastic fire ant aggregations and using a combination of experiment and simulation, a strategy to trigger ferrofluid droplets into forming microswarms exhibiting both liquid-like and solid-like behaviors is reported. By spatiotemporally programming an applied magnetic field, microswarms can be liquefied to implement reversible elongation with a high aspect ratio and solidified into entireties to perform overturning and bending behaviors. It is demonstrated that reconfigurability enables the microswarm to be a mobile dexterous micromanipulator, acting not only as a soft “octopus arm” to explore a confined environment and grasp a targeted object but also adaptively navigate multiple terrains, such as uneven surfaces, curved grooves, complex mazes, high steps, narrow channels, and even wide gaps. This microrobotic swarm can reconfigure both shapes and tasks based on the demands of the environment, presenting novel solutions for a variety of applications.     

The mechanical and thermal properties,CMAS corrosion resistance,and the wettability of novel thermal barrier material GdTaO4

Because the CMAS corrosion and phase transformation at elevated temperatures above 1250 °C have limited the applications of traditional YSZ, the design of novel thermal barrier materials is a hotspot. GdTaO₄ is considered as a type of potential novel thermal barrier material owing to its low thermal conductivity. In this study, the mechanical and thermal properties, CMAS corrosion resistance, and the wettability of the GdTaO₄ were studied and compared with that of YSZ. The results show that the coefficient of thermal expansion and hardness of GdTaO₄ are 14.1 × 10⁻⁶ K⁻¹ (1350 °C) and 534.2 Hv_0.3 respectively. The thickness of CMAS reaction layer of GdTaO₄ is ~30.8 μm after 24 h reaction at 1350 °C, which is thinner than that of YSZ. After corrosion reaction, the CMAS glass aggregated instead of completely disappearing or continuously extending over the surface of GdTaO₄. The main reaction product is Ca₂Ta₂O₇, and the anorthite phase may not be detected, which is similar to YTaO₄. By comparison, the dense substrate of YSZ became porous and CMAS glass has disappeared after 10 h. CMAS corrosion at 1350 °C. The on-line contact angle results show that the wettability of CMAS on GdTaO₄ is worse than that on YSZ at 1350 °C, while the opposite of the work of adhesion, which indicates that GdTaO₄ can remove liquid CMAS more easily than YSZ TBCs during the service. Furthermore, the corrosion depth and areas of GdTaO₄ are smaller than those of YSZ in the same situation. These findings suggest that GdTaO₄ possesses better high-temperature properties and CMAS corrosion resistance than YSZ as a kind of potential of thermal barrier material.     

Conceptualizing “free-from” food consumption determinants: A systematic integrative literature review focused on gluten and lactose

BackgroundGluten- and lactose-free products are registering a sudden rise in the market, particularly among tolerant people, and this leads to consumer confusion and nutritional inadequacies. The number of studies around this trend has steadily increased in the last 10 years, as scholars from different disciplines have tried to rationalize consumers’ behaviours in these foods’ choice. However, the scientific debate appears fragmented and lacks an integrated view.ObjectivesWe conducted a systematic integrative review of consumers’ determinants of gluten-free and lactose-free consumption to frame the state of the art and research gaps.Methods45 English language articles reporting quantitative empirical studies ranging from 1971 and 2019 were analysed. First we categorized the consumption determinants in six factors applying the model proposed by Koster and Mojet, then we proposed a new integrated conceptualization inspired by Bronfenbrenner’s Transtheoretical Model. Moreover, differences and similarities between tolerant and intolerant consumers will be highlighted.ResultsResearch on intolerant consumers focused more on individuals’ determinants, in terms of awareness, trust, morality, and capability to read nutritional facts (as purchase facilitators); while studies targeting tolerant consumers focused more on objective product characteristics (with price and availability in supermarkets as barriers for consumption). In this target the subjective perspective has been studied only referring to the risk for developing psychological issues in the restrictive diet.ConclusionAs information is lacking in the scientific debate, we suggest for future research the integration of consumers’ subjective implicit levers to decipher free-from purchase behaviours.     

Microstructure,tribological behavior and magnetic properties of Fe−Ni−TiO2 composite coatings synthesized via pulse frequency variation

The Fe−Ni−TiO₂ nanocomposite coatings were electrodeposited by pulse frequency variation. The results showed that the nanocomposite with a very dense coating surface and a nanocrystalline structure was produced at higher frequencies. By increasing the pulse frequency from 10 to 500 Hz, the iron and TiO₂ nanoparticles contentswere increased in expense of nickel content. XRD patterns showed that by increasing the frequency to 500 Hz, an enhancement ofBCC phase was observed and the grain size of deposits was reduced to 35 nm. The microhardness and the surface roughness were increased to 647 HV and 125 nm at 500 Hz due to the grain size reduction and higher incorporation of TiO₂ nanoparticles into the Fe−Ni matrix (5.13 wt.%). Moreover, the friction coefficient and wear rate values were decreased by increasing the pulse frequency;while the saturation magnetization and coercivity values of the composite deposits were increased.     

Nonlinear modal analysis via non‐parametric machine learning tools

Modal analysis is an important tool in the structural dynamics community; it is widely utilised to understand and investigate the dynamical characteristics of linear structures. Many methods have been proposed in recent years regarding the extension to nonlinear analysis, such as nonlinear normal modes or the method of normal forms, with the main objective being to formulate a mathematical model of a nonlinear dynamical structure based on observations of input/output data from the dynamical system. In fact, for the majority of structures where the effect of nonlinearity becomes significant, nonlinear modal analysis is a necessity. The objective of the current paper is to demonstrate a machine learning approach to output‐only nonlinear modal decomposition using kernel independent component analysis and locally linear‐embedding analysis. The key element is to demonstrate a pattern recognition approach which exploits the idea of independence of principal components from the linear theory by learning the nonlinear manifold between the variables. In this work, the importance of output‐only modal analysis via “blind source” separation tools is highlighted as the excitation input/force is not needed and the method can be implemented directly via experimental data signals without worrying about the presence or not of specific nonlinearities in the structure.     

Modeling online user behaviors with competitive interactions

Online user behaviors are increasingly modulated by social media. Extant literature mainly focuses on investigating how network structures affect user behaviors. However, recent empirical results demonstrate that user behaviors and network structures usually coevolve dynamically, and topological patterns turn out to be inadequate for characterizing real-world user behaviors. In this paper, we present a dynamic model to deal with this challenge. This proposed model is mainly governed by two competing principles: homophily and homeostasis. Empirical evaluations of three online real-world datasets suggest that the proposed dynamic model can well predict long-range online user behaviors.     

Adaptive control of unactuated dynamical systems through interconnections: Stability and performance guarantees

This article studies control and performance enforcement for a class of uncertain dynamical systems that consist of actuated and unactuated portions physically interconnected to each other. The proposed approach stabilizes the overall interconnected system in the presence of unknown physical interconnections as well as system uncertainties. Performance guarantees are enforced, individually, on the actuated as well as unactuated portions of the interconnected system via this approach. For enforcing these performance guarantees, a set-theoretic model reference adaptive control approach is used, in conjunction with linear matrix inequalities, to restrict the respective system error trajectories of the actuated and unactuated dynamics inside a priori, user-defined compact sets. The efficacy of the proposed approach is demonstrated using simulations.     

Numerical investigation into the decoupling effects of hydrogen blending on flame structure and soot formation in a laminar ethylene diffusion flame

Numerical calculations were conducted to explore the various effects of hydrogen blending on flame properties and soot behaviors in an ethylene coflow diffusion flame, based on a fully step-by-step decoupling method, by introducing several virtual species into the gas-phase mechanism. Results show that the concentration of OH increases under the chemical effect of hydrogen due to an enhanced rate of H₂ + O ↔ OH + H. The soot yield, primary number density, and average primary number per aggregate decrease under dilution effect while these increase under chemical effect. The enhancements of hydrogen-abstraction-carbon-addition (HACA) rates and polycyclic aromatic hydrocarbon (PAH) condensation rates are responsible for soot mass addition under chemical effect. Both the oxidation rates by O₂ and OH are delayed under the chemical effect because of lower concentrations of O₂ and OH in the sooting zone. The overall effect of higher surface growth rates and delayed oxidation rates results in an increased soot volume fraction (SVF).     

淬火配分处理对锻态Fe-0.2C-9Mn-3.5Al钢显微组织及力学行为的影响

分析了淬火配分处理对锻态Fe-0.2C-9Mn-3.5Al钢显微组织及力学行为的影响。结果表明,热处理态试验钢主要由块状δ-铁素体、马氏体和板条状残留奥氏体等多相构成;残留奥氏体的体积分数随等温淬火温度升高而增大,在310 ℃时达到峰值;310 ℃等温淬火后在400 ℃配分3 min时可以获得较优的综合力学性能,抗拉强度和断后伸长率分别为1175 MPa和21.50%,强塑积达到25.26 GPa·%;应力-应变曲线中存在着明显的“锯齿”状起伏,可能与亚稳态的残留奥氏体集中转变为马氏体有关。     

覆岩结构类型与开采覆岩损害特征分析

煤层开采打破了上覆岩层原有的平衡,必然引起岩层的移动、破断,导致应力场和裂隙场的改变,工作面出现矿压显现。上覆岩层的岩性和组合结构对工作面开采覆岩损害特征分布影响显著,一般岩性越坚硬,上覆岩层应力集中程度越高,采动裂隙越发育,矿压显现也越明显;坚硬岩层尤其是关键层对覆岩的破断运动起控制作用,覆岩破断发展到一定层位后软弱岩层往往是抑制覆岩破断进一步向上发展的关键。当工作面上覆岩层同时存在远近场关键层时,近场关键层的周期性破断引起裂隙带范围内岩层的运动和工作面周期来压;而远场关键层的周期性破断导致地表裂缝或台阶下沉,工作面压力急剧上升,有时甚至导致煤矿动压灾害,尤其是远近场关键层同步破断时动力现象更明显。通过地面钻孔使远场关键层提前破断是防止此类动力灾害的关键。