Abstract
Robust ionic sensing materials that are both fatigue-resistant and self-healable like human skin are essential for soft electronics and robotics with extended service life. However, most ...existing self-healable artificial ionic skins produced on the basis of network reconfiguration suffer from a low fatigue threshold due to the easy fracture of low-energy amorphous polymer chains with susceptible crack propagation. Here we engineer a fatigue-free yet fully healable hybrid ionic skin toughened by a high-energy, self-healable elastic nanomesh, resembling the repairable nanofibrous interwoven structure of human skin. Such a design affords a superhigh fatigue threshold of 2950 J m
−2
while maintaining skin-like compliance, stretchability, and strain-adaptive stiffening response. Moreover, nanofiber tension-induced moisture breathing of ionic matrix leads to a record-high strain-sensing gauge factor of 66.8, far exceeding previous intrinsically stretchable ionic conductors. This concept creates opportunities for designing durable ion-conducting materials that replicate the unparalleled combinatory properties of natural skins more precisely.
The issue of aeroengine oscillations over high-attitude and low-speed flight envelope has been an unsolved problem due to their classified nature and hard reproduction in simulated altitude test ...stand. Efforts have been sought for either structural integrity or component damage. However, it is rarely realized that the oscillations can be an inherent property of the engine itself. Consequently, a dynamical system approach is proposed in this paper to demonstrate that engine oscillations are recurring over high-attitude and low-speed flight envelope, yet they can be suppressed through appropriate control designs. However, the resulting design can be compromised with the conventional high-gain control where the transient and steady-state performance must be balanced with disturbance attenuation performance. Examples are given to illustrate and validate the claims made through the en route analysis.
Abstract
We report the development of a coating system relying on the incorporation of SiO
2
@ZnO core–shell nanospheres in polyurethane media as a novel approach to achieve longevity and ...sustainability in marine transport. This polymeric coating showed significant improvement in surface abrasion resistance, the transition from a hydrophilic state to a hydrophobic state (~ 125.2° ± 2°), improved antifungal, antibacterial and antialgae effects which make the proposed coating ideal to protect steel surfaces against biofouling. To substantiate our claims, we performed X-ray diffraction, Transmission electron microscopy, Fourier transform infrared spectroscopy, scanning acoustic microscopy, Thermogravimetric analysis (TGA), contact angle measurements, antimicrobial (antialgal, antibacterial, antifungal) tests and Taber abrasion tests (ASTM D1044 and D4060) to highlight the mechanical and biological functionality as well as the bonding configuration of this coating. The wear analysis of the Taber abraded coating using SEM and optical microscopy showed significant improvement in the adhesion and shear resistance achieved by the SiO
2
@ZnO core–shell nanospheres incorporated PU coating which was a contrasting feature compared to using PU alone. The overall investigations we performed led us to find out that the addition of 4% (wt.) SiO
2
@ZnO core–shell nanoparticles to the PU media deposited on the low carbon steel surface demonstrated remarkable antimicrobial performance with almost no bacterial growth, significant reductions in growth for algae to about 90% and fungus to about 95%.
Investment of clean energy industry aims at developing clean alternative energy sources to substitute fossil fuels, the consumption of which leads to climate change and air pollution. However, how ...the supply and demand of steam coal affect the investment remains an extremely understudied issue, as the extant research focuses on crude oil, while steam coal satisfies most of the energy demand in emerging economies like China. This study empirically investigates the time-varying co-movements between steam coal prices and clean energy stock indices in China at the sectoral level; the former denotes the supply and demand, and the latter represents the investment. Five clean energy sectors are considered, including geothermal power, hydrogen power, nuclear power, solar power and wind power. The studied period is from Jan 2, 2008 to Feb 28, 2019. The analysis is carried out using a VAR-DCC-GARCH framework. The empirical findings indicate the presence of significant bi-directional volatility spillover between the steam coal market and the clean energy stocks. We further portray and explain the dynamic conditional correlation among steam coal prices, clean energy sectoral indices and an environmental under the fluctuating China's stock markets. Based on the empirical evidence, we provide policy implications to facilitate the development of the clean energy industry.
•Co-movements between steam coal and clean energy investment are investigated.•Sectoral clean energy stock indices are employed.•Significant bi-directional volatility transmission is observed.•Strong stock market tends to weaken risk and volatility spillovers.
In this paper, the design and underpinning technical principles of the novel design of a negative pressure wave (NPW)-based pipeline leak detection system has been reported, which is configured using ...fiber Bragg grating (FBG) pressure sensors. To evaluate this, a pipeline leakage test platform has been established and experiments have been conducted, to verify the performance of a system using this FBG-based approach. The results show that a system using FBG-based sensors can accurately determine the pressure change trends along the pipeline and thus allow the calculation of the NPW velocity online. A key comparison is made with traditional NPW detection techniques, showing that the novel detection system is capable of achieving the higher leak-location accuracy and the detection of smaller leakage volumes. This arises from the ability of the FBG-based system to allow an increased number of sensors to be multiplexed along the pipeline. Their corresponding output signals generated show a very satisfactory, high signal-to-noise ratio. The system has been evaluated, especially in its response to extraneous signals and thus disturbances caused by the pump starting or stopping can be eliminated. This was achieved through an analysis of the time sequence of the pressure changes captured by the multisensor array being carried out and thus immunity to such effects demonstrated. The system has thus been designed to minimize the instances where a false alarm occurs.
Display omitted
•Graphene is an effective lubricant at 200 °C when velocity is larger than 0.5 μm/s.•Friction of graphene decreases with the velocity increasing at high temperatures.•The average ...friction of graphene at 360 °C is nearly twice that at 25 °C.•Wear of graphene is induced by the huge deformation of substrate under thermal.
Graphene is a useful solid lubricant for flexible micro/nanoelectromechanical systems (MEMS/NEMS) because of its beneficial mechanical properties. However, understanding the tribological and wear characteristics of graphene on polymer substrates under high-temperature conditions is essential for predicting whether graphene will fail as a solid lubricant for flexible substrates in high-temperature environments. Herein, the friction and wear characteristics of monolayer graphene on flexible polydimethylsiloxane (PDMS) substrates are studied by atomic force microscopy using a heated tip. The friction of graphene before wear is more stable than that of PDMS, demonstrating that graphene can be used as a solid lubricant to stabilize the stick-slip motion of the tip on the flexible substrate at elevated temperatures. The friction of graphene shows an increasing trend with the heating temperature increasing due to an enlarged tip-graphene contact area. However, the friction of graphene considerably decreases with the tip sliding velocity increasing at a speed of less than 0.5 µm/s, resulting from a reduced tip-graphene contact area. The thermally-induced wear of graphene is caused by the coupling effect of the temperature and the sliding velocity. These results can provide an in-depth understanding of graphene as a solid lubricant for flexible polymer-based MEMS/NEMS devices in high-temperature environments.
The performance of the high speed trains depends critically on the quality of the contact in the pantograph-catenary interaction. Maintaining a constant contact force needs taking special measures ...and one of the methods is to utilize active control to optimize the contact force. A number of active control methods have been proposed in the past decade. However, the primary objective of these methods has been to reduce the variation of the contact force in the pantograph-catenary system, ignoring the effects of locomotive vibrations on pantograph-catenary dynamics. Motivated by the problems in active control of vibration in large scale structures, the author has developed a geometric framework specifically targeting the remote vibration suppression problem based only on local control action. It is the intention of the paper to demonstrate its potential in the active control of the pantograph-catenary interaction, aiming to minimize the variation of the contact force while simultaneously suppressing the vibration disturbance from the train. A numerical study is provided through the application to a simplified pantograph-catenary model.
A variety of nonlinear control design methods have been proposed for controlling severe nonlinear processes over the past three decades. The vast majority of approaches take a nonlinear affine ...representation of the system dynamics. It appears that many system dynamics can also be represented by a state-dependent model structure. Control of state-dependent systems has been investigated resulting in design methodologies such as state-dependent Riccati equation approach, state-dependent parameter and proportional–integral–plus approach, and the nonlinear generalized minimum variance approach. This article describes yet another approach based on a receding horizon strategy. Important results on optimal control are obtained. Implementation issues are also discussed. The proposed approach is validated through its application to a 25-tray binary distillation column process.
Vibration distribution comprises both vibration control and harvesting. Active vibration distribution control represents a generic yet challenging problem to be addressed in many engineering ...applications. Current norm-optimization-based methods would require significant modification for its solutions. This paper proposes a restricted control method where a variety of results concerning active vibration distribution through restricted topology control and restricted single node control are obtained. Important issues associated with both parametric constraints and performance limit are also given considerations. A systematic design methodology is thus established for active vibration distribution through restricted controls. The theoretical results are exemplified with numerical examples providing detailed design procedures.
For multi-attribute decision-making problems with interval numbers whose attribute weights are completely unknown, it is difficult to compare the value of interval numbers. So this paper proposes a ...method based on TOPSIS and the weighted parameter to deal with it. Firstly, this paper transforms the interval number matrix into two exact number matrices which reduces sorting complexity. Secondly, a parameter is given when determining the weights with entropy weight in order to reflect all the information of the interval numbers. Then TOPSIS is used to determine the order of each scheme. In addition, the average value of the ranking number is used to reflect the actual situation better. Finally, the analysis of the car purchase case shows the proposed method is feasible and practical. And the comparative analysis with the other method based on practical application dataset demonstrates the proposed method is stable and effective.
PDF
