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A variational-hemivariational inequality that describes stationary Stokes equations for the incompressible fluid with mixed nonlinear boundary conditions is studied. We discuss the equivalence of different weak formulations together with the results on unique solvability. The mixed finite element method of P1b/P1 pair is used to discretize the inequality problem and error bounds are derived. Numerical simulations based on Uzawa method are provided to confirm the predicted results of convergence order. [ABSTRACT FROM AUTHOR]

A lot of methods are applied in the numerical solution of contact problems, among which the most widely used method is known as Uzawa algorithm. A contact problem can transform into a saddle problem. We use Uzawa algorithm for this saddle format. Because this form can get both displacements for nodes and outward normal components of stress vectors for boundary nodes. Although the Uzawa algorithm is easy to implement, its convergent velocity is slow. Taking this algorithm as a fixed point iteration, we can use the Anderson acceleration to improve the convergent velocity. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) harvesting living environmental energy has been demonstrated to be a potential energy source for internet of things, for its unique properties, such as high-output performance, clean, sustainability, low-cost etc., which have resulted in an explosive growth of related research in the past several years. However, due to the unique features of electrical output signals of TENGs like the pulsed output with random amplitude and frequency, ultra-high voltages and impedance, the electrical power generated by TENGs is hard to be delivered to the load efficiently or stored directly by the classical power management methods. Meanwhile, the mechanical energy from the environment is time dependent, unstable and sometime unpredictable, but the power required to drive electronics is regulated with a fixed input voltage and power. So it is important to store the generated energy in a battery or capacitor, so that it can be used to power a device sustainably. Fortunately, both the power management and energy storage for TENG have obtained significantly progress recently. Here, this paper reviews the progress made in power management and storage, including theoretical development, charge boosting, buck converting, energy storage, and the new enabled applications, aiming at building a self-charging power unit (SCPU) that can be a standard power package for sustainable operation of an electronic device. Finally, we will give an outlook for future development of applying SCPU for internet of things. Triboelectric nanogenerators (TENG), has attracted worldwide interest and undergone exponential growth since its invention in 2012. This article reviews the power management and effective energy storage of TENG towards a self-charging power unit and self-sustainable power source using TENG, and proposes prospects for next-step development of power management for TENG. Image 1 • Review the recent development of power management for the triboelectric generator. • Summarize the theoretical model and signal characteristics of triboelectric generator. • Summarize the charge boosting and voltage bucking converting methods for triboelectric generator. • Summarize the energy storage and enabled applications by power management method. [ABSTRACT FROM AUTHOR]

In this paper we consider a mathematical model which describes a quasistatic process for a viscoelastic body in contact with an obstacle or a foundation. The variational formulation of the problem is in the form of a system coupling a nonlinear integral equation with a history-dependent hemivariational inequality. We establish a fully discrete scheme of the abstract problem and derive a result on error estimate. [ABSTRACT FROM AUTHOR]

Abstract Human skin is the largest organ, which covers the human body and provides us the mechanical stimuli to help us interact with the outer environment. Inspired from the properties of human skin, imitating of the complicated human sensation using stretchable electronic devices becomes one of the most exciting research fields due to its vast potential application fields like wearable electronics, healthcare monitoring and artificial intelligence. To mimic real human skin, the huge sensor network is required to attach the body, where it seems critical to guarantee the energy supply at the same time. Nowadays, the emerging triboelectric nanogenerator (TENG), which can transduce the mechanical energy into the electrical energy based on the contact electrification and electrostatic induction, provides an attractive solution for the energy problem to work as the self-powered sensor. The self-powered sensor can generate electrical signal by itself, responsing to the stimulation from the environment without further energy supply devices. With four fundamental working modes and three main detection modes, TENG could develop versatile configurations to realize the various kinds of sensation. The mechanical compliance and stretchability together with the electrical conductance can be fulfilled beneficial from the advancement of material and micro/nano fabrication technology. In this way, the TENG based self-powered electronic skins (e-skins) have been developed with rational design to accomplish multifunctions of sensing including the pressure, position, strain, sliding and so on. It is expected that the self-powered e-skin will continue its fast development and make more progress to make the e-skin come into human life in the near future. Graphical abstract fx1 Highlights • Review the recent development of the triboelectric generator based self-powered electronic skin. • Summarize the working mechanism including the signal generation, signal type and signal detection. • Summarize the design principle of the electronic skinintegrating the mechanical stretchability and electrical conductance. • Summarize separate self-powered sensors and self-powered system. [ABSTRACT FROM AUTHOR]

Abstract The rapid advancements of lightweight, customized electronics have imposed a significant challenge on sustainable and maintenance-free micro-energy systems. For the sake of solving the limited power supply and low integration, it seems urgent to develop the flexible energy devices through structure design and performance optimization. Here, a high-efficiency self-charging smart bracelet is proposed by seamlessly combining flexible freestanding triboelectric nanogenerator, power management module with stretchable double-sided micro-supercapacitors. For energy-generating component, the FPCB-based freestanding triboelectric nanogenerator and power management module are adopted with excellent output performance, which obtains peak voltage of 305 V, and maximum power efficiency of 69.3%. Additionally, the double-sided micro-supercapacitors based on CNT-PDMS elastomer are designed to work stably and reliably as the stretchable energy-storing component, the capacitance of which maintains more than 96.87% even under 20% stretching strain. During human normal motions, this smart bracelet could be utilized for scavenging random motion movements and then simultaneously storing in the energy storage device through the high-efficiency power management module to develop a self-powered system for portable devices. As an effective and efficient power supply solution, this proposed self-charging smart bracelet demonstrates admirable potential to power a temperature-humidity meter or pedometer, which owns huge potentials in micro-energy wearable electronics and lays the solid foundation on the smart appliance. Graphical abstract Self-charging smart bracelet is integrated with freestanding triboelectric nanogenerator, power management module and double-sided micro-supercapacitors among the Ecoflex substrate. The smart bracelet could harvest and simultaneously store human motion energy, which could act as wearable power source for self-powered portable electronics. This smart bracelet represents a facile approach and promising improvement to develop stretchable and wearable electronics in the practical applications and next generation self-powered systems. fx1 Highlights • High efficiency self-charging smart bracelet consists of F-TENG, D-MSC and PMM among the same substrate. • With double-sided layout, the stretchable MSC is based on the CNT-PDMS conductive elastomer with electrochemical stability. • Utilizing FPCB technique, the F-TENG and PMM are fabricated together to harvest mechanical energy effectively and efficiently. • The self-charging smart bracelet could scavenge walking motion energy and sustainably drive portable electronics. [ABSTRACT FROM AUTHOR]

Abstract Portable and wearable sensors have attracted considerable attention, which could perceive and respond to ambient stimuli accurately. For the sake of solving the limited power supply and low integration, it is critical to develop and combine functional electronics with flexible energy devices. In this work, we designed an all-in-one sensing patch integrated with piezoresistance sensor and micro-supercapacitor with the porous CNT-PDMS elastomer. Taking the advantage of porous structure with piezoresistivity and elastomer with electrochemical performance, the piezoresistance sensor shows high sensitivity (0.51 kPa−1) and wide detection range as functional fraction, and micro-supercapacitor maintains excellent areal capacitance and cycling stability after 6000 cycles as energy storage fraction, respectively. Assembled with piezoresistance sensor and micro-supercapacitor, the sensing patch could be easily attached on the epidermal skin for joint and muscle monitor with the corresponding resistance response. With high sensitivity and mechanical robustness, such sensing patch could be further utilized as a 3D touch in user identification and safety communication through feature parameter extraction and signal decoding. After packaged into the sensing patch matrix, it could be achieved for static pressure sensing and dynamic tactile trajectory. Therefore, the all-in-one sensing patch shows feasibility in real-time pressure recognition and human-machine interfaces. Graphical abstract An all-in-one sensing patch is integrated with piezoresistance sensor and micro-supercapacitor based on the porous CNT-PDMS elastomers. The porous CNT-PDMS elastomer is synthesized with solution-evaporation method, which could be modulated by the sugar templates and content ratio. Such piezoresistance-sensing patch could be utilized as 3D touch in user identification and safety communication through parameter extraction and signal decoding. Packaged into the sensing matrix, it shows feasibility in spatially mapping resolved pressure information about static pressure sensing and dynamic tactile trajectory. fx1 Highlights • All-in-one patch is integrated with piezoresistance sensor and micro-supercapacitor. • CNT-PDMS elastomer is prepared with mechanical durability and electrical stability. • All-in-one sensing patch works as 3D touch in user identification and communication. • Sensing matrix shows feasibility in static pressure sensing and dynamic tactile trajectory. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method based on deep neural networks to solve obstacle problems. By introducing penalty terms, we reformulate the obstacle problem as a minimization optimization problem and utilize a deep neural network to approximate its solution. The convergence analysis is established by decomposing the error into three parts: approximation error, statistical error and optimization error. The approximate error is bounded by the depth and width of the network, the statistical error is estimated by the number of samples, and the optimization error is reflected in the empirical loss term. Due to its unsupervised and meshless advantages, the proposed method has wide applicability. Numerical experiments illustrate the effectiveness and robustness of the proposed method and verify the theoretical proof. [ABSTRACT FROM AUTHOR]

This paper presents a digitalized self-powered triboelectric strain gauge (DSSG) for the first time. Different from conventional resistive or capacitive analogue strain responsive mechanisms, adopting the output of grated triboelectrication as sensing signal for static and dynamic strain measurement allows for digitalized strain measurement with excellent accuracy, sensitivity and linearity. Instead of analyzing voltage/current value of sliding-mode triboelectric nanogenerator (S-TENG) to evaluate strain, the DSSG exploits a grated triboelectric electrode to generate periodical output signals when the designed elastomer has relative movement with the grated electrode. A promoted real-time analysis system (RAS) enables the analysis and display of the digitalized signals. Benefiting from the micro-manufacturing techniques of grated electrode, DSSG reaches a remarkable gauge factor as high as 130 with optimized design of geometrical parameters. The results of static strain measurement prove the feasibility of using such DSSG as a self-powered transducer of tensile forces, with a minimum resolution for tensile force detection of 120 mN per cycle. At the same time, dynamic strain sensing assisted by signal processing system provides possibility of using such DSSG for real-time elbow joint motion detection and posture analysis, thereby indicating its great potentials for human-machine interface, prosthetic, and biomechanical applications. [ABSTRACT FROM AUTHOR]

Fingertip is the region with the largest density of mechanoreceptors in human body. Inspired by its complicated anatomical structure, we design a fingertip-like electronic skin (e-skin) that can simultaneously detect the movements from lateral and vertical directions. The device includes three parts that correspond to fingerprint, epidermis and dermis of the human being, respectively. The fabricated double spiral carbon nanotube-polydimethylsiloxane (CNT-PDMS) electrodes and substrate mimic the structure of fingerprint and epidermis, respectively. Based on triboelectrification effect, the double spiral CNT-PDMS electrodes can generate alternating voltage with different frequencies when sliding across different rough surfaces, which behaves like fast adapting (FA) in real skin. Porous CNT-PDMS is used for detecting pressure, mimicking the function of slow adapting (SA) and the structure of dermis. A cost efficient way to fabricated porous CNT-PDMS is adopted and it can modulate the porosity and resistance at the same time, which provides a way to modulate its sensitivity. With the help of both sliding sensing and pressure sensing, this device can execute many complicated tasks such as differentiating roughness of surfaces and holding-releasing execution, which greatly expands the application fields of e-skin. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) has emerging as an important approach for energy harvesting. However, low charging efficiency as well as low power conversion efficiency have restricted its practical application for powering traditional electronics. Here we propose a power management (PM) strategy by extracting maximum energy from TENG and transferring the energy to storage unit employing optimized Inductor-Capacitor (LC) oscillating. PM module using this strategy designed shown universality and high-efficiency for different modes TENG. Over 2600 times improvement in stored energy than standard circuit was achieved, and more than 72% alternating current (AC) to direct current (DC) power transfer efficiency was obtained for different modes TENGs. The regulated and managed output shown the ability as a power source for the continuously working of commercial electronics, such as LED bulbs, calculators and pedometers. Our work provides an effective, universal and practical strategy for efficiently power management of TENG from theoretical derivation and experimental validation, which is promising to serve as a standard PM module for TENG as well as to guide its design. [ABSTRACT FROM AUTHOR]

With the rapid development of wearable electronics like artificial e-skins and smart patch, harvesting biomechanical energy and realizing self-powered sensing are of essential importance for achieving sustainable and efficient function of the system. Here we report a flexible hybrid device that can be conformally attached on soft surface like human skin to harvest diversity touch energies based on electrospun nanofiber mat. Facilitated by the working mechanisms of triboeletric and piezoelectric, the device can generate maximum peak power up to 84 μW/cm 2 and 0.11 μW/cm 2 for the TENG and PENG part when stimulated by a compressive stress, which can enhance the energy harvesting efficiency and expand its application areas. By virtue of the high sensitivity of the piezoelectric nanomaterial, the device can also be attached on different parts of body for real-time monitoring the human physiological signals such as respiratory information and radial artery pulse, which shows potential value in self-powered e-skins and healthcare monitoring systems. [ABSTRACT FROM AUTHOR]

This research is aimed to evaluate the feasibility and efficacy of a piezoelectric thinfilm (PETF) based, implantable and self-powered monitor for blood pressure (BP) through theoretical, in vitro and in vivo studies. A 3-dimensional simulation model revealed that both the stresses of aorta wall and the generated electric potential by device were proportional to systolic BP. With an in vitro testing system, an excellent linearity ( R 2 >0.99) was achieved between the peak output voltage of device and flow pressure, with a high-sensitivity of 173 mV/mmHg which is significantly higher than reported results. A maximum instantaneous power of 2.3 μW was reached in vitro , indicating a robust self-powered capability. Excellent stability of the device was also achieved for more than 50,000 operating cycles. In vivo experiment was carried out in adult Yorkshire porcine. A favorable linearity ( R 2 =0.971) with a sensitivity of 14.32 mV/mmHg was obtained, and the device output a maximal instantaneous power of 40 nW in vivo . Based on these characteristics of the device, we established an implantable, self-powered and visualized blood pressure monitoring system for in vitro and in vivo demonstration. A hypertension status could be alarmed visually in real-time using this system, without a built-in battery. Integrated with a coupling function of energy harvesting and biomedical sensing, this new technique shows a promising perspective in the field of the implantable healthcare monitoring. [ABSTRACT FROM AUTHOR]

In this article, we present an electrode-free triboelectric generator for harvesting biomechanical energy from human motions through triboelectrification between shoe sole and ground. A thin film of porous ethylene-vinyl acetate copolymer (EVA) is designed and pasted on shoe sole to serve as the friction surface. Electricity is generated by the contacting friction of shoe sole with ground surface during walking, which makes no initial vertical gap needed in shoe sole. At the same time, human body is employed as the natural electrode instead of fabricated electrodes, and the electricity can be obtained from any part of human body. In addition, output performances are characterized by using three different conductors as reference electrode. The output voltage of 810 V is achieved and charge of over 550 nC is transferred in one step of an adult׳s walking. Meanwhile, 76 blue LEDs are lighted through a watch as output node. Owing to the advantage of body electrode, it has potential applications in wearable electronics and implantable devices. [ABSTRACT FROM AUTHOR]

This research is aimed to evaluate the feasibility and efficacy of generating electric power utilizing the pulsating energy of ascending aorta with a flexible and implantable piezoelectric generator (PG) through in vitro and in vivo studies. In the in vitro study, the max output voltage ( V max), current ( I max) and power ( P max) of the PG were 10.3 V, 400 nA and 681 nW respectively. The quantity of electric charging by one pulse was about 7–9 nC. Factors affecting its output performance were investigated with single variable experiments. We further implanted the PG to wrap around the ascending aorta of a porcine to investigate the output performance in vivo. The V max and I max of the implanted PG were 1.5 V and 300 nA under the heart rate of 120 bpm and the blood pressure of 160/105 mmHg. The instantaneous output power was 30 nW with a long-lasting duration of 700 ms and 77.8% duty ratio. The implanted PG could charge for a 1 μF capacitor to 1.0 V within 40 s. [ABSTRACT FROM AUTHOR]

Abstract: The iterative penalty method for Stokes equations is an effective algorithm. In this paper, we discuss the bilinear-constant velocity–pressure element for the Stokes equations and present the error estimates for the iterative penalty method using this element. The key technique we use is the local checkerboard pattern. Numerical experiments are given which are consistent with our analysis. [Copyright &y& Elsevier]

Abstract: The effect of calcium phosphate surface deposit and the surface adsorption of the serum proteins, bovine serum albumin (BSA) and fibrinogen, on the corrosion resistance and electrochemical behavior of (cp)titanium in phosphate buffer saline solution (pH 7.4) was investigated at physiological temperature, 37°C, using electrochemical impedance spectroscopy and dc electrochemical polarization techniques. The formation of calcium phosphate deposit on the Ti surface decreased both the corrosion rate at the open circuit potential (OCP) and the anodic reaction current in the high anodic potential range (>2.6V). Addition of BSA significantly moved the OCP towards a more negative (cathodic) potential and inhibited the cathodic corrosion reaction, but did not significantly change the corrosion resistance at the OCP. Addition of fibrinogen showed a similar, but less pronounced effect than BSA. The possible mechanisms leading to these observed effects are discussed. [Copyright &y& Elsevier]

Abstract: In this paper, a Fourier spectral method for numerically solving Cahn–Hilliard equation with periodic boundary conditions is developed. We establish their semi-discrete and fully discrete schemes that inherit the energy dissipation property and mass conservation property from the associated continuous problem. we prove existence and uniqueness of the numerical solution and derive the optimal error bounds. we perform some numerical experiments which confirm our results. [Copyright &y& Elsevier]

A bovine serum albumin protein-containing calcium phosphate coating (BSA/brushite) was prepared by electrochemically assisted co-precipitation onto a hydroxyapatite (HA) coated Ti-6Al-4 V surface. Electrochemically assisted co-precipitation of BSA/brushite coatings onto HA resulted in a 70-fold increase in BSA inclusion compared to simple adsorption, and was subsequently released by a slower mechanism (15% loss over 70 h). Thus, this electrochemically assisted co-precipitation technique provides an efficient method of protein incorporation at physiological temperature, with a potential for sustained release of therapeutic agents as may be required for metallic implant fixation. [Copyright &y& Elsevier]

• Asymmetric linear cutting silicon wafer without path deviation is realized by prefabricating crack on laser scanning path. • The slice-shape of tensile stress around crack-tip induces an unbiased propagation. • The minimum required laser power is a prerequisite for obtaining good kerf quality. • The appropriate V always produces small surface roughness, but not the smallest. The laser induced thermal-crack propagation (LITP) has been reported to have excellent kerf quality in the cutting of silicon wafer. However, the trajectory deviation problem under asymmetric cutting have obstructed the application of this technology in silicon wafer cutting. In this study, a pre-crack guiding laser cleaving (PCGLC) method has been presented to solve the problem of path deviation in asymmetric linear cutting of silicon wafer. The effects of the pre-crack parameters including groove width and groove depth as well as the processing parameters including laser power and laser scanning speed on the processing quality are investigated in experiments. The interaction effects of laser power and laser scanning speed on kerf quality are discussed. A parameter selection guidance based on minimum required laser power is proposed and the optimum kerf quality is obtained. Thermal crack propagation simulation reveals the none-deviation mechanism in PCGLC. From experimental and simulation studies, the PCGLC can obtain a good processing quality with good kerf quality and unbiased trajectory. [ABSTRACT FROM AUTHOR]

This paper is concerned with the recovery of an unknown symmetric density function in the weighted Helmholtz equation with Dirichlet boundary conditions from the lowest few eigenvalues. By using the piecewise constant function to approximate the density function and using the Rayleigh–Ritz approach to discretize the differential equation, the continuous inverse eigenvalue problem is converted to a related matrix inverse eigenvalue problem and then a least squares problem for the discrete model is formulated. The solution of the least squares problem via an iterative method is discussed and then an approximation to the unknown density is recovered. Numerical experiments are given to confirm its competitiveness. [ABSTRACT FROM AUTHOR]

[Display omitted] • The composite dispersants of MLS and AAD were used for improving the properties of CPWS. • The CD-2 with m MLS : m AAD = 1:1 was superior to others in viscosity-reducing and stabilizing ability. • The Δ E LUMO-HUMO of H 2 O was higher compared to those of MLS and AAD. • The adsorption energy of composite dispersant with CP reached −169.36 kcal/mol based on MD simulation. • The total interaction energy among CP particles after absorbing dispersant was positive. To optimize the utilization efficiency of coal pitch (CP), an innovative composite dispersant was designed and employed in the preparation of coal pitch water slurry (CPWS) by effectively combining modified sodium lignosulfonate (MLS) and amphoteric polycarboxylate (AAD) based on the principle of complementary advantages. The effects of the proportion of MLS to AAD on the characteristics of CPWS were systematically analyzed and assessed by various technical methods, including apparent viscosity, rheological behavior, static stability, adsorption behavior, etc. Results indicated that the CPWSs utilizing distinct composite dispersants belonged to the category of yield pseudoplastic fluids and had a good correlation with the Herschel-Bulkley model. Among them, the CD-2, composite dispersant with a mass ratio of MLS:AAD = 1:1, exhibited superior performance in terms of viscosity reduction and stabilization properties. It demonstrated the maximum adsorption capacity (5.23 mg/g) and adsorption layer thickness (7.22 nm) compared to other dispersants. Meanwhile, it could significantly increase the wettability (with a contact angle of 74.5°) and the absolute Zeta potential value (32.5 mV) of CP. The density functional theory (DFT), molecular dynamics (MD) simulation, and extended Derjaguin-Landua-Verwey-Overbeek (eDLVO) theory were carried out to investigate the interaction mechanism of composite dispersant with CP and the interaction energy among CP particles. The differences in energy levels between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HUMO) of MLS and AAD were significantly smaller than that of H 2 O. The hydrophobic groups of composite dispersants were efficiently adsorbed onto CP, while the hydrophilic groups adsorbed water molecules, with an adsorption energy reaching −169.36 kcal/mol. The steric hindrance of composite dispersant exerted a crucial influence on the dispersion of CPWS, enabling CP particles to be stabilized in water. The present study offers a novel approach to enhance the characteristics of CPWS and establishes a theoretical foundation for the design of efficient composite dispersants. [ABSTRACT FROM AUTHOR]

Abstract: We present two iterative methods for solving the Falkner–Skan equation based on the quasilinearization method. We formulate the original problem as a new free boundary value problem. The truncated boundary depending on a small parameter is an unknown free boundary and has to be determined as part of solution. Using a change of variables, the free boundary value problem is transformed to a problem defined on [0,1]. We apply the quasilinearization method to solve the resulting nonlinear problem. Then we propose two different iterative algorithms by means of a cubic spline solver. Numerical results for various instances are compared with those reported previously in the literature. The comparisons show the accuracy, robustness and efficiency of the presented methodology. [Copyright &y& Elsevier]

The anodic iron dissolution in 0.5 mol dm−3 perchloric acid (HClO4) was investigated by the electrochemical impedance spectroscopy, the potentiodynamic sweep and the scanning electron microscopy measurements. The anodic polarization behavior of iron in HClO4 solution showed that the strong current oscillations occurred in a narrow potential region, particularly the pitting corrosion was observed in the active dissolution region. These characteristics were quite different from those of iron in the sulfuric acid (H2SO4). At the potentials 82 and 132 mV more positive than the corrosion potential (−482 mV vs. SCE), the impedance spectra for the iron in HClO4 displayed two inductive arcs; however, by gradually increasing potential the lower frequency inductive arc disappeared at −300 mV at first, and then the higher frequency inductive arc changed into a capacitive arc at −250 mV. Based on the impedance display of iron at various potentials, a reaction model involving two adsorbed intermediate species was proposed, in terms of which the impedance behavior at different potentials were described. Occurrence of the pitting corrosion in active dissolution region was explained. [ABSTRACT FROM AUTHOR]