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As a new malignant tumor therapy method with low side effect, high safety and efficiency, magnetic induction hyperthermia (MIH) has attracted great attention in recent years. As magnetic induction heating media, magnetic nanoparticles (MNPs) are critical for the development of MIH. For clinical safety, the MNPs need a high heating efficiency to reduce the applied dose, minimizing the risk of side effect. Increasing the saturation magnetization and initial susceptibility, adjusting the magnetocrystalline anisotropy constant and particle size to the optimal values are the effective methods of improving heating efficiency. On the other hand, a suitable Curie temperature is desired to realize the self-regulation of the therapy temperature, avoiding the use of clumsy and expensive temperature monitoring and control devices. Substituting the magnetic ions in tetrahedral (A) site of the spinel ferrite with nonmagnetic ions or magnetic ions with smaller magnetic moments can effectively reduce the superexchange interaction between the A and B (octahedral) sites, decreasing Curie temperature. Yet, the reduction of the Curie temperature by ion doping usually reduces the saturation magnetization, decreasing heating efficiency. Increasing the fraction of heat generated by relaxation loss and increasing the saturation magnetization may be used to improve the heating efficiency.

The Triple Periodic Minimal Surface (TPMS) has emerged as a new approach for producing open cell porous scaffolds for biomedical applications. However, different from the traditional scaffolds, the TPMS scaffolds always exhibit anisotropic elastic behaviors and consequently the simple mechanical testing is not capable to provide a full characterization of their mechanical behaviors. Additionally, it is still unclear if the TPMS scaffolds possess the similar anisotropic behaviors as the natural bones. The aim of the present study was to analyze the anisotropic elastic behaviors of TPMS based scaffolds using the numerical homogenization method and the analytical analysis approach. Five widely-used TPMS scaffold topologies (Diamond, Gyroid, Fischer-Koch S, Schwarz P and F-RD) were investigated. The independent elastic constants were determined from the analytical analysis and then, the values for these independent constants were determined using the finite element (FE) unit cell models of the scaffolds combined with the periodic boundary condition. The analytical analysis revealed that the Diamond, Gyroid and Fischer-Koch S topologies are threefold rotational symmetric and consequently have seven independent elastic constants. The Schwarz P and F-RD topologies are cubic symmetric and have three independent elastic constants. The FE analysis showed that the Diamond, Gyroid and Fischer-Koch S based scaffolds have only three non-zero independent elastic constants, implying the cubic symmetric property of these scaffolds. All the independent elastic constants decreased quadratically with the increase of scaffold porosity. The absolute difference between the Zener anisotropic factor and one increased the most for the Gyroid based scaffold, while the value for the Fischer-Koch S based scaffold increased the least. The present study revealed that all the five TPMS scaffolds possess cubic symmetry, limiting their anisotropic behaviors. The information on the Zener anisotropic factor and the relationship between the scaffold elastic constants and the porosity can facilitate the selection and design of scaffolds in biomedicine and relevant fields.

This paper investigates the effect of curing history on the strength behaviour and cohesive properties of adhesively bonded corrugated sandwich structures with a structural adhesive. Three-point bending tests under both longitudinal and transverse loading directions were taken into account. The selected curing histories of adhesively bonded corrugated sandwich structures were: a) 2 h at temperature of 40 °C; b) 2 h at 40 °C and then 2 h at 60 °C; c) 2 h at 40 °C, then 2 h at 60 °C and 1 h at 80 °C. To predict adhesive joint mechanical behaviour with different curing conditions, bulk tensile, Double Cantilever Beam, and End-Notched Flexure tests were conducted for material characterisation and verification of the subsequent developed numerical analysis. The glass transition temperatures (Tg) of the adhesive with different curing histories were determined using differential scanning calorimetry method. Crack propagation and stress distribution in the adhesive layer was simulated using the bilinear traction-separation law of Cohesive Zone Model. The predicted critical ultimate loads and the corresponding failure modes were proved to be in good correlation with the experimental observation. The presented study revealed that gradual step-wise increasing in curing temperature and duration can effectively strengthen the mechanical performance and fracture resistance of adhesively bonded corrugated sandwich structures.

This paper is concerned with the mean-square exponential stability and performance analysis, stabilization, dissipative control and dissipativity-based sliding mode control (SMC) problems for discrete-time switched stochastic hybrid systems. Such systems can be also regarded as switched hybrid systems with stochastic perturbation. Event detectors, which can save computational resource, are designed to determine whether the current data should be transmitted or not in the design process. Firstly, by proposing an average dwell time method combining with a switched (mode-dependent) Lyapunov function, a sufficient condition is established under the event-triggering scheme, which guarantees that the considered switched stochastic system is mean-square exponentially stable, and then an explicit parametrization of the desired stabilization controller is also given. Secondly, the event-triggering dissipativity analysis and the dissipative control problems are investigated. A dissipativity performance condition is proposed to guarantee the mean-square exponential stability and strict dissipativity for the discrete-time switched stochastic system, and then the dissipative controller is implemented by the state feedback. Thirdly, a switched observer is constructed to estimate unavailable state variables, based on which a differential-type sliding surface function is designed, with which the sliding mode dynamical equations can be easily obtained. The resulting closed-loop system with sliding mode dynamics is an autonomous switched stochastic system. Dissipativity analysis and synthesis are both investigated for the closed-loop system, and consequently sufficient conditions are derived, which pave the way for solving the event-triggering observer-based dissipative sliding mode control problem. Moreover, an event-triggering output-based SMC law is first synthesized to drive the system trajectories to enter a predefined sliding vicinity. Finally, illustrative examples are employed to validate the proposed controller design schemes.

Hypertension is one of the most common chronic and cardiovascular diseases, with the largest number of deaths. According to clinical experience, long-term hypertension will cause cardiac hypertrophy and other complications, and heart structure remodeling will significantly change the energy characteristics of the heart chambers, and impair heart function. Research shows that, early hypertension can be diagnosed by the blood flow and energy loss in the left ventricle. Therefore, it is important to choose an appropriate method to simulate and predict the flow domain of this ventricle.This study took the left ventricular flow field of patients with hypertensive myocardial hypertrophy as the research object, used MATLAB-SIMULINK to establish a closed-loop network cardiovascular model, provided flow boundary conditions for the computational fluid dynamics (CFD) numerical simulation method, and, finally, completed a co-simulation.This article compared the degree of agreement between the energy loss in different phases of the heart cavity and clinical experimental data and summarized the characteristics of the flow field in patients with hypertensive myocardial hypertrophy. The analysis of three simulation groups (control group, non-left ventricular hypertrophy group, and left ventricular hypertrophy [LVH] group) showed that the vortices in the LVH group were irregular and not fully developed, accompanied by significant energy loss.The simulation method used in this study is basically consistent with the clinical data. Myocardial hypertrophy has a significant influence on the blood flow of the left ventricle. Changes in the blood flow make the left ventricular vortex distribution abnormal during the rapid systole and rapid ejection periods, leading to a series of dangerous factors, including increased energy loss and a low cardiac ejection fraction.

Hydrogels based on chitosan/hyaluronic acid/β-sodium glycerophosphate demonstrate injectability, body temperature sensitivity, pH sensitive drug release and adhesion to cancer cell. The drug (doxorubicin) loaded hydrogel precursor solutions are injectable and turn to hydrogels when the temperature is increased to body temperature. The acidic condition (pH 4.00) can trigger the release of drug and the cancer cell (Hela) can adhere to the surface of the hydrogels, which will be beneficial for tumor site-specific administration of drug. The mechanical strength, the gelation temperature, and the drug release behavior can be tuned by varying hyaluronic acid content. The mechanisms were characterized using dynamic mechanical analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and fluorescence microscopy. The carboxyl group in hyaluronic acid can form the hydrogen bondings with the protonated amine in chitosan, which promotes the increase of mechanical strength of the hydrogels and depresses the initial burst release of drug from the hydrogel.

By adding dimethyl sulfoxide (DMSO), nano titanium dioxide (TiO2) and sodium carbonate (Na2CO3) to polyvinyl alcohol (PVA), the PVA-TiO2 composite hydrogel membrane with high mechanical properties and photocatalytic ability was prepared using the freeze–thaw cycle method. The addition of DMSO and TiO2 can effectively improve the mechanical strength of the composite hydrogel membrane and its photocatalytic degradation efficiency of dye. By optimizing the raw material ratio and preparation process, the tensile strength of the prepared composite membrane can reach 14.3 MPa, which is the highest among the reported membrane of its kind. The maximum tensile toughness is 8.16 MJ/m3, indicating the good ductility. The maximum adsorption capacity of methylene blue (MB) calculated from Langmuir isotherm model is 318.47 mg/g and after 4 d nature light treatment, the dye removal rate can reach 99.85%.

This paper investigates the problem of adaptive fuzzy tracking control for a category of pure-feedback nonlinear systems with time-varying delay and unknown dead zone. Fuzzy logic systems are used to identify unknown functions existing in systems. Mean-value theorem is introduced to overcome the difficulty arising from the pure-feedback structure in designing controller. Based on the information of dead-zone slopes, dead zone is handled. Only one adaptive parameter needs updating online by considering the norm of membership function vectors rather than all sub-vectors. Moreover, utilizing the adaptive backstepping technique, a novel adaptive fuzzy tracking control scheme is developed to guarantee all signals of the closed-loop systems are semi-globally uniformly ultimately bounded, and the tracking error can be regulated to the origin with a small neighborhood. The stability of the closed-loop system is proved and simulation results are given to demonstrate the effectiveness of the proposed control approach.

Magnetic Resonance Elastography (MRE) provides a non-invasive method to characterize the mechanical response of the living brain subjected to harmonic loading conditions. The peak magnitude of the harmonic strain is small and the excitation results in harmless deformation waves propagating through the brain. In this paper, we describe a three-dimensional computational model of the brain for comparison of simulated harmonic deformations of the brain with MRE measurements. Relevant substructures of the head were constructed from MRI scans. Harmonic wave motions in a live human brain obtained in an MRE experiment were used to calibrate the viscoelastic properties at 50 Hz and assess accuracy of the computational model by comparing the measured and the simulated harmonic response of the brain. Quantitative comparison of strain field from simulations with measured data from MRE shows that the harmonic deformation of the brain tissue is responsive to changes in the viscoelastic properties, loss and storage moduli, of the brain. The simulation results demonstrate, in agreement with MRE measurements, that the presence of the falx and tentorium membranes alter the spatial distribution of harmonic deformation field and peak strain amplitudes in the computational model of the brain.

The design and fabrication of transition metal oxides (TMOs) anode with superior lithium storage performance remains a challenge. Herein, we demonstrate one-pot hydrothermal method combined with post-calcination for the construction of interconnected porous N-doped carbon-coated cobalt/iron oxides nanocomposite (CFO@N-C) as lithium-ion batteries (LIBs) anode. This facile approach gives CFO@N-C many interesting characters such as rich porous structure, fine cobalt/iron oxides’ nanocrystals (

The aim of this paper is to improve the reliability of Proton Electrolyte Membrane Fuel Cell (PEMFC) stack by designing the clamping force and the thickness difference between the membrane electrode assembly (MEA) and the gasket. The stack reliability is directly determined by the component reliability, which is affected by the material property and contact stress. The component contact stress is a random variable because it is usually affected by many uncertain factors in the production and clamping process. We have investigated the influences of parameter variation coefficient on the probability distribution of contact stress using the equivalent stiffness model and the first-order second moment method. The optimal contact stress to make the component stay in the highest level reliability is obtained by the stress-strength interference model. To obtain the optimal contact stress between the contact components, the optimal thickness of the component and the stack clamping force are optimally designed. Finally, a detailed description is given how to design the MEA and gasket dimensions to obtain the highest stack reliability. This work can provide a valuable guidance in the design of stack structure for a high reliability of fuel cell stack.

This paper studies the problem of adaptive output tracking control for a class of nonlinear systems subject to unknown time delay and input saturation. To address the delay and the input saturation, some reasonable assumptions and an auxiliary system are introduced. The fuzzy logic approach is employed to approximate the unknown functions in the system. An observer is designed to estimate the unavailable system states. The dynamic surface control (DSC) technique is utilized to avoid the problem of explosion of complexity. By combining the backstepping and DSC methods, a bounded control input is designed to ensure that all signals of the closed-loop system are bounded and the tracking error can fluctuate around the origin within a small neighborhood. Finally, two examples are presented to demonstrate the effectiveness and potential of the proposed new design techniques.

The wetting and spreading characteristics of a water drop on a surface is highly dependent on the geometric parameters of the micro-texture of the surface. To obtain a stable Cassie drop, the condition that the pillar height must be higher than the sag height of the meniscus is a necessary, yet not a sufficient, condition. From the viewpoint of energy minimization, a new criterion was proposed to design the height of the pillar for achieving a stable and robust anti-adhesive drop state. To ensure such a composite interface, the height of the pillars should be taller than the critical height where the critical contact angle is equal to the intrinsic contact angle. If this height requirement is not met, the drop exists in either a Wenzel or a metastable Cassie state. The numerical simulations using the Volume-of-Fluid method in Fluent support the above proposals.

Proton exchange membrane fuel cell (PEMFC) stacks usually undergo vibration during packing, transportation, and serving time, in particular for those used in the automobiles or portable equipment. To study the stack vibration response, based on finite element method (FEM), a mode analysis is carried out in the present paper. Using this method, we can distinguish the local vibration from the stack global modes, predict the vibration responses, such as deformed shape and direction, and discuss the effects of the clamping configuration and the clamping force magnitude on vibration modes. It is found that when the total clamping force remains the same, increasing the bolt number can strengthen the stack resistance to vibration in the clamping direction, but cannot obviously strengthen stack resistance to vibration in the translations perpendicular to clamping direction and the three axis rotations. Increasing the total clamping force can increase both of the stack global mode and the bolt local mode frequencies, but will decrease the gasket local mode frequency.

This paper aims to investigate the relationship between local moisture concentration and mesoscale mechanical properties of epoxy adhesive under elevated temperature. Araldite® 2015 was chosen as the target adhesive due to its curing stability and possible validation with previously published literatures. The specimens were aged at 60 °C in deionised water and 5%wt NaCl solution, separately, with the water ingress evaluated by Fickian diffusion model. Nanoindentation was utilised to characterise the mesoscale modulus and hardness distribution along the water diffusion path. Then Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were conducted to investigate the variation of functional groups and microstructure, respectively. The results show that mechanical properties degrade as ageing duration increases, with higher degradation observed in the edge region where higher moisture concentration exists. Besides, higher ageing temperature leads to larger decrease in mechanical properties of saturated specimens. An empirical relation between local mechanical properties and moisture concentration was established. Chemical and morphology performance of adhesives also exhibited variations when saturated. The obtained local moisture-mechanical relationship can then be used to improve the accuracy of numerical simulation on the environmental durability of structural adhesive in future work.

Ferrite magnetic nanoparticles (MNPs) with spinel structure are of great significance in the study of magnetic induction hyperthermia (MIH). The effect of element doping on the magnetic properties of MNPs is crucial. Here, we report the influence of the Mg2+ substitution on Curie temperature (Tc), magnetic properties, and heating efficiency of MgxZn0.8-xCo0.2Fe2O4 (0.1 ≤ x ≤ 0.5) nanoparticles synthesized by hydrothermal method. With the increase of Mg2+ content, Tc increases from 36.7 °C to 242.9 °C due to the enhancement of the A-B super-exchange interaction. The specific saturation magnetization increases from 35.5 emu·g−1 to 53.3 emu·g−1 and then remains constant, which is caused by the effect of Yafet-Kittle angle and magnetic moment. The specific absorption rate (SAR) increases from 3.5 W·g−1to 82.7 W·g−1, which may be ascribed to the effect of size and specific saturation magnetization of the nanoparticles. When x = 0.3, the stable temperature under the alternating magnetic field (32 kA·m−1, 100 kHz) reaches 44.7 °C with the SAR of 49.0 W·g−1. The low toxicity to cells and high heating efficiency endow the MNPs the potential in MIH.

Great progress has been made on the research of proton exchange membrane fuel cell (PEMFC) in the past 20 years, especially in the key materials and components such as proton exchange membrane (PEM), catalytic layer (CL), gas diffusion layer (GDL), membrane electrode assembly (MEA), bipolar plate (BPP), endplate (EP) etc. There are a lot of studies on those materials and structures as well as several literature reviews on their chemical and physical properties. However, structure design of PEMFC stack is a key technology as it connects lab-based study with large-scale industrial applications. There is so far no systematic review on the structure design, manufacture, optimization, clamping theory and technology of large PEMFC stacks. In this article, a systematic review is presented for the progresses made in structure optimization and manufacturing technologies of EPs and BPPs, mechanical properties of structure materials, including PEM, GDL and MEA, optimization design of clamping load, anti-vibration and reliability designs of large PEMFC stacks. Finally, discussions, challenges and prospects are made on the materials and structure designs of large PEMFC stacks. It is expected that this review can provide a systematic comprehension and direction for the structure optimization of high performance PEMFC stacks.

The problem of robust adaptive sliding mode control for semi-Markovian jump systems with actuator faults is investigated in this paper. The uncertainties considered in this paper satisfy norm-bounded form, and bounds of nonlinearity, actuator faults and external disturbance are unknown. Then, the influences of the actuator faults, unknown nonlinearity and disturbance can be effectively attenuated via a novel adaptive sliding mode controller. The reachability of sliding mode surface can be guaranteed by the adaptive sliding mode controller. Using Lyapunov stability theory, sufficient conditions are derived to guarantee the stochastic stability of the sliding mode dynamics. Finally, a numerical example is exploited to demonstrate the effectiveness of the proposed method.

This paper investigates the problem of fuzzy adaptive backstepping control for a category of nonlinear strict-feedback systems. Input delay is considered in the design process. Fuzzy logic systems are used to identify the unknown nonlinear functions existing in the systems. To handle the input delay, an integral item is introduced. For the general problem of "explosion of complexity" in adaptive backstepping control approach, dynamic surface control technique is introduced to avoid it. Based on the adaptive backstepping control approach, a fuzzy adaptive controller with adaptive parameters is constructed to guarantee all signals of the closed-loop system are bounded and system states can be regulated to the origin. Finally, simulation results are provided to illustrate the effectiveness of the proposed methodology.

This paper investigates the problem of filter-based fault detection for a class of nonlinear networked systems subject to parameter uncertainties in the framework of the interval type-2 (IT2) T–S fuzzy model-based approach. The Bernoulli random distribution process and logarithm quantizer are used to describe the measurement loss and signals quantization, respectively. In the framework of the IT2 T–S fuzzy model, the parameter uncertainty is handled by the membership functions with lower and upper bounds. A novel IT2 fault detection filter is designed to guarantee the residual system to be stochastically stable and satisfy the predefined H ∞ performance. It should be mentioned that the proposed filter does not use the same premise variables, number of fuzzy rules and membership functions as the fuzzy model, which will lead to more flexible design. Finally, two illustrative examples are provided to demonstrate the usefulness of the approach proposed in this paper.

This paper investigates the problem of static output-feedback control of discrete-time nonlinear networked control systems with data packet dropouts on the basis of the fuzzy-model-based Takagi-Sugeno (T-S) approach. The nonlinear system is modeled via T-S fuzzy model. Both imperfect sensor-to-controller (S/C) and controller-to-actuator (C/A) links are considered via a novel data model. Some slack matrices are introduced to reduce the conservativeness. By constructing fuzzy Lyapunov function, the sufficient conditions are derived to guarantee the resulting closed-loop system to be stochastically stable as well as the predefined H ∞ performance index. Finally, some simulation results are given to demonstrate the effectiveness of the proposed results. HighlightsDifferently from existing results with the common quadratic Lyapunov function, the fuzzy membership function dependent Lyapunov function is adopted to derive the main results, which may facilitate achieving less conservative Results.A novel data compensation model is proposed, in which a compensation gain is designed to regulate the compensated data for the successive data loss case. With such model, the effect of imperfect communication network can be decreased effectively.The single-step linear matrix inequality method is borrowed to derive the static output-feedback controller design criteria, which is helpful to obtain less conservative results.

This paper studies the problem of observer-based fuzzy control for a class of nonlinear networked control systems (NCSs) in the framework of interval type-2 (IT2) Takagi-Sugeno (T-S) fuzzy model. Both imperfect communication channels and parameter uncertainties are taken into consideration. Bernoulli random distribution is used to describe such unreliable communication environment. Nonlinear NCSs are modeled via the IT2 T-S fuzzy model, in which membership functions with lower and upper bounds can capture and express parameter uncertainties. The observer is designed to observe unmeasurable state variables. Moreover, based on these techniques, sufficient conditions are derived to guarantee the resulting closed-loop system to be stochastically stable and possess the property of external disturbance attenuation. Finally, a numerical example is provided to illustrate the effectiveness of the approach proposed in this paper.

A simplified analysis method for large proton exchange membrane fuel cell (PEMFC) stack is proposed to obtain the optimal clamping force if the stack is subjected to an impact acceleration. The PEMFC stack is first simplified to an equivalent stiffness-mass model consisting of a number of springs and point masses in order to get the parameterized structural characteristics. Based on this model, the effects of the structural parameters and impact acceleration on the structural stress of components can be analyzed efficiently. We then discuss how to obtain the proper range of clamping force for a given PEMFC stack according to the structural strength, gas tightness, and non-slippage between the contact components under impact.

The present paper, firstly, establishes a calculation model of intrinsic dissipation, based on the double exponential regression for the one-dimensional distribution of specimen surface temperature variation. Then, an energy method is proposed for rapid evaluation of high-cycle fatigue parameters (i.e., fatigue limit and S–N curve). The energy method takes intrinsic dissipation as the fatigue damage indicator, and eliminates the interference of internal friction causing no damage on fatigue life evaluation. An experimental research on FV520B stainless steel was performed, in order to verify the feasibility and validity of the energy method, as well as the calculation model.

The macroporous, high porosity and mechanically strong poly (vinyl alcohol) (PVA) hydrogels were developed using agarose (AG) as the pore inducing agent. The AG not only incurs the formation of macropores by promoting the nucleation and growth of ice particles, but also strengthens the mechanical properties by increasing the crystallinity of PVA and the inter-molecular hydrogen bonds. The in vitro cell experiments imply that the obtained PVA hydrogels is cytocompatible and the chondrocytes can proliferate in the macropores.

In this work, a parameter identification approach was developed based on a combined experimental-numerical approach to determine the optimal set of adhesive parameters in adhesively bonded specimen subjected to various post curing treatments. End-Notched Flexure (ENF) testing was conducted to characterise the Mode II fracture property under both recommended and post curing conditions, providing benchmark data for the numerical analysis stage. Experimental results revealed that Mode II fracture energy was effectively affected by the post curing history, with higher temperature and longer curing duration leading to enhanced fracture resistance. The numerically identified Cohesive Zone Model (CZM) parameters using multi-island genetic algorithm provided good correlation in Mode II fracture energies between Finite element (FE) modelling and experimentally measured values, thus extensive experimental characterisation work to determine the adhesive parameters can be effectively eliminated.

Both low Curie temperature (Tc) and high specific absorption rate (SAR) are desired for magnetic nanoparticles (MNPs) used in magnetic induction hyperthermia (MIH). Here, we report novel MNPs (Zn0.54Co0.46Cr0.6Fe1.4O4) with a Tc of 48.8 °C, which meets the requirement for the self-regulating of MIH therapeutic temperature. This low Tc can be attributed to the weak A-B super-exchange interactions caused by the substitution of Zn2+ and Cr3+. The SAR of the MNPs under clinical applied AC magnetic field (16 kA·m−1, 100 kHz) is up to 6.53 W·g−1, which is mainly contributed by the relaxation loss. The short relaxation time, caused by the low magnetocrystalline anisotropy, may take responsibility for the occurrence of the relaxation loss. While the low magnetocrystalline anisotropy is related to the low occupation ratio of Co2+ in B sites. The in vitro experiments indicate the self-regulating temperature nature and biocompatibility of the MNPs.

This paper deals with the dissipativity problem for interval type-2 (IT2) stochastic fuzzy neural networks subject to discrete and distributed time-varying delays. Firstly, a new type of IT2 stochastic fuzzy neural network with parameter uncertainties is proposed. The parameter uncertainties can be efficiently tackled by lower and upper membership functions and relative weighting functions. Secondly, according to Ito differential formula and stochastic analysis scheme, a new dissipativity condition is obtained. In the design process, the dissipativity condition can be transformed to convex optimization problem. Finally, a numerical example is proposed to reveal the feasibility of the proposed approach.

In this paper, the robust finite-time state estimation problem of the uncertain Markovian jump neural networks with partly unknown transition probabilities is investigated. In the neural networks, there are a set of modes, which are determined by Markov chain. First, we design a state observer to estimate the neuron states. Second, based on Lyapunov stability theory, a robust stability sufficient condition is derived such that the uncertain Markovian jump neural networks with partly unknown transition probabilities are robust finite-time stable. Then, the robust stability condition is expressed in terms of linear matrix inequalities (LMIs), which can be easily solved by standard software. Finally, a numerical example is given to demonstrate the effectiveness of the proposed new design techniques.

This paper investigates the problem of output tracking for nonlinear systems with actuator fault using interval type-2 (IT2) fuzzy model approach. An IT2 state-feedback fuzzy controller is designed to perform the tracking control problem, where the membership functions can be freely chosen since the number of fuzzy rules is different from that of the IT2 T-S fuzzy model. Based on Lyapunov stability theory, an existence condition of IT2 fuzzy H ∞ output tracking controller is obtained to guarantee that the output of the closed-loop IT2 control system can track the output of a given reference model well in the H ∞ sense. Finally, two illustrative examples are given to demonstrate the effectiveness and merits of the proposed design techniques.

Iron oxide particles with the diameter being 5–10 nm were attached onto the sidewalls of multi-walled carbon nanotubes (MWCNTs) by the thermal decomposition of cyclopentadieny iron (II) dicarbonyl dimmer. The red shift of G-mode from 1579 cm − 1 to 1571 cm − 1 in the Raman profile of the decorated MWCNTs is indicative of the attachment of nanoparticles. Electron energy loss spectroscopy and X-ray photoelectron spectroscopy analyses reveals that the attached nanoparticles are composed of a maghemite phase. Transmission electron microscopy suggests the maghemite particles are covered with amorphous carbon materials and form a core–shell structure.

A new method, based on the infrared thermography, was proposed and applied to rapidly determine the fatigue behavior of Q235 steel. The temperature evolution due to localized microplasticity was considered as the fatigue damage indicator, and good predictions were confirmed between the predicted values and the traditional values. The temperature patterns of the hot-spot zone on the specimen surface were tightly linked with the physical evolution of the fatigue damage in order to identify the damage status for safety evaluation. Based on the limiting energy theory, an energetic damage model was established to predict the residual fatigue life.

A simple, economical and scalable technique is demonstrated to make conductiveyarn. Singlewalledcarbonnanotubes (SWCNTs) are non-covalently functionalized with dye (Acid Red 91) and dispersed in water; while cottonyarn is treated with poly (ethylene imine). When the resulting yarn is immersed in the SWCNT dispersion, SWCNTs self-assemble onto the yarn due to electrostatic forces between the functionalized nanotubes and yarn. Scanning electron microscopy, transmission electron microscopy and Raman spectroscopy indicate the assembly of carbonnanotubes. The SWCNT functionalized yarn exhibits reasonable electrical conduction behaviour and are then used to make chemiresistors. The electrical resistance of the chemiresistors used as sensors increases on exposure to ammonia gas, which can be explained in terms of electron transfer between gas molecules and SWCNTs.

The applications of infrared thermographic method and the relationship between the microstructures and mechanical properties of materials were reviewed. Experimental tests, using the thermographic method, have been carried out in order to evaluate the fatigue behavior of cruciform welded joints subjected to a high mean stress. A good agreement was achieved between the predicted values and those obtained by the traditional procedures. The fatigue life of the welded joint was significantly decreased since the high mean stress accelerated the fatigue microcrack initiation and propagation. The residual fatigue life was well predicted using the energy model of Miner's law advanced in the present paper. Though both the microstructures were tempered martensite along with secondary phase particles, the mechanical properties of the base metal were better than that of the weld seam due to the unfavorable influence of the thermal welding. The welded joints, undergoing fatigue loading, failed at the weld toe or the weld seam, indicating typical fatigue fracture features. Two fatigue mechanisms, involving the crack initiation at persistent slip bands and inclusions, were found by use of SEM.

Electrical contact resistance (ECR) is one of the most important factors affecting the ohmic loss in proton exchange membrane (PEM) fuel cells. Dominated by the contact pressure at the interface of two neighboring components, the ECR can be reduced by increasing the clamping force applied on fuel cell stack. However, too large a clamping force will result in excessive resistance to the transport of reactants in the gas diffusion layer (GDL) and even damage to the fuel cell components. Therefore, for a given clamping force, the minimum ECR is expected by making the pressure distribution as uniform as possible. This paper investigates two questions: (a) how to evaluate the distribution of non-uniform pressure based on the ECR, and (b) in what situation will a uniform pressure distribution reduce the ECR obviously, i.e., the sensitivity of the contact resistance to the pressure distribution.

End plates of the proton exchange membrane fuel cell (PEMFC) need to be well designed because their strength and rigidity directly affect the clamping pressure distribution and thus affect the performance and lifetime of fuel cell stacks. In this paper, a multi-objective topology optimization model of the end plates in a PEMFC stack with nonlinear contact boundary conditions was established to obtain an optimized structural design. It was found that the design improved with topology optimization is not only light but also meets manufacturability requirements. This provides good guidance for the design of a high-performance end plate.

We developed an equivalent capillary model of a microscale fiber-fence structure to study the microscale evolution and transport of liquid in a porous media and to reveal the basic principles of water transport in gas diffusion layer (GDL). Analytical solutions using the model show that a positive hydraulic pressure is needed to drive the liquid water to penetrate through the porous GDL even consisting of the hydrophilic fibers. Several possible contributions for the water configuration, such as capillary pressure, gravity, vapor condensation, wettability and microstructures of the GDL, are discussed using the lattice Boltzmann method (LBM). It is found that the distribution manners of the fibers and the spatial mixed-wettability in the GDL also play an important role in the transport of liquid water.

A high efficient assembly technique for large proton exchange membrane fuel cell (PEMFC) stacks is proposed for obtaining the optimal clamping load. Using the equivalent stiffness model proposed in Part I of this study, we show how to design the structure components for a large PEMFC stack. First, we give a design demonstration based on the structural strength of the stack. We then discuss how to obtain the optimal clamping load for a given PEMFC stack according to the requirements of the interface contact resistance and permeability of the gas diffusion layer. Finally, we discuss the effects of the equivalent stiffness of the spring washer on the structure thermal stress.

A high efficient assembly technique for large proton exchange membrane fuel cell (PEMFC) stacks is proposed to obtain the optimal clamping load. The stack system is considered as a mechanical equivalent stiffness model consisting of numerous elastic elements (springs) in either series or parallel connections. We first propose an equivalent stiffness model for a single PEM fuel cell, and then develop an equivalent stiffness model for a large PEMFC stack. Based on the equivalent stiffness model, we discuss the effects of the structural parameters and temperature on the internal stress of the components and the contact resistance at the contact interfaces, and show how to determine the assembly parameters of a large fuel cell stack using the equivalent stiffness model. Finally, a three-dimensional finite element analysis (FEA) for a single PEMFC is compared with what the equivalent stiffness model predicts. It is found that the presented model gives very good prediction accuracy for the component stiffness and the clamping load.