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Fatigue analysis is of great significance for thin-walled structures in the spacecraft industry to ensure their service reliability during operation. Due to the complex loadings of thin-walled structures under thermal–structural–acoustic coupling conditions, the calculation cost of finite element (FE) simulations is relatively expensive. To improve the computational efficiency of dynamic reliability analysis on thin-walled structures to within acceptable accuracy, a novel probabilistic approach named DC-ILSSVR was developed, in which the rotation matrix optimization (RMO) method was used to initially search for the model parameters of least squares support vector regression (LS-SVR). The distributed collaborative (DC) strategy was then introduced to enhance the efficiency of a component suffering from multiple failure modes. Moreover, a numerical example with respect to thin-walled structures was used to validate the proposed method. The results showed that RMO performed on LS-SVR model parameters provided competitive prediction accuracy, and hence the reliability analysis efficiency of thin-walled pipe was significantly improved. [ABSTRACT FROM AUTHOR]

Since their debut in 2012, triboelectric nanogenerators (TENGs) have attained high performance in terms of both energy density and instantaneous conversion, reaching up to 500 W m−2 and 85%, respectively, synchronous with multiple energy sources and hybridized designs. Here, a comprehensive review of the design guidelines of TENGs, their performance, and their designs in the context of Internet of Things (IoT) applications is presented. The development stages of TENGs in large‐scale self‐powered systems and technological applications enabled by harvesting energy from water waves or wind energy sources are also reviewed. This self‐powered capability is essential considering that IoT applications should be capable of operation anywhere and anytime, supported by a network of energy harvesting systems in arbitrary environments. In addition, this review paper investigates the development of self‐charging power units (SCPUs), which can be realized by pairing TENGs with energy storage devices, such as batteries and capacitors. Consequently, different designs of power management circuits, supercapacitors, and batteries that can be integrated with TENG devices are also reviewed. Finally, the significant factors that need to be addressed when designing and optimizing TENG‐based systems for energy harvesting and self‐powered sensing applications are discussed. [ABSTRACT FROM AUTHOR]

Ex vivo heart perfusion has been shown to be an effective means of facilitating the resuscitation and assessment of donor hearts for cardiac transplantation. Over the last ten years however, only a few ex vivo perfusion systems have been developed for this application. While results have been promising, a system capable of facilitating multiple perfusion strategies on the same platform has not yet been realized. In this paper, the design, development and testing of a novel and modular ex vivo perfusion system is described. The system is capable of operating in three unique primary modes: the traditional Langendorff Mode, Pump-Supported Working-Mode, and Passive Afterload Working-Mode. In each mode, physiological hemodynamic parameters can be produced by managing perfusion settings. To evaluate heart viability, six experiments were conducted using porcine hearts and measuring several parameters including: pH, aortic pressure, lactate metabolism, coronary vascular resistance (CVR), and myocardial oxygen consumption. Pressure-volume relationship measurements were used to assess left ventricular contractility in each Working Mode. Hemodynamic and metabolic conditions remained stable and consistent across 4 h of ex vivo heart perfusion on the ex vivo perfusion system, validating the system as a viable platform for future development of novel preservation and assessment strategies. [ABSTRACT FROM AUTHOR]

In this paper, free vibrations of cylindrical nanoshells made of nanoporous metal foam are investigated for the first time. Based on the modified couple stress theory and Love's thin shell theory, the governing equations of the present system are derived by using Hamilton's principle. Two types of nanoporosity distribution are considered in the construction of the nanoporous shells. Then, the Navier method and Galerkin method are utilized to solve natural frequencies of the nanoporous shells under different boundary conditions. Afterwards, a detailed parametric study is conducted. Results show that the nanoporosity type, the material length scale parameter, the porosity coefficient, the length-to-radius ratio, and the radius-to-thickness ratio play important role on the free vibrations of nanoporous shells. To check the validity of the present analysis, the results are compared with those in previous studies for the special cases. [ABSTRACT FROM AUTHOR]

Abstract In the present work, nonlinear dynamics of fluid-conveying functionally graded material (FGM) sandwich nanoshells is investigated. In order to describe the large-amplitude motion, the von Kármán nonlinear geometrical relations are taken into account. Compressibility and viscidity of the fluid are neglected, and the velocity potential and Bernoulli's equation are used to describe the fluid pressure acting on the nanoshells. Based on the classical shell theory and incorporating the surface stress effect, the governing equations are derived by using Hamilton's principle. After that, the Galerkin method is used to discretize the equation of motion, resulting in a set of ordinary differential equations with respect to time. The ordinary differential equations are solved analytically by utilizing the method of multiple scales. Results show that the surface stress plays important roles on the nonlinear vibration characteristics of fluid-conveying FGM sandwich thin-walled nanoshells. Furthermore, the fluid speed, the power-law index, the fluid mass density, the core thickness and the initial surface tension can also influence the vibration characteristics of fluid-conveying FGM sandwich nanoshells. Highlights • A fluid-conveying functionally graded sandwich nanoshell model is developed. • Surface stress influence is considered in the present analysis. • Thin shell theory is employed to model the fluid-conveying nanotube. • Nonlinear vibration of fluid-conveying FGM sandwich nanoshells is studied analytically. [ABSTRACT FROM AUTHOR]

Abstract This paper performs nonlinear vibration analysis of metal foam circular cylindrical shells reinforced with graphene platelets. An improved Donnell nonlinear shell theory is employed to formulate the present model. The graphene platelet reinforced material properties are evaluated by the Halpin–Tsai equation. Different types of porosity and graphene platelet (GPL) distribution are taken into account. Governing equations are derived via Hamilton's principle and then they are transformed to ordinary differential equations using the Galerkin method. Afterwards, nonlinear frequencies of the system are solved by using the multiple scale method. Our findings demonstrate that GPL reinforced metal foam (GPLRMF) shells exhibit hardening-spring vibration characteristics. The nonlinear to linear frequency ratio of the shell closely relates to the porosity distributions and GPL patterns. The effect of geometrical size of graphene platelets on nonlinear vibration characteristics of GPLRMF cylindrical shells is also highlighted. [ABSTRACT FROM AUTHOR]

Thin cylindrical shells are commonly employed to connect adjacent disks in large rotating machinery. The vibration characteristics of coupled cylindrical shell and annular plate components have a significant influence on the rotor dynamics. This paper provides a general approach for the vibration analysis of a rotating cylindrical shell coupled with an annular plate. The Sanders shell theory and Mindlin plate theory are employed to calculate the strain energy of the shell and plate, respectively. The Coriolis and centrifugal effects due to the rotation are taken into account. The artificial spring technique is adopted to simulate the coupling and boundary conditions. By taking Chebyshev polynomials as the admissible functions, the Rayleigh–Ritz method is employed to derive the motion equations for the rotating shell-plate combination. The approach proposed is validated by comparing with the available results in literature and finite element analysis results. The traveling wave motion of the coupled shell and plate structure is investigated. The effects of the geometric parameters and the boundary and coupling conditions on the vibration behavior of the coupled structure are evaluated. The present approach can not only evaluate free vibrations of coupled shell and plate structures, but also be extended to vibration analysis of disk–drum rotors involving cylindrical shells. [ABSTRACT FROM AUTHOR]

This paper presents the modeling and experimental parametric study of a nonlinear multi-frequency broad bandwidth piezoelectric vibration-based energy harvester. The proposed harvester consists of a tri-leg compliant orthoplanar spring (COPS) and multiple masses with piezoelectric plates attached at three different locations. The vibration modes, resonant frequencies, and strain distributions are studied using the finite element analysis. The prototype is manufactured and experimentally investigated to study the effect of single as well as multiple light-weight masses on the bandwidth. The dynamic behavior of the harvester with a mass at the center is modeled numerically and characterized experimentally. The simulation and experimental results are in good agreement. A wide bandwidth with three close nonlinear vibration modes is observed during the experiments when four masses are added to the proposed harvester. The current generator with four masses shows a significant performance improvement with multiple nonlinear peaks under both forward and reverse frequency sweeps. [ABSTRACT FROM AUTHOR]

In this paper, the free vibration characteristics of cylindrical shells with arbitrary boundary conditions are investigated. The Sanders shell theory is used to calculate the elastic strain energy. Artificial springs are implemented at the ends of the shells to represent the arbitrary boundary conditions. The shell displacements are expanded by three different sets of formulations, namely, the modified Fourier series, the Orthogonal polynomials, and the Chebyshev polynomials. A unified solution for the three different types of expansion functions is developed using the Rayleigh-Ritz method. The unified solution is validated by comparing with the available results in the literature. The accuracy, convergence rate, and computational efficiency of the three expansion functions are compared. Based on the comparison studies, the Chebyshev polynomials of high computational efficiency are selected to investigate the influence of boundary conditions on the free vibration characteristics of cylindrical shells. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting technology is regarded as a remedy to the short-life battery issue in low-power electronic devices, and has been extensively studied in the past two decades. Although a variety of new structures and mechanisms have been proposed for piezoelectric energy harvesters (PEHs), there is not much progress made on the piezoelectric materials that play a determinant role in PEHs performance. Most energy harvesters are still constructed with lead zirconate titanate (PZT). Recently, the new-generation piezoelectric materials PMN-PT and PZN-PT single crystals are proposed and start to be used in transducers. Their electromechanical coupling factor ( k 33 ) is over 90%, and the piezoelectric coefficient ( d 33 ) can reach three times of that of PZT. This study characterizes the PMN-PT and PZN-PT single crystals used in energy harvesters, compared with the polycrystalline PZT, in terms of charging capacitors. Systematic discussions are presented on the voltage, power and energy responses, as well as the reverse coupling effect on the mechanical response and the self-discharge effect of capacitors. Furthermore, a self-powered synchronized switch harvesting on inductor (SSHI) circuit is constructed and tested with the new single-crystal based energy harvesters. Experiments indicate that PMN-PT and PZN-PT can significantly boost the charging capability of energy harvesters, and that performance can be further enhanced by the SSHI circuit. [ABSTRACT FROM AUTHOR]

A miniature-positioning device with a large stroke motion has attracted more and more attentions in these years because of the intensive development in precision engineering. In this paper, we have achieved the large stroke actuating and the high precision positioning, as well as realized a multi-degree-of-freedom in-plane motion using the developed Galfenol impact drive mechanism (IDM) actuator. In order to enhance the system robustness, two pieces of U-shape Galfenol (iron–gallium alloy) have been employed as the driving elements with a bias magnetic field contributed by a permanent magnet to generate the swing motion that amplifies the propelling inertia force. The current amplitude modulation has been applied in the precision positioning of the actuator under the quasi-static condition because of the motion step-size fineness. The results show that the actuator is able to achieve a sub-micrometer positioning accuracy that has reached the measurement limit of our setup. Meanwhile, the frequency modulation method has been explored in the large stroke actuation with a high motion speed. We have found out that this design is capable of achieving an accurate positioning without the frequency modulation because of the intrinsic fine step-size of the actuator. In addition, a rectangular in-plane motion has been realized with the image-based control for the multi-degree-of-freedom positioning. The actuator has an inductive impedance with a resistance of 3.796 Ω and an inductance of 0.4697 mH. Under the present driving ratings, the power consumption is smaller than 1.97 W while the reactive power can be ignored. Moreover, the experimental load analysis indicates that the design can achieve a maximum carry-load-to-weight ratio of 6.5. [ABSTRACT FROM AUTHOR]

This paper presents modeling and design of an active structural acoustic control (ASAC) system for controlling the low frequency sound field transmitted through an aircraft cabin window. The system uses stacked piezoelectric elements arranged in a manner to generate out-of-plane actuation point forces acting on the window panel boundaries. A theoretical vibro-acoustic model for an active quadruple-panel system is developed to characterize the dynamic behavior of the system and achieve a good understanding of the active control performance and the physical phenomena of the sound transmission loss (STL) characteristics. The quadruple-panel system represents the passenger window design used in some classes of modern aircraft with an exterior double pane of Plexiglas, an interior dust cover pane and a glazed dimmable pane, all separated by thin air cavities. The STL characteristics of identical pane window configurations with different piezoelectric actuator sets are analyzed. A parametric study describes the influence of important active parameters, such as the input voltage, number and location of the actuator elements, on the STL is investigated. In addition, a mathematical model for obtaining the optimal input voltage is developed to improve the acoustic attenuation capability of the control system. In general, the achieved results indicate that the proposed ASAC design offers a considerable improvement in the passive sound loss performance of cabin window design without significant effects, such as weight increase, on the original design. Also, the results show that the acoustic control of the active model with piezoelectric actuators bonded to the dust cover pane generates high structural vibrations in the radiating panel (dust cover) and an increase in sound power radiation. High active acoustic attenuation can be achieved by designing the ASAC system to apply active control forces on the inner Plexiglas panel or dimmable panel by installing the actuators on the boundaries of one of the two panels. In some cases, increasing the actuator numbers in the structure advances the active control performance by controlling more structural modes; however, this decreases the STL of the passive control system because of the increase in structure-borne sound transmission paths of the stiffer piezoelectric actuators. [ABSTRACT FROM AUTHOR]

Vibration energy harvesting has been a research subject of growing interest over the past few years, and is envisaged as a remedy to the unsatisfactory battery issue in low-power electronic devices. In this study, we propose a new magnetostrictive transducer to harvest energy from finger tapping. Galfenol is selected as the transducing material due to its high piezomagnetic coefficient and excellent machinability. To effectively harness energy in low-frequency conditions, we develop a frequency up-conversion mechanism that succeeds in converting vibration below 10 Hz from finger tapping up to the system's resonance of a few hundred Hz. Furthermore, multiple impacts are induced in each working cycle deliberately to boost the efficiency. A comprehensive model is built and solved to analyze the mechanical-magnetic-electrical coupling system. Based on the model, we elucidate the design criteria for high-performance magnetostrictive transducers. A prototype is fabricated with a Galfenol beam of 0.5 × 5 × 25 mm 3 and, under finger tapping, it generates 5.3 mW power and instantaneously lights up 10 commercial LEDs and a numeric LCD. [ABSTRACT FROM AUTHOR]

The article reports on the study conducted by the Department of Mechanical and Industrial Engineering of the University of Toronto regarding steering control of commercial three-axle vehicle in Toronto, Ontorio. Researchers found that steering control laws of commercial three-axle vehicle can be improved by adding steering of rear wheels. When they experimented it on combined roads, they proposed the optimization of design parameters because of the cornering stiffness of front, middle and rear wheels and outer disturbance which are considered as uncertain parameters varying over a limited range.

This paper presents an optimization methodology in reliability design of a prismatic cantilever beam with a point load applied at the tip. In this methodology, the constraints consist of probability failures as well as fatigue failure criteria. The first-order second-moment and first-order reliability methods are adopted to assess the probability failure based on the concept of reliability indices. The corresponding fatigue criterion is defined as the crack initiation phase in both stress and strain models, respectively. The elements required for the probabilistic fatigue life calculations are then discussed. In this optimization model, the total weight of the beam is considered as the objective function. However, all geometries, applied loads, and material properties are considered as random variables. The sequential quadratic optimization technique is implemented and a code is developed to solve the nonlinear optimization problem. Results show that using the proposed optimization methodology significantly improves the accuracy of calculation in comparison with using the conventional deterministic analysis. We also conclude that the strain-based fatigue criterion is more realistic than the traditional stress--based analysis. Finally, the Monte Carlo simulation is conducted to validate the results in each case. [ABSTRACT FROM AUTHOR]

In this paper, a fully vibro-acoustic model for sound transmission across a multi-pane aircraft window is developed. The proposed model is efficiently applied for a set of window models to perform extensive theoretical parametric studies. The studied window configurations generally simulate the passenger window designs of modern aircraft classes which have an exterior multi-Plexiglas pane, an interior single acrylic glass pane and a dimmable glass (“smart” glass), all separated by thin air cavities. The sound transmission loss (STL) characteristics of three different models, triple-, quadruple- and quintuple-paned windows identical in size and surface density, are analyzed for improving the acoustic insulation performances. Typical results describing the influence of several system parameters, such as the thicknesses, number and spacing of the window panes, on the transmission loss are then investigated. In addition, a comparison study is carried out to evaluate the acoustic reduction capability of each window model. The STL results show that the higher frequencies sound transmission loss performance can be improved by increasing the number of window panels, however, the low frequency performance is decreased, particularly at the mass–spring resonances. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the multi-pulse global bifurcations and chaotic dynamics for the nonlinear, non-planar oscillations of the parametrically excited viscoelastic moving belt using an extended Melnikov method in the resonant case. Using the Kelvin-type viscoelastic constitutive law and Hamilton''s principle, the equations of motion are derived for the viscoelastic moving belt with the external damping and parametric excitation. Applying the method of multiple scales and Galerkin''s approach to the partial differential governing equation, the four-dimensional averaged equation is obtained for the case of 1:1 internal resonance and primary parametric resonance. From the averaged equations obtained, the theory of normal form is used to derive the explicit expressions of normal form with a double zero and a pair of pure imaginary eigenvalues. Based on the explicit expressions of normal form, the extended Melnikov method is used for the first time to investigate the Shilnikov-type multi-pulse homoclinic bifurcations and chaotic dynamics. The paper demonstrates how to employ the extended Melnikov method to analyze the Shilnikov-type multi-pulse homoclinic bifurcations and chaotic dynamics of high-dimensional nonlinear systems in engineering applications. Numerical simulations show that for the nonlinear non-planar oscillations of the viscoelastic moving belt, the Shilnikov-type multi-pulse chaotic motions can occur. Overall, both theoretical and numerical studies suggest that the chaos for the Smale horseshoe sense in motion exists. [Copyright &y& Elsevier]

Abstract: This paper presents the development of a remotely operated mobile robot system with a hybrid mechanism whereby the locomotion platform and manipulator arm are designed as one entity to support both locomotion and manipulation interchangeably. The mechanical design is briefly described as well as the dynamic simulations used to analyze the robot mobility and functionality. As part of the development, this paper mainly focuses on a new generalized control hardware architecture based on embedded on-board wireless communication network between the robot’s subsystems. This approach results in a modular control hardware architecture since no wire connections are used between the actuators and sensors in each of the mobile robot subsystems and also provides operational fault-tolerance. The effectiveness of this approach is experimentally demonstrated and validated by implementing it in the hybrid mobile robot system. The new control hardware architecture and mechanical design demonstrate the qualitative and quantitative performance improvements of the mobile robot in terms of the new locomotion and manipulation capabilities it provides. Experimental results are presented to demonstrate new operative tasks that the robot was able to accomplish, such as traversing challenging obstacles, and manipulating objects of various capacities; functions often required in various challenging applications, such as search and rescue missions, hazardous site inspections, and planetary explorations. [Copyright &y& Elsevier]

Abstract: A modified finite difference approach to simulate transverse vibrations of an axially moving string is presented. The stress is treated as a new unknown in discretization of the spatial variable. A set of differential-algebraic equations is established based on the discreted governing equation and the constitutive relation. For linear vibrations, a conserved functional is employed to test the algorithm, and the 1, 2, 3, 4-term truncated modal analytical solutions are compared with the numerical solution. For the free nonlinear vibration, a new conserved functional is used to check the algorithm. Effects of the transport speed on the free and forced nonlinear vibrations are numerically investigated. [Copyright &y& Elsevier]

A new and efficient computation of the normal forms is developed in this paper for high dimensional non-linear systems, and the computational method is applied to non-planar non-linear oscillations of a cantilever beam. The method developed here has the advantage of directly calculating the coefficients of the normal forms and the associated near identity non-linear transformations for three different cases, that is, (1) the case of two pairs of pure imaginary eigenvalues; (2) the case of one non-semisimple double zero and a pair of pure imaginary eigenvalues; and (3) the case of two non-semisimple double zero eigenvalues. The final partial differential equations of various resonant cases appear in a canonical form whose solutions can be conveniently obtained using polynomial equations. With the aid of the Maple software, a symbolic program for computing the normal forms of high dimensional non-linear systems is given. Comparing the method developed here with other methods of computing the normal forms, it is understood that we may, respectively, obtain the normal forms, the coefficients of the normal forms and the associated near identity non-linear transformations for three resonant cases by using a same main Maple symbolic program. Moreover, the method is easy to apply to engineering problems. The normal forms of the averaged equations and their coefficients for non-planar non-linear oscillations of the cantilever beam under combined parametric and forcing excitations are calculated for two resonant cases. [Copyright &y& Elsevier]

Establishment of damage accumulation models for reflecting the combined damage mechanism on the fatigue behavior of aero-engine turbine blades is crucial for their safety. In this work, a novel combined high and low cycle fatigue (CCF) life prediction methodology is presented as a basis of that to consider the interaction between low and high cycle fatigues. Accordingly, a dynamic reliability model is proposed to study the operational reliability of turbine blades under CCF loadings. Moreover, experimental data of materials along with the collected field data from the actual turbine blades are applied to validate the CCF life prediction model and the dynamic reliability model. The validation of the results is conducted by a comparison analysis, which indicates that the proposed life prediction method yields better accuracy, while the dynamic reliability model is proved to be more in line with the outcomes derived by the Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

In this study, the thermo-hygro-mechanical bending and vibration of functionally graded material (FGM) microbeams with microporosity defect are investigated. The mathematical model of the system is developed by using the sinusoidal beam theory and the modified couple stress theory. Based on Hamilton's principle, the governing equations and boundary conditions of imperfect FGM microbeams are derived. Then, Navier's method is utilized to calculate the deflections and natural frequencies of the system. Analytical results are presented to illustrate the effects of the microporosity volume fraction, the microporosity distribution type, the power-law index, the temperature and the moisture on the static bending and free vibration of imperfect FGM microbeams. [ABSTRACT FROM AUTHOR]

This paper reports a novel hybridized flexible electromagnetic–triboelectric generator for vibration/deflection monitoring as it is implemented in a cantilever or clamped-clamped configuration. The proposed self-powered sensor operates based on the concepts of electromagnetism and triboelectricity. The fabricated device consists of a stack of magnets and coils, a flexible tube as the main body, and also, highly flexible, mechanically and thermally durable, and cost-effective polymeric materials. The configuration of the electromagnetic component is optimized based on the magnetization direction of the utilized magnets. The device can effectively convert the shear force and bending moment to electrical voltage through the hybridized system with exerting an external force. The performance of the self-powered sensor is investigated for different cases including a single stack and also a double stack of magnetic components. The design of the triboelectric component of the device is based on the vertical contact separation mode. Results of the paper show how the change of configuration of the magnetic components alters the electrical output of the sensor. A detailed experimental analysis is provided to show the capability of the device under different excitation conditions for both triboelectric nanogenerator (TENG) and electromagnetic generator (EMG) components of the sensor. As the experimental analysis shows, the proposed self-powered system has the potential to be utilized for knee rehabilitation, as it shows explicit results under periodical bending load with different frequencies and amplitudes of excitation. [ABSTRACT FROM AUTHOR]

We proposed a nonlinear multi-mode tri-leg compliant orthoplanar spring piezoelectric vibration-based energy harvester (COPS-PVEH), which provided the improved performance using a pure geometric nonlinearity, in terms of a wide bandwidth, and a high-voltage output in forward and reverse sweeps. This paper presents an application of magnetic force interaction to further enhance the performance of the COPS-PVEH. A repulsive magnetic force is added to the spring to change the harvester system’s stiffness. A lumped parameter model is derived and analytically solved for the designed harvester with a magnetic coupling. The experiments are carried out by adding a moving magnet at the center of the spring and a pair of fixed magnets at the top and bottom sides of the harvester. Both experimental data and simulation results show the benefits brought through the dynamics of a magnetic oscillator. In an experiment by adding magnetic force, a slight increase is observed in the operating bandwidth and a 10% increase in the magnitude of voltage output is achieved at the same excitation level. The magnetic interaction on the COPS-PVEH with an addition of multiple masses has also achieved an increase in voltage output and bandwidth. In addition, the gap between the three vibration modes has been reduced. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting is envisioned as an ideal complement to batteries for long-life operation of wireless or remote electronic devices. Most piezoelectric energy harvesters (PEHs) utilize piezoelectric plates or discs as the energy transducing elements, and they cannot generate enough power for most potential applications. In this study, we explore a new way of using arc-shaped piezoelectric patches as the core transducing elements in energy harvesters to improve their performance. An analytical model is developed via the Castigliano’s theorem to elucidate the low stiffness characteristic of the arc-shaped structure. A finite element analysis is conducted, and the results indicate that high and evenly-distributed stress can be easily induced in the arc-shaped PEHs. Prototypes are fabricated with arc-shaped piezoelectric elements and flat piezoelectric plates, respectively, and tested under the same conditions. The experimental data demonstrate that the arc-shaped PEHs are capable of generating 2.55–4.25 times as much power as the equivalent flat-plate PEHs. This study lays the foundation to enhance energy harvester performance by utilizing arc-shaped piezoelectric structures. [ABSTRACT FROM AUTHOR]

Abstract: The goal of cardiac tissue engineering is to restore function to the damaged myocardium with regenerative constructs. Human embryonic stem cell–derived cardiomyocytes (hESC-CMs) can produce viable, contractile, three-dimensional grafts that function in vivo. We sought to enhance the viability and functional maturation of cardiac tissue constructs by cyclical stretch. hESC-CMs seeded onto gelatin-based scaffolds underwent cyclical stretching. Histological analysis demonstrated a greater proportion of cardiac troponin T–expressing cells in stretched than non-stretched constructs, and flow sorting demonstrated a higher proportion of cardiomyocytes. Ultrastructural assessment showed that cells in stretched constructs had a more mature phenotype, characterized by greater cell elongation, increased gap junction expression, and better contractile elements. Real-time PCR revealed enhanced mRNA expression of genes associated with cardiac maturation as well as genes encoding cardiac ion channels. Calcium imaging confirmed that stretched constructs contracted more frequently, with shorter calcium cycle duration. Epicardial implantation of constructs onto ischemic rat hearts demonstrated the feasibility of this platform, with enhanced survival and engraftment of transplanted cells in the stretched constructs. This uniaxial stretching system may serve as a platform for the production of cardiac tissue-engineered constructs for translational applications. [Copyright &y& Elsevier]

• A simple and efficient CCF life prediction model is proposed to calculate the approximate threshold damage. • Fatigue tests of specimen are conducted for investigating the threshold damage. • Framework for estimating fatigue life involving threshold damage value under CCF loadings is presented by checking the threshold damage against current HCF damage. • The threshold damage-based model provides more accuracy predictions than others, especially near the level of threshold damage value. Life prediction based on the damage mechanics of aero-engine turbine blades is crucial for performing their strength design and ensuring the operational reliability under combined high and low cycle fatigue (CCF) loadings. In view of this, a simple and efficient life prediction method is developed to consider the interaction of high cycle fatigue (HCF) and low cycle fatigue (LCF) without any additional material constants, and as a basis of that a new nonlinear damage accumulation model is proposed by introducing threshold damage of the component related to material type and current HCF damage. In order to validate the presented methodology, model predictions were compared with the experimental data sets of turbine blades and its alloy materials. The predicted results indicate that the simple life prediction model is capable of estimating the fatigue life quickly with an acceptable accuracy in contrast to other four existing ones. Moreover, the threshold damage-based method provides the higher prediction accuracy than others due to improved HCF damage determined by the damage threshold. [ABSTRACT FROM AUTHOR]

Purpose: Windkessel impedance analysis has proven to be an effective technique for instituting artificial afterload on ex situ hearts. Traditional fixed parameter afterload modules, however, are unable to handle the changing contractile conditions associated with prolonged ex situ heart perfusion. In this paper, an adjustable afterload module is described comprising of three fully adjustable sub-components: a systemic resistor, a proximal resistor and a compliance chamber., Methods: Using a centrifugal pump, the systemic resistor and compliance chamber were subjected to testing across their operating ranges, whereby the predictability of resistance and compliance values was evaluated. The components were then assembled, and the full module tested on three separate porcine hearts perfused for 6 h with success defined by the ability to maintain physiological systolic and diastolic aortic pressures across flow rate variability., Results: For both the systemic resistor and compliance chamber, experimental measurements agreed with their theoretical equivalents, with coefficients of determination of 0.99 and 0.97 for the systemic resistor and compliance chamber, respectively. During ex situ perfusion, overall 95% confidence intervals demonstrate that physiological systolic (95-96.21 mmHg) and diastolic (26.8-28.8 mmHg) pressures were successfully maintained, despite large variability in aortic flow. Left ventricular contractile parameters, were found to be in line with those in previous studies, suggesting the afterload module has no detrimental impact on functional preservation., Conclusions: We conclude that due to the demonstrable control of our afterload module, we can maintain physiological aortic pressures in a passive afterload working mode across prolonged perfusion periods, enabling effective perfusion regardless of contractile performance.

This article presents a primed left ventricle heart perfusion method to generate physiologic aortic pressure (AoP) and perform functional assessment. Isolated hearts of male Yorkshire pigs were used to study the hemodynamic behaviors of AoPs generated in the primed left ventricle heart perfusion (n = 6) and conventional (zero-loaded left ventricle) Langendorff perfusion (n = 6). The measurement results show that left ventricular pressure generated in the primed left ventricle heart perfusion is a determinant of physiologic AoP (i.e. systolic and diastolic pressures within physiologic range). The aortic pulse pressure (systolic pressure = 124.5 ± 1.7 mm Hg, diastolic pressure = 87.8 ± 0.9 mm Hg, aortic pulse pressure = 36.7 ± 2.6 mm Hg) from the primed left ventricle heart perfusion represents close match with the in vivo physiologic data. The volume in the left ventricle remains constant throughout the primed left ventricle heart perfusion, which allows us to perform isovolumetric left ventricular pressure measurement in ex vivo heart perfusion (EVHP). Left ventricular contractility measurements (maximum and minimum rates of left ventricular pressure change) were derived for cardiac assessment. In summary, the proposed primed left ventricle heart perfusion method is able to create physiologic AoP and enables left ventricular functional assessment in EVHP in porcine hearts.

Bio-inspired technologies have remarkable potential for energy harvesting from clean and sustainable energy sources. Inspired by the hummingbird-wing structure, we propose a shape-adaptive, lightweight triboelectric nanogenerator (TENG) designed to exploit the unique flutter mechanics of the hummingbird for small-scale wind energy harvesting. The flutter is confined between two surfaces for contact electrification upon oscillation. We investigate the flutter mechanics on multiple contact surfaces with several free-standing and lightweight electrification designs. The flutter driven-TENGs are deposited on simplified wing designs to match the electrical performance with variations in wind speed. The hummingbird TENG (H-TENG) device weighed 10 g, making it one of the lightest TENG harvesters in the literature. With a six TENG network, the hybrid design attained a 1.5 W m -2 peak electrical output at 7.5 m/s wind speed with an approximately linear increase in charge rate with the increased number of TENG harvesters. We demonstrate the ability of the H-TENG networks to operate Internet of Things (IoT) devices from sustainable and renewable energy sources.