The acoustic scattering by a submerged spherical elastic shell near a free surface, and insonified by plane waves at arbitrary angles of incidence is analyzed in an exact fashion using the classical separation of variables technique. To satisfy the boundary conditions at the free surface as well as on the surface of the spherical elastic shell, the mathematical problem is formulated using the image method. The scattering wave fields are expanded in terms of the classical modal series of spherical wave functions utilizing the translational addition theorem. Quite similar to the problem of scattering by multiple spheres, the numerical computation of the scattered wave pressure involves the solution of an ill-conditioned complex matrix system the size of which depends on how many terms of the modal series are required for convergence. This in turn depends on the value of the frequency, and the proximity of the spherical elastic shell to the free surface. The ill-conditioned matrix equation is solved using the Gauss-Seidel iteration method and Twersky’s method of successive iteration double checking each other. Backscattered echoes from the spherical elastic shell are extensively calculated and displayed. The result also demonstrates that the large amplitude low frequency resonances of the echoes of the submerged elastic shell shift upward with proximity to the free surface. This can be attributed to the decrease of added mass for the shell vibration.

Constrained layer damping can be an effective method to control transverse vibration of thin structures. The commonl used equation of motion governing the behavior of constrained layer damped Euler-Bernoulli beams, originally derived b Mead and Markus (1969), does not account for the relative transverse motion between the constraining layer and the base beam. When a soft viscoelastic layer or a stiff constraining layer is used, this relative transverse motion may become significant. To account for this motion, Miles and Reinhall (1986) developed a model that included the thickness deformation of the viscoelastic layer. The purpose of this paper is to demonstrate the existence of the thickness deformation through experiments and to investigate the validity of the Miles and Reinhall model. Experimental results show that the thickness deformation is significant in the high frequency range, and that the inclusion of the thickness deformation improves the accuracy of the analytical model.

Stamping is employed in a wide range of applications including household appliances, automobiles, vessel, and aerospace. Due to the discrete flow energy-intensive processes and dynamic energy changes in stamping production, it has great potential for energy savings. There still lacks an effective method to monitor and analyze the energy efficiency in stamping workshop. To this end, this paper proposes an energy efficiency monitoring and analysis system based on Internet of Things (IoT). The characteristics in stamping workshop are first analyzed, the energy consumption is decomposed, and the makespan is quantified. Besides, energy efficiency indicators of energy efficiency in the press machine, specific energy consumption in the part, and energy efficiency in the workshop are analyzed and defined. Then the detailed information about the energy efficiency monitoring and analysis system as data acquisition, data transmission, data storage, data analysis, and display based on IoT is presented. Finally, a forklift stamping workshop was investigated to validate the effectiveness of the proposed method. The interface and the results of the data analysis showed that the proposed system can monitor the energy efficiency in the stamping workshop comprehensively. Furthermore, potential opportunities for energy consumption reduction and efficient production can be identified.

It is experimentally confirmed that the response speed of photo-induced deformation lags far behind the photovoltage and it is difficult to control the magnitude of the photo-induced electric field in PLZT ceramic due to the serious residual photovoltage. The primary purpose of this article is to control the photovoltage of PLZT for a photovoltaic-electrostatic driven servo system proposed in this paper. The control equations of photovoltage for photovoltaic-electrostatic driven servo system are derived based on the mathematical model of PLZT with coupled multi-physics fields. Parameters of photovoltage of PLZT ceramic during the illumination phase and light off phase are identified through the static experiment. Based on simple on-off control strategy, real-time switching the UV light via an optical shutter is adopted to achieve the desired photovoltage. Then, the closed-loop photovoltage control experiments for photovoltaic-electrostatic driven servo system based on PLZT ceramic are carried out. The experimental results show that the photovoltage can be successfully controlled at the target degree by switching the UV light with an optical shutter. The control strategy can be applied in the photovoltaic-electrostatic driven servo system to achieve the target degree of angular or displacement deflection.

PLZT actuators taken as one type of photo-deformable actuators have been widely applied for micro-driven systems and active vibration control of photostrictive laminated flexible structures. However, the slow response of photodeformation of single patch PLZT actuator greatly affects its application. In this paper, the main factors for the slow response of the PLZT actuator are investigated using experimental method. The increasing temperature during light on state and the residual photovoltage and photodeformation during light off state are considered to be the main factors for the slow response of the PLZT actuator. To improve the driving performance of PLZT ceramic, some effective measures through reducing the effect of increasing temperature and eliminating residual photovoltage and photodeformation are proposed and experimentally validated in this paper. Considering the effective measures proposed in this paper, two novel optical driving mechanisms based on PLZT bimorph and multi-patches combination for driving source are proposed.

Lead lanthanum zirconate titanate (PLZT) ceramic has draw significant attention for its promising application as a wireless photo-driven micro actuator. However, the residual photovoltage and photo-induced strain have a great influence on the response speed of photostrictive effect and prevent PLZT ceramic from using as a micro actuator, especially in high frequency dynamic field. In this paper, the coupled opto-piezo-thermo-elastic fields in PLZT ceramics were analyzed, based on which the mathematical equations of temperature, voltage and deformation during the light switched off phase were established. After that, the photostrictive static experiments were performed to validate the mathematical equations proposed.

This paper addresses the problem of motion tracking of human skeleton system using non-invasive vision based sensors. The proposed approach combines synergistic paradigms of image processing, kinematics of rigid bodies and Extended Kalman Filtering scheme to estimate the motion of a human limb system. This approach solely depends on the measurement obtained from the vision sensors without involving any wearable or inertial sensors to measure the motion parameters. In this paper we propose fusion of two filtering schemes — the optical flow equations applied to raw images obtained from the Microsoft Kinect and extended Kalman filter for human skeleton considered as a system of kinematic linkages. The strategy proposed in this paper yields near optimal results as is demonstrated with the help of experiments performed using the Microsoft Kinect sensor and compared using accurate tracks obtained from 24-Camera Optitrack motion capture system.

Photodeformable materials can transform light energy into mechanical energy without electromagnetic noise. Lanthanum modified lead zirconate titanate (PLZT) ceramics are one kind of photodeformable materials. Since light is an environment-friendly, remotely controllable stimulus, the actuation based on PLZT ceramics is green driven and non-contact driven, which has many advantages in micro-driven and structure vibration control. In this paper, light-driven and active control of paraboloidal thin shells laminated with PLZT actuators is studied. Based on the new photostrictive mathematical model of PLZT and mode shape functions obtained using membrane theory, the control equations of photostrictive laminated paraboloidal thin shells are deduced. Active control scheme for the photostrictive laminated thin shell structure is obtained through combining the illumination scheme and the control algorithm. Active vibration control simulation analysis for the two modes of the paraboloidal shell with two actuator configurations is carried out using Newmark- β method. Simulation results show that the control scheme is suitable and effective for the photostrictive laminated paraboloidal thin shell, and the control effect is affected by the actuator configuration.

Lead lanthanum zirconate titanate (PLZT) ceramics can transform the light energy into the mechanical energy without electric lead wires. The optical and direct drive based on PLZT ceramics, which is also green drive and non-contact drive, has many advantages in micro-driven and structure vibration control. However, the response of the photo-deformation is far slower than the photovoltage and the photocurrent, and the hysteresis and nonlinear of the photo-deformation prevent PLZT from applying to actuation and active structure vibration control. In this paper, a novel mathematical model based on the photovoltaic effect and the viscoelastic effect was established. The novel mathematical model was validated through experiments. According to the new expression of photo-deformation, the viscoelastic effect leading to the hysteresis and nonlinear of the photostrictive response was analyzed.

Mesenchymal stem cells (MSCs) are a multi-potential cell type that can be induced to differentiate to a variety of tissue-specific cell phenotypes, including cartilage (chondrogenesis) and bone (osteogenesis). Given this multi-potentiality, MSCs are a promising cell source for exploring developmental paradigms and for tissue engineering (TE) applications. For cartilage formation assays, MSCs are collected in high-density pellets and treated with specific biofactors, including TGF-β superfamily members and dexamethasone in a chemically defined medium (CM) [1]. During chondrogenesis, extracellular matrix (ECM) rich in glycosaminoglycan (GAG) and type II collagen is synthesized. While MSC chondrogenesis is well-characterized using existing protocols, the effect of alternative biofactors, their doses and combinations requires laborious combinatorial studies [2]. High-throughput screening (HTS) overcomes this limitation through the simultaneous layout and query of a large number of conditions within a single plate. HTS depends on the use of precise robotic liquid handling systems and on the development of sensitive, validated, and readily quantifiable assays. In a recent study, we optimized cell culture and assay procedures for HTS by minimizing cell number, handling and culture duration [3]. We successfully reduced the time scale from 21 to 7 days and the number of cells required from 225K to 30K cells per pellet. Further, we developed a novel in-well digestion protocol to enable high-throughput analysis and minimize handling. In this study, we have further streamlined these assays for HTS by providing a rapid and robotic approach for layout, culture, and analysis of ECM deposition using ‘micro’ MSC pellets (10K cells per pellet) in a 384-well format. Furthermore, we have carried out an initial screen of the NINDS small molecule library and demonstrated the feasibility of this technology for use in HTS of chondrogenesis.

Articular cartilage lines the surfaces of joints and functions to absorb shock and distribute load. To date, few strategies exist for restoring damaged articular surfaces; therefore, cartilage tissue engineering (TE) has emerged as a means to generate functional replacement tissues. To optimize growth and maturation of TE constructs, various methodologies have been employed, including 3D culture, coupled with mechanical stimulation [1] and growth factor supplementation [2]. Recently, studies have shown that temporal application of TGF-β3 enhances the compressive properties and GAG content of chondrocyte-laden hydrogels to near-native levels after the removal of this morphogen [3, 4]. However, as chondrocytes may prove impractical for clinical use, mesenchymal stem cells (MSCs) have been increasingly utilized in cartilage TE. While MSCs are able to undergo chondrogenesis and deposit cartilaginous extracellular matrix (ECM), they have not demonstrated functional parity with chondrocytes [5]. One recent study showed MSCs were able to maintain a chondrocytic phenotype after brief exposure of TGF-β3, though mechanical and biochemical properties were not assessed [6]. In this study, we evaluated these properties in chondrocyte- and MSC-laden hydrogels with transient exposure of TGF-β3 in a chemically defined medium. In addition, we explored the effects of varying seeding density in MSC-laden constructs on functional properties. We hypothesized that transient application of TGF-β3 would improve functional properties of MSC-laden constructs in a seeding density-dependent manner, and that these changes would be marked by differences in cartilaginous gene expression, particularly of enzymes involved in proteoglycan synthesis.

Degeneration of cartilage resulting from trauma or disease processes is an increasingly prevalent problem in the aging population. Intrinsic repair of cartilage is limited and few methodologies exist, short of prosthetic replacement, for restoring damaged articular surfaces. These realities engender a need for new strategies for extrinsic repair. One strategy, tissue engineering, generates replacement cartilage composed of scaffolds and differentiated chondrocytes [1]. In addition to chondrocytes, recent work has demonstrated that mesenchymal stem cells (MSCs) isolated from bone marrow may be induced to take on a chondrocyte-like phenotype [2]. Tissue engineered constructs of either cell type can yield near-native properties (though those derived from MSCs are typically lower) [3]. While such constructs may be surgically implanted to replace areas denuded of cartilage, one factor to consider is that these defect sites exist in an already inflamed joint [4]. In addition, surgical interventions trigger further inflammatory responses, greatest in the area of intervention [5]. Recent literature has shown that pro-inflammatory cytokines, such as interleukin-1beta (IL-1β), instigate catabolic destruction not only of cartilage explants, but also of chondrocyte-based engineered cartilage constructs [6–9]. Still other studies have shown that un-differentiated MSCs themselves may exert an anti-inflammatory effect on their local environment [10–12]. Thus the current study examined the effect of varying doses of IL-1β exposure on both chondrocyte- and MSC-based engineered cartilage constructs to determine the relative sensitivity of neo-cartilage derived from each cell type to cytokine induced degradation.

Articular cartilage provides a low-friction bearing surface for transmitting the forces that arise with joint motion. Because cartilage possesses a limited capacity for repair, trauma or progressive joint disease leads to destruction of the joint surface [1]. Limitations in current repair strategies have increased interest in cartilage tissue engineering (TE), although to date, generating a construct with the mechanical complexity of the native tissue remains a challenge. In our previous long-term free swelling studies, and in other gel systems, the tensile properties of cell-seeded hydrogels remain far lower than those of the native tissue [2–4]. One approach for furthering tissue growth is the application of mechanical signals to engineered constructs. In developing joints, inhibition of mechanical forces results in incomplete cartilage formation [5,6]. Mechanical forces continue to play a vital role in cartilage maturation after birth; physiologic loading remodels the tissue and increases the tensile properties and spurs development of anisotropy [7,8]. In chondrocyte-seeded TE constructs, dynamic axial mechanical stimulation improves compressive properties and biochemical content [9], though the collagen content and tensile and dynamic properties remain low. As the tensile properties of cartilage emerge with load-bearing use, more complete recapitulation of the mechanical environment that arises with motion may further the maturation of engineered constructs. To test this hypothesis, we developed a sliding contact bioreactor mimicking two contacting cartilage layers and show that ECM gene expression is modulated by this loading modality depending on the duration of loading and pre-maturation of the construct.

Compared with the traditional actuators, the photostrictive actuators have huge advantages in applying in the hostile environments. The cantilever structure made of PLZT bimorph is used to increase the mechanical displacement because of the smaller photostrictive displacement of one PLZT patch. However, when one side of the PLZT bimorph was irradiated by the ultraviolet light with wavelength of 365nm, the response of the photodeformation is far slower than the photovoltage and the photocurrent, which prevents it from using in the high-frequency dynamic applications. In this study, a novel mathematical model of PLZT patch based on the photovoltaic effect and viscoelastic effect was proposed. And the tip deflection equation of PLZT bimorph was derived by the linear theory of viscoelasticity and constitutive relations of PLZT. And then the factors influencing the tip deflection were obtained by using the numerical analysis. Simultaneously, the hysteresis phenomenon of PLZT patch was explained.

For the sake of studying dynamic characteristics and the response of dynamic stiffness to driving frequency in metal helical spring, the paper studied on rolling stock spring (helical spring). The paper adopted FEM to establish the finite element model of the spring, calculate out steady-state spring’s response and draw frequency-amplitude characteristic curve of the spring. The results indicate that spring dynamic stiffness is increasing with the increase of driving frequency in general tendency, dynamic stiffness is minimal and smaller than static stiffness corresponding to resonant frequencies and, however, dynamic stiffness is maximal and greater than static stiffness corresponding to anti-resonant frequencies. In order to apply the result in simulation, the paper proposed an equivalent algorithm, compared the calculating result of the equivalent model with one of the spring model and found that the gap between them was very small. So remarkable dynamic characteristic exists in metal helical spring and it is doable to make multi-degree of freedom system be equivalent to continuous spring system.

Mesenchymal stem cells (MSCs) are a multi-potential cell type that can differentiate toward a variety of tissue-specific phenotypes, including cartilage. Given their chondrogenic potential, MSCs are a promising cell source for cartilage tissue engineering (TE). However, while MSCs readily undergo chondrogenesis in 3D culture and deposit a cartilage-like matrix, the mechanical properties of MSC-seeded constructs are greatly inferior to chondrocyte-seeded constructs similarly maintained [1]. To date, optimization strategies for enhancing functional MSC chondrogenesis, including increasing seeding density and transient application of growth factor, have shown limited success [3]. Using microarray analysis, we have recently demonstrated that mis-expression of certain genes, including lubricin, chondromodulin and RGD-CAP, a collagen associated protein, may underlie this disparity in mechanical function [2]. In this study, we examined dynamic compression as an alternative method to enhance MSC differentiation. Previous work using chondrocyte-based constructs have demonstrated that matrix biosynthesis and mechanical properties were improved with the application of cyclic compression [4]. Furthermore, upregulation of lubricin was observed when surface motion was applied to chondrocyte-seeded porous scaffolds [5]. While significant effort has gone toward optimizing loading parameters to direct tissue growth of chondrocyte-based constructs, few studies have examined the effects of mechanical stimulation on MSC-based constructs. Some have demonstrated positive effects on MSC chondrogenesis with application of compressive loading [6, 7], while others have shown that long-term loading may adversely affect the developing mechanical properties of MSC-seeded constructs [8]. In this study, we examined the effects of repeated dynamic compressive loading on MSC chondrogenesis and showed that mechanical properties and gene expression were modulated by this loading modality.

Tendons are dense, fibrous tissues connecting muscle to bone, and their primary function is to transmit muscle forces to the appropriate skeletal elements, thereby enabling movement. In the limb, flexion and extension of the hand (autopod) and wrist are controlled by long tendons that insert into muscles in the arm (zeugopod) [1]. Although tendons are critically important in mediating joint movement, the cellular and molecular events underlying tendon formation remain largely unknown. Using the transcription factor Scleraxis (Scx), which labels all tendon progenitors, we previously showed that in the mouse limb bud, Scx-expressing tendon progenitors are first induced in the mesenchyme underneath the ectoderm at E10.5; at E12.5, progenitors are loosely organized between the cartilage condensations and developing muscles, condensing to form distinct tendons by E13.5 [2]. By E14.5, limb tendon patterning is largely complete, with continued elongation and deposition of matrix from this stage onward.

Articular cartilage is a load-bearing surface whose mechanical function arises from its unique properties. The structural and mechanical properties of mature cartilage are inhomogeneous through the depth and anisotropic. Tissue maturation is directed by mechanical forces; loading induces remodeling of the immature matrix, leading to increases in compressive and tensile properties and the development of tissue anisotropy [1, 2]. Limitations in cartilage repair strategies have engendered numerous efforts to engineer functional replacements. As mesenchymal stem cells (MSCs) undergo chondrogenesis in 3D culture, this cell type has been increasingly utilized in these efforts [3]. Despite their initial promise however, generating MSC-based constructs with the mechanical complexity and integrity of cartilage remains a challenge; the properties of MSC-seeded hydrogels are consistently lower than those of the native tissue [4, 5]. As mechanical stimulation is critical to cartilage development and maturation, bioreactor systems that simulate the native mechanical environment of cartilage may bridge these functional disparities. Indeed, dynamic axial compression enhances the compressive properties of both chondrocyte- and MSC-based engineered cartilage, though collagen content remains low [6, 7]. While promising, these studies were not designed to generate either depth-dependence or constructs with improved tensile properties. We therefore developed a new sliding contact bioreactor system that can better recapitulate the mechanical stimuli arising from joint motion (two contacting cartilage layers). In previous experiments using this system, we demonstrated improved expression of chondrogenic genes with short-term sliding contact of MSC-seeded agarose; these changes in gene expression were dependent on both axial strain and TGF-β supplementation [8]. Furthermore, FEM analysis of sliding contact showed that tensile strains (parallel to the sliding direction) and fluid efflux/influx were depth-dependent and highest in the region closest to the construct surface [8]. In the current study, we applied long-term sliding contact to MSC-seeded agarose constructs using the optimized parameters previously determined. We hypothesized that sliding contact would improve tensile properties and direct depth-dependent matrix remodeling.

Articular cartilage lines the surfaces of joints and transmits the forces arising from locomotion. The poor ability of cartilage to self-repair has motivated efforts to engineer replacements that recapitulate this load-bearing function. While chondrocyte-laden constructs have been generated with near-native mechanical properties, limitations in chondrocyte availability may preclude their clinical use. Therefore, mesenchymal stem cells (MSCs), which can undergo chondrogenesis in 3D culture, have emerged as a promising alternative [1]. However, although MSCs deposit a cartilaginous matrix, mechanical and biochemical properties are lower than those achieved with chondrocytes [1, 2]. Using microarray analysis, we recently showed that limitations in functional MSC chondrogenesis may stem from incomplete or incorrect molecular induction; molecular differences were observed between donor-matched differentiated chondrocytes and newly differentiated MSCs over 8 weeks of culture [2]. While some genes remained consistently low in MSCs compared to chondrocytes, others gradually increased with time, approaching chondrocyte levels by 8 weeks. As these molecules may underlie the functional disparity between chondrocytes and MSCs, we hypothesized that longer culture durations may improve MSC-seeded construct properties and chondrogenesis. To test this hypothesis, we characterized the evolution of functional properties of MSC- and chondrocyte-seeded constructs over 4 months of in vitro culture in pro-chondrogenic medium.