Epithelium, a highly dynamic system, plays a key role in the homeostasis of the intestine. However, thus far a human intestinal epithelial cell line has not been established in many countries. Fetal tissue was selected to generate viable cell cultures for its sterile condition, effective generation, and differentiated character. The purpose of the present study was to culture human intestinal epithelial cells by a relatively simple method. Thermolysin was added to improve the yield of epithelial cells, while endothelin-3 was added to stimulate their growth. By adding endothelin-3, the achievement ratio (viable cell cultures/total cultures) was enhanced to 60% of a total of 10 cultures (initiated from 8 distinct fetal small intestines), allowing the generation of viable epithelial cell cultures. Western blot, real-time PCR and immunofluorescent staining showed that cytokeratins 8, 18 and mouse intestinal mucosa-1/39 had high expression levels in human intestinal epithelial cells. Differentiated markers such as sucrase-isomaltase, aminopeptidase N and dipeptidylpeptidase IV also showed high expression levels in human intestinal epithelial cells. Differentiated human intestinal epithelial cells, with the expression of surface markers (cytokeratins 8, 18 and mouse intestinal mucosa-1/39) and secretion of cytokines (sucrase-isomaltase, aminopeptidase N and dipeptidylpeptidase IV), may be cultured by the thermolysin and endothelin-3 method and maintained for at least 20 passages. This is relatively simple, requiring no sophisticated techniques or instruments, and may have a number of varied applications.

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In this paper, boundary control is designed for a Timoshenko beam system with the input dead-zone. By the Hamilton's principle, the dynamics of the Timoshenko beam system is represented by a distributed parameter model with two partial differential equations and four ordinary differential equations. The bounded part is separated from the input dead-zone and then forms the disturbance-like term together with the boundary disturbance, which finally acts on the Timoshenko beam system. Boundary control, based on the Lyapunov's direct method, is proposed to ensure the Timoshenko beam converge into a small neighbourhood of zero, where stability of the system is also analysed. Besides, the existence and uniqueness of the solution of the Timoshenko beam system are proved. Simulations are provided to reveal the applicability and effectiveness of the proposed control scheme. NomenclatureL length of the Timoshenko beam M mass of the tip payload ρ uniform mass per unit length of the Timohenko beam EI bending stiffness of the Timoshenko beam I ρ uniform mass moment of inertia of the cross section of the Timoshenko beam J inertia of the tip payload K K = kAG k a positive constant depending on the shape of the cross section of the Timoshenko beam A cross-sectional area of the Timoshenko beam G modulus of elasticity in shear w(x, t) transverse displacement of the Timoshenko beam at the position x and time t u(t) and τ (t) two control inputs with dead-zone d(t) unknown time-varying boundary disturbance on the tip payload f(x, t) disturbance of the Timonshenko beam

Self-excited vibration of a flexibly supported shafting system in a gravity water tunnel was observed in the testing of friction of water-lubricated rubber bearings. The measured vibrations indicated that the self-excited vibration, characterized by a single-mode vibration modulated by the shaft speed, emerged at a specific speed and grew stronger as the shaft speed decreased, but it would cease at a very low-speed. To explain the mechanism of instability, a dynamic model of the system was built. The substructure synthesis method was employed to model the dynamics of the shafting system, which was divided into two subsystems: the flexible support and the shaft. Before the synthesis, natural frequencies and modes of the subsystems were computed by the finite element method. According to the modal parameters and connecting conditions, a synthesized model was built to take into account the friction between the shaft and the bearing. The fourth-order Runge–Kutta method was used to solve the dynamic equations, and the influences of physical parameters on vibration stability were analyzed. The results have shown that certain vibration modes of the flexible support tend to be unstable under the excitation of the friction. Both the simulation and experimental results have exhibited that the unstable modes are associated with the torsional vibration of the flexible support, which are in fact lightly damped and accordingly can be easily excited by the circumferential friction. Therefore, the coupling between the torsional vibration of the flexible support and the friction of the water-lubricated rubber bearing is the main factor leading to the vibration instability.

The propulsion shafting system of ships is usually supported, in part, by water-lubricated rubber bearings, which often work at mixed or boundary lubrication state under heavy-load and low-speed conditions, resulting in strong friction on the bearing-shaft interface and even abnormal vibration in the overall system. In addition, bearing misalignment can further affect the distribution of friction and consequently change the lateral and torsional vibration characteristics of the shafting system. In this work, the rubber bearing was simplified into parallel-distributed springs and the water film was neglected. The dynamic model of the propulsion shafting system was built with the finite element method and reduced by mode truncation. The coupled effect of bearing misalignment and friction was subsequently analyzed with this reduced model and the fourth-order Runge-Kutta method. Finally, lateral and torsional vibration characteristics of the overall system under different bearing misalignment were obtained, which can be used in the identification or diagnosis of abnormal vibration induced by friction.

In order to suppress lateral vibration transmission and reduce acoustic radiation of a shafting-hull coupled system, a new approach using electromagnetic bearings in the shafting system is proposed. The dynamic characteristics of the electromagnetic bearings, especially the equivalent stiffness and damping as well as the applicable scope of linearization of the electromagnetic bearings, are analysed at first. With the equivalent parameters, a dynamic model of the shaftinghull coupled system is established subsequently by using the frequency response synthesis method to derive frequency response functions associated with the lateral vibrations. Finally, the influence of the control parameters of the electromagnetic bearings on vibration transmission in the shafting-hull system is studied. Analysis results indicate that lateral vibration responses are suppressed significantly when electromagnetic bearings are introduced into the shafting-hull system, and as a result, sound radiation of the system is reduced, which demonstrates that the proposed approach is effective in controlling vibration transmission in the shafting system.

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This paper proposes a new adaptive algorithm for the active vibration control of time-varying systems in the presence of broadband or narrowband disturbances. The new algorithm combines the conventional filtered-x least mean square algorithm with the recursive prediction error (RPE) algorithm after the gradient modification of the RPE algorithm. The modified RPE algorithm is used to estimate the model of the control path online. The well-known filtered-x least mean square (FxLMS) algorithm is effective for the uncertain or time-varying systems, and adopts an auxiliary white noise approach to estimate the model of the control path online. However, the auxiliary excitation will degrade the control performance to some extent. In the new algorithm, the auxiliary excitation is eliminated at the expense of a larger computational burden. The influence of the estimated finite impulse response series on the convergence is also discussed. A propulsion shafting model with the time-varying dynamics is established by frequency response function synthesis. Numerical simulation for the established model is presented to demonstrate the superior performance of the proposed algorithm as compared with the FxLMS algorithm.