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An asymptotic output feedback controller for the hydraulic systems with model uncertainty compensation and prescribed performance is proposed here, where state observers, funnel function and nonlinear adaptive controller are integrated via backstepping technology. Only position signal is available in the process of controller design, the velocity and load pressure are estimated by observers. And, the adaptive control law is carried out to approximate disturbance. Then, a funnel function is introduced to guarantee the prescribed tracking error performance and the potential singularity problem in prescribed performance control is avoided. Furthermore, the whole closed system is proved to be asymptotically stable using Lyapunov method. Comparative experimental results performed on hydraulic systems are studied to illustrate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

Volterra’s model for population growth in a closed system consists in an integral term to indicate accumulated toxicity besides the usual terms of the logistic equation. Scudo in 1971 suggested the Volterra model for a population u(t) of identical individuals to show crowding and sensitivity to “total metabolism”: du/dt=au(t)-bu2(t)-cu(t)∫0tu(s)ds. In this paper our target is studying the existence and uniqueness as well as approximating the following Caputo-Fabrizio Volterra’s model for population growth in a closed system:  CFDαu(t)=au(t)-bu2(t)-cu(t)∫0tu(s)ds, α∈[0,1], subject to the initial condition u(0)=0. The mechanism for approximating the solution is Homotopy Analysis Method which is a semianalytical technique to solve nonlinear ordinary and partial differential equations. Furthermore, we use the same method to analyze a similar closed system by considering classical Caputo’s fractional derivative. Comparison between the results for these two factional derivatives is also included. [ABSTRACT FROM AUTHOR]

We generalize the Maxwell drop evaporation equation to cover the range from closed system to open system through semiclosed system where the evaporation is restricted to an arbitrary degree which we show how to characterize. We first consider a suspended drop, and then a drop contacting a surface where the surface's vicinity restricts the evaporation paths. We show how to use these results to obtain arbitrary values of vapor pressure by simple manipulations of the numbers and sizes of droplets added to the system for a constant leak size, or, alternatively, control the leak size with a valve for given sizes of drops. We further show how to use this result to quantify a leakage in a system. Such a leakage is characterized using a single parameter (leakage length) which the described method calibrates. The calibrated leakage length can be used for systematic control of vapor concentrations within the chamber. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4548-4553, 2016 [ABSTRACT FROM AUTHOR]

Closed cycle systems offer an opportunity for solar energy harvesting and storage all within the same material. Photon energy is stored within the chemical conformations of molecules and is retrieved by a triggered release in the form of heat. Until now, such solar thermal fuels (STFs) have been largely unavailable in the solid-state, which would enable them to be utilized for a multitude of applications. A polymer STF storage platform is synthesized employing STFs in the solid-state. This approach enables uniform films capable of appreciable heat storage of up to 30 Wh kg−1 and that can withstand temperature of up to 180 °C. For the first time a macroscopic energy release is demonstrated using spatial infrared heat maps with up to a 10 °C temperature change. These findings pave the way for developing highly efficient and high energy density STFs for applications in the solid-state. [ABSTRACT FROM AUTHOR]

A novel, simple, compact, efficient system based on a unit operation of bubble stripping was developed for intensive methanol (MeOH) removal from crude biodiesel (BDF) which was synthesized by potassium hydroxide-catalyzed transesterification reaction of triacylglycerol (TAG) with MeOH. As TAG both rapeseed oil and used cooking oil were tested. In the system, gas was supplied by a gas pump through a gas bubbler into the crude biodiesel, then the exit gas containing MeOH vapor passed through a condenser (0°C) and the condensed MeOH was collected in a vessel. MeOH-free gas from the condenser returned into the inlet of the gas pump, thus gas was circulated in a closed system. After the intensive MeOH removal by the bubble stripping, insoluble sediment always appeared in the biodiesel so that it was removed by centrifugation. As a final step, trace amounts of potassium (K) and free glycerol were removed by adsorbent treatment. MeOH, K, free glycerol, fatty acid methyl ester, and water contents, acid, and iodine values and oxidation stability of the purified biodiesel cleared the specifications of EN 14214 Standard. The proposed dry process consisting of the three steps will be applicable to an industrial production of high-quality biodiesel. Practical applications: Bubble stripping that has been developed in this study is simple but very effective to remove almost completely residual methanol from the crude biodiesel. Compared with the conventional wet process, the dry process that authors' have proposed has no necessity of washing water, hence no waste water treatment. Elimination of sediment after the intensive residual MeOH removal by the bubble stripping before the final adsorption step will make it possible to decrease significantly the amount of the adsorbent (kg) required per kg of the crude biodiesel or to prolong the life span of its packed bed column, resulting in the cost reduction of the biodiesel production. The proposed dry process consisting of the three steps will be applicable to an industrial production of high-quality biodiesel. [ABSTRACT FROM AUTHOR]