Variable structure robust controller design for blood glucose regulation for type 1 diabetic patients: A backstepping approach

Diabetes mellitus type 1 occurs when β‐cells in the pancreas are destroyed by the immune system. As a result, the pancreas cannot produce adequate insulin, and the glucose enters the cells to produce energy. To elevate the glycaemic concentration, sufficient amount of insulin should be taken orally or injected into the human body. Artificial pancreas is a device that automatically regulates the level of body insulin by injecting the requisite amount of insulin into the human body. A finite‐time robust feedback controller based on the Extended Bergman Minimal Model is designed here. The controller is designed utilizing the backstepping approach and is robust against the unknown external disturbance and parametric uncertainties. The stability of the system is proved using the Lyapunov theorem. The controller is exponentially stable and hence provides the finite‐time convergence of the blood glucose concentration to its desired magnitude. The effectiveness of the proposed control method is shown through simulation in MATLAB/Simulink environment via comparisons with previous studies.     

Modeling the instability of CNT tweezers using a continuum model

Carbon nanotube (CNT) tweezers are composed of two parallel cantilever CNTs with a distance in between. In this paper, the static response and instability of CNT-made nano-tweezers is theoretically investigated considering the effects of Coulomb electrostatic force and van der Waals molecular attraction. For this purpose, a nano-scale continuum model is employed to obtain the nonlinear constitutive equation of the nano-tweezers. The Euler–Bernoulli beam theory is applied to model the elastic response of the CNT. The van der Waals attraction is computed from the simplified Lennard-Jones potential. In order to solve the nonlinear constitutive equation of the system, three approaches, e.g. the hemotopy perturbation method (HPM), the Adomian decomposition (AD) and the finite difference method (FDM) are employed. The obtained results are in good agreement with the experimental measurements. As a case study, freestanding CNT tweezers has been investigated and the detachment length and minimum initial gap of the tweezers are determined. Moreover, the effective operation range of the van der Waals attraction that affects the instability behavior of the CNT tweezers is discussed.     

A size-dependent model for instability analysis of paddle-type and double-sided NEMS measurement sensors in the presence of centrifugal force

Paddle-type and double-sided nanostructures have much potential for measuring the angular speed in rotary systems and aerospace applications. While most investigations in the literature have concentrated on the electromechanical performance of conventional beam-type nanostructures, few researchers have addressed the performance of these systems. The pull-in instability of the cantilever paddle-type and double-sided sensors in the presence of the centrifugal force have been investigated. The nonlinear governing equations are solved and the obtained results are compared with the numerical solution. The influences of the van der Waals force, geometric parameters, angular speed, and size phenomenon on the instability performance have been demonstrated.     

A Robust Tracking Controller for Electrically Driven Robot Manipulators: Stability Analysis and Experiment

 In this paper, a robust controller for electrically driven robotic systems is developed. The controller is designed in a backstepping manner. The main features of the controller are: 1) Control strategy is developed at the voltage level and can deal with both mechanical and electrical uncertainties. 2) The proposed control law removes the restriction of previous robust methods on the upper bound of system uncertainties. 3) It also benefits from global asymptotic stability in the Lyapunov sense. It is worth to mention that the proposed controller can be utilized for constrained and nonconstrained robotic systems. The effectiveness of the proposed controller is verified by simulations for a two link robot manipulator and a four-bar linkage. In addition to simulation results, experimental results on a two link serial manipulator are included to demonstrate the performance of the proposed controller in tracking a given trajectory.     

Location-inventory problem in supply chains: a modelling review

A location-inventory problem (LIP) aims to integrate strategic supply chain design decisions with tactical and operational inventory management decisions. This study provides an extensive review of the existing literature of LIP modelling. A mathematical model is presented for a basic LIP, which can be further developed to incorporate additional features for use in real-world scenarios. We also discuss the evolution of LIP modelling literature over the past three decades and provide summary tables outlining characteristics of the published works including key modelling attributes and objective function cost components. Additional classifications are completed based on the solution methods adopted and real-world applications investigated. Our observations provide important insights and identify potential directions for future research in the field.     

Investigation of the fracture mechanism and mechanical properties of polystyrene/silica nanocomposite in various silica contents

There is limited research on the effect of silica on the mechanical properties of polystyrene. For this lack of information, this study has focused on the fracture mechanism and mechanical properties of Polystyrene/silica nanocomposite. Transmission electron microscopy showed proper dispersion of nanoparticles in PS matrix in both low and high filler loadings. Scanning electron microscopy, TOM micrography, and non-contact surface profiler were used to study the fracture surface and fracture mechanism characteristics of the nanocomposite. It seems that the debonding mechanism is an important mechanism in toughening of Polystyrene/silica nanocomposites. In addition, mechanical behavior of the samples was investigated. Tensile, flexural, and compressive strength and also impact and plain-strain fracture toughness of nanocomposite samples showed different behaviors in low and high nanoparticle loadings and interestingly, we found an optimum value less than 2% for nanoparticle loading in which we observed the highest improvement in mechanical properties of the nanocomposite.     

A hydrophobically-modified alginate gel system: utility in the repair of articular cartilage defects

Alginate is a family of natural polysaccharides, widely used in industry and medicine for many applications, with its non toxic nature, gentle sol/gel transition procedure and low cost, alginate inferior biomechanical properties have limited its utility especially in tissue engineering. Additionally, ionically cross-linked alginate hydrogels generally lose most of their initial mechanical and swelling properties within a few hours in physiological solution. In order to overcome these limitations, the referenced alginate was treated by covalent fixation of octadecyl chains onto the polysaccharide backbone by esterification. In semi dilute solution, intermolecular hydrophobic interactions of long alkyl chains result in the formation of physical hydrogels, which can then be reinforced by the addition of calcium chloride. FTIR studies clearly showed the presence of ester bonds at 1612 and 1730?cm(-1) indicating that the alkyl groups are incorporated in the backbone of resulting polymer. The endothermic peak and exothermic peak present in the DSC thermogram of Alg-C18 had shifted to lower temperatures comparing to native alginate (from 106 to 83°C and from 250 to 245°C, respectively) due to the esterification reaction that leads to high hydrophobic nature of the modified sample. From rheological experiments, it can be inferred that the combination of both calcium bridges and intermolecular hydrophobic interaction in the treated alginate leads to enhanced gel strength accompanied by more stable structure in physiological solution comparing to native sodium alginate hydrogel. Finally, the modified alginate tended to have no toxic effects on mesenchymal stem cell culture, rather it supported MSC chondrogenic differentiation.     

Modeling the effect of intermolecular force on the size-dependent pull-in behavior of beam-type NEMS using modified couple stress theory

Experimental observations reveal that the physical response of nanostructures is size-dependent. Herein, modified couple stress theory has been used to study the effect of intermolecular van der Waals force on the size dependent pull-in of nanobridges and nanocantilevers. Three approaches including using differential transformation method, applying numerical method and developing a simple lumped parameter model have been employed to solve the governing equation of the systems. The pull-in parameters i.e. critical tip deflection and instability voltage of the nanostructures have been determined. Effect of the van der Waals attraction and the size dependency and the importance of coupling between them on the pull-in performance have been discussed.     

Performance Analysis of Sliding Window Turbo Decoding Algorithms for 3GPP FDD Mode

In this paper we analyze the performance of a turbo decoder using two sliding window algorithms for the frequency division duplex (FDD) mode of the Third Generation Partnership Project (3GPP) standard. Focusing on the solution for the user equipment, we compare fixed-point realizations of the sliding window algorithms in terms of the computational complexity and memory requirements. We show that the bit and frame error rate performance of the sliding window scheme strongly depends on the guard window size. Furthermore, simulation results indicate that relatively small guard window sizes can significantly decrease the iteration gain for large frames. Finally, optimization of the windowing parameters achieves the desired trade-off between the performance degradation introduced by a windowing approach and the computational complexity and memory utilization.