A new approach to the electrostatic pull-in instability of nanocantilever actuators using the ADM–Padé technique

AbstractIn this paper, the Adomian decomposition method and Padé approximants are integrated to study the deflection and pull-in instability of nanocantilever electromechanical switches. In a distributed parameter model, intermolecular forces, including Casimir forces, are taken into account considering their range of application. A closed form power series solution based on Adomian polynomials is obtained. The obtained analytic results are compared with numerical solution. The Adomian method is accurate for small deflections, but the results of a pull-in instability study demonstrate that the accuracy of the Adomian solution is not as good for small deflections. Thus, to increase the accuracy of the Adomian solution for the pull-in instability, the Adomian power series is converted to Padé approximants. The results of the present method are compared with the numerical results as well as those of the Adomian decomposition method and other methods reported in the literature. The results obtained using the ADM–Padé are remarkably accurate compared with the numerical results. The proposed technique can be easily extended to solve a wide range of instability problems. Finally, the minimum initial gap and the detachment length of the actuator that does not stick to the substrate due to the intermolecular attractions, which is an important parameter for the pull-in instability of a nanocantilever actuator, are calculated using Adomian–Padé approximants

Deterministic normal contact of rough surfaces with adhesion using a surface integral method

The fundamental problem of adhesion in the presence of surface roughness and its effect on the prediction of friction has been a hot topic for decades in numerous areas of science and engineering, attracting even more attention in recent years in areas such as geotechnics and tectonics, nanotechnology, high-value manufacturing and biomechanics. In this paper a new model for deterministic calculation of the contact mechanics for rough surfaces in the presence of adhesion is presented. The contact solver is an in-house boundary element method that incorporates fast Fourier transform for numerical efficiency. The adhesive contact model considers full Lennard-Jones potentials and surface integration at the asperity level and is validated against models in the literature. Finally, the effect of surface roughness on the adhesion between surfaces was studied, and it was shown that the root mean square gradient of surface roughness can change the adhesive pressures irrespective of the root mean square surface roughness. We have tested two adhesion parameters based on Johnson's modified criteria and Ciavarella's model. We showed that Civarella's model introduces the most reasonable criteria suggesting that the RMS roughness and large wavelength of surfaces roughness are the important parameters of adhesion between rough surfaces

The Effects of Lyophilization on the Physico-Chemical Stability of Sirolimus Liposomes

Purpose: The major limitation in the widespread use of liposome drug delivery system is its instability. Lyophilization is a promising approach to ensure the long-term stability of liposomes. The aim of this study was to prepare sirolimus-loaded liposomes, study their stability and investigate the effect of lyophilization either in the presence or in the absence of lyoprotectant on liposome properties. Methods: Two types of multi-lamellar liposomes, conventional and fusogenic, containing sirolimus were prepared by modified thin film hydration method with different ratio of dipalmitoylphosphatidylcholine (DPPC), cholesterol and dioleoylphosphoethanolamine (DOPE), and were lyophilized with or without dextrose as lyoprotectant. Chemical stability investigation was performed at 4°C and 25°C until 6 months using a validated HPLC method. Physical stability was studied with determination of particle size (PS) and encapsulation efficiency (EE %) of formulations through 6 months. Results: Chemical stability test at 4°C and 25°C until 6 months showed that drug content of liposomes decreased 8.4% and 20.2% respectively. Initial mean EE % and PS were 72.8 % and 582 nm respectively. After 6 months mean EE % for suspended form, lyophilized without lyoprotectant and lyophilized with lyoprotectant were 54.8 %, 62.3% and 67.1 % at 4°C and 48.2%, 60.4 % and 66.8 % at 25°C respectively. Corresponding data for mean PS were 8229 nm, 2397 nm and 688nm at 4°C and 9362 nm, 1944 nm and 737 nm at 25°C respectively. Conclusion: It is concluded that lyophilization with and without dextrose could increase shelf life of liposome and dextrose has lyoprotectant effect that stabilized liposomes in the lyophilization process

Verification of bee algorithm based path planning for a 6DOF manipulator using ADAMS

In this article the end effector displacement control for a manipulator robot with 6 rotational joints on a predetermined 3-dimensional trajectory is investigated. Since for any end effector position there are more than a single set of answers, regarding to robot parts orientation, finding a method which gives the designer all existing states will lead to more freedom of action. Hence two different methods were applied to solve robot inverse kinematic issue. In the first method ADAMS software was considered, which is a well-known software in the field of solving inverse kinematic problems, and after that BA algorithm is used as an intelligent method. This method is one of the fastest and most efficient methods among all existing ones for solving non-linear problems. Hence problem of inverse kinematic solution is transformed into an affair of optimization. Comparison of results obtained by both models indicates the reasonable performance of BA because of its capability in providing the answers from all existing states along with the privilege of no need to 3D modeling

An in vitro aerosolization efficiency comparison of generic and branded salbutamol metered dose inhalers

Background: Due to the high rate of pulmonary diseases, respiratory drug delivery systems have been attracted excessive attention for the past decades. Because of limitations and growing drug bill, physicians are encouraged to prescribe generically whenever possible. The purpose of this study was to evaluate whether there was any significant difference in aerosolization performance between a reference brand Salbutamol (A) Metered Dose Inhalers (MDIs) and two generic products (B and C). Methods: The aerosolization performance of MDIs was evaluated by calculating aerosolization indexes including fine particle fraction (FPF), fine particle dose (FPD), geometric standard deviation (GSD) and mass median aerodynamic diameters (MMAD) by using the next generation impactor. Results: Although aerosolization indexes of MDI A were superior than the Iranian brands, but the differences were not statistically significant. Conclusion: These results verified that generic MDIs deliver similar quantities of Salbutamol to the reference brand and aerosolization performance parameters of generic Salbutamol MDIs did not differ significantly from the reference brand

Development of a novel low-calorie lime juice based prebiotic/ high-antioxidant beverage using combined design optimization methodology

A novel lime-juice based low-calorie functional beverage was developed by using D- optimal combined design optimization. For the preparation of the beverage, the following functional ingredients were used; lime juice, lime peel essential oil (LEO) as a flavoring agent and bioactive component, sucralose as a low-calorie sweetener, inulin/polydextrose (I/P) mixture as prebiotics fibers, pectin as a thickening agent and soluble dietary fiber, lutein as a carotenoid colorant and antioxidant, and peppermint extract (ME) as a flavoring agent and bioactive component. A combined design consisting of one mixture factor (LEO/ME ratio), one numeric factor (lutein concentration), and one categoric factor (presence or absence of prebiotics) was used for optimizing the functional beverage based on the sensory quality. Regression models were adequately fitted to the data of sensory acceptance with a determination coefficient >90%. The sample containing a mixture of prebiotics, 2:3 (v/v) ratio of LEO: ME, and 3 mg/100 ml lutein was selected as the best formulation among the six optimal beverages which was suggested by design expert software. This final optimum sample showed the highest total phenolic (44.22 mg gallic acid equivalents/L) and flavonoid (25.49 mg quercetin equivalents/L) contents, as well as its antioxidant activity (as DPPH• scavenging), was 38.30

Mechano-Chemical Modelling of Boundary Lubrication

Boundary lubrication is known to be significantly important in the design of machine parts. The decrease in the efficiency of the system as well as its durability when operating in boundary lubrication conditions highlights the importance of this regime. Boundary lubrication involves many different physical, chemical and mechanical phenomena which make it difficult to understand the real mechanisms of friction, wear and lubrication. Tribochemistry is undoubtedly one of the most important processes occurring in boundary lubrication. Modelling such a complicated process needs a robust physical and chemical modelling framework that is capable of capturing different phenomena. The majority of the modelling attempts in boundary lubrication covers the contact mechanics of rough surfaces with different numerical approaches. Despite the importance of the tribochemistry and its effect in reducing friction and wear of boundary lubricated contacts, there is no comprehensive modelling framework that considers tribochemistry into the boundary lubrication models. In this work, tribochemistry was implemented into the deterministic contact mechanics simulation for elastic-perfectly plastic contact of rough surfaces. A tribochemical model for the growth of the ZDDP antiwear additive was developed based on the thermodynamics of interfaces that combines formation and removal of the tribofilm. The tribochemical model was then coupled with the contact mechanics model which was developed based on potential energy principles. A modification to Archard’s wear equation was proposed which accounts for the role of ZDDP tribofilm in reducing the wear. This model was proposed based on the experimental observations of ZDDP in reducing wear. The numerical framework was then validated against experiments. The wear prediction capability of the model was validated against experiments from Mini-Traction Machine in a rolling/sliding contact. The model is able to predict changes in the topography of the surfaces and this was validated with experiments on a Micro Pitting Rig (MPR). The model shows a good potential in capturing the behaviours in boundary lubrication and opens new ways for further developments and testing the effect of different parameters in tribochemistry and wear. It can give insights in better understanding the real mechanisms of tribochemistry and also help in optimizing boundary lubricated contacts