Sharif Digital Repository

In this study, a reliable and predictive model namely, least-squares support vector machine (LS-SVM) was developed to predict dye removal efficiency. Four LS-SVM models have been developed and tested using more than 630 series of experimental data which were obtained from our previous paper. These data consist of adsorbate type, adsorbent dosage, initial dye concentration, salt, absorbance time and dye removal efficiency. Direct Red 31 (DR31), Direct Green 6 (DG6) and Acid Blue (AB92) were used as a model dyes. The results show that the developed model is more accurate and reliable with the average absolute relative deviation of 0.678%, 0.877%, 0.581% and 0.978% for single systems and... 

This research reports the remarkable effects of Zr-based metal–organic framework, i.e. UiO-66, on cross-linked network structure and mechanical behaviors of ethylene-propylene diene monomer (EPDM) rubber under sulfur vulcanization systems. To this end, EPDM rubber was vulcanized with conventional (CV), semi-efficient (SEV) and efficient (EV) vulcanization systems. In addition, EPDM nanocomposites containing 5 phr UiO-66 with all three vulcanization systems were also prepared, for the sake of comparison with their corresponding unfilled samples. While the unfilled EPDM vulcanizates showed expectable behaviors in cross-linking density estimated by swelling experiment and cure-rheometer... 

The focus of this research is on the fabrication of aluminium-B4C and aluminium-ZrSiO4 composites by vortex method as a liquid phase process of metal matrix composites. SEM observations show that reinforcement particles are dispersed homogeneously throughout the aluminium matrix. Density, mechanical properties such as hardness and tensile strength of Al base MMCs containing different volume fractions (5, 10 and 15 %) of micro-reinforcements are examined separately and compared with those of monolithic aluminium. Results show that mechanical properties of samples are noticeably higher than those of the monolithic aluminium. The optimum amount of reinforcement in this... 

Swarm motion is an amazing collective behavior in nature for energy saving. Inspiring this natural phenomenon in microorganisms’ swimming, we have proposed a motion strategy for a swarm of microrobots to reduce their energy consumption during path tracking. The investigated microrobot is an artificial Self-Propelled Microswimmer (SPM) with high maneuverability at low Reynolds number flow (Re ≪ 1). In this study, we have demonstrated that forming a swarm behavior with minimum energy consumption requires the microswimmers to be close enough to each other, since at small distances the hydrodynamic interactions of microswimmers reduce their energy consumption. Moreover, we also showed that... 

Swarm motion is an amazing collective behavior in nature for energy saving. Inspiring this natural phenomenon in microorganisms’ swimming, we have proposed a motion strategy for a swarm of microrobots to reduce their energy consumption during path tracking. The investigated microrobot is an artificial Self-Propelled Microswimmer (SPM) with high maneuverability at low Reynolds number flow (Re ≪ 1). In this study, we have demonstrated that forming a swarm behavior with minimum energy consumption requires the microswimmers to be close enough to each other, since at small distances the hydrodynamic interactions of microswimmers reduce their energy consumption. Moreover, we also showed that... 

Artificial Intelligence (AI) is a novel and fascinating tool in the control of robots. In this study, using a reinforcement learning approach, we have trained an artificial three-disk microrobot in order to learn how to swim at low Reynolds number flow (Re≪1) like the behavior of young microorganisms. Here, as the first contribution, we introduced a discrete model of a novel microswimmer. As the second contribution, we demonstrated that, using the proposed intelligent method, the microswimmer will be able to not only escape the physical constraints of swimming in a viscous medium, but also find the best sequence of actuation to reach the target point in a stochastic environment. The proposed... 

In the current study, two series of antimicrobial dressings conjugated with silver sulfadiazine (SSD) and silver nanoparticles (AgNPs) were developed and evaluated for chronic wound healing. Highly porous polycaprolactone (PCL)/polyvinyl alcohol (PVA) nanofibers were loaded with different concentrations of SSD or AgNPs and compared comprehensively in vitro and in vivo. SSD and AgNPs indicated a strong and equal antimicrobial activity against S. aureus. However, SSD had more toxicity against fibroblast cells over one week in vitro culture. An in vivo model of wound healing on male Wistar rats was developed with a full thickness wound. All the wound dressings indicated enough flexibility and... 

The brushless doubly fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind generator. However, it suffers from lower efficiency and larger dimensions in comparison with the doubly fed induction generator. A major part of drawbacks arises from undesirable spatial harmonics of air-gap magnetic field. Calculation of core loss is an important issue in optimal design studies to improve the performance characteristics. The iron loss is higher and has a more complex nature in BDFIGs in contrast with conventional machines. Furthermore, additional losses cannot be ignored due to a high level of spatial harmonics distortion. This paper aims to... 

We study stationary entanglement properties of an optomechanical system containing an atomic ensemble. We focus onto the case of the movable mirror strongly coupled to the cavity field through both radiation pressure and photothermal force. Exploiting a quantum Langevin equation approach we investigate the bipartite entanglement properties of various bipartite subsystems as well as stationary tripartite entanglement of the system. We particularly study robustness of the atom-mirror entanglement against temperature. We show that, even though the photothermal force is a dissipative force, it can significantly improve the cavity mediated atom-mirror entanglement  

Cooling and entanglement in optomechanical systems coupled through radiation pressure and photothermal force are studied. To develop the photothermal model, we derive an expression for deformation constant of the force. By exploiting linearized quantum Langevin equations, we investigate the dynamics of such systems. According to our analysis, in addition to separate action of radiation pressure and photothermal force, their cross-correlation effect plays an important role in the dynamics of the system. We also achieve an exact relation for the phonon number of the mechanical resonator in such systems, and then we derive an analytical expression for it at the weak-coupling limit. At the... 

A new strict proposal for determining radiation pressure coupling to optical resonator devices has been developed. Our evidence shows that the effect of the anti-Stokes wave cannot be neglected. It is shown that Stokes and anti-Stokes frequencies of all orders will participate in the optomechanical effect. Furthermore, we have shown that for the input pump power, there exists a threshold value for instability behavior. Radiation pressure can couple mechanical modes of a cavity to its optical modes, leading to parametric oscillation instability. Here we present an approximate analysis of such a nonlinear effect with Hamilton's least action principle. Loss in every mode has been taken into... 

In the present work, a combination of a dynamic explicit finite element model and the low cycle fatigue theory is used to simulate the steady-state abrasive wear occurring between an as-cast eutectoid steel and a carbide-tungsten disk. While the low cycle fatigue theory has been used to model wear in softer non-ferrous alloys, this work shows its applicability and accuracy for use in harder alloys, such as the eutectoid steel used in this research which is strengthened with added chromium. The novelty of this work lies in calculating the Manson-Coffin relation constants from a coupled finite element model with experimental tests instead of the previously used Slip line method. The D... 

2D-reduced graphene oxide-based nanocomposites (rGO) have been studied frequently for the photocatalytic degradation of organic pollutants due to their remarkable charge carrier properties. In this work, NiFe2O4@Ti-doped ZnO magnetically separable nanoparticles loaded on N-doped rGO nanosheets using a one-step hydrothermal technique. The crystal structural and functional group of samples were analyzed using X-ray diffraction (XRD) and Fourier-transform infrared spectra (FTIR), respectively. Field emission scanning electron microscopy (FESEM) images show ZnO nanoparticles covered NiFe2O4 nanospheres and the binary nanocomposite properly anchored on rGO. Furthermore, these results were... 

There are various cases in physics and engineering sciences (especially communications) where one requires the envelope probability density function (pdf) of the sum of several random sinusoidal signals. According to the correspondence between a random sinusoidal signal and a random vector, the sum of random vectors can be considered as an abstract mathematical model for the above sum. Now it is desired to obtain the pdf of the length of the resulting vector. Considering the common and reasonable assumption of uniform distributions for the angles of vectors, many researchers have obtained the pdf of the length of the resulting vector only for special cases. However in this paper, the pdf is... 

Nowadays, application of renewable energies has taken a rapid trend. Wind energy is among those mostly used for this purpose. Doubly Fed Induction Generators (DFIG) are widely used in wind power plants due to several advantages such as partial rating converter, capability of decoupled active and reactive power control, etc. Application of a suitable control strategy is of great importance in wind power plants. In this paper, the parameters of a hybrid controller are calculated using Particle Swarm Optimization (PSO) subjected to satisfying the required criteria in output active and reactive powers of a DFIG. In the proposed system Direct Power Controller (DPC), Variable Structure Controller... 

From 1970s, studies have been conducted on the hydraulic design of stepped spillways and many empirical formulas were developed. Despite the simple geometry of these spillways, their hydraulic behavior is complicated. As a result, for many cases, the physical models are studied to verify the design. Numerical simulation is considered as a tool to reduce the laboratory tests, in order to save time and money. Furthermore, the parameters which are not investigated or measured in physical models could be evaluated. In this paper, the results of numerical simulations are compared with the results of physical models and empirical formulas for the spillway of Renwick dam studied in a 1/8 scale... 

The brushless doubly-fed induction generator (BDFIG) has substantial benefits, which make it an attractive alternative as a wind turbine generator. The aim of this work is to present a nodal-based magnetic equivalent circuit (MEC) model of the BDFIG which provides performance characteristics and flux density distributions. The model takes into account stator winding distributions, special configuration of rotor bars, slotting effects, teeth saturation, flux fringing and current displacement effects. The real flux tubes are considered for creating an MEC network and calculating its non-linear elements. A method for simplifying the rotor magnetic network has been applied and Gauss elimination... 

Partial state estimation of dynamical systems provides significant advantages in practical applications. Likewise, pre-compensator design for multi variable systems invokes considerable increase in the order of the original system. Hence, applying functional observer to pre-compensated systems can result in lower computational costs and more practicability in some applications such as fault diagnosis and output feedback control of these systems. In this note, functional observer design is investigated for pre-compensated systems. A lower order pre-compensator is designed based on a H2 norm optimization that is designed as the solution of a set of linear matrix inequalities (LMIs). Next, a... 

The paper presents a vector model for a Brushless Doubly-Fed Machine (BDFM). The BDFM has 4 and 8 pole stator windings and a nested-loop rotor cage. The rotor cage has six nests equally spaced around the circumference and each nest comprises three loops. All the rotor loops are short circuited via a common end-ring at one end. The vector model is derived based on the electrical equations of the machine and appropriate vector transformations. In contrast to the stator, there is no three phase circuit in the rotor. Therefore, the vector transformations suitable for three phase circuits can not be utilised for the rotor circuit. A new vector transformation is employed for the rotor circuit...