Sharif Digital Repository

This paper presents a stabilizing controller design method for quasi resonant (QR) converters described by a class of piecewise linear (PWL) models. The generalized state-space averaging technique (GSSA) is applied for the modeling and analysis of the half-wave zero current switching quasi-resonant (HW-ZCS-QR) buck converter. The nonlinear GSSA model of the converter is reconstructed using a piecewise linearizing technique. Subsequently, the piecewise linear models are combined together, to form a unified model, using a fuzzy modeling approach. The stability of the applied method has been investigated using Lyapunov method. Finally, a linear Hinfty; controller synthesis method is applied to... 

Green and simple synthesis strategies have gained tremendous popularity for the production of anisotropically-shaped noble metallic nanoparticles. The long-term stability of the produced particles, the short timescale of the target reaction(s), as well as the use of non-toxic chemicals, are pivotal features of a useful green procedure. Herein we describe a simple and convenient wet-chemical approach to synthesize stable, non-toxic and water-soluble small gold nanotriangles (GNTs) and gold nanospheres (GNSs) in one step at room temperature, using Tween 20 and Tween 80, respectively. A high level of purity and monodispersity was obtained for the GNTs, in addition to an excellent colloidal... 

This paper presents different applications of a vector model developed by the authors in Brushless Doubly-Fed Machine (BDFM) studies including analysis, control and simulations. The BDFM considered consists of a nested-loop type rotor. The vector model, which considers all the loops in each rotor nest, is derived using BDFM coupled-circuit model equations and by applying appropriate vector transformations. Three vector transformations are employed for the derivation of vector model corresponding to two three-phase windings in the stator and the rotor circuit. Each transformation consists of an angle which is, in general, unspecified and must be assigned appropriately depending on the... 

Graphene, a two-dimensional (2D) sheet of sp2-hybridized carbon atoms packed into a honeycomb lattice, has led to an explosion of interest in the field of materials science, physics, chemistry, and biotechnology since the few-layers graphene (FLG) flakes were isolated from graphite in 2004. For an extended search, derivatives of nanomedicine such as biosensing, biomedical, antibacterial, diagnosis, cancer and photothermal therapy, drug delivery, stem cell, tissue engineering, imaging, protein interaction, DNA, RNA, toxicity, and so on were also added. Since carbon nanotubes are normally described as rolled-up cylinders of graphene sheets and the controllable synthesis of nanotubes is well... 

In this work, central composite design (CCD) as a statistical experimental design method is performed to prepare nickel nano-particle of different magnetic domain regimes by the modified polyol process. It is shown that not only the concentration of the different chemicals but also the injection rate is determining for the morphology and magnetic properties. The average diameter of the synthesized nickel NPs is smaller than the critical single domain size and thus the single domain or pseudo-single domain nickel nano-particles can be prepared based on Day's plot  

This technical note considers the fixed-order H∞ output feedback control design problem for linear time invariant (LTI)systems. The objective is to design a fixed-order controller with guaranteed stability and closed-loop H∞ performance. This problem is NP-hard due to the non-convex rank constraint which appears in the formulation. We propose an algorithm for non-iterative direct synthesis (NODS) of reduced order robust controllers. NODS entails initial computation of two positive-definite matrices via full-order convex LMI conditions. These are then utilized by appropriate eigenvalue decomposition to directly obtain a suboptimal convex formulation for the fixed-order controller  

Transparency is a measure of performance in haptic devices. In order to improve transparency and reduce the difference between the impedance transmitted to the user and the target impedance it is necessary to compensate for the dynamics of the haptic device. Due to stability reasons improvement of transparency is limited. Passivity as a stability criterion has been used widely in design and analysis of haptic devices, Since passivity is a conservative criterion, it acts as an obstacle in improving transparency of the haptic interfaces. In this paper instead of passivity, robust stability of the interaction is studied in the presence of parametric uncertainties due to variations in user hand... 

In this paper an analytical method and a PDE-based solution to control temperature distribution in FGM plates is introduced. For the rectangular FGM plate under consideration, it is assumed that the material properties such as thermal conductivity, density, and specific heat capacity, vary in the width direction (y); and the governing heat conduction equation of the plate is a second-order partial differential equation. Since there has been little control synthesis work for PDE-based systems as compared to the abundance of control design techniques available for ordinary differential equations (ODEs), most of the proposed control approaches for continuous domain rely on discretizing the PDE... 

The study on the mechanism of the shape evolution of nanocrystaline particles is an important and emerging field, which is applicable in the shaped control synthesis of nanoparticles. As an alternative to transmittance electron microscopy (TEM), which is already used in the study of nanoparticles, in this article a simple spectrophotometric method has been proposed utilizing the advantages of chemometrics methods in analyzing overlapped and complex spectral data. The evolutionary visible absorbance data of CdSe quantum dots through particle formation were analyzed by factor analysis, evolving factor analysis, and multivariate curve resolution-alternative least-squares analysis, by which four... 

A cost-effective, durable, and easy-to-produce improvement in bifunctional electrocatalysts for water splitting is crucial for future renewable energy systems. In this present study, shape-controlled one-dimensional (1D) phosphorized cobalt (CoP) on 3D porous nickel foam (NiF) was synthesized through successive treatment of commercial NiF with acetone and ethanol, followed by hydrothermal growth of Co and final process of phosphorization by thermochemical reactions. The evaluations of products proved reduced overpotential (270 mV at 10 mA. cm−2 for hydrogen evolution reaction (HER) process and a low overpotential of 320 mV to reach a high current density of 20 mA. cm−2), low Tafel slope... 

To evaluate the selectivity and efficiency of solid phase microextraction (SPME) fiber coatings, synthesized by sol-gel technology, roles of precursors and coating polymers were extensively investigated. An on-line combination of capillary microextraction (CME) technique and high performance liquid chromatography (HPLC) was set up to perform the investigation. Ten different fiber coatings were synthesized in which five of them contained only the precursor and the rests were prepared using both the precursor and coating polymer. All the coatings were chemically bonded to the inner surface of copper tubes, intended to be used as the CME device and already functionalized by self-assembly...