A zero-current switching switched-capacitor DC-DC converter with reduction in cost,complexity, and size

This paper presents a new step-up switched-capacitor (SC) DC-DC converter which has many advantages such as reduction in investment cost, control complexity, number of components, voltage stress on components, and size over traditional topologies. In the proposed structure, power switches are reduced in number which in turn leads to the merits mentioned earlier and makes the converter more suitable for industrial applications. Furthermore, a previously introduced zero-current switching (ZCS) method is used here which provides soft switching for the devices. There is also a reduction in the number of required inductors to achieve ZCS due to the decreased number of switches in the proposed converter. The proposed converter is validated by comprehensive simulation results in MATLAB Simulink environment and also precise experimental results which show the acceptable performance of the proposed topology.     

High-blocking-voltage UMOSFETs with reformed electric field distribution

A high-performance vertical GaN metal–oxide–semiconductor field-effect transistor (MOSFET) with a U-shaped gate (UMOSFET) and high blocking voltage is proposed. The main concept behind this work is to reform the electric field distribution to achieve high blocking voltage. The proposed structure includes p-regions in the drift region, which we call reformed electric field (REF) regions. Simulations using the two-dimensional SILVACO simulator reveal the optimum doping concentration, and width and height of the REF regions to achieve the maximum depletion region at the breakdown voltage in the drift region. Also, the electric field distribution in the REF-UMOSFET is reformed by producing additional peaks, which decreases the common peaks under the gate trench. We discuss herein the impact of the height, width, and doping concentration of the REF regions on the ON-resistance (R_ON) and blocking voltage. The blocking voltage, specific ON-resistance, and figure of merit \( \left( {{\text{FOM}} = \frac{{V_{{{\text{BR}}}}^{2} }}{{R_{{{\text{ON}}}} }}} \right) \) are 1140 V, 0.587 mΩ cm² (V_GS = 15 V, V_DS = 1 V), and 2.214 GW/cm², respectively. The blocking voltage and FOM are increased by about 72 % and 171 % in comparison with a conventional UMOSFET (C-UMOSFET).     

Bi-supported Ziegler–Natta TiCl4/MCM-41/MgCl2 (ethoxide type) catalyst preparation and comprehensive investigations of produced polyethylene characteristics

Bi-supported Ziegler–Natta catalysts (TiCl₄/MCM-41/MgCl₂ (ethoxide type)) were synthesized to improve the morphology and the properties of polyethylene. The morphology control is a crucial issue in polymerization process, while tailoring the properties of polymers is needed for specific applications. The catalysts were synthesized in different ratios of two supports with impregnation method. The polymerization process was carried out in atmospheric slurry reactor. The catalysts were characterized with scanning electron microscopy - energy dispersive X-ray spectroscopy (SEM–EDX), inductively coupled plasma, Fourier transform infrared spectrometry (FTIR), and Brunauer-Emmett-Teller (BET) methods. The polymers were analyzed with scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry, FTIR, and tensile-strength analyses. Ubbelohde viscometer and frequency sweep measurements showed that the synthesized polymers are ultra-high-molecular-weight polyethylene. Mechanical properties of polymers showed higher Young's modulus in samples containing MCM-41, having higher thermal stability supported by TGA analysis. SEM images of bi-supported catalyst showed a controlled spherical morphology with uniform size distribution. SEM analysis support that the polymers replicate their morphology from catalyst, improving their morphology comparing to MgCl₂-supported catalyst. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48553.     

Hydrophilicity improvement of silicone rubber by interpenetrating polymer network formation in the proximal layer of polymer surface

A novel method composed of an interpenetrating polymer network (IPN) formation reaction in aqueous solution was developed to improve the hydrophilicity of silicone rubber (SR) substrate. This solution phase method is compatible, simple, and convenient for some sensitive biomedical applications of SR devices because of using water as reaction solvent instead of harmful chemicals. In this work, a sequential interpenetrating polymer network formation in the proximal layer of SR surface, using poly(2-hydroxyethyl methacrylate) (PHEMA), as the second network was conducted so that led to actually surface modification resulting in an improved hydrophilicity. The modified surfaces were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) to assess the wettability, chemical composition and morphology of the surface modified PDMS. The results indicated that the surface modification method offered a novel and facile approach to improve the hydrophilicity of SR without altering its bulk properties. This method could be suitable for biomedical applications because of using water as a monomer solvent and polymerization medium.     

Synthesis of Ferrocene-Based Hyperbranched Polyether and Its Catalytic Performance for Thermal Decomposition of Ammonium Perchlorate

A series of ferrocene-based hyperbranched polyethers (HBPE-Fc) with different ferrocene content were synthesized by esterification of ferrocenecarbonyl chloride and hyperbranched polyether (HBPE). ¹H NMR and FT-IR were used to confirm the structure of HBPE and HBPE-Fc. GPC was used to calculate the molecular weights. The catalytic performance of the synthesized HBPE-Fc for thermal decomposition of ammonium perchlorate (AP) was investigated by TG and DTG techniques. The results showed that HBPE-Fc exhibited good catalytic activity on the thermal decomposition of AP. The influence factors on catalytic performances, such as substitution degree of ferrocene and mass ratio of AP/HBPE-Fc were discussed as well.     

Damage mechanism at different transpassive potentials of solution-annealed 316 and 316l stainless steels

Electrochemical impedance spectroscopy (EIS), anodic polarization and scanning electron microscopy techniques were used to investigate the damage mechanism in the transpassive potential region of AISI ...     

Simulation of CNT based mass resonator sensor and investigation on the effect of vacancy defect on sensing performances

Microsystem Technologies - In this paper carbon nanotube (CNT) as a mass resonator sensor has been modelled by molecular structural mechanics approach. Then the effect of a single vacancy defect...     

Design of sliding mode and model reference adaptive control strategies for multivariable tape transport mechanism: a performance comparison

This paper presents sliding mode control and model reference adaptive control strategies for the tape transport mechanism. A nonlinear multivariable MIMO model of the process, consisting of take-up and supply reel servos for tape tension control and capstan servo for speed control is considered. The sliding mode control is applied for the nonlinear dynamic model of the process, while the model reference adaptive control deals with the linearized one. Moreover, in order to associate with the realistic model of system, design of controllers is accomplished with respect to parametric uncertainties. It is shown that both control strategies can guarantee asymptotic stability of the closed-loop system and tracking of desired outputs with the appropriate pace in the presence of uncertainties. Finally, simulation results demonstrate the effectiveness of the proposed controllers.