Experimental analysis and prediction of viscoelastic creep properties of PP/EVA/LDH nanocomposites using master curves based on time–temperature superposition

Prediction of viscoelastic behavior of polymers over a long‐term period is of vital importance for engineering applications. An attempt was made to uncover the interplay between the morphology and viscoelastic behavior of compatibilized polypropylene/ethylene vinyl acetate (EVA) copolymer blends in the presence of layered double hydroxide (LDH) nanoplatelets. The time–temperature superposition (TTS) principle and WLF equations were merged to obtain master curves of storage modulus at defined reference temperatures enabling prediction of storage modulus at high frequency ranges which are not experimentally measureable. Moreover, the creep compliance master curves were acquired for different reference temperatures to predict the creep compliance of nanocomposites over long period of times. It was found that the presence of LDH decreases the creep compliance at long period of times while it decreases the unrecoverable deformation of EVA domains. A simple mechanism was proposed to explain the creep and recovery behavior of samples blend at different temperatures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46725.     

An adaptive series control for an interior permanent magnet synchronous motor with actuator compensation

An adaptive series speed control system for an interior permanent magnet synchronous motor (IPMSM) drive is presented in this paper. This control system consists of a current and a speed control loop, and it is intended to improve the drive’s speed tracking performance as well as to compensate for voltage distortions caused by non-ideal characteristics of the drive’s actuator, which is a voltage source inverter (VSI). To achieve these goals, a simple model that captures these characteristics of the VSI is developed and embedded in the motor’s electrical model. Then, based on the resulting model, an adaptive proportional-integral (PI) control for the current loops is designed, allowing for state regulation and actuator compensation. Additionally, to improve the drive’s speed tracking performance, a proportional-model-reference adaptive controller (MRAC) is designed for the speed loop. Techniques from machine learning are used for designing the MRAC to effectively address nonlinearities and uncertainties in the speed dynamic. Finally, simulation results are presented to illustrate the outstanding performance of the proposed multi-loop controller.     

A reliable and efficient micro-protocol for data transmission over an RTP-based covert channel

Multimedia Systems - As the VoIP steganographic methods provide a low capacity covert channel for data transmission, an efficient and real-time data transmission protocol over this channel is...     

A wideband beam shaping reflector antenna using model predictive control

A novel method based on model predictive control (MPC) is presented for synthesis and optimization of a wide band reflector antenna with cosecant squared and flat‐topped radiation patterns. The proposed system is a doubly curved reflector antenna with nonlinear dynamic equation. This article investigates design and optimization of a double ridged horn reflector antenna operating within the frequency range of 8 to 18 GHz. In order to synthesize the proposed reflector antenna, MPC is used to achieve the desired radiation cosecant pattern. This method utilizes system model and tries to find the best control effort for minimizing the cost function by predicting the future behavior. The system differential equation is comprised of first and second order derivatives, so MPC can be a good solution for synthesis of a doubly reflector antenna. MPC optimizer operates based on state space model, so the proposed system is linearized in the operating range. Maximum error, the average error and side lobe level of this method for the radiation pattern of the proposed wideband antenna respectively are 1.4, 0.9, and ?20 dB. Simulation results of the radiation pattern in CST and HFSS software show that the proposed reflector antenna can be used in broadband surveillance radar systems.     

Ambipolar leakage suppression in electron–hole bilayer TFET: investigation and analysis

In this paper, we propose and simulate two new structures of electron–hole bilayer tunnel field-effect transistors (EHBTFET). The proposed devices are n-heterogate with \(\hbox {M}_{1}\) as overlap gate, \(\hbox {M}_{2}\) as underlap gate and employs a high-k dielectric pocket in the drain underlap. Proposed structure 1 employs symmetric underlaps (Lgs = Lgd = Lu). The leakage analysis of this structure shows that the lateral ambipolar leakage between channel and drain is reduced by approximately three orders, the OFF-state leakage is reduced by one order, and the \(I_{\mathrm{ON}}/I_{\mathrm{OFF}}\) ratio is increased by more than one order at \(V_\mathrm{{GS}}=V_{\mathrm{DS}} =1.0\) V as compared to the conventional Si EHBTFET. The performance is improved further by employing asymmetric underlaps (\(\hbox {Lgs}\ne \hbox {Lgd}\)) with double dielectric pockets at source and drain, called as proposed structure 2. The pocket dimensions have been optimized, and an average subthreshold swing of 17.7 mV/dec (25.5% improved) over five decades of current is achieved with an ON current of \(0.23~\upmu \hbox {A}/\upmu \hbox {m}\) (11% improved) in proposed structure 2 in comparison with the conventional EHBTFET. Further, the parasitic leakage paths between overlap/underlap interfaces are blocked and the OFF-state leakage is reduced by more than two orders. A high \(I_{\mathrm{ON}}/I_{\mathrm{OFF}}\,\hbox {ratio}~>10^{9}\) (two orders higher) is achieved at \(V_{\mathrm{DS}} =V_{\mathrm{GS}} =1.0~\hbox {V}\) in the proposed structure 2 in comparison with the conventional one.     

Homogeneous polymerization of ethylene using an iron‐based metal catalyst system

An iron‐based catalyst of 2,6‐bis‐[1‐(2‐methylphenylimino)ethyl]pyridine iron dichloride was prepared. The ligand was prepared using 2,6‐diacetylpyridine as the starting chemical under controlled conditions. The preparation procedure was followed using ¹³C‐NMR, ¹H‐NMR, FT‐IR, MS (mass spectroscopy), and elemental analysis methods. The homogeneous polymerization of ethylene was carried out using the prepared catalyst in toluene media. Methyl aluminoxane (MAO) was used as a cocatalyst. The effect of the [Al] : [Fe] molar ratio, polymerization temperature, and monomer pressure of 202,000 to 454,500 Pa on the polymerization behavior were studied. The highest activity of the catalyst was obtained at 30°C, the activity decreased with increasing temperature, while increasing pressure linearly increased its activity. The molecular weight distribution of the polyethylene obtained was 1.25 to 1.72. A weight average molecular weight of 7.1 × 10⁴ and 1.5 × 10³ were obtained. The crystallinity of the polymer was about 19% and its melting point was about 65°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1517–1522, 2007     

Analysis and implementation of a new zero current switching flyback inverter

In this paper, a novel zero current switching (ZCS) flyback inverter in discontinuous conduction mode (DCM) is proposed. In the proposed flyback inverter, the ZCS for the primary switch is achieved by adding a simple auxiliary circuit to the conventional flyback inverter. Also, the auxiliary switch is turned on and turned off at ZCS condition. Therefore, the switching losses of the switches are negligible, which increases the efficiency and allows higher switching frequency and more compact design. The resonant auxiliary cell is activated only in short transition times that makes its conduction losses negligible. Furthermore, the voltage overshoot of the main switch is limited during the turn-off process, which allows utilization of lower voltage metal-oxide semiconductor field-effect transistors (MOSFETs) with low conduction losses and low cost. The detailed operation of the flyback inverter with auxiliary circuit and design considerations are presented. Simulation and experimental results are presented to verify the performance of the proposed inverter.     

Response of Triangular-Shaped Leaky Aquifers to Rainfall-Induced Groundwater Recharge: an Analytical Study

Different aspects of groundwater mound dynamics in triangular-shaped aquifers are investigated analytically under spatially uniform recharge of time-varying rate. The aquifer response is analyzed relying on 2-D linearized Boussinesq equation, subject to two different configurations of hydrogeological boundary conditions (constant-head streams and no-flow barrier). The aquifer is homogeneous, isotropic and rests over a horizontal, semipervious layer, through which vertical leakage can take place. Point-recharge formula (Green’s function) is first derived for the intended aquifer domain and then properly converted to accommodate the effect of rainfall-induced areal recharge. Components of groundwater budget are evaluated in terms of volumetric rates, taking into account the jointed effects of leakage, mound storage and outflow to adjacent streams. The resulting expressions are then proven to obey the expected mass balance in a rigorous mathematical fashion. Hypothetical examples illustrating main features of flow field are presented, with attention paid on groundwater equpotentials and streamlines. The computed mound profiles appear to agree well with numerical results from finite element method. Further, the most influential parameters affecting each component of groundwater budget are identified with the help of sensitivity analysis. Finally, the combined effects of a pumping well and rainfall-induced mound are discussed. The present solution may serve as a test case for verifying numerical schemes that are being developed for more comprehensive mound analysis.