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.     

A CNFET-based hybrid multi-threshold 1-bit full adder design for energy efficient low power applications

In this article, a low-power and energy-efficient hybrid full adder circuit is proposed, which is implemented based on multi-threshold NAND and NOR gates and transmission gate multiplexers. In order to implement this circuit, carbon nano tube field effect transistors are utilised. For evaluating the proposed design, comprehensive simulations are performed with regard to the most important aspects power, delay and power-delay product. The results are presented and displayed the superiority of the proposed cell in different voltage levels, load conditions, temperatures and robustness against process variations.     

A Two Stage Variable-Gain Low-Noise Amplifier for X-Band in 0.18 µm CMOS

In this paper a variable gain low noise amplifier (VG-LNA) is designed and analyzed for X band in 0.18 µm CMOS technology. A two-stage structure is utilized in the proposed VG-LNA and its gain, which is controlled by an on-chip voltage (V_cnt), has continuous and almost linear variations. The required range for V_cnt can be initiated from 0.5 V, also the variations of gain doesn’t ruin reflection loss (S11), return loss (S12) and noise figure (NF). The best performance of this VG-LNA is at 10 GHz frequency with 1 GHz bandwidth. In the center frequency, the maximum gain is 20.8 dB that continuously and linearly decreases to 4 dB by increasing V_cnt. Also S11 and S12 in this frequency are lower than ?27 and ?38 dB, respectively. NF is lower than 2 dB in the mentioned frequency range and NF_min is equal to 1.2 dB, while the third-order intercept point (IIP3) equals to 8.27 dBm in the best condition and always stays above ?10 dBm. The main advantage of the proposed structure in compare with the similar structures is not only the key parameters don’t ruin by the gain variations, but also increment of V_cnt operation range (0.5 V to V_dd), leads to expanding gain control range. These results are achieved while the power consumption is 8.4 mW with 1.8 V supply voltage and the chip area is 0.56 mm².     

Novel Metamaterial Compact Planar MIMO Antenna Systems with Improved Isolation for WLAN Application

In this paper, two element multiple input–multiple output (MIMO) meander line antenna systems with improved isolation performance and compact size are proposed and fabricated in WLAN frequency band. To increase isolation among antenna elements, a novel metamaterial spiral S-shaped resonator is embedded between two radiating elements. The proposed resonator has planar configuration and miniaturized size and is capable of blocking electromagnetic propagation between antenna elements by exhibiting negative effective permeability in the desired frequency band. To illustrate and evaluate the design process, two design samples are fabricated and tested in WLAN frequency band and the agreement among measurement and simulation results approves the design method. In the frequency range of 2.38–2.48 GHz, some MIMO communication system requirements like total active reflection coefficient, envelope correlation coefficient and capacity loss are tested on design samples which show satisfactory results, so this method can be employed in designing array antennas for small mobile communication systems. The designed MIMO antenna systems separated by 13.8 mm (less than λ/9), has better than ??40 dB isolation coefficient and near zero correlation coefficient and capacity loss at the operating frequency (2.4 GHz).

     

The microstructural characterization of semi-solid slurries

Due to recent interest in semi-solid metal (SSM) processing, there is a need for fundamental knowledge on the formation and solidification of primary particles. The primary particle size, distribution, morphology, and percentage are the main concerns because particle quantity and size affect not only the mechanical properties of as-cast SSM parts but also the flow characteristics of SSM slurries during die filling. Microstructural characterization is a basic tool for measuring the critical parameters that influence the resulting properties. This article describes the tools and techniques available for structural analysis of SSM slurries. It also attempts to elucidate the ambiguities and interpretations of special structural features.     

Toughening MoSi2 with niobiúm metal—effects of morphology of ductile reinforcements

Morphology effect of ductile reinforcements was evaluated using a four-point bend test on chevron-notched MoSi₂ composites reinforced with 20 vol. % niobium. The niobium used had three different morphologies, i.e., fibre, foil and particle. The thickness of the foils was 250 m, while the fibres and particles had diameters of 250 and 200 m, respectively. Toughness of MoSi₂ composites was increased from 3.3 MPa m^1/2 for the matrix to 15 MPa m^1/2 with the incorporation of the Nb fibres or foils. The particulate composites also exhibited an increase in toughness (7 MPa m^1/2). The toughening achieved was mainly attributed to ductile phase bridging in all the composites tested. The relatively small toughness improvement in the particulate composites was ascribed to the embrittlement of the Nb particles. The results indicate that toughening by crack bridging depends mainly on the intrinsic properties of the ductile bridging ligaments rather than on their morphology, and that the embrittlement of the bridging ligament is detrimental to the toughening of the composites.Previously known as L. Xiao.     

A machine learning-based dynamic link power control in wearable sensing devices

Wireless Networks - The main research challenges on developing Wireless Body Area Networks (WBAN) are related to the quality of the communication link and energy consumption. This article combines...     

Improving the reliability of Byzantine fault‐tolerant distributed software‐defined networks

This paper presents a method to improve the reliability and fault tolerance of distributed software‐defined networks. This method is called “BIRDSDN (Byzantine‐Resilient Improved Reliable Distributed Software‐Defined Networks).” In BIRDSDN, a group communication is implemented among the controllers of the whole clusters. This method can detect the crash failure and Byzantine failure of any controller and undertakes a fast detection and recovery scheme to select the controllers to take over the orphan switches. BIRDSDN takes into account the reliability of the nodes considering the failure probability of intracluster and intercluster links, topology, load, and latency. The numerical results show that this approach performs better than the other approaches regarding failure detection, recovery, latency, throughput, reliability, and packet loss.     

Securing Wireless Sensor Networks Against Denial‐of‐Sleep Attacks Using RSA Cryptography Algorithm and Interlock Protocol

Wireless sensor networks (WSNs) have been vastly employed in the collection and transmission of data via wireless networks. This type of network is nowadays used in many applications for surveillance activities in various environments due to its low cost and easy communications. In these networks, the sensors use a limited power source which after its depletion, since it is non‐renewable, network lifetime ends. Due to the weaknesses in sensor nodes, they are vulnerable to many threats. One notable attack threating WSN is Denial of Sleep (DoS). DoS attacks denotes the loss of energy in these sensors by keeping the nodes from going into sleep and energy‐saving mode. In this paper, the Abnormal Sensor Detection Accuracy (ASDA‐RSA) method is utilized to counteract DoS attacks to reducing the amount of energy consumed. The ASDA‐RSA schema in this paper consists of two phases to enhancement security in the WSNs. In the first phase, a clustering approach based on energy and distance is used to select the proper cluster head and in the second phase, the RSA cryptography algorithm and interlock protocol are used here along with an authentication method, to prevent DoS attacks. Moreover, ASDA‐RSA method is evaluated here via extensive simulations carried out in NS‐2. The simulation results indicate that the WSN network performance metrics are improved in terms of average throughput, Packet Delivery Ratio (PDR), network lifetime, detection ratio, and average residual energy.     

Phenylhydrazinium Iodide for Surface Passivation and Defects Suppression in Perovskite Solar Cells

In recent years, hybrid perovskite solar cells (HPSCs) have received considerable research attention due to their impressive photovoltaic performance and low‐temperature solution processing capability. However, there remain challenges related to defect passivation and enhancing the charge carrier dynamics of the perovskites, to further increase the power conversion efficiency of HPSCs. In this work, the use of a novel material, phenylhydrazinium iodide (PHAI), as an additive in MAPbI₃ perovskite for defect minimization and enhancement of the charge carrier dynamics of inverted HPSCs is reported. Incorporation of the PHAI in perovskite precursor solution facilitates controlled crystallization, higher carrier lifetime, as well as less recombination. In addition, PHAI additive treated HPSCs exhibit lower density of filled trap states (10¹⁰ cm^?2) in perovskite grain boundaries, higher charge carrier mobility (≈11 × 10^?4 cm² V^?1 s), and enhanced power conversion efficiency (≈18%) that corresponds to a ≈20% improvement in comparison to the pristine devices.