Preparation and characterization of a superabsorbent slow‐release fertilizer with sodium alginate and biochar

A novel hydrogel was synthesized through the graft copolymerization of acrylic acid (AA) and acrylamide (AM) onto sodium alginate with ammonium persulfate as the initiator, methylene bisacrylamide as the crosslinking agent, and calcium chloride as the precipitating agent. Rapeseed meal biochar made at 300 °C was also used. A series of graft copolymers with various molar ratio of AA to AM was prepared. The structures of the hydrogels were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The free absorbency and rate of release were investigated. The grafting efficiency increased as the concentration of AM increased. There was a considerable percentage of nitrogen in the graft copolymers, and the release rate of nitrogen from fertilizer in soil and water decreased with increasing concentration of AM. The water retention of soil without hydrogel remained at 63 and 53.4% on the 10th and 20th days, but with the hydrogels, it was above 70% even on the last day. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45966.     

Genetically modified multiuser detection for code division multipleaccess systems

The problem of multiple access interference (MAI) and intersymbol interference (ISI) suppression in code division multiple access (CDMA) systems is considered. By combining the theory of multiuser detection (MUD) and evolutionary computation, a hybrid genetic engine is proposed, suitable for the detection of CDMA signals in the presence of MAI and ISI. The proposed hybrid detector structure can be extended to most multiuser detectors and used as the base detector within the structure. Using random selection, mutation and crossover operators and a unique chromosome structure, the genetic algorithm evolves the base detector to a group of more efficient detectors in terms of bit-error rate performance. First, a new packet-level genetic MUD technique, using a conventional single user detector as the base detector, is proposed for asynchronous CDMA (ACDMA) with negligible ISI. Then the signal-subspace-based minimum mean square error detector is chosen as a base detector and wrapped inside the hybrid genetic engine to evolve to a better structure nearly to eliminate both ISI and MAI. The novelty of the proposed structure is the way the deterministic closed-form solution of the base detector is mapped to a genetic engine resulting in a group of more efficient and adaptive detectors     

An energy-efficient power allocation scheme for millimeter-wave MIMO-NOMA systems

There are many challenges in fifth generation (5G) telecommunication systems, due to the increasing demands and applications. The most important of which are need to have higher energy efficiency (EE) and spectral efficiency (SE). They are critical in the practical multiple-input multiple-output (MIMO) telecommunication systems. Non-orthogonal multiple access (NOMA) methods and millimeter-waves can be used in conjunction with MIMO systems to improve their EE and SE performance. In this paper, we investigate the application of NOMA and mm-Wave transmission in the downlink of MIMO systems. Then, we formulate the optimization problem for users in MIMO-NOMA systems to maximize the EE that is subject to minimum data rate to satisfy required quality of service (QoS) and maximum transmission power. To achieve the optimal power allocation for users, we reach a problem for the EE maximization that is non-convex and solution of the optimization problem is not trivial. We exploit a lower bound of the data rate and the Lagrange dual function to convert it to a convex and unconstrained problem, which is easy to solve. In the next step, we derive a relation for determining the optimal power allocation of users. In addition, a numerical algorithm is presented that can be used to solve the problem. According to the simulation results of the proposed algorithm, our method performs better and provides higher EE than both orthogonal multiple access and equal power allocation schemes.     

Detection and classification of sleep apnea using genetic algorithms and SVM‐based classification of thoracic respiratory effort and oximetric signal features

Sleep apnea is a relatively prevalent breathing disorder characterized by temporary interruptions in airflow during sleep. There are 2 major types of sleep apnea. Obstructive sleep apnea occurs when air cannot flow through the upper airway despite efforts to breathe. Central sleep apnea occurs when the brain fails to signal to the muscles to maintain breathing. The standard diagnostic test is polysomnography, which is expensive and time consuming. The aim of this study was to design an automatic diagnostic and classifying algorithm for sleep apneas employing thoracic respiratory effort and oximetric signals. This algorithm was trained and tested applying a database of 54 subjects who had undergone polysomnography. A feature extraction stage was conducted to compute features. An optimal genetic algorithm was applied to select optimal features of these 2 kinds of signals. The classification technique was based on the support vector machine classifier to classify the selected features in 3 classes as healthy, obstructive, and central sleep apnea events. The results show that our automated classification algorithm can diagnose sleep apnea and its types with an average accuracy level of 90.2% (87.5‐95.8) in the test set and 90.9% in the validation set with high acceptable accuracy.     

钢管混凝土柱中的新型钢截面

在现代工程建设中,钢管混凝土（CFT）柱已逐渐成为高层建筑、桥梁等结构系统中的核心构件。在钢管混凝土的承载能力分析中有效参数有：钢与混凝土之间的粘结、钢管局部屈曲强度、混凝土徐变和连接处柱的负荷状态。考虑到这些有效参数,提议一种新截面,可用于高层建筑及大跨度桥梁。所提议钢截面的主要特点是内部纵向对称加劲肋。对此种截面（圆形和八角形）和钢管混凝土柱的常用截面进行轴向和循环荷载作用下的对比分析。同时采用有限元建模进行多种不同的分析。结果表明：新型截面在轴向和循环荷载下的强度和延性均有所增强,因此建议在施工中可采用此种截面。     

Quantum Monte Carlo simulation of dissipative transport using Bohmian trajectories

In this paper, a Monte Carlo method is proposed, which utilizes Bohmian trajectories to simulate dissipative transport in one-dimensional quantum devices. The proposed method, similar to the classical Monte Carlo method, is capable of simulating both elastic and inelastic scattering effects, with the distinction that quantum effects such as tunneling are also included. At first, the Bohmian trajectories for the wave packets injected from the right and the left contacts are obtained by solving the time-dependent Schrodinger equation, and then scattering effects are included via stochastic changes applied on the electron trajectories. We have shown that the results of the proposed model agree well with those of NEGF formalism.     

Grain Refinement through Shear Banding in Severely Plastic Deformed A206 Aluminum Alloy

The present work is conducted to study the microstructure and texture evolutions in an as‐cast A206 aluminum alloy after applying severe plastic deformation. Toward this end, the material is severely deformed through accumulative back extrusion (ABE) technique at 200 °C and followed by assessing the room temperature mechanical properties of the products. The macro shear‐bands formation in the highly strained regions can result in grain refinement through the geometric dynamic recrystallization mechanism. A significant refinement is also characterized within the micro shear‐bands; this is attributed to the intensified substructure development and the occurrence of continuous dynamic recrystallization. The corresponding inverse pole figure maps show similar orientation for these newly refined grains with the parent ones. A random texture is produced through sub‐grain rotation to dissimilar orientation at the intersection of micro‐bands. The assessment of mechanical properties of the processed materials reveal significant increase in both yield and ultimate tensile strength values. The hardness profiles also demonstrate a relatively homogenous microstructure after three and five ABE passes holding a mean hardness value of 183 Vickers.     

Mobility assisted spectrum aware routing protocol for cognitive radio ad hoc networks

We propose a mobility assisted spectrum aware routing （MASAR） protocol for cognitive radio ad hoc networks （CRAHNs）, providing robustness to primary user activity and node mobility. This protocol allows nodes to collect spectrum information during a spectrum management interval followed by a transmission period. Cognitive users discover next hops based on the collected spectrum and mobility information. Using a beaeonless mechanism, nodes obtain the mobility information and spectrum status of their neighbors. A geographical routing scheme is adopted to avoid performance degradation specially due to the mobility of the nodes and the activity of the primary users. Our scheme uses two approaches to find either short or stable routes. Since mobility metrics have a significant role in the selection of the next hop, both approaches use a reactive mobility update process assisted by mobility prediction to avoid location errors. MASAR protocol performance is investigated through simulations of different scenarios and compared with that of the most similar protocol, CAODV. The results indicate that MASAR can achieve significant reduction in control overhead as well as improved packet delivery in highly mobile networks.     

Microstructural Analysis of Fusion Zone in Gas Tungsten Arc-Welded Newly Developed Co-Based Superalloy

Metallurgical and Materials Transactions A - The fusion zone (FZ) microstructure of a newly developed gas tungsten arc-welded cobalt-based superalloy called CoWAlloy1 is characterized. Elemental...     

Ti alkoxide-based catalyst system in selective ethylene dimerization: High performance through modifying by alkylsilanes

Butene-1 production through a selective ethylene dimerization is one of the largest industrial processes, which is catalyzed by homogeneous catalyst system. The common industrial catalyst system is comprised of Ti alkoxide-based catalysts in combination with AlEt₃ as an activator. In this study, the alkylsilanes were used as novel improving agents in the catalyst system for highly selective ethylene dimerization to butene-1. The nature and concentration of alkylsilanes on the dimerization rate, catalyst yield, by-product production, and selectivity to butene-1 were investigated in detail. It was found that alkylsilanes improved the productivity and selectivity of the catalyst. Moreover, the content of the solid by-product considerably decreased. The performance of the modified catalyst system was noticeably higher than that of the nonmodified one. Totally, it was proved that alkylsilanes could play a modifying role in the selective ethylene catalytic dimerization process.