Adaptive predistortion using threshold decomposition‐based piecewise linear modeling

A new adaptive predistortion approach for nonlinear power amplifiers based on the piecewise linear (PWL) approximation of nonlinear functions is presented. The PWL model is obtained using threshold decomposition (TD) of the input‐output characteristics. The TD based PWL model is used to develop a baseband predistorter using both the direct and the indirect learning architectures. The proposed predistorter is proved to provide a better performance in suppressing nonlinear distortion than conventional polynomial predistorters and a reduced hardware complexity as compared to lookup table (LUT) approach. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Fuzzy functions with LSE

“Fuzzy Functions” are proposed to be determined by the least squares estimation (LSE) technique for the development of fuzzy system models. These functions, “Fuzzy Functions with LSE” are proposed as alternate representation and reasoning schemas to the fuzzy rule base approaches. These “Fuzzy Functions” can be more easily obtained and implemented by those who are not familiar with an in-depth knowledge of fuzzy theory. Working knowledge of a fuzzy clustering algorithm such as FCM or its variations would be sufficient to obtain membership values of input vectors. The membership values together with scalar input variables are then used by the LSE technique to determine “Fuzzy Functions” for each cluster identified by FCM. These functions are different from “Fuzzy Rule Base” approaches as well as “Fuzzy Regression” approaches. Various transformations of the membership values are included as new variables in addition to original selected scalar input variables; and at times, a logistic transformation of non-scalar original selected input variables may also be included as a new variable. A comparison of “Fuzzy Functions-LSE” with Ordinary Least Squares Estimation (OLSE)” approach show that “Fuzzy Function-LSE” provide better results in the order of 10% or better with respect to RMSE measure for both training and test cases of data sets.     

A novel Arabic OCR post-processing using rule-based and word context techniques

International Journal on Document Analysis and Recognition (IJDAR) - Optical character recognition (OCR) is the process of recognizing characters automatically from scanned documents for editing,...     

Synthesis of high molecular weight aromatic polyesters via integrated alternating ring-opening copolymerization and chain extension methods

Due to their good mechanical properties, high molecular weight polyesters (PEs) are highly desirable for a wide range of applications especially in the packaging industry. However, the synthesis of high molecular weight polymers by energy efficient methods is difficult. In this study, a series of semi-aromatic PEs were synthesized via the alternating ring-opening copolymerization (ROCOP) of phthalic anhydride (PA) and cyclohexene oxide (CHO) using a salen chromium(III) complex as a catalyst and 4-(dimethylamino)pyridine as a cocatalyst. By varying the molar ratios between CHO and PA, PEs of different molecular weights were obtained. Hexamethylene diisocyanate was used as a chain extender that further increased the molecular weights of these PEs. These chain extended aromatic polyesters (PE-Xs) showed significant improvement in the glass transition temperature (T_g) values. Thus, integration of ROCOP with the chain extension method can be used as an effective strategy to prepare high molecular weight PEs with improved thermal stabilities and enhanced mechanical properties. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47200.     

WSANFlow: An Interface Protocol Between SDN Controller and End Devices for SDN-Oriented WSAN

When dealing with a Wireless Sensor and Actuator Network (WSAN) structure, one of the challenging problems is lack of flexibility in such network operations as establishment, management, and configuration. Software-defined Networking (SDN) is a promising technology for a simpler, more flexible, and less overworked network structure. Integration of SDN as a solution into the existing WSAN structures seems to be a strong candidate of deployment solutions for next generation WSAN systems. In order to get enhanced performance results for WSAN systems, we proposed an interface protocol, referred to as WSANFlow, which is responsible for all the communications between SDN controller (SDNC) and SDN-oriented end devices. The SDNC in this approach has the network intelligence and is capable of handling all the control and management operations related to the network. Thus, advanced communication operations can be managed and efficiently optimized efficiently by the SDN controller and then, subsequently, corresponding instructions can be delivered to end devices using the proposed WSANFlow protocol. In the study, we analyzed the proposed framework performance, in terms of power consumption ratio, throughput, and end to end delay metrics. Then, we compared the results with those of a ZigBee-based counterpart for different workloads such as; light, heavy and heavier load which modelizes a video stream of mild parameters. The results show that not only has the overall performance of the existing WSAN system been enhanced, but also control and management operations have been simplified by the proposed model.     

Preparation of hybrid PU/PCL fibers from steviol glycosides via electrospinning as a potential wound dressing materials

In this study, the synthesis and application of biocompatible steviol glycosides based polyurethane/poly (ε-caprolactone) (PU/PCL) fibers was performed by electrospinning as a potential wound dressing materials that can be used for the closure of nonhealing wounds. During electrospinning, steviol glycoside-based polyurethane structures were used in blend formation with poly (ε-caprolactone) for easy producibility. Steviol glycosides are a natural abundant and easily accessible source as the main component of the wound dressing material due to their free hydroxyl groups, high biocompatibility, and hydrophilicity. The structure of steviol glycosides is composed of saccharide units and the free OH groups. Thus, steviol glycosides act as a crosslinker within the polyurethane structure and provides mechanical strength. For the production of steviol glycosides based PU/PCL fibers first, the steviol glycosides as a monomer were isolated from the stevia rebudiana. Then, polyurethane structures containing stevia glycoside were synthesized with hexamethylene diisocyanate, lactose and PEG-200 by solution polymerization technique. PCL was added to the prepared polyurethanes in a ratio of 1:2 and formation of nanofiber structure. The prepared wound dressing material was characterized by Fourier transform infrared, atomic force microscopy, and scanning electron microscope techniques. Swelling degree, water content and oxygen permeability assay of the steviol glycosides based PU/PCL wound dressing material was determined. In biocompatibility test, cell viability value of PU/PCL fibrous materials in indirect cytotoxicity test was determined as 86.9% and cell adhesion on hybrid PU/PCL fibers was showed as morphological. In accordance with this target, the steviol glycosides based PU/PCL wound dressing material can be produced easily and low cost. As a result, the wound dressing materials obtained with their high biocompatibility and low costs will be an effective and fast method for the healing of open wounds of diabetics.     

Synthesis and characterization of PMMA composites activated with starch for immobilization of L‐asparaginase

Poly (methyl methacrylate) (PMMA)–starch composites were prepared by emulsion polymerization technique for L‐asparaginase (L‐ASNase) immobilization as highly activated support. The hydroxide groups on the prepared composites offer a very simple, mild and firm combination for enzyme immobilization. The pure PMMA and PMMA‐starch composites were characterized as structural, thermal and morphological. PMMA‐starch composites were found to have better thermal stability and more hydrophilic character than pure PMMA. L‐ASNase was immobilized onto PMMA‐starch composites contained the different ratio of starch (1, 3, 5, and 10 wt %). Immobilized L‐ASNase showed better performance as compared to the native enzyme in terms of thermal stability and pH. K_m value of immobilized enzyme decreased approximately eightfold compared with the native enzyme. In addition to, immobilized L‐ASNase was found to retain 60% of activity after 1‐month storage period at 4 °C. Therefore, PMMA‐starch composites can be provided more advantageous in terms of enzymatic affinity, thermal, pH and storage stability as L‐ASNase immobilization matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43421.     

Structure and Microwave Dielectric Behavior of A‐Site‐Doped Sr(1−1.5x)CexTiO3 Ceramics System

The ion valence state, phase composition, microstructure, and microwave dielectric properties of Sr_(1?1.5x)Ce_xTiO₃ (x = 0.1–0.67, SCT) ceramics were systematically investigated. Sr_(1?1.5x)Ce_xTiO₃ ceramics were produced with gradual structural evolution from a cubic to a tetragonal and turned to an orthorhombic structure in the range of 0.1 ≤ x ≤ 0.67. Above a critical Ce proportion (x = 0.4), microstructural changes and normal grain growth initially occurred. On the basis of chemical analysis results, the reduction of Ti⁴⁺ ions was hastened by tetravalent ions (Ce⁴⁺). By contrast, this reduction was inhibited by trivalent ions (Ce³⁺). The observed dielectric behavior was strongly influenced by phase composition, oxygen vacancies (), and defect dipoles, namely, () and (). Temperature stable ceramics sintered at 1350°C for 3 h in air yielded an intermediate value of dielectric constant (ε_r = 40), with the smallest reported value of temperature coefficient of resonant frequency (τ_f = +0.9 ppm/°C), and quality factor (Q × f = 5699 GHz) at x = 0.6.     

Numerical Study on Heat Transfer Between Turbulent Flow and Porous Rectangular Cylinders with Uniform Injection or Suction

The heat transfer characteristics of the flow around rectangular cylinders having various aspect ratios with uniform injection or suction through the rear, top, bottom, and all surfaces have been studied numerically. The effects of injection or suction on heat transfer have been linked to the analysis via wall functions of the velocity and temperature sublayers. The computational code employed in the present study was verified with a typical benchmark problem of the flow around a square cylinder. The results show that the heat transfer between the main flow and rectangular cylinders is substantially influenced by injection or suction—that is, suction enhances the heat transfer, while injection through the rear surface provides some thermal protection.