Peak‐to‐average power ratio reduction and digital predistortion effects in power amplifiers in OFDM system

In this paper, the effects of peak‐to‐average power ratio reduction in nonlinear power amplifiers (PAs) by considering memory effects and of digital predistortion are investigated. A new predistortion technique is proposed, which is called the complex gain memory predistortion (CGMP) method. The CGMP is applied to compensate the dynamic memory effects of PAs. The conventional partial transmit sequence method is applied for peak‐to‐average power ratio reduction, and combining it with the CGMP results in efficiency enhancement and spectrum efficiency improvement. Simulation and results are examined with the two types of PAs and with an OFDM signal with quadrature phase‐shift keying modulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Polyhydroxybutyrate/chitosan/bioglass nanocomposite as a novel electrospun scaffold: fabrication and characterization

Scaffolds and their features play a central role in tissue engineering; so this study is based on the production of a series of electrospun PHB/Chitosan/nBG nanocomposite scaffolds with 9 wt% polyhydroxybutyrate, 10, 15 and 20 wt% chitosan and 7.5, 10 and 15 wt% nanobioglass (nBG). Electrospinning process was performed with optimal conditions of spinning machine including voltage of 16 kV, syringe-collector spacing of 16 cm, and output rate of 1 µl per hour. The developed phases and the formation of chemical bonds between ceramic and polymer bands were studied through XRD and FTIR analyses. The FE-SEM and TEM analyses showed uniform morphology of nanofibers and dispersion of bioglass nanoparticles in the fiber structure. The presence of 10 wt% bioglass nanoparticles and 15 wt% chitosan increased the tensile strength of fibers to 3.42 MPa, which was about four times greater than strength of control sample (pure PHB). The developed fibers were kept 28 days in SBF solution and 60 days in PBS solution to assess their bioactivity and biodegradability. The results showed that the presence of bioglass nanoparticles leads to a dramatic increase in absorption of calcium and phosphorus ions and weight loss of scaffold. The developed scaffold can be used for bone and teeth tissue engineering applications.     

Reinforced concrete deep beam shear strength capacity modelling using an integrative bio-inspired algorithm with an artificial intelligence model

The design and sustainability of reinforced concrete deep beam are still the main issues in the sector of structural engineering despite the existence of modern advancements in this area. Proper understanding of shear stress characteristics can assist in providing safer design and prevent failure in deep beams which consequently lead to saving lives and properties. In this investigation, a new intelligent model depending on the hybridization of support vector regression with bio-inspired optimization approach called genetic algorithm (SVR-GA) is employed to predict the shear strength of reinforced concrete (RC) deep beams based on dimensional, mechanical and material parameters properties. The adopted SVR-GA modelling approach is validated against three different well established artificial intelligent (AI) models, including classical SVR, artificial neural network (ANN) and gradient boosted decision trees (GBDTs). The comparison assessments provide a clear impression of the superior capability of the proposed SVR-GA model in the prediction of shear strength capability of simply supported deep beams. The simulated results gained by SVR-GA model are very close to the experimental ones. In quantitative results, the coefficient of determination (R²) during the testing phase (R² = 0.95), whereas the other comparable models generated relatively lower values of R² ranging from 0.884 to 0.941. All in all, the proposed SVR-GA model showed an applicable and robust computer aid technology for modelling RC deep beam shear strength that contributes to the base knowledge of material and structural engineering perspective.

     

An efficient recommender system algorithm using trust data

The Journal of Supercomputing - Smart services are a concept that provides services to the citizens in an efficient manner. The online shopping and recommender system can play an important role for...     

The Ameliorative Effect of Dexamethasone on the Development of Autoimmune Lung Injury and Mediastinal Fat-Associated Lymphoid Clusters in an Autoimmune Disease Mouse Model

In our previous study, we revealed the ameliorative therapeutic effect of dexamethasone (Dex) for Lupus nephritis lesions in the MRL/MpJ-Fas ^lpr/lpr (Lpr) mouse model. The female Lpr mice developed a greater number of mediastinal fat-associated lymphoid clusters (MFALCs) and inflammatory lung lesions compared to the male mice. However, the effect of Dex, an immunosuppressive drug, on both lung lesions and the development of MFALCs in Lpr mice has not been identified yet. Therefore, in this study, we compared the development of lung lesions and MFALCs in female Lpr mice that received either saline (saline group “SG”) or dexamethasone (dexamethasone group “DG”) in drinking water as a daily dose along with weekly intraperitoneal injections for 10 weeks. Compared to the SG group, the DG group showed a significant reduction in the levels of serum anti-dsDNA antibodies, the size of MFALCs, the degree of lung injury, the area of high endothelial venules (HEVs), and the number of proliferating and immune cells in both MFALCs and the lungs. A significant positive correlation was observed between the size of MFALCs and the cellular aggregation in the lungs of Lpr mice. Therefore, this study confirmed the ameliorative effect of Dex on the development of lung injury and MFALCs via their regressive effect on both immune cells’ proliferative activity and the development of HEVs. Furthermore, the reprogramming of MFALCs by targeting immune cells and HEVs may provide a therapeutic strategy for autoimmune-disease-associated lung injury.     

Interrelationship of thermal and mechanical properties of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate)/graphene nanocomposites

In the present work, attempts were made to investigate the thermal and mechanical properties of melt‐processed poly(ethylene terephthalate) (PET)/poly(ethylene 2,6‐naphthalate) (PEN) blends and its nanocomposites containing graphene by using differential scanning calorimetry and tensile test experimenting. The results showed that crystallinity, which depends on a blend ratio, completely disappeared in a composition of 50/50. By introducing graphene to PET, even in low concentrations, the crystallinity of samples increased, while the nanocomposite of PEN indicated reverse behavior, and the crystallinity was reduced by adding graphene. In the case of PET‐rich (75/25) nanocomposite blends, by increasing the nano content in the blend, the crystallinity of the samples was enhanced. This behavior was attributed to the nucleating effect of graphene particles in the samples. From the results of mechanical experiments, it was found in PET‐rich blends that by increasing the PEN/PET ratio, the modulus of samples decreased, whereas in the case of PEN‐rich blends, a slight increment of modulus is seen as a result of the increment of the PEN/PET ratio. The two contradicting behaviors were attributed to the reduction of crystallinity of PET‐rich blends by enhancement of PEN/PET ratio and the rigid structure of PEN chains in PEN‐rich blends. Unlike the different modulus change of PET‐rich and PEN‐rich blends, the nanocomposites of these blends similarly indicated an increment of modulus and characteristics of rigid materials by increasing the nano content. Furthermore, the same behavior was detected in nanocomposites of each polymer (PET and PEN nanocomposites). The alteration from ductile to rigid conduction was related to the impedance in the role of graphene plates against the flexibility of polymer chains and high values of graphene modulus. J. VINYL ADDIT. TECHNOL., 23:210–218, 2017. © 2015 Society of Plastics Engineers     

Investigation of antimicrobial properties and in-vitro bioactivity of Ce3+-Sr2+dual-substituted nano hydroxyapatites

Dual doped calcium apatite has been widely focused as it enhances the osteoconductive property for the possible applications in orthopedic and dental implants. In this work, we investigate the antimicrobial and bioactive properties of cerium/strontium (Ce³⁺/Sr²⁺) co-substituted hydroxyapatite (HA) nanoparticles synthesized by sol-gel assisted precipitation method. The structure, morphology, functional groups, photoluminescence, and thermal stability of the developed systems are examined. The comparative studies performed among the pure HA, Sr²⁺, and Ce³⁺-substituted HA nanoparticles illustrate higher antibacterial activity with lowered apatite-forming ability and biocompatibility for the Ce³⁺-substituted HA. However, the Ce³⁺/Sr²⁺co-substituted HA exhibits better biocompatibility, apatite-forming ability, and good antimicrobial properties. Sr²⁺ ion inclusion leads to better biological properties and compromise the cytotoxic nature of the Ce³⁺-HA. In addition, the Ce³⁺/Sr²⁺-HA nanoparticles prevent thermal decomposition up to 700°C, pointing also toward the possibility of this co-substituted HA in bone implant applications.     

Thermal performance of different pond cells under actual climatic conditions in Qatar

Experimental work was undertaken to study the thermal performance of three different pond cells under actual climatic conditions of Qatar. The first cell was an open pond. In the second unit, a finned radiator, painted black, was placed over the pond. In the third cell, the water was contained in a polyethylene bag. Experimental results indicated that the exposed pond cell came out best, when considered in terms of how quickly the temperature of the stored water could be reduced, and how low that temperature could be. The water in the exposed pond was cooled directly (by evaporation and radiation to sky) whereas in the case of the finned radiator cell, heat had to be transferred from the stored water to the radiator, and then from the radiator to the surrounding. In the case of water-in-bag cell, evaporation was eliminated and radiative exchange with the sky was reduced due to the partial transparency of the polyethylene bag (in the infrared region).     

Inverse Identification of Thermal Properties of Charring Ablators

The modified Levenberg-Marquardt method is used for simultaneous estimation of decomposition kinetic coefficients and temperature-dependent thermophysical properties of charring ablators with a moving boundary over a wide temperature range. No prior information is used for the functional forms of the unknown thermal conductivity and specific heat. The procedure used differs from the traditional one in that it does not require prescribed time-dependent surface heat flux, recession rate, and pyrolysis gas mass flow rate. These time-dependent quantities may recover during an iterative procedure. The measured temperatures are simulated numerically by the Charring material ablation code, which accounts for unsteady ablation. The method can determine unknown parameters in an efficient manner with reasonable accuracy, without exact advance knowledge about the net surface heat flux, surface recession, and gas flux through the material.     

The Effect of Ethanol on Nanostructures of Mixed Cationic and Anionic Surfactants

Micellization of tetradecyl trimethyl ammonium bromide (TTAB) and sodium dodecyl sulfate (SDS) in water–ethanol (ET) micellar solutions, with the weight percent of ET changing within the range 0–30, was studied by means of surface tension and conductivity measurements. Surface tension measurements also provided information about the dependence of the surface excess concentration, the minimum area per surfactant molecule, and the standard Gibbs energy of adsorption on the added weight percent of the organic solvent. Information about the degree of counterion dissociation and phase transition was obtained through conductivity measurements. Cyclic voltammetry (CV) and dynamic light scattering (DLS) was also employed to investigate the mixed micellar behavior of the binary mixtures. It was shown that an excess of cationic surfactant and ET resulted in a phase transition of vesicles and large micelles to mixed micelles. The regular solution theory approximation was used to determine various micellar parameters of ideal systems. The regular solution interaction parameter (β) suggests that the formation of mixed micelles is due to the synergistic interactions in the case of TTAB/SDS systems and becomes affected by the water/ET ratio.