Interference Management and Six-Sector Macrocells for Performance Improvement in Femto–Macro Cellular Networks

Femtocells are considered as a solution for indoor high data rate demands. Interference mitigation is a fundamental challenge in two-tier femto–macrocell networks. In this paper, we consider six-sector macrocell layout for reducing the co-tier interference in the macrocell network and cross-tier interferences from macrocell to femtocell network. As interference reduces, the whole of available spectrum can be used in each macrocell which increases the spectrum efficiency. We also consider interference-level algorithm to allocate resource for femtocell in which macrocell uses the whole of spectrum. In the coverage area of each sector, femtocell uses a portion of the spectrum that is not used by the macrocell users. This approach ignores the high co-channel interference from the macrocell network to the femtocell network and vice versa in each sector. Simulation results show that the proposed layout and interference management scheme reduce the downlink interference and increase the efficiency of the orthogonal frequency division multiple access (OFDMA)-based femtocell and macrocell. Consequently, system throughput and outage probability are improved significantly.     

Optical Characterization of Donor Doped Ternary Alloy Ga1-xNxAs and GaN-Ga1-xNxAs MQW by Using Infrared Fourier Transform Spectroscopy

In this work polarized infrared Fourier transform spectroscopy is employed to study the electronic and optical properties of doped Ga_1-xN_xAs ternary alloy and GaN-Ga_1-xN_xAs MQW. We have analyzed the far infrared spectra of GaN-GaNAs MQW by using a simple macroscopic theory base on effective medium approximation model. The dispersion curve of coupled LO phonon- plasmon modes were calculated from the polarized infrared reflectivity data. The GaNAs layer shows two-mode behavior in the infrared spectral range, a GaAs-like and a GaN-like sublattices. We detect the transverse optic phonon of GaN sublattice around 475 cm^-1. The origin of the sharp feature in p-polarization reflectivity about 300 cm^-1 as well as the dip at LO phonon frequency of GaAs sublattice are due to Brewster mode. The Brewster mode is couple strongly to plasmon mode. Attenuated total reflection spectroscopy has been used to excite and investigate surface plasmon and surface polariton.     

Efficient contrast enhancement of images using hybrid ant colony optimisation,genetic algorithm,and simulated annealing

In this paper, we propose a hybrid algorithm including Genetic Algorithm (GA), Ant Colony Optimisation (ACO), and Simulated Annealing (SA) metaheuristics for increasing the contrast of images. In this way, contrast enhancement is obtained by global transformation of the input intensities. Ant colony optimisation is used to generate the transfer functions which map the input intensities to the output intensities. Simulated annealing as a local search method is utilised to modify the transfer functions generated by ant colony optimisation. And genetic algorithm has the responsibility of evolutionary process of ants? characteristics. The employed fitness function operates automatically and tends to provide a balance between contrast and naturalness of images. The results indicate that the new method achieves images with higher contrast than the previously presented methods from the subjective and objective viewpoints. Further, the proposed algorithm preserves the natural look of input images.     

Structural, Optical and Magnetic Properties of Mn-doped CdS Diluted Magnetic Semiconductor Nanoparticles

Diluted magnetic CdS:Mn nanoparticles were synthesized by the aqueous solution method with different manganese (Mn²⁺) concentrations (x=7?C10?atom?%) at room temperature in nitrogen atmosphere and capped with Thiogelycerol. The X-ray diffraction patterns of CdS nanoparticles with different Mn doping concentration indicated that samples have hexagonal structure at room temperature. Energy dispersive X-ray spectroscopy confirmed incorporative of Mn ions in CdS nanoparticles. UV-Visible spectroscopy is used to investigate optical absorption of Mn-doped CdS. From photoluminescence measurement it was found that the intensity of the luminescence spectra decreases by increasing Mn²⁺ dopant ions at high precursor concentration. Also, the room temperature ferromagnetic behavior of Mn-doped CdS nanoparticles is discussed by using hysteresis measurement results.     

On Modeling Hydrogen-Induced Crack Propagation Under Sustained Load

The failure of hydrogen containment components is generally associated with subcritical cracking. Understanding subcritical crack growth behavior and its dependence on material and environmental variables can lead to methods for designing structural components in a hydrogen environment and will be beneficial in developing materials resistant to hydrogen embrittlement. In order to identify the issues underlying crack propagation and arrest, we present a model for hydrogen-induced stress-controlled crack propagation under sustained loading. The model is based on the assumptions that (I) hydrogen reduces the material fracture strength and (II) crack propagation takes place when the opening stress over the characteristic distance ahead of a crack tip is greater than the local fracture strength. The model is used in a finite-element simulation of crack propagation coupled with simultaneous hydrogen diffusion in a model material through nodal release. The numerical simulations show that the same physics, i.e., diffusion-controlled crack propagation, can explain the existence of both stages I and II in the velocity versus stress intensity factor (V–K) curve.     

The role of Co ion substitution in SnFe2O4 spinel ferrite nanoparticles: Study of structural,vibrational, magnetic and optical properties

In order to accurately investigate the effect of cobalt substitutions in tin ferrite (SnFe₂O₄) properties, we prepared Co_xSn_1-xFe₂O₄ nanoparticles for different Co concentrations, x?=?0.0, 0.25, 0.50, 0.75, and 1.00 using a simple co-precipitation method. X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX) and diffuse reflectance spectra (DRS) are used to study of structural, magnetic, morphology, and optical properties. The XRD and FTIR results confirmed the formation of cubic spinel structure. The lattice parameter and unit cell volume of tin ferrite nanoparticles were found to increase by entering and increasing Co⁺² content in 0.25, and then significantly decrease for higher contents. In accordance with the XRD results, a slight shift in main band υ₁ (${\mathit{Fe}}_{\mathrm{tetra}}^{+3}?O)$ to lower wavenumber and then to higher wavenumber were observed in the IR spectra of Co content x?<?0.25 and x?>?0.25, respectively. In turn to, saturation magnetization, remanent magnetization and anisotropy constant of SnFe₂O₄ nanoparticles were gradually increased for x?=?0.50 and then decreased for x?>?0.50.     

On the environmental similitude for fracture in the SENT specimen and a cracked hydrogen gas pipeline

We investigate the use of laboratory fracture specimens to ascertain the resistance to hydrogen embrittlement of a hydrogen pipeline with an axial crack on the inner diameter (ID) surface. In particular, we study the interaction of hydrogen with material elastoplasticity in single edge notch tension (SENT) specimens loaded in hydrogen gas at a pressure of 15 MPa. We find that the transient and steady state hydrogen concentration fields in the neighborhood of the crack tip in the SENT specimen and the real-life pipeline are essentially the same. This environmental similitude warrants the use of the SENT specimen in a gaseous hydrogen environment to examine the compatibility of steel pipelines with hydrogen.     

The Relationship Between Crack-Tip Strain and Subcritical Cracking Thresholds for Steels in High-Pressure Hydrogen Gas

Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. Thresholds for crack extension under rising displacement, K _THi, for crack extension under constant displacement, $ K_{\text{THi}}^{*} $ , and for crack arrest under constant displacement K _THa, were identified. These values were not found to be equivalent, i.e. K _THi < K _THa <  $ K_{\text{THi}}^{*} $ . The hydrogen assisted fracture mechanism was determined to be strain controlled for all of the alloys in this study, and the micromechanics of strain controlled fracture are used to explain the observed disparities between the different threshold measurements. K _THa and K _THi differ because the strain singularity of a stationary crack is stronger than that of a propagating crack; K _THa must be larger than K _THi to achieve equivalent crack tip strain at the same distance from the crack tip. Hydrogen interacts with deformation mechanisms, enhancing strain localization and consequently altering both the nucleation and growth stages of strain controlled fracture mechanisms. The timing of load application and hydrogen exposure, i.e., sequential for constant displacement tests and concurrent for rising displacement tests, leads to differences in the strain history relative to the environmental exposure history and promotes the disparity between $ K_{\text{THi}}^{*} $ and K _THi. K _THi is the only conservative measurement of fracture threshold among the methods presented here.     

Effect of Carbon Shell on the Structural and Magnetic Properties of Fe3O4 Superparamagnetic Nanoparticles

Carbon-encapsulated iron oxides (Fe₃O₄/C) with a core/shell structure have been successfully synthesized by using a simple two-step hydrothermal method at 180 ^°C. Fe₃O₄ core nanoparticles were prepared by coprecipitation under two conditions. Synthesized nanoparticles were characterized by transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. TEM images and FTIR results prove that carbon coated iron oxide is formed and the estimated size for most of them is below 11 nm, which was consistent with the XRD result. The Williamson–Hall (W–H) method has been used to calculate crystallite sizes and lattice strain based on the peak broadening of the Fe₃O₄ and Fe₃O₄/C nanoparticles. The results of VSM imply that the Fe₃O₄ core and core–shell nanoparticles are superparamagnetic. The saturation magnetization of Fe₃O₄ and Fe₃O₄/C are 49 emu/gr and 40 emu/gr, respectively. The magnetic behaviors reveal that the amorphous carbon shell can decrease the saturation magnetization of Fe₃O₄ nanoparticles due to core–shell interface effects and shielding.