Resource allocation in OFDMA networks based on interior point methods

This paper studies a joint optimization problem of sub‐carrier assignment and power allocation in orthogonal frequency division multiple access (OFDMA) wireless networks. A major challenge in solving the optimization problem is non‐convexity caused by the combinatorial nature of sub‐carrier assignment problem and/or non‐convex objective functions. To address the combinatorial complexity, we formulate the resource allocation problem as an optimization problem with continuous variables. We propose a novel approach based on a penalty function method and an interior point method (PM/IPM) to solve the problem. In specific, using a two‐step implementation, the penalty method is applied first to convert the non‐convex feasible region to a convex one. Then, the interior point method is deployed to solve the problem which is non‐convex only in the objective function. To evaluate the performance of PM/IPM, we apply a genetic algorithm (GA) that achieves near optimal solutions of the problem by iterative searching. Copyright © 2009 John Wiley & Sons, Ltd.     

Temperature dependence of copper diffusion in different thickness amorphous tungsten/tungsten nitride layer

The amorphous W/WN films with various thickness (10, 30 and 40 nm) and excellent thermal stability were successfully prepared on SiO₂/Si substrate with evaporation and reactive evaporation method. The W/WN bilayer has technological importance because of its low resistivity, high melting point, and good diffusion barrier properties between Cu and Si. The thermal stability was evaluated by X-ray diffractometer (XRD) and Scanning Electron Microscope (SEM). In annealing process, the amorphous W/WN barrier crystallized and this phenomenon is supposed to be the start of Cu atoms diffusion through W/WN barrier into Si. With occurrence of the high-resistive Cu₃Si phase, the W/WN loses its function as a diffusion barrier. The primary mode of Cu diffusion is the diffusion through grain boundaries that form during heat treatments. The amorphous structure with optimum thickness is the key factor to achieve a superior diffusion barrier characteristic. The results show that the failure temperature increased by increasing the W/WN film thickness from 10 to 30 nm but it did not change by increasing the W/WN film thickness from 30 to 40 nm. It is found that the 10 and 40 nm W/WN films are good diffusion barriers at least up to 800°C while the 30 nm W/WN film shows superior properties as a diffusion barrier, but loses its function as a diffusion barrier at about 900°C (that is 100°C higher than for 10 and 40 nm W/WN films).     

Role of local and urban textures in promoting social interactions of residents and emphasizing living centers theory of Christopher Alexander

Local and urban squares play a crucial role in the presence and participation of people and in their interaction promotion. Alexander explained the profound geometric relations and discipline in nature, using the concept of life phenomenon theory and living structures. He believes that humans can revive creatures through creating strong centers and an integrated whole. This study selects Avicenna tomb square and center of Aqajani Beig neighborhood, Hamedan. The main research questions include what the role of Alexander’s theory of living centers is in promoting the social interaction in local and urban square and which pattern of Alexander’s theory mostly affects social interactions in squares and how the individual factors impact social interactions in local and urban squares. Results reveals that patterns of Alexander’s theory are efficient in promoting social interactions in local and urban squares. Individual factors are not effective in this regard, but strong centers and urban square contradictions are more effective in resident’s social interactions than that of void spaces and strong centers. Architects, planners, and urban designers can apply the results in designing new urban and local squares.     

Synthesis of Graphene Oxide/Iron Oxide/Au Nanocomposite for Quercetin Delivery

This study focused on developing a superparamagnetic graphene oxide-based nanocomposite consisting of iron oxide (IO) and gold nanoparticles for quercetin delivery. For this purpose, the structure and morphology of the designed nanocomposite (GO/IO/Au) were investigated by several characterization methods such as fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, vibrating-sample magnetometer (VSM) analysis, field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM). Then, the biocompatibility of the synthesized nanocomposite was studied by Brine shrimp Artemia lethality assay, red blood cell hemolysis assay, and MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay. Moreover, the GO/IO/Au nanocomposite efficiency as an anticancer drug delivery system was evaluated in vitro conditions. The results showed that the designed nanocomposite is highly biocompatible and possesses a favorable magnetization (M_s?=?29.2 emu.g^?1) making it a good candidate for biomedical applications. Also, it was confirmed that GO/IO/Au nanocomposite is a potent drug carrier that can effectively deliver quercetin to cancer cells.

     

Facile route for synthesis of strontium hexaborate crystalline powders

In this paper, a solid-state reaction route was developed to synthesize SrB₆O₁₀ crystalline powders. Regarding the last preparation methods, a short process time of synthesis was achieved that has not reported before. The prepared sample was characterized using various methods, such as X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and diffuse reflection spectroscopy. The obtained results proved that the prepared sample at temperature 840°C with 2.5 h duration consists of SrB₆O₁₀ crystalline powders with 4.96 eV bandgap.