Showing papers by "Amirkabir University of Technology published in 2014"

Evolution Towards 5G Multi-tier Cellular Wireless Networks: An Interference Management Perspective

Abstract: The evolving fifth generation (5G) cellular wireless networks are envisioned to overcome the fundamental challenges of existing cellular networks, e.g., higher data rates, excellent end-to-end performance and user-coverage in hot-spots and crowded areas with lower latency, energy consumption and cost per information transfer. To address these challenges, 5G systems need to adopt a multi-tier architecture consisting of macrocells, different types of licensed small cells, relays, and device-to-device (D2D) networks to serve users with different quality-of-service (QoS) requirements in a spectrum and energy-efficient manner. Starting with the visions and requirements of 5G multi-tier networks, this article outlines the challenges of interference management (e.g., power control, cell association) in these networks with shared spectrum access (i.e., when the different network tiers shares the same licensed spectrum). It is argued that the existing interference management schemes will not be able to address the interference management problem in prioritized 5G multi-tier networks where users in different tiers have different priorities for channel access. In this context, a survey and qualitative comparison of the potential existing cell association and power control schemes is provided to demonstrate their limitations for interference management in 5G networks. Open challenges are highlighted and guidelines are provided to modify the existing schemes in order to overcome these limitations and make them suitable for the emerging 5G systems.

Evolution Towards 5G Multi-tier Cellular Wireless Networks: An Interference Management Perspective

Abstract: The evolving fifth generation (5G) cellular wireless networks are envisioned to overcome the fundamental challenges of existing cellular networks, for example, higher data rates, excellent end-to-end performance, and user-coverage in hot-spots and crowded areas with lower latency, energy consumption, and cost per information transfer. To address these challenges, 5G systems will adopt a multi-tier architecture consisting of macrocells, different types of licensed small cells, relays, and device-to-device (D2D) networks to serve users with different quality-of-service (QoS) requirements in a spectrum and energy-efficient manner. Starting with the visions and requirements of 5G multi-tier networks, this article outlines the challenges of interference management (e.g. power control, cell association) in these networks with shared spectrum access (i.e. when the different network tiers share the same licensed spectrum). It is argued that the existing interference management schemes will not be able to address the interference management problem in prioritized 5G multi-tier networks where users in different tiers have different priorities for channel access. In this context a survey and qualitative comparison of the existing cell association and power control schemes is provided to demonstrate their limitations for interference management in 5G networks. Open challenges are highlighted and guidelines are provided to modify the existing schemes in order to overcome these limitations and make them suitable for the emerging 5G systems.

Response surface analysis of photocatalytic degradation of methyl tert-butyl ether by core/shell Fe3O4/ZnO nanoparticles.

Abstract: The degradation of methyl tert-butyl ether (MTBE) was investigated in the aqueous solution of coated ZnO onto magnetite nanoparticale based on an advanced photocatalytic oxidation process. The photocatalysts were synthesized by coating of ZnO onto magnetite using precipitation method. The sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibration sample magnetometer (VSM). Besides, specific surface area was also determined by BET method. The four effective factors including pH of the reaction mixture, Fe3O4/ZnO magnetic nanoparticles concentration, initial MTBE concentration and molar ratio of [H2O2]/ [MTBE] were optimized using response surface modeling (RSM). Using the four-factor-three-level Box–Behnken design, 29 runs were designed considering the effective ranges of the influential factors. The optimized values for the operational parameters under the respective constraints were obtained at PH of 7.2, Fe3O4/ZnO concentration of 1.78 g/L, initial MTBE concentration of 89.14 mg/L and [H2O2]/ [MTBE] molar ratio of 2.33. Moreover, kinetics of MTBE degradation was determined under optimum condition. The study about core/shell magnetic nanoparticles (MNPs) recycling were also carried out and after about four times, the percentage of the photocatalytic degradation was about 70%.

Competitive supply chain network design: An overview of classifications, models, solution techniques and applications

Abstract: Supply chain network design (SCND) determines the structure of a chain and affects its costs and performance. SCND deals with a variety of decisions such as determining number, size and location of facilities in a supply chain (SC) and may include tactical decisions (such as distribution, transportation and inventory management policies) as well as operational decisions (such as fulfilling customers demand). SCND has a voluminous literature. Most of the literature deals with a single SC and ignores the existing competitor SCs and future emerging ones. However, SCs compete together to capture more market shares. Even if there is not any competitor at the moment, SCs should be prepared for possible future competitive situation at the SCND stage. On the other hand, many competitive models assume that the supply chain network (SCN) and its structure already exist. Few research papers consider both aspects of design and competition. In this paper, we provide a review of SCND literature and highlight the effects of competitive environment on SCND. We review, classify, and introduce the major features of the proposed models in both SCND and competition literature. After investigating proposed competitive SCND models we develop a general framework for modeling the competitive SCND problems considering managerial insight and propose potential areas for future research.

A Decentralized Cooperative Control Scheme With Obstacle Avoidance for a Team of Mobile Robots

Abstract: The problem of formation control of a team of mobile robots based on the virtual and behavioral structures is considered in this paper. In the virtual structure, each mobile robot is modeled by an electric charge. The mobile robots move toward a circle, and due to repulsive forces between the identical charges, regular polygon formations of the mobile robots will be realized. For swarm formation, a virtual mobile robot is located at the center of the circle, and other mobile robots follow it. In the introduced approach, each mobile robot finds its position in the formation autonomously, and the formation can change automatically in the case of change in the number of the mobile robots. This paper also proposes a technique for avoiding obstacles based on the behavioral structure. In this technique, when a mobile robot gets close to an obstacle, while moving toward its target, a rotational potential field is applied to lead the mobile robot to avoid the obstacle, without locating in local minimum positions.

Carbon Dioxide Separation from Flue Gases: A Technological Review Emphasizing Reduction in Greenhouse Gas Emissions

Abstract: Increasing concentrations of greenhouse gases (GHGs) such as CO2 in the atmosphere is a global warming. Human activities are a major cause of increased CO2 concentration in atmosphere, as in recent decade, two-third of greenhouse effect was caused by human activities. Carbon capture and storage (CCS) is a major strategy that can be used to reduce GHGs emission. There are three methods for CCS: pre-combustion capture, oxy-fuel process, and post-combustion capture. Among them, post-combustion capture is the most important one because it offers flexibility and it can be easily added to the operational units. Various technologies are used for CO2 capture, some of them include: absorption, adsorption, cryogenic distillation, and membrane separation. In this paper, various technologies for post-combustion are compared and the best condition for using each technology is identified.

Effect of layer thickness and printing orientation on mechanical properties and dimensional accuracy of 3D printed porous samples for bone tissue engineering.

Abstract: Powder-based inkjet 3D printing method is one of the most attractive solid free form techniques. It involves a sequential layering process through which 3D porous scaffolds can be directly produced from computer-generated models. 3D printed products' quality are controlled by the optimal build parameters. In this study, Calcium Sulfate based powders were used for porous scaffolds fabrication. The printed scaffolds of 0.8 mm pore size, with different layer thickness and printing orientation, were subjected to the depowdering step. The effects of four layer thicknesses and printing orientations, (parallel to X, Y and Z), on the physical and mechanical properties of printed scaffolds were investigated. It was observed that the compressive strength, toughness and Young's modulus of samples with 0.1125 and 0.125 mm layer thickness were more than others. Furthermore, the results of SEM and μCT analyses showed that samples with 0.1125 mm layer thickness printed in X direction have more dimensional accuracy and significantly close to CAD software based designs with predefined pore size, porosity and pore interconnectivity.

New Application of SWARA Method in Prioritizing Sustainability Assessment Indicators of Energy System

Abstract: A major topic among the current researches on energy is a sustainable energy development and assessment. An importance of energy system is obvious in our life. There are many important energy applications. There are heating and cooling, power generation, desalination, air conditioning and so on. By the year 2020 world will need 50% more energy than today and the Asia-Pacific region will become world's largest consumer of energy. In 21-st century, world faces with the challenge of converting its fossil fuels energy base to the sustainable energy sources. Regarding the increasing rise of the energy demand and consumption, virtually everyone in the world must implement an integrated resource planning (IRP). It is vitally important to achieve sustainable growth. Sustainability assessment of energy system is one of the important issues in policy making all around the world. Decision making on energy system is very risky and difficult and therefore cannot be individual. Multi Criteria Decision Making (MCDM) is a renowned methodology in decision making and evaluation. Some of the most famous MCDM tools are as following: AHP, ANP, TOPSIS, ELECTRE, MUSA, AKUTA, VIKOR, PROMETHEE, SAW, MOORA, COPRAS, COPRAS-G, SWARA, FARE. A Step-wise Weight Assessment Ratio Analysis (SWARA) method is one of the new MCDM methods presented in 2010. SWARA method is applied for some reasons in this paper. Firstly, SWARA’s perspective is different from other similar methods like AHP, ANP and FARE. SWARA gives the chance for decision and policy makers to select their priority based on the current situation of environment and economy. In this method, expert has an important role on evaluations and calculating weights. The ability to estimate experts’ opinion about importance ratio of the criteria is the main element of this method. SWARA is developed for identifying importance of criteria and relative weights of each criterion. Current research applies SWARA as a new framework for evaluating and prioritizing sustainability assessment indicators of energy system. General indicator system consists of Resource Indicator, Environment Indicator, Economic Indicator and Social Indicator and their sub-criterions. For instance, complex environmental indicator consists of CO2, SO2 and NOX indicators while complex economic indicator consists of energy costs, investment and efficiency indicators. The research revealed that the most important indicator is Social (0.342). Then, the range of indicators is as following: Environmental (0.284), Economic (0.212) and Resource (0.162). Finally, the research shows that this methodology can be useful as a framework to operate with sustainability assessment indicators of the energy system. Also, this methodology can be used for decision making in real issues of future researches in different areas. The results of this methodology also can be compared to other methods such as AHP and ANP. DOI: http://dx.doi.org/10.5755/j01.ee.24.5.4526

Design and evaluation of chitosan/hydroxyapatite composite nanofiber membrane for the removal of heavy metal ions from aqueous solution

Abstract: The performance of chitosan/hydroxyapatite (Cs/HAp) composite nanofiber membrane prepared by electrospinning process for the removal of lead, cobalt and nickel ions from aqueous solution was investigated. The prepared nanofiber membranes were characterized by FTIR, SEM and BET analysis. A response surface methodology based on Box–Behnken Design (BBD) was used to predict the average diameter of electrospun nanofibers. In optimum conditions (voltage of 18.90 kV, tip-collector distance of 15.60 cm and flow rate of 0.43 ml/h), the minimum experimental fiber diameter was obtained 198 nm which was in good agreement with the predicted value by the BBD analysis (200.6 nm). Then, the adsorption experiments were carried out to investigate the effect of different adsorption parameters, such as contact time, initial concentration and temperature in a batch system. The kinetic and equilibrium data were well described by pseudo-second-order and Langmuir models, respectively. Thermodynamic parameters were evaluated to obtain the nature of adsorption process onto the Cs/HAp composite nanofibers. The obtained results of reusability of nanofiber membrane after five sorption–desorption cycles offer promising potential in industrial activities.

Constructing a Novel No-Equilibrium Chaotic System

Abstract: This paper introduces a new no-equilibrium chaotic system that is constructed by adding a tiny perturbation to a simple chaotic flow having a line equilibrium. The dynamics of the proposed system are investigated through Lyapunov exponents, bifurcation diagram, Poincare map and period-doubling route to chaos. A circuit realization is also represented. Moreover, two other new chaotic systems without equilibria are also proposed by applying the presented methodology.

Social life cycle assessment for material selection: a case study of building materials

Abstract: Purpose Sustainability of a material-based product mainly depends on the materials used for the product itself or during its lifetime. A material selection decision should not only capture the functional performance required but should also consider the economical, social, and environmental impacts originated during the product life cycle. There is a need to assess social impacts of materials along the full life cycle, not only to be able to address the “social dimension” in sustainable material selection but also for potentially improving the circumstances of affected stakeholders. This paper presents the method and a case study of social life cycle assessment (S-LCA) specialized for comparative studies. Although the authors’ focus is on material selection, the proposed methodology can be used for comparative assessment of products in general.

Evaluation of commercial PTFE membranes in desalination by direct contact membrane distillation

Abstract: In this study, nine flat-sheet commercially available hydrophobic PTFE membranes were used in desalination by direct contact membrane distillation and their characteristics were investigated under different operating conditions including feed temperature, feed flow rate, cold stream flow rate, and feed concentration. Membrane properties, i.e. pore size, thickness, support layer, and salt rejection were also studied. Moreover, membrane module designs including flow arrangements (co-current, counter-current and tangential) for process liquid and depth both on hot and cold sides were tested experimentally. Finally, the long-term performance of the selected membranes for direct contact membrane distillation as a stand-alone desalination process was investigated. The results indicated that increasing feed temperature, hot feed flow rate, and module depth on the cold side led to increase permeate flux. On the other hand, increasing membrane thickness and module depth on the hot side (at constant flow rate) had negative effects on the flux. The highest permeation flux and salt rejection was achieved when the membranes with a pore size of 0.22 μm were used in the cross-current follow arrangement of hot and cold streams. In addition, the requirements for support layer for a successful DCMD process has been extensively discussed.

Analyses of the impact of climate change on water resources components, drought and wheat yield in semiarid regions: Karkheh River Basin in Iran

Abstract: Water resources availability in the semiarid regions of Iran has experienced severe reduction because of increasing water use and lengthening of dry periods. To better manage this resource, we investigated the impact of climate change on water resources and wheat yield in the Karkheh River Basin (KRB) in the semiarid region of Iran. Future climate scenarios for 2020–2040 were generated from the Canadian Global Coupled Model for scenarios A1B, B1 and A2. We constructed a hydrological model of KRB using the Soil and Water Assessment Tool to project water resources availability. Blue and green water components were modeled with uncertainty ranges for both historic and future data. The Sequential Uncertainty Fitting Version 2 was used with parallel processing option to calibrate the model based on river discharge and wheat yield. Furthermore, a newly developed program called critical continuous day calculator was used to determine the frequency and length of critical periods for precipitation, maximum temperature and soil moisture. We found that in the northern part of KRB, freshwater availability will increase from 1716 to 2670 m3/capita/year despite an increase of 28% in the population in 2025 in the B1 scenario. In the southern part, where much of the agricultural lands are located, the freshwater availability will on the average decrease by 44%. The long-term average irrigated wheat yield, however, will increase in the south by 1.2%–21% in different subbasins; but for rain-fed wheat, this variation is from −4% to 38%. The results of critical continuous day calculator showed an increase of up to 25% in both frequency and length of dry periods in south Karkheh, whereas increasing flood events could be expected in the northern and western parts of the region. In general, there is variability in the impact of climate change in the region where some areas will experience net negative whereas other areas will experience a net positive impact. Copyright © 2013 John Wiley & Sons, Ltd.

New Extendable Single-Stage Multi-input DC–DC/AC Boost Converter

Abstract: This paper presents a new extendable single-stage multi-input dc-dc/ac boost converter. The proposed structure comprises of two bidirectional ports in the converter's central part to interface output load and battery storage, and several unidirectional input ports to get powers from different input dc sources. In fact, the proposed topology consists of two sets of parallel dc-dc boost converters, which are actively controlled to produce two independent output voltage components. Choosing two pure dc or two dc-biased sinusoidal values as the converter reference voltages, situations of the converter operating in two dc-dc and dc-ac modes are provided, respectively. The proposed converter utilizes minimum number of power switches and is able to step up the low-level input dc voltages into a high-level output dc or ac voltage without needing any output filter. The converter control system includes several current regulator loops for input dc sources and two voltage regulator loops for generating the desired output voltage components, resulting in autonomously charging/discharging the battery to balance the power flow. Due to the converter inherent multi-input multioutput control system, the small signal model of the converter is extracted and then the pole-placement control strategy via integral state feedback is applied for achieving the converter control laws. The validity and effectiveness of the proposed converter and its control performance are verified by simulation and experimental results.