A Novel Scheduling Algorithm for Low and High Mobility Users in Multi-hop WiMAX Network

QoS provisioning and high capacity for high mobility users are considered as the distresses of broadband wireless communications (BWC) and specifically the key technology of WiMAX. Hence, the scheduling and resource allocation algorithms play the main role in this regard. In the research conducted on scheduling algorithms in WiMAX network, two principal methods of AMC and PUSC are used. The high capacity in AMC mode algorithms is achieved by considering the low speed users. Conversely, in PUSC mode algorithms, speed does not affect the network performances; however, the capacity is low. To date, the importance of presenting QoS and maintaining the network capacity for the users with different speeds has not been acknowledged yet. This paper presents novel scheduling algorithms and also new frame partitioning scheme which are proper for the users with different mobility speeds. The new algorithm uses two modes of AMC and PUSC simultaneously to maintain the high capacity of the network. QoS is also provided. The simulation results reveal that our algorithm increases capacity while it presents low packet delay and packet loss rate in the presence of both high and low mobility speed users.     

Graphene oxide based carbon composite as adsorbent for Hg removal:Preparation,characterization, kinetics and isotherm studies

The presence of Hg in the aqueous media is known to cause severe health issues in both humans and animals.Many technologies and especially adsorbents have been applied for its removal.In this study,a graphene oxide-carbon composite (GO-CC) as a new adsorbent was prepared by sol gel procedure and characterized using field emission scanning electron microscopy,BET and EDX.The effects of different variables including solution pH,contact time,adsorbent dose and GO ratio in adsorbent matrix on the removal capacity of Hg were studied.The isotherm data correlated well with the Langmuir isotherm model.Further analysis recommended that the Hg2+ adsorption process is governed by the intra-particle and external mass transfer,in which the film diffusion was the rate restrictive step.The presented composite has maximum absorption capacity,qmax of 68.8 mg· g-1,which is comparable with carbon based adsorbent reported in the previous publications.(C) 2017 The Chemical Industry and Engineering Society of China,and Chemical Industry Press.All rights reserved.     

Fully Solution‐Processed Small Molecule Semitransparent Solar Cells: Optimization of Transparent Cathode Architecture and Four Absorbing Layers

Semitransparent solar cells (SSCs) can open photovoltaic applications in many commercial areas, such as power‐generating windows and building integrated photovoltaics. This study successfully demonstrates solution‐processed small molecule SSCs with a conventional configuration for the presently tested material systems, namely BDTT‐S‐TR:PC₇₀BM, N(Ph‐2T‐DCN‐Et)₃:PC₇₀BM, SMPV1:PC₇₀BM, and UU07:PC₆₀BM. The top transparent cathode coated through solution processes employs a highly transparent silver nanowire as electrode together with a combination interface bilayer of zinc oxide nanoparticles (ZnO) and a perylene diimide derivative (PDINO). This ZnO/PDINO bilayer not only serves as an effective cathode buffer layer but also acts as a protective film on top of the active layer. With this integrated contribution, this study achieves a power conversion efficiency (PCE) of 3.62% for fully solution‐processed SSCs based on BDTT‐S‐TR system. Furthermore, the other three systems with various colors exhibited the PCEs close to 3% as expected from simulations, demonstrate the practicality and versatility of this printed semitransparent device architecture for small mole­cule systems. This work amplifies the potential of small molecule solar cells for window integration.     

Determining the internal quantum efficiency of organic Bulk Heterojunctions based on mono and bis–adduct fullerenes as acceptor

With the aid of optical modeling, the internal quantum efficiencies of organic Bulk Heterojunction (oBHJ) photovoltaic devices based on low band gap polymer of poly[(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,5′-diyl] (Si-PCPDTBT) blended with the acceptors of 1-(3-Methoxycarbonyl) propyl-1-phenyl [6,6] C61 (PCBM) and bis–adduct (bis–PCBM) are determined. The Si-PCPDTBT:bis–PCBM devices show considerably lower short circuit current density (J_sc) as compared to the Si-PCPDTBT:PCBM devices. The results show that 30% of this smaller J_sc is due to the lower optical absorption of bis–PCBM, while the major losses originate from the electrical losses. It is found that for the best Si-PCPDTBT:bis–PCBM devices with an active layer thickness in the range of 70–100 nm, the inefficient charge generation within the bis–PCBM domains is the major contribution to the whole losses. Increasing the active layer thickness of Si-PCPDTBT:bis–PCBM device significantly enhances recombination losses in polymer/bis–fullerene matrix.     

Photovoltaic properties of benzotriazole containing alternating donor–acceptor copolymers: Effect of alkyl chain length

A series of variable alkyl chain length substituted donor–acceptor (D–A) conjugated polymers with thiophene ring as the donor and benzotriazole moiety as the acceptor has been investigated in bulk heterojunction solar cells. The optical and electrochemical properties showed that the absorption onsets and the energy levels of the copolymers were not affected by alkyl substitution revealing 1.9 eV of optical band gap. The morphologies of the blend film can be fine-tuned by increasing the chain length attached to the benzotriazole unit. Photovoltaic devices were fabricated using (6,6)-phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM) and (6,6)-phenyl-C₇₁-butyric acid methyl ester (PC₇₀BM) as the acceptors. The maximum performance was achieved with a V_oc of 0.75 V, J_sc of 3.70 mA/cm², FF of 45% and a PCE of 1.23% for the PTBT-DA10:PC₇₀BM device using 1:4 w/w ratio in chlorobenzene (CB).     

The neglected influence of zinc oxide light-soaking on stability measurements of inverted organic solar cells

Although zinc oxide (ZnO) is one of the most commonly used materials for electron transport layers in organic solar cells (OSCs), it also comes with disadvantages such as the so-called light-soaking issues, i.e., its need for exposure to UV light to reach its full potential in OSCs. Here, the impact of ZnO light-soaking issues on stability measurements of OSCs is investigated. It is found that in the absence of UV light a reversible degradation occurs, which is independent of the used active layer material and accelerates at higher temperatures but can be undone with a short UV exposure. This reversible aging is attributed to the re-adsorption of oxygen, which for manufacturing reasons is trapped at the interface of ZnO, even in an oxygen-free environment. This oxygen can be removed with a UV pretreatment of the ZnO but at the expense of device efficiency and production that has to take place in an oxygen-free environment. This study establishes that stability measurements of ZnO-containing OSCs must be performed exclusively with a light source including a UV part since the usage of a simple white light source – as often reported in the literature – can lead to erroneous results.     

A novel ultrasonic assisted-reverse micelle procedure to synthesize Eu-MOF nanostructure with high sono/sonophotocatalytic activity: a systematic study for brilliant green dye removal

Journal of Materials Science: Materials in Electronics - In recent years, one of the growing environmental concerns has been contamination of water sources by dyes. For solving this problem,...