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21.
Melike Erol‐Kantarci 《International Journal of Network Management》2015,25(6):454-470
Uploading and downloading content have recently become one of the major reasons for the growth of Internet traffic volume. With the increasing popularity of social networking tools and their video upload/download applications, as well as the connectivity enhancements in wireless networks, it has become a second nature for mobile users to access on‐demand content on‐the‐go. Urban hot spots, usually implemented via wireless relays, answer the bandwidth need of those users. On the other hand, the same popular contents are usually acquired by a large number of users at different times, and fetching those from the initial content source each and every time makes inefficient use of network resources. In‐network caching provides a solution to this problem by bringing contents closer to the users. Although in‐network caching has been previously studied from latency and transport energy minimization perspectives, energy‐efficient schemes to prolong user equipment lifetime have not been considered. To address this problem, we propose the cache‐at‐relay (CAR) scheme, which utilizes wireless relays for in‐network caching of popular contents with content access and caching energy minimization objectives. CAR consists of three integer linear programming models, namely, select relay, place content, and place relay, which respectively solve content access energy minimization, joint minimization of content access and caching energy, and joint minimization of content access energy and relay deployment cost problems. We have shown that place relay significantly minimizes the content access energy consumption of user equipments, while place content provides a compromise between the content access and the caching energy budgets of the network. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
22.
John A. Gil-Corrales Alvaro L. Morales Melike Behiye Yücel Esin Kasapoglu Carlos A. Duque 《International journal of molecular sciences》2022,23(9)
In this work, a finite periodic superlattice is studied, analyzing the probability of electronic transmission for two types of semiconductor heterostructures, GaAs/AlGaAs and InSe/InP. The changes in the maxima of the quasistationary states for both materials are discussed, making variations in the number of periods of the superlattice and its shape by means of geometric parameters. The effect of a non-resonant intense laser field has been included in the system to analyze the changes in the electronic transport properties by means of the Landauer formalism. It is found that the highest tunneling current is given for the GaAs-based compared to the InSe-based system and that the intense laser field improves the current–voltage characteristics generating higher current peaks, maintaining a negative differential resistance (NDR) effect, both with and without laser field for both materials and this fact allows to tune the magnitude of the current peak with the external field and therefore extend the range of operation for multiple applications. Finally, the power of the system is discussed for different bias voltages as a function of the chemical potential. 相似文献
23.
Ayse Kalemtas Gulsum Topates Hüseyin Özcoban Hasan Mandal Ferhat Kara Rolf Janssen 《Journal of the European Ceramic Society》2013,33(9):1507-1515
In this study, porous β-Si3N4 ceramics containing limited amount of Sm2O3 and CaO as sintering aids were produced by addition of potato starch (10 and 20 vol.%) and partial sintering. Two different Si3N4 powders, α- and β-, were used as starting materials. Scanning electron microscopy investigations revealed that development of elongated β-Si3N4 grains were much more pronounced when α-Si3N4 starting powder was used. Even though porosity values of the compositions prepared by using α-Si3N4 (~57.0–58.4%) is significantly higher than the samples produced by β-Si3N4 (42.6%), no significant change was observed for the bending strength, fracture toughness and Weibull modulus. This indicates that microstructural features have a significant contribution to the mechanical properties of the porous materials in terms of bending strength and fracture toughness. 相似文献
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Gulsum Melike Urper Reyhan Sengur-Tasdemir Turker Turken Volodymyr V. Tarabara Ismail Koyuncu 《分离科学与技术》2017,52(13):2120-2136
Membrane-based separation is now established as one of staple technologies used in water treatment and reuse applications. Nanofiltration, in particular, can be a cost-effective solution for removing large ions and low-molecular-weight compounds from water. Nanofiltration membranes have been manufactured mostly as flat sheets and used in spiral wound modules. Hollow fiber geometry, however, offers several advantages over flat sheet and other configurations. This paper overviews recent developments in the design of hollow fiber nanofiltration membranes and provides a comparative analysis of two main methods of their fabrication: interfacial polymerization and phase inversion. 相似文献
26.
Marta Martins Önder Metin Melike Sevim Biljana Šljukić César A.C. Sequeira Tansel Sener Diogo M.F. Santos 《International Journal of Hydrogen Energy》2018,43(23):10686-10697
5 nm palladium nanoparticles (Pd NPs) are synthesized and assembled on reduced graphene oxide-iron oxide nanocomposite (rGO-Fe3O4) to be used in oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) studies in alkaline media. The structure and morphology of the resulting Pd/rGO-Fe3O4 hybrid material are evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) analyses. The electrochemical behavior of Pd/rGO-Fe3O4 hybrid material for the ORR and BOR is investigated by voltammetry with rotating disk and rotating ring disk electrode and electrochemical impedance spectroscopy, enabling evaluation of the number of exchanged electrons, Tafel slope, exchange current density and activation energy. The results reveal that ORR at Pd/rGO-Fe3O4 proceeds as a 2-electron process with Tafel slope of 0.133 V dec?1, while BOR proceeds as a 5.6-electron process with Tafel slope of 0.350 V dec?1 and exchange current density of 1.38 mA cm?2. The BOR activation energy was found to be 12.4 kJ mol?1. Overall, this study demonstrates the good efficiency of Pd/rGO-Fe3O4 hybrid material for BOR. 相似文献
27.
Cybernetics in the United States has evolved through three identifiable periods. In the first period of the 1950s and 1960s there was a primary concern with designing control systems and with building machines to emulate human reasoning. In the second period of the 1970s and 1980s the focus of attention was on the biologyof cognition and constructivist philosophy. In recent years increasing attention has been given to social systems. Whereas the work on the biology of cognition required that attention be shifted from what was observed to the observer, the recent interest in social systems requires an emphasis on multiple observers and their beliefs. The third period of social cybernetics or the cybernetics of conceptual systems is illustrated by considering constructivist cybernetics as a conceptual system created to promote the evolution of certain social systems in a preferred direction. 相似文献
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29.
A survey on packet size optimization for terrestrial,underwater, underground,and body area sensor networks
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Melike Yigit H. Ugur Yildiz Sinan Kurt Bulent Tavli V. Cagri Gungor 《International Journal of Communication Systems》2018,31(11)
Packet size optimization is a critical issue in wireless sensor networks (WSNs) for improving many performance metrics (eg, network lifetime, delay, throughput, and reliability). In WSNs, longer packets may experience higher loss rates due to harsh channel conditions. On the other hand, shorter packets may suffer from greater overhead. Hence, the optimal packet size must be chosen to enhance various performance metrics of WSNs. To this end, many approaches have been proposed to determine the optimum packet size in WSNs. In the literature, packet size optimization studies focus on a specific application or deployment environment. However, there is no comprehensive and recent survey paper that categorizes these different approaches. To address this need, in this paper, recent studies and techniques on data packet size optimization for terrestrial WSNs, underwater WSNs, wireless underground sensor networks, and body area sensor networks are reviewed to motivate the research community to further investigate this promising research area. The main objective of this paper is to provide a better understanding of different packet size optimization approaches used in different types of sensor networks and applications as well as introduce open research issues and challenges in this area. 相似文献
30.
Journal of Porous Materials - Highly porous carbons (PCs) were successfully developed through KOH chemical activation process from petroleum asphaltene for the efficient removal of pharmaceutical... 相似文献