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RISS 인기검색어
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- 저자 : P. N. Gajjar (검색결과 2 건)
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Electronic, Magnetic and Optical Properties of 2D Metal Nanolayers: A DFT Study
Prabal Dev Bhuyan,Sanjeev K. Gupta,Deobrat Singh,Yogesh Sonvane,P. N. Gajjar 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.4
In the recent work, we have investigated the structural, electronic, magnetic and optical properties of graphene-like hexagonalmonolayers and multilayers (up to fi ve layers) of 3 d -transition metals Fe, Co and Ni based on spin-polarized density functionaltheory. Here, we have taken two types of pattern namely AA-stacking and AB-stacking for the calculations. The bindingenergy calculations show that the AA-type confi guration is energetically more stable. The calculated binding energies of Fe,Co and Ni-bilayer monolayer are − 3.24, − 2.53 and − 1.94 eV, respectively. The electronic band structures show metallicbehavior for all the systems and each confi gurations of Fe, Co and Ni-atoms. While, the quantum ballistic conductancesof these metallic systems are found to be higher for pentalayer than other layered systems. The density of states confi rmsthe ferromagnetic behavior of monolayers and multilayers of Fe and Co having negative spin polarizations. We have alsocalculated frequency dependent complex dielectric function, electronic energy loss spectrum and refl ectance spectrum ofmonolayer to pentalayer metallic systems. The ferromagnetic material shows Different permittivity tensor ( ɛ ), which is dueto high spin magnetic moment for n-layered Fe and Co two-dimensional (2D) nanolayers. The theoretical investigation suggeststhat the electronic, magnetic and optical properties of 3 d -transition metal nanolayers off ers great promise for their usein spintronics nanodevices and magneto-optical nanodevices applications.
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Multi-Secondary Transformer: A Modeling Technique for Simulation - II
Patel, A.,Singh, N.P.,Gupta, L.N.,Raval, B.,Oza, K.,Thakar, A.,Parmar, D.,Dhola, H.,Dave, R.,Gupta, V.,Gajjar, S.,Patel, P.J.,Baruah, U.K. Journal of International Conference on Electrical 2014 Journal of international Conference on Electrical Vol.3 No.1
Power Transformers with more than one secondary winding are not uncommon in industrial applications. But new classes of applications where very large number of independent secondaries are used are becoming popular in controlled converters for medium and high voltage applications. Cascade H-bridge medium voltage drives and Pulse Step Modulation (PSM) based high voltage power supplies are such applications. Regulated high voltage power supplies (Fig. 1) with 35-100 kV, 5-10 MW output range with very fast dynamics (${\mu}S$ order) uses such transformers. Such power supplies are widely used in fusion research. Here series connection of isolated voltage sources with conventional switching semiconductor devices is achieved by large number of separate transformers or by single unit of multi-secondary transformer. Naturally, a transformer having numbers of secondary windings (~40) on single core is the preferred solution due to space and cost considerations. For design and simulation analysis of such a power supply, the model of a multi-secondary transformer poses special problem to any circuit analysis software as many simulation softwares provide transformer models with limited number (3-6) of secondary windings. Multi-Secondary transformer models with 3 different schemes are available. A comparison of test results from a practical Multi-secondary transformer with a simulation model using magnetic component is found to describe the behavior closer to observed test results. Earlier models assumed magnetising inductance in a linear loss less core model although in actual it is saturable core made-up of CRGO steel laminations. This article discusses a more detailed representation of flux coupled magnetic model with saturable core properties to simulate actual transformers very close to its observed parameters in test and actual usage.
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