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Experimental Comparison of Five Approximation Algorithms for Minimum Vertex Cover
Imran Khan,Sangeen Khan 보안공학연구지원센터 2014 International Journal of u- and e- Service, Scienc Vol.7 No.6
Numerous approximation algorithms have been presented by researchers for approximation of minimum vertex cover, all of these approaches have deficiencies in one way or another. As minimum vertex cover is NP-Complete so we can’t find out optimal solution so approximation is the way left but it is very hard for someone to decide which one procedure to use, in this comparison paper we have selected five approximation algorithms and have drawn detailed experimental comparison. Best available benchmarks were used for the comparison process which was to compare multiple algorithms for the same task on different aspects. Extensive results have been provided to clarify the selection process, probability of production optimal solutions, run time complexity and approximation ratio were factors involved in the process of selection.
Imran Khan,홍지상 한국물리학회 2018 Current Applied Physics Vol.18 No.5
Using the first principles method, we studied the electronic structure and magnetocrystalline anisotropy of site dependent 4d, 5d element doping in α″-Fe16N2. We found that different Fe sites contributed differently for magnetocrystalline anisotropy. For instance, on d-site doping, we obtained perpendicular magnetocrystalline anisotropy while the h-site doping resulted in an in-plane magnetocrystalline anisotropy in all the studied systems. The impurity doping induces local lattice distortions near the impurity site. However, the volume of the cell and total magnetic moment of the doped systems were not much affected. This local lattice distortion together with the spin-orbit coupling effect associated with heavy 4d, 5d element mainly contributed to enhancing the magnetocrystalline anisotropy. The enhancement of the magnetocrystalline anisotropy results in almost 15 to 67% enhancement of the coercivity for 4d element doping while we found 80 to 137% enhancement for 5d element doping. The maximum energy products were also enhanced compared to the pure α″-Fe16N2. The maximum enhancement was observed in Rh and Pt doped systems where the energy products were 119–120 MGOe. These results may suggest that substitutional doped α″-Fe16N2 system can be used as potential rare earth free permanent magnet.
Imran Khan,홍지상 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.11
Using the first principles method, we investigated the interface effect on the electronic structure and the magnetic properties of multilayer Fe16N2/Ag/Fe16N2 and Fe16N2/Au/Fe16N2. The thicknesses of Ag (100) and Au (100) were fixed to three monolayers, and the lattice mismatch was about 1%. The magnetic moment of Fe atoms at the interface was suppressed due to hybridization with non-magnetic Ag and Au atoms. Due to this reduction in the magnetic moments and also because of the non-magnetic volume of the Ag and Au layer, an overall 40% suppression of the magnetization was found in both systems. The hybridization between interface Ag (Au) and Fe atoms and the spin-orbit coupling associated with Ag (Au) atoms mainly contributed to the enhancement of the magnetocrystalline anisotropy. The magnetocrystalline anisotropy constant was enhanced from 0.57 MJ/m3 in pure Fe16N2 to 1.58 MJ/m3 and 0.89 MJ/m3 in Fe16N2/Ag/Fe16N2 and Fe16N2/Au/Fe16N2 multilayer systems, respectively. This enhancement in magnetocrystalline anisotropy results in an enhancement of the coercive field. The coercive fields were about 30 and 16.7 kOe in the Ag and the Au multilayer systems, respectively. Overall, we found substantial enhancements in the magnetocrystalline anisotropy constant and the coercive field due to the interface effect. This finding may suggest that the Fe16N2/Ag/Fe16N2 and the Fe16N2/Au/Fe16N2 structures can be utilized for potential rare-earth-free permanent magnets.
Khan, Imran,Lee, Kyeong-Lim,Fakruzzaman, Md.,Song, Seok-Hwan,Ihsan-ul-Haq,Mirza, Bushra,Yan, Chang ,Guo,Kong, Il-Keun Portland Press Ltd. 2016 Bioscience reports Vol.36 No.2
<P>Coagulansin-A (withanolide) is the steroidal lactone obtained from <I>Withania coagulans</I> which belong to Solanaceae family. The present study investigated the effects of coagulansin-A on bovine oocyte maturation and embryo development <I>in vitro</I>. All these oocytes were aspirated from the ovaries obtained from Korean Hanwoo cows at a local abattoir. To determine whether coagulansin-A has beneficial effects on bovine oocyte maturation <I>in vitro</I>, 355 oocytes per group (control and treated) in seven replicates were subjected with different concentrations (1, 2.5, 5, 7.5 and 10 μM) of coagulansin-A. The coagulansin-A was added in the <I>in vitro</I> maturation (IVM) media followed by <I>in vitro</I> fertilization (IVF) and then <I>in vitro</I> culture (IVC). Only treatment with 5 μM coagulansin-A remarkably (<I>P</I><0.05) improved embryos development (Day 8 blastocyst) having 27.30 and 40.01% for control and coagulansin-A treated groups respectively. Treatment with 5 μM coagulansin-A significantly induced activation of heat shock protein 70 (HSP70) (<I>P</I><0.05). Immunofluorescence analysis revealed that 5 μM coagulansin-A treatment also significantly inhibited oxidative stress and inflammation during bovine embryo development <I>in vitro</I> by decreasing 8-oxoguanosine (8-OxoG) (<I>P</I><0.05) and nuclear factor-κB (NF-κB) (<I>P</I><0.05)<I>.</I> The expressions of HSP70 and NF-κB were also conformed through real-time PCR (RT-PCR). Additionally, the terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) assay confirmed that coagulansin-A treatment significantly improved the embryo quality and reduced bovine embryo DNA damage (<I>P</I><0.05). The present study provides new information regarding the mechanisms by which coagulansin-A promotes bovine embryo development <I>in vitro</I>.</P>
Electronic Structure and Magnetic Properties of Nd2Fe14B
Imran Khan,Jisang Hong 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.12
We studied the electronic structure and the magnetic properties of Nd2Fe14B by using the full potential linearized augmented plane wave method. The density functional theory was employed with Hubbard-type on-site Coulomb potential U to treat the localized 4f electrons of Nd. We found that the ferrimagnetic (ferri) configuration between the Fe and the Nd sublattice was more stable than the ferromagnetic (ferro), and the difference between the ferri and the ferro was 940 meV. The calculated spin magnetic moments for different Fe and Nd sites were in good agreement with previously reported values. Regardless of the relative spin direction between the Nd and the Fe sublattices, the spin and the orbital magnetic moments were always anti-parallel in the Nd atom, and the orbital magnetic moment was larger than the spin magnetic moment. We found that the total magnetic moment in the ferrimagnetic state was larger than that in the ferromagnetic state, and this feature originated from the orbital magnetic moment in Nd atoms. The calculated total magnetic moment per formula unit was in close agreement with the experimentally reported value.
Site Preferences for La and Pr in Nd2Fe14B Permanent Magnet: A First Principles Study
Imran Khan,Jisang Hong 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.10
Using the first principles method, we studied the site preference and the magnetic ground state of rare-earth elements La and Pr doped Nd2Fe14B permanent magnet. It was found that the La preferred the f-site doping at low doping ratio (12.5 %) while the g-site was more favorable at high doping (25 %). For the Pr impurity, we observed the opposite behavior because the site preference was switched. In addition, the spin configuration also depended on the impurity type and concentration. An antiferromagnetic (AFM) type spin configuration was found at both lower and higher doping ratios of La. For the Pr impurity, at a lower doping ratio, the AFM spin configuration was still preserved. However, the ferromagnetic spin configuration was more stable at a high doping ratio. Through impurity-substitution energy calculations, we found that the La impurity preferred to enter into the 2:14:1 phase at low doping, but it favored the grain-boundary phase at high (25 %) doping ratio. On the other hand, we observed that the Pr always preferred the main phase for both low and high doping concentrations.