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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.
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.
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.
Energy‐balance node‐selection algorithm for heterogeneous wireless sensor networks
Imran Khan,Dhananjay Singh 한국전자통신연구원 2018 ETRI Journal Vol.40 No.5
To solve the problem of unbalanced loads and the short network lifetime of heterogeneous wireless sensor networks, this paper proposes a node‐selection algorithm based on energy balance and dynamic adjustment. The spacing and energy of the nodes are calculated according to the proximity to the network nodes and the characteristics of the link structure. The direction factor and the energy‐adjustment factor are introduced to optimize the node‐selection probability in order to realize the dynamic selection of network nodes. On this basis, the target path is selected by the relevance of the nodes, and nodes with insufficient energy values are excluded in real time by the establishment of the node‐selection mechanism, which guarantees the normal operation of the network and a balanced energy consumption. Simulation results show that this algorithm can effectively extend the network lifetime, and it has better stability, higher accuracy, and an enhanced data‐receiving rate in sufficient time.
KHAN, Mohammed Abdul Imran,ALAM, Md. Shabbir,SYED, Ahsan Jamil Korea Distribution Science Association 2021 The Journal of Asian Finance, Economics and Busine Vol.8 No.3
The ability of entrepreneurs to arrange working capital is the key to maximizing the profitability of small- and medium-sized enterprises and the wealth of entrepreneurs. The study investigates the correlation between entrepreneurs' working capital management and the profitability of SMEs listed on six Gulf Cooperation Council (GCC) stock exchanges between 2019 and 2020. The secondary data is collected from the financial statements of SMEs listed on the six GCC stock exchanges. Actual sample for the research study was a total of 136 small- and medium-sized enterprises selected using purposive sampling methods. Four research models were considered in this analysis, all ending up affecting gross profits. The selected entrepreneurial SMEs were listed on six different Gulf Cooperation Council stock exchanges during 2019-2020. The fixed financial assets ratio, financial debt ratio, and company size are used as control variables and data were analyzed using multiple regression. The research results demonstrate that there is a statistically significant negative correlation between profitability measured by gross profit and cash cycle and the components of the cash cycle (including days of accounts receivable and days of inventory). The study further reveals that there is no significant correlation between gross profit and days of accounts payable.
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.