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Ghulam Abbas Ashraf,Lanting Zhang,Waseem Abbas,Ghulam Murtaza 한국물리학회 2019 Current Applied Physics Vol.19 No.4
The substitution of numerous cations into hexagonal ferrite has been extensively used to endow novel properties and functionalities for various applications. In the present work Gd-Tl substituted barium hexaferrites prepared by co-precipitation process, having the composition Ba0.75Cu0.25(GdxTl0.5-x)Fe11.5O19 (x=0.0, 0.25 and 0.50). The hexaferrite formation during calcination of sample x=0.25 was confirmed by TGA/DSC which was processed at 1000 °C for 3 h. The analysis of X-ray diffraction depicts the existence of magneto-plumbite structure with the formation of a minor secondary α–Fe2O3 phase x≤0.0 and BaFe2O4 phase x≤0.50. UV–Vis spectra reveal the dropping down behavior in the optical energy band gap from 2.47 eV to 1.74 eV. The grains with hexagonal platelet-like shape having size of 0.415–0.446 μm of magnetic powder nanoparticles (MPs) are observed by SEM images. The energy dispersive spectrometer (EDS) analysis was employed for presence of ferrite elements within a single particle. Hysteresis loops signifies the magnetization (Ms) and remnant magnetization (Mr) first increases up to x=0.25 then reduces with the substitution (x) increment; contrarily, the coercivity (Hc) exhibited initially decreased with maximum content of Tl at x=0.0 then increases at x=0.25 after that it decreases at x=0.50. Maximum values such as Ms (51.727 emu/g), Mr (28.061 emu/g), and Hc (4.057 kOe) are attained for x=0.25 at room temperature. The synthesized magnetic nanoparticles are found to be suitable for microwave absorbing materials, permanent magnets, catalyst, high density recording media and optoelectronic devices.
Dynamic Modeling and Control of DFIG for Wind Energy Conversion System Using Feedback Linearization
Ghulam Sarwar Kaloi,Jie Wang,Mazhar Hussain Baloch 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.5
This paper presents a dynamic modeling and control of doubly fed induction-generator (DFIG) based variable speed wind-turbine. The dynamic model of DFIG is incorporated with all system components which provide simple design and controls. The penetration of wind power is increasing into electrical networks, which necessitates more comprehensive studies to recognize the interaction between the wind farms and the power grid. This paper presents the dynamic model of a DFIG based wind turbine connected to the grid system in the dq-synchronous reference frame. In this article, the feedback linearization method has proposed a controller in order to reduce the oscillation and stabilize the wind turbine system parameters based on feedback linearization concepts. Based on the nonlinear control system, the proposed approach is applied to the rotor side converter and grid side converter. The damping of the DFIG is improved in transient response. In addition, the oscillation of the stator current and DC link voltage during the generator voltage dip are reduced. To the best of author’s knowledge, the proposed control outcomes compared with conventional controller verified the effectiveness, having better performance through simulation tool Matlab.
A Self-Excitation Scheme for a Brushless Synchronous Generator
Ghulam Jawad Sirewal,Muhammad Ayub,Byung-il Kwon 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
This paper proposes a self-excitation scheme for a brushless wound rotor synchronous generator. The proposed generator excitation scheme uses thyristor switches to control zero-sequence third harmonic current flow to the neutral wire of the three-phase armature winding. In the generating operation when line three phase currents flow, thyristor switching creates current flowing to the neutral wire. This current is rectified and fed to an additional winding on the stator called stator harmonic winding. Current in the stator harmonic winding generates additional magneto-motive force (MMF) component along with the fundamental component which is generated from threephase armature winding. 2D finite element analysis in ANSYS Maxwell 19.0 is performed to validate the working of the self-excited brushless generator scheme.
Ghulam Shabbir,Seiji Kojima,고재현 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.12
The effect of prepoling and aging time on the dielectric properties of (1 − x)Pb(Mg1/3Nb2/3)O3- xPbTiO3 single crystals with x = 0.33 were investigated by dielectric spectroscopy. The prepoling along the [001] direction induced low-temperature dielectric anomalies which disappeared by thermal cycling even within the ferroelectric phase. This suggested that the field-induced dielectric anomalies are associated with metastable states due to inherent disorder and quenched random fields in relaxors. The temporal change in the capacitance at constant temperature in the ferroelectric phase showed that the aging rate became larger with increasing temperature. It indicates that the activation barrier for the relaxation processes of polar domains and/or polar nanoregions is higher at lower temperature.
Ghulam Mustafa AHEER,Muhammad Asif AZIZ,Asifa HAMEED,Amjad ALI 한국곤충학회 2009 Entomological Research Vol.39 No.3
Susceptibility of field populations of Helicoverpa armigera (Lepidoptera: Noctuidae) from Punjab, Pakistan to selected insecticides was evaluated using the leaf dip method. The resistance factors varied between populations. The general trends were low to moderate resistance to endosulfan; very low to low resistance to chlorpyrifos and profenofos; very low resistance to spinosad, indoxacarb and thiodicarb; moderate to high resistance to bifenthrin; high to very high resistance to cypermethrin; and very high resistance to lambda-cyhalothrin. Integrated pest management strategies aimed at reducing pesticide application, such as rotating the conventional insecticides having low resistance with newly developed synthetic insecticides and conserving natural enemies, are recommended.
GHULAM FARID,LAXMI RATHOUR,SIDRA BIBI,MUHAMMAD SAEED AKRAM,LAKSHMI NARAYAN MISHRA,VISHNU NARAYAN MISHRA The Korean Society for Computational and Applied M 2023 Journal of applied and pure mathematics Vol.5 No.1/2
The Hadamard type inequalities for fractional integral operators of convex functions are studied at very large scale. This paper provides the Hadamard type inequalities for refined (α,h-m)-convex functions by utilizing Liouville-Caputo fractional (L-CF) derivatives. These inequalities give refinements of already existing (L-CF) inequalities of Hadamard type for many well known classes of functions provided the function h is bounded above by ${\frac{1}{\sqrt{2}}}$.
Ghulam Farid,Sidra Bibi,Laxmi Rathour,Lakshmi Narayan Mishra,Vishnu Narayan Mishra 강원경기수학회 2023 한국수학논문집 Vol.31 No.1
We aim in this article to establish variants of the Hadamard inequality for Caputo fractional derivatives. We present the Hadamard inequality for strongly $(s,m)$-convex functions which will provide refinements as well as generalizations of several such inequalities already exist in the literature. The error bounds of these inequalities are also given by applying some known identities. Moreover, various associated results are deduced.