Browsing by Author "Arifur Rahman, Mohammad"

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    Effect of copper substitution on the magnetic properties of Fe2.5Zn0.5-xCuxO4
    (Department of Physics (PHY), 2013-02) Arifur Rahman, Mohammad; Hossain, Dr. A.K.M. Akther
    Polycrystalline Fe2.5Zn0.5-xCuxO4 ferrites with x= 0.00-0.45 have been synthesized by the standard solid state reaction technique. Pellet- and toroid -shaped samples are prepared from the ferrite powders and sintered at various temperatures in air for 5 hours. Samples prepared from each composition are sintered at various temperatures (1050-1150C) and structural and surface morphology are studied by X-ray diffraction (XRD). The magnetic properties of these ferrites are characterized with high frequency (100 kHz-120 MHz) Impedance Analyzer. The influence of microstructure, various cation distribution and sintering temperature on the complex initial permeability of these samples are discussed. X-ray diffraction pattern show the formation of spinel structure. Lattice parameters are calculated using the Nelson -Riley function. It is also found that the lattice constant decreases with increasing Cu content, obeying Vegard‘s law due to smaller ionic radius (0.65Å) of Cu2+ compared to Zn2+ (0.74Å ). This result is explained with the help of ionic radii of substituted cations. The microstructural study shows that both sintering temperatures and cations substitutions have great influence. As the sintering temperature increases, the bulk density increases (depending on compositions), and hence the porosity decreases for all compositions. The initial permeability increases at a certain composition (up to x=0.30) beyond that decreasing. It is also observed that the real part of initial permeability increases with sintering temperatures for all ferrites because high sintering temperature helps to develop uniform grain. The real part of the initial permeability ( / i ) remains fairly constant in the frequency range up to some critical frequency which is called resonance frequency. The highest / i for each sample has been observed sintered at 1150 ºC because the microstructure is homogeneous with a uniform size distribution.The loss factor increases with increasing of Cu content and sintering temperature. The relative quality factor Q both increases with increasing sintered temperature and Cu content up to x=0.30 then decreasing. For inductors used in filter applications, the quality factor is often used as a measure of performance. It is observed that the sample sintered at 1150ºC is of the highest Q value (3688) for Fe2.5Zn0.20Cu0.30O4 samples.
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    Erosion of left bank of the Padma river at Mawa-Dighirper reach and its socio-economo impact
    (Department of Institute of Water and Flood Management (IWFM), 2008-07) Arifur Rahman, Mohammad; Munsur Rahman, Dr. Md.
    The Padma River is highly dynamic and meander in naturc. Bank erosion severely affects the socioeconomic condition of the affected reach and not only causes suffering to the people living along its course but also national losses due to loss of cultivated land, settlements, commercial centers and infrastructures. The present research tries to understand the bank erosion of Mawa- Dighirper reach and its present and future socioeconomic impact. In the present study, a large number of good quality digital data have been prepared from satellite imageries and these data are used to evaluate the channel shifting in the ,tudy reach. The income level of about 70 percent respondents has become less due tn change in their working environment. After displacement 28% became day labor, about 16% of the affected are adopted tampo and bus driving, 16% started to work in the gannents and cold storage factories. A total of 78 percent of the households reported having been displaced by erosion at least once; out of them, 80 percent household reported multiple displacements. Eighty eight percent affected household migmtcd and resettled at the adjacent villages and unions. The affected people have a tendency and attitude to remain close to their homestead, relatives and surroundings. Most of the School going children gave up their studies forever due to school shift. About 66 percent of the respondent reported that the educational facilities were deteriorated. The sinuosity of the recent active bend is 1.02. A Hickin and Nanson type empirical model for the estimation of bank erosion rate was tested in the present study reach. It was observed that the co-efficient of erosion and exponent values for positive trend are 229 and 0.71, respectively and the co-efficient of erosion and exponent values for negative trend are 1280 and 1.77, respectively. '" • The satellite imageries of 1989 to 2006 indicate that, the left bank of the Padma River at Mawa. Dighirper reach is severely affected by erosion. Lohajang, Teotia, Dighirper and Hasail-Banari union are almost disappearing and Ohaida union become extinct due to hank erosion of the study reach. ln the lime span of the last 17 years the concerned area of thc study reach decreased by about 40 km1,Seven hundred and fifty crorc taka at land value have been lost due to erosion.