http://rulrepository.ru.ac.bd/handle/123456789/9 2026-04-07T21:43:57Z http://rulrepository.ru.ac.bd/handle/123456789/1153 Intrinsic Features of Nonlinear Waves in Dusty Plasmas Salam, Md. Abdus Dusty plasmas are electrically conducting ionized gases (macroscopically quasi-neutral) that comprise positively and negatively charged dust particles in addition to ions and electrons. Dusty plasmas exist in the Earth's magnetosphere, cometary tails, planetary rings, asteroid rings, rotating stars, and many other astronomical environments. In dusty plasmas, various types of nonlinear waves, such as solitary waves, shock waves, etc., may be propagated. The presence of dust particles makes the plasma system more complex. Besides, the characteristics of nonlinear waves can be substantially affected by different forces and plasma parameters. We theoretically investigate the characteristics of dust-ion-acoustic solitary and shock waves, where the plasma species follow different particle distributions. The higher-order nonlinear and dispersive (or dissipative) effects on the waves are examined. We also investigate various kinds of effects, such as magnetic, adiabatic, parametric, etc., while it is illustrated that how they change the wave characteristics. An inhomogeneous KdV-type or modified KdV-type equation is obtained for demonstrating the solitary waves, whereas an inhomogeneous modified Burgers-type equation is obtained for the shock waves. The reductive perturbation method is extensively used for incorporating the higher-order effects into the KdV, modified KdV, and modified Burgers equations. The re-normalization technique, the Abel’s theorem, and the method of variation of parameters are used for adding higher-order nonlinear and dispersive (or dissipative) effects into the solutions. We deal with the theoretical investigation of the combined effect of the magnetic field and plasma rotation on the nonlinear features of obliquely propagated dust-ion-acoustic solitary waves in a magnetized dusty plasma. From the investigation, it is found that the overall impact of the magnetic field, oblique rotation, electron temperature, and dust concentration has a crucial role in changing the amplitude, width, and phase speed of the dust-ion-acoustic solitary waves. The results are expected to be helpful in describing the rotating flows of magnetized plasma that are believed to exist in the rotating stars, the pulsar magnetosphere, and other rotating astronomical objects. We also explore the dynamic behaviors of multi-solitons as well as multi-shocks that propagate in a magnetized dusty plasma. The simplified Hirota method and the Cole-Hopf transformation are applied to construct the multi-soliton or multi-shock solutions. We observe that the magnetic field has a decreasing effect on the multi-soliton amplitudes and widths, whereas the dust concentration has an increasing effect on the amplitudes and widths of both types of waves. The obtained results might be helpful to describe the solitary and shock waves propagated in the Earth's mesosphere, Jupiter's magnetosphere, cometary tails, etc., in which dust particles are commonly seen. This Thesis is Submitted to the Department of Applied Mathematics, University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD) 2024-01-01T00:00:00Z http://rulrepository.ru.ac.bd/handle/123456789/1136 Studies of the Effects of Annealing, Partial Degassing and Light Soaking on Sputtered A-Si:H Films Through Analysis of Infrared and Thermal Effusion Results Hashem, Md. Abul Hydrogenated amorphous silicon, a-Si:H, is a promising material with ideal properties for various types of optoelectronic devices. At the same time, the material suffers from some serious disadvantages including Staebler wronski effect (SWE), in which the efficiency of a solar cell decreases gradually with prolong exposure to light. It is believed that the quality of a-Si:H alloy is closely related to its hydrogen content and to the nature of silicon-hydrogen bonds. On the otherhand, hydrogen has indirect influence on the occurrence of SWE. a-Si:H often contains significant amount of impurities such as oxygen and nitrogen which have sufficient influence on their optoelectronic properties. Hence, the various bonding configurations involving Si, H, O and N has been studied to investigate their role in the light induced structural changes in a-Si network. Infrared spectroscopy (IR) and thermal hydrogen effusion (TE) have been used to characterize the sputtered a-Si:H samples. The results have been analyzed to study the nature of the silicon-hydrogen, silicon-oxygen and silicon-nitrogen bonds and to identify the effects of partial degassing, annealing and light soaking on these bonds. The samples were prepared by reactive radio frequency sputtering under different deposition conditions to produce hydrogen contents ranging from 10 to 35 at.%. Slightly contaminated samples were found to contain oxygen and nitrogen concentrations up to ~3 and 1.5 at.% respectively. Samples were deposited, generally, onto crystalline silicon (100) with few exceptions onto stainless steel substrates at a deposition rate of -4 nm/min. The substrate temperature was controlled at ~120 °C and the thickness of the films were from -0.08 to 6 um. Different sets of samples were subjected to partial degassing (in vacuum), annealing (in hydrogen atmosphere) and light soaking (under sun light AM1). Infrared absorption spectra, from 370 to 5000 cm', were obtained using a fourier transform infrared spectrometer. A quadrupole mass spectrometer was used to monitor the evolution of hydrogen. Several computer softwares were used to analyze the resulting data. Uncontaminated samples show three hydrogen-related distinct features at 650, 850-895 and 2090 cm1 due to wagging, bending and stretching vibrations, respectively, of the various silicon-hydrogen bonds. Nitrogen containing samples show, in addition, a features at 790 cm1. Samples containing oxygen exhibit the distinct features at 940-980 and 1000-1045 cm1 regions due to Si-O-Si and H/Si-SiO2-O-SIO2-Si/H configurations respectively. The evolution of weakly bonded hydrogen occured at different temperatures; more contaminated samples, having evolutions peaks at higher temperatures, indicate better stability to thermal degradation. Incorporation and/or movement of oxygen atoms are also a consequence of partial degassing. Higher hydrides are related to 850-895 cm' doublet and have lesser contribution to feature at 650 cm. The peak at 2000 cm1 has contributions from (Si-H2), and clustered Si-H. The 2090 cm'' peak is a result of Si-H2, (Si-H2), Si-H3 and Si-H groups. In annealed samples, some IR inactive hydrogen become IR active and there is evidence of the movement of oxygen atoms from the bulk of the film towards the film- substrate interface. The peaks at 2000 and 2090 cm moves towards higher wavenumber with increasing annealing temperatures. Oxygen atoms become mobile as a result of prolonged illumination and seem to move through a-Si network. Also the oxygen atoms in the crystalline Si-O form new configurations and /or diffuse into the bulk of a-Si:H film. No evidence of the movement of the nitrogen atoms through a-Si network was observed. Some weak Si-H bonds are broken and the hydrogen atoms become mobile in the a-Si network. Thus it appears that hydrogen atoms move through an a-Si:H network as a result of the breaking of Si-H bonds due to the trapping of free-charge carrier following illumination. This creates dangling bonds in the interior of the material. After prolonged illumination, the overall number of new dangling bonds becomes large enough to cause permanent structural damage or photodegradation in the interior of the film. This Thesis is Submitted to the Department of Physics, University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD) 1998-07-01T00:00:00Z http://rulrepository.ru.ac.bd/handle/123456789/1115 Determinants of Health Condition and Estimation of Demographic Parameters of Street Children in Dhaka City, Bangladesh Shahiduzzaman, Md. Health and demographic condition of street children are important issues for the development of any country. Several researchers estimated that a substantial percent of total street children in Bangladesh are living in the Capital City, Dhaka, Bangladesh. But no study is available which concentrated to in-depth study of health condition and estimation of demographic parameters for the street children. So the aim of this study is to identify the determinants of health condition and estimation of demographic parameters of street children in Dhaka city, Bangladesh. We have used convenient sampling for selection of samples. The data were collected from 1108 street children in different places of Dhaka City using a comprehensive questionnaire. In this study, x2 statistic was used to test the significance of the association between the dependent and independent variables of the street children. Binary logistic regression model was also employed to identify the effect of the some important independent variables on dependent variable. To have a smooth pattern of age 3 years moving average technique and "4253H twice" smoothing technique were applied in this study. It was found that among total sample data 84.9% were male and only 15.1 % were female. Age structure of street children followed a polynomial function of degree four. Probability of dying (qJ calculated for street Children showed an expected pattern. The migration rate from rural to urban of male street children was higher than that of female street children. Migration rate of street working children was the highest among four types of street children. Migration rate of street children of illiterate fathers was higher than that of street children of literate fathers. Migration rate of street children of illiterate mothers was higher than that of street children of literate mothers. This Thesis is Submitted to the Department of Population Science and Human Resource Development, University of Rajshahi, Rajshahi, Bangladesh for The Degree of Doctor of Philosophy (PhD) 2021-01-01T00:00:00Z http://rulrepository.ru.ac.bd/handle/123456789/1114 Study of Radicals and Semisimple Classes of Rings Dey, Kalyan Kumar The concept of the radical of a ring was introduced by Artin for rings with the descending chain condition with a view to obtaining a nice structure theorem for the ring. The idea was to single out the Toblerone part, of a ring, called the radical of the ring, and factor out the original ring with respect to the radical. The resulting ring, termed, semi simple has a nice description. Radica1s for rings without chain conditions were proposed by Koethe, Jacobson, Brown, McCoy, Levitzki and others for a similar purpose in an attempt to generalize Artin 's radical. All these attempts were later further generalized by Kurosh and Amitsur to define the concept of a general radical of a ring and the cones ponding semi simple ring and study these in their generality. Andrunakievic advanced these studies further. The class of rings which are radicals of themselves with respect to some radical is called a radical class, or simply, a radical, and the correponding class of the semisimple rings is called a semisimple class. A class rings may be simultaneously a radical ring with respect to some radical and a semisimple ring with respect to another radical. Such a class of rings is called a semisimple radical class. In this thesis we have studied radical classes, semisimple classes and semisimple radical classes of rings…………………. This Thesis is Submitted to the Department of Mathematics, University of Rajshahi, Rajshahi, Bangladesh for The Degree of Master of Philosophy (MPhil) 2002-01-01T00:00:00Z