Browsing by Author "Kare, Anno"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item The Dynamics of Accretion Disks around Compact Stars with Complex Magnetic Fields(Addis Ababa University, 2014-04) Kare, Anno; Wetro, Legesse (PhD)Strongly magnetized stellar objects have magnetospheres characterized by such activities that define the geometry of the inner edge of the disk as well as control the inflow of matter to the NS surface itself. Of all possible components of the surface magnetic field of the central object (neutron star-NS), we have only considered the quadrupole term to investigate what ever is going on nearer to the surface of the NS. There is a highly important difference of the accretion flow in a quadrupolar and dipolar magnetic fields. The dipolar magnetic field will in the end always present a barrier to the accretion flow since the field lines are perpendicular to the plane of the disk, but the quadrupolar magnetic field will in the simplest case lie in the plane of the disk, and thus it will rather channel the accretion flow all the way down to the stellar equator. This work involves a mathematical treatment of an accretion disk around a magnetized star. In order to define the disk structure magnetohydrodynamic (MHD) equations are solved in cylindrical coordinates. For the detailed results an ordinary differential equation (ODE) derived from the angular momentum equation is numerically solved. So, both Keplerian and non-Keplerian cases of thin accretion disk are solved. Further, introductory work on slim disk is included as a part of this work. The results of our analysis indicate the existence of two different regions: a super-Keplerian innermost region and a broader sub-Keplerian outer region. The effects of stellar and toroidal magnetic fields on the variations of viscosity, temperature and density have also been studied. We have identified the nature of the inner portion of an accretion disk. The velocity of the transition varies from corotating magnetospheric boundary to super-Keplerian for low density inner most portion of accretion disk, that extends from 0:5RM to the peak and then to sub-Keplerian. Our results are applicable to accreting astrophysical systems such viii ix as neutron stars (NSs) and white dwarfs (WDs). It can also explain observational results not yet fully backed with theoriesItem Efficiency of Gas Filled Detector for the Detection of Beta and Gamma Radiations(Addis Ababa University, 2006-07) Kare, AnnoThere are many forms of radiation –heat, light, radar, radio waves etc. differ from one another in frequency but not in kind. The so called “kinds” of radiation are characterized by the techniques used to produce and detect them; The classical theory of Maxwell applies to all these radiations and all are ultimately due to the acceleration of electrical charges. Except for differences of frequency, and observation made on one’Kind “of radiation must also be true of all other kinds. Radiation is energy in the form of waves or particles. The great majority of it occurs naturally and we are all exposed to it all of the time .It is all around us-in atmosphere, the earth, our food our bodies and from cosmic rays, from outer space and medical X-rays. Radiation can be produced from a variety of sources. There are two broad types - ionizing and non-ionizing radiation - classified in terms of their effects on matter. Non-ionizing radiation includes some ultra violet light, visible and infrared light, microwaves, radar and radio waves. Ionizing radiation is that which has enough energy to remove an electron from an atom, thereby producing an ion - an electrically charged atom or grouping of atoms. Cosmic rays, x-rays and the radiation emitted by the decay of radioactive substances are examples of ionizing radiation. Although they are types of radiation, alpha and beta particles and neutrons are not parts of the electro-magnetic spectrum because they are particles not waves. We are most affected by ionizing radiation, which deposits some of its energy as a result of electrical interactions when it passes through matter. It can be harmful to the human body in excessive doses because it can damage individual cells, possibly resulting in damage to organs, or other long-term effects. Radiologist discovered that repeated exposure of their hands to X-rays resulted in skin burns. This discovery led to the wide spread use of X-rays in the treatment of cancer. Also it was realized that excessive exposure of the body to radiation could result in radiation different in their biological effect on tissues even when the absorbed dose is the same. This basically depends on ionizing power of radiation. The relative biological effectiveness of electrons and positions are the same. Whereas, heavy ionizing particles such as alpha particles and fission fragments produce much greeter biological effect. However, containing it, shielding against it, moving away from it, or removing the source can gain effective protection from radiation. Radiation has the same effect, whether from natural or man-made sources. Most people receive their greatest exposure to radiation from the naturally occurring radioactive gas radon. It is produced as a result of the decay of uranium - which is present in all rocks and soils. We all breathe it every day and it accounts for about 50 per cent of our total radiation dose. In fact, about 85 per cent of our total dose is the result of naturally occurring radiation. Medical sources, such as x-rays, account for a further 14 per cent. The fall-out from past nuclear weapons tests and incidents such as Chernobyl amount to 0.2 per cent and discharges from the nuclear industry total much less than 0.1 per cent It may be wondered why it is, if the surfaces of all bodies are continually emitting radiant energy, that all bodies do not eventually radiate away all their internal energy and cool down to a temperature of absolute zero. The answer is that they would do so if energy were not supplied to them in some way. In the case of filament of an eclectic lamp, energy is supplied electrically to make up for the energy radiated. As soon as the energy supply is cut off, bodies do, infact, cool down very quickly to room temperature. The reason that they don not cool further is that their surroundings (the walls, and other objects in the room) are also radiating and some of this radiant energy is intercepted, absorbed and converted into internal energy. The same thing is true of all other objects in the room –each is both emitting and absorbing radiant energy simultaneouslyItem Efficiency of Gas Filled Detector for The Detection of Beta and Gamma Radiations(Addis Ababa University, 2006-07) Kare, Anno