Browsing by Author "Tadesse, Mesfin"

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    Applications of Integrated Geophysical Techniques to Map Subsurface Structures, Contributing to Ground Water Flow in the Ziway – Langano Corridor, Central Main Ethiopian Rift
    (Addis Ababa Universty, 2017-06) Tadesse, Mesfin; Alemu, Abera (PhD)
    The aim of this MSc thesis is to evaluate subsurface structural influences on groundwater flow in the Ziway - Langano Corridor area located in the central main Ethiopian rift using integrated geophysical methods which include gravity and magnetic method. The study is deemed to be an essential resource in evaluating the subsurface geologic structures. The surface geology of the study area ranges in composition from volcanic rocks of rhyolite, pyroclastic, obsidian, and ignimbrite rocks, to sedimentary rocks of lacustrine sediment and alluvial deposits. It is determined that the tectonic setting and rock types of an area are important in establishing the distribution of the groundwater flow. Existence of subsurface structures which include faults, fractures, and veins have been investigated in the Ziway – Langano Corridor using horizontal gradient gravity map and tilt derivative magnetic map compiled for the study area. These geophysical investigation results have identified subsurface geologic structures which are responsible for the flow of groundwater from Lake Ziway towards Lake Langano. In addition to this, field observations made during the magnetic survey have confirmed the flow of ground water from Lake Ziway towards Lake langano. This conclusion is also confirmed by the existence of hot springs at the northern shore of Lake Langano which is missing at the southern shore of Lake Ziway. This work has shown that there are no east west structures that favor the flow of groundwater. Hence, the direction of groundwater flow in the study area takes place from Lake Ziway towards Lake Langano being controlled by the N-S and NE-SW oriented faults and fractures mapped in the Ziway – Langano corridor.
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    A S'tring Theory Approach To the Three- Dimensionai Ising Model
    (Addis Ababa University, 1989-06) Tadesse, Mesfin
    The thre(!"-d"lmctlsional ISing mode"' (3DII~) hilS been Olie td the unsolved problems in physics. Polyakov hiS sugg0sted ~hlt It may be possible to solve this model via the string theory methods. The 3DHl in the cl'itical regime can be assu.I.il-'i;d' to corr-espond to the fermionic string which s.pans a 2"0 world-sheet. The 301M also corresponds to theconventtonal-.2 anct.(" Lagrangia field theories. It can be shown that the scaling dimenstons of these two and three-dimensional fields are proportional. Tha constant of proportionality is heuristically identified with the Hausdorff dimension of the ~Iol·ld-sheet. Computercalculatio" of the Hausdorff dimension and the scaling dtmeos10ns of the 3D i:onventional field, the results of which artl available in the literature, enable numerical evaluation of the critical exponent! m and B of the. Ising model. Thesa agrae well with experimental results
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    A String Theory Approach to the Three-dimensional Ising Model
    (Addis Ababa University, 1989-06) Tadesse, Mesfin; Mojurnder, M.A . (PhD)
    Th.pans a 20 world-sheet. The 3D 1M a lso co rr esponds to the conventional , .2 a~d . 4 La gr an gia field t heori es . It can be shown that t he scaling di~ens i o ns of these two and three-d i mensi onal fie l ds are proportional. The co ns t an t of proportionalttz is he uristically ide nt ified wi th the Ha usdorff dimens 'ion o f the world -sheet . Computer cal cu la tio" of th e Hausdorff di mension and t he scal i ng dimensions of the 3D conven tio nal field , the resu l ts of which are available tn the literature , enable numer i cal evaluation of the critical expo nent~ " and B 0'" t he · Ising mode l. These agree well with ex peri me ntal results . .The l si ng mod e l f irst appaa r ~d i n the t hesi s of Ernst I si ng i n 1925. Thi s mode l was. of cour se . one di mens i ona l and. to 1 5 in 9 '~ di sap poi ntment, di d no t e xh ib i t a phas e t r ansiti on. The t wo and t hr ee-d i me nsional Is ing mode l s are i ndeed only t wo of s t at i stica l mo de l s wh ich undergo phase trans it i ons •. The two-dimens i onal Is i ng model was first consi der ed by ,"" Pei erl s i n 1936. In 1941. Kramers and . Wanni-er de t ermined the critical t emperature (the t r ans i tion point) by assum ing i ts existe nce . The year 1944 cou ld be thought of as the beg i rt ~ n g of a new era in the s tu dy of the phys i cs of phase tran s i t i ons. -- .... 1n t hi s year, L.Ons ager pre s en t ed a paper i n which i t has been sh own r ig oro us ly thdt the two - dimens i onal ISing medel 8)!hibit ed a phase t ra ns ition. The pa r t i tion funct i on f or the two-dimens i onal Is ing model was oota i ned by co nve rt ing t he model into a system of fr ee ~', a jorana f ermi ons . This shows tha t t he two-dimen s ional 1's'; ng mode l is equivalent t o a free quantum field theory of fe rm i /) i'iS, 1 , 2 ,.,e t hods . 3 The model is also treated by usi ng combinatorial The three-dmensional Ising madel, ' (301M) still rema i ns one of the problems in phySics for which no exact solutio ns have been pos sib le yet. Even if the partition func t ion ha s ' not been found the critica l exponen t s have been determined by t he ser i es and r eno r mal is a t ion group methods . The values of J the c r itica l ~xpon e nts obtained i n th i s manner have beenc om pared witt, those obtained experimentally . Recent develop- , mellts :n the string theory i,a ve l ed t o the expectation tha t the 3DIM might be ~oJ va b le in the not too distant f ut ure ty t ~chntij~es t hat are bei ng developed cu;rently. It, hDwe~er . a pp ear~ th at the current leuel of development has not yet reached the stage where one could bPply t he st ri ng tl,eory to calculate t he partition function or even the critica l expone nts . Ho wever, as we shall see . by a combination of the ideas of the , string t heory with the results of renormalisation group stud i es one could predict some of the critical exponents. This paper is organized as follows: Chapter 1 i s a r eview of the 301M and its possible representation by the string theory. Of course. here. we made use of analogy to the two-dimensional Ising model in deriving the partition function. Polyakov' s interpretation is menti oned. Chapter Ii deal s with thf bQsonic string, Also, in this chapter. the s upersymme trised form of the string~that is to say the fermloni c str i ng- is considered. Chapter III is a discussion of the attempts at the calculati on of the' values of the critical exponent. In ChapterIV we have a short discussion of the a,pplication tJ:ki ~ the r enormalization group t~ the Ising model. A heuristic application of the ideas of the string model is made to some result of the re norma lization group for caltulattng the numerical values of the critical exponents. This is done in Chapter V. Finally, we discuss ' briefly the results and the fut ~re ' possib'litte~.