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Item Collective Phenomea In Highly Excited Bose Gas(Addis Ababa University, 1981-06) Tilahun, Tesfayee}wij:ed gas is meant a 90."1 in which thet'e exisi: a s.i9nificant number of exalted particles. Tlw number of ~jxcited part 1cles depends on external sources (la.ser illumination, electron beams, etc.) and can be arbitrary. In typical case" the number of excited atoms N .i" smaller than the number of pal;t.icles .in the 1 ground state. As.is \'1e11 lmoVin the energy of interaction between pa,'ticles in the same quantum Bt_ate is proportional to lid' ~Ihere R 1s the distance between partlcles. 'I'his shortrange interaction is responslblc 1:or tho coll()ct:i,ve properties of 1:he convelltional gas Huch as condensation and pha"e transitions. '1'he int_m:action hel:vl8cn dlf ferently·-exci'ced particles 1s proportional to I/n 3 and can be 21ttnlctive as Vlell as repulsive. 'rhus, t_he ava:llab.il.ity of even a comparaU.vely small number of excited -paxticles can and does l(-lad to 21 signU'icant change of the propertles of th,~ gas compared \~i til the non-(~xcited gas. The properties of Huch exc:l.tec1 (jas are invest.i.gated on the basis of the second'-quantJzecl Hilmil tonian and the method of equations of IUo-tion of Green functions. 1~hiB method yields I in a most natural and direct "THY, the enor(w~spectrulU of elllmentary excitations and t:he t:hGl:l!lodynaroiGCll functions of excited gasItem The Mathematical Basis Gauge Theories of The Yang-Mills type and Dirac Monopoles(Addis Ababa University, 1982-06) Kebede, Temesgenl\fter? g90metric and intuitive introduction to ~~n-trivial fibe~ bundleJ~ a precise presentation of principal fiber bundles ~ith Lie group structure is given. The methods of differential geometry are set up. It is , 'I ,,' I shown how a gauge potent~alcan be regarded as a connection in some fiber' bundle" an1 the corresponding gauge field as,the associated curvat~re. l\s an example of a physical case which l,,'ads to the 'Jon[;ide~ati.on of non-trivi.al' bundles I th~magne~i~ monoPol~ is! introduced in its Dirac form together 'I ' \,;;lth some notiol;ts of du~tity symmetry (self dual fields). 'I ' t1onopoles 'in t~e recent \~u-Yang formulation I and electrodynamicswit~ mohbpoles identified with non-trivial , i U(l) bundles are studiedl The yang-~lills action functional , , :is, def ined. : I I 'of the -'.-;' of the of the " ,The i Y~ng-Millsl field equation are derived in terms . I ,fielo (curvature) i. , , i The dual synunetric counterparts " I field e~uations a~e , I established as a consequence ~ianchi identitY~f differential geometry. It is , S'hO\'ll) hovi the global asp'ects of, the theory (f ini teness of the action and the boundary conditions on the gauge p~tentials) ~re;encoded lin the structure of a bundle. The . ' I asymptotically vanishing; gauge potentials (or pure gauges) ~;e classified usi,ng th I notions of instantoI,l number and homotopyItem Physico- Mathematical Details of Electrical Methods of Geophysical Prospecting and Some Applications on the Analysis and Interpretation of Data from Selected Sites in Ethiopia(Addis Ababa University, 1983) Kassa, Gebrechristos; F . Zhakupov, Dr . PaikenBasic theoretical foundations are discussed as a preliminary , followed by a description of t he various electrode spreads together with the relevant mathematical and physical considerations.Item Surface Wave Dispresion between North and East Africa(Addis Ababa University, 1983-06) kebede, Fekadu; Asfaw, Laike Mariam (PhD)A comprehensive study of dispersion of surface Rayleigh waves for three paths: Gulf of Aden - Addis Ababa (GOA - AAE), Red Sea Addis Ababa (RES - AAE) and Arab republic of Egypt - Addis Ababa (ARE - AAE), lying between north and east Africa is made. Earlier studies of surface wave dispersion in the region were made for short epicentral distances without considering contribution by different modes. The problem of contribution by different modes to dispersion is inherent at short epicentral distance ranges. Rayleigh wave trains identified from seismograms of Addis Ababa seismic station (AAE) are enlarged and digitized. The results are analysed using fixed window Fourier analysis and moving window analysis (Landisman et a1. 1969). These methods have advantages in displaying different modes which otherwise would be absent if the usual peak and trough method is used. Dispersion curves obtained by the above methods and the usual peak and trough method are compared with theoretical dispersion curves generated for different crustal models. An efficient algorithm developed for solving the period equation on a computer (Dunkin 1965; Robert H. Herrman personal communication 1980 ) is used to obtain theoretical dispersion curves up to ten modes. However, in this study the fundamental and first modes were found adequate to explain the seismogram observations. A total of 150 theoretical models each with multimode outputs were considered. A crustal thickness of 27 km with high Poisson's ratio overlying an anomalous mantle (,d-- = 7.2 km/sec) 4 km thick is found for GOA - AAE path. For RES - AAE and ARE - AAE paths crustal thicknesses of 37 km and 38 km respectively overlying a normal mantle are found. The Poisson's ratios for these paths are similar to that of a 'normal continental crust. Regarding resolution of modes for the period range considered in this study both moving and fixed window methods give similar results indicating that the former method is superfluousItem Crustal Modelling from Gravity data in the Ethiopian Rift(Addis Ababa University, 1983-06) Alemu, Abera; Asfaw, Laike Mariam (PhD)A detailed gravity survey of the Main Ethiopian Rift Valley between latitudes 70 N and SON, has shown that there is a broad relative positive Bouguer anomaly over the whole of the Rift floor, and this anomaly is superimposed on the regional, broad negative anomaly of the Ethiopian and Somali Plateau. The broad relative positive anomaly over the rift floor is between 60 and 100 km wide and has an amplitude of 30 - 60 mga!. On the broad relative positive anomaly over the rift floor are superimposed other short-wave length relative positive anomalies which seem to be situated along the displacement lines of the Wonji Fault Belt. There are also much narrower relative positive anomalies along the margins of the rift other than those associated with the \'Ionji Fault Belt. In their interpretation of the gravity minimum near the center of profile C (page 47), Searle and Gouin (1972) suggested that this gravity minimum is due to low density lavas of the Aluto volcano and they further a.8sociated the volcano with a small negative anomaly. On the contrary the present survey shows that the volcano is associated with a relative positive anomaly of magnitude comparable to the short-wave length rela.tive positive anomalies along the displacement lines of the Vionji Fault Belt. Due to both, denser spacings of gravity stations and quality of data, it is believed that the present gravity survey of the Main Ethiopian Rift between latitudes 70N and SON defines more accurately the location of the gravity anomalies (both the negative and the positive anomalies). The priliminary interpretations of the gravity anomalies made in this work are corroborated by bore hole data Wigs. 10, 11 ) and surface geology (F.ig. 2) of the study area. Furthermore, inferred density measurements on surface rocks and Cores from production bores in the Olkaria geothermal field of Kenya (Table 2) have been utilizedItem X-Ray Structure Analysis of Thin Film Solar Cell Materials(Addis Ababa,University, 1983-06) Ahmed, Salah; Neumann, H.g. (PhD)X-ray diffractomery is used for studying the crystalline Structure of thin filr cds/cu xs (where x is slightly less than or egual to 2)solar call materials the different films prepared are cas cuxs and sho2. The cds filrs are prepared by;Item Monopole Synchrotron Riidiation and Electron-Monopole Scattering(a, 1983-06) Kassahun, FessehaThe power radiated per harmonic into a unit solid angle by a monopole in uniform circular motion is computed. Then the polar.ization of monopole synchrotron radiation is investigated, and found to have certain distinct features compared "lith that of electron synchrotron radiation. This, we hope, may serve as a theoretical }x,ckgroulld in the search for monopoles. Finally, the energy transferred fr.om a scattered monopole to all electr.on initially at rest is determinedItem Giant Quantum Osciltions of Ultrasonic Absorption by Metals in the Phase Transition of Ordep 2 1/2(Addis Ababa University, 1983-06) Wetro, LegesseThe absorntion coefficient r of a normal metal like any on0 of the thermodynamic and kinematic properth,s of the metal greatlv clenenc:1s unon the .state in "lhich the motul is found. Z\t Iml enough ter~n8ratures and the metal goinq through electronic nhase transition, the absorntion coefficient under the action of an external magnetic fielc:1 is shown to assume different values in differ.ent regions of Z, the par.amoter of PT'-2~. In PT-?!z ilssoiated with apnearance of a neN spheroidal cavity, it is found to bo lo\'] and monotonous b810w a certain threshold value Z* while ShOl'IS Giant Quantu!T1. Oscillations (GQO) with exponentially rising amplitude for values Z »z*, t the conditions of observation of GIIO l'-e infT kn T «hl1 « I Z I . In PT-?!z associated "lith breaking of the Fermi neck the absorpt:. ion coefficient ShO"IS strict dependence on the angle of orientation of the Plv.gnetic field (e). Near a=o, it is found to behave in the same 'qay as in the apnearance of a snheroidal cavity NhereaB near a critical shows a sharp anisotropy of the value of the angle 8Cy it root .. type (0 - 8 rz - cr t Wherever hal/pears as a symbol here after in this manu·, scriDt it must be read as toItem Peculiarities of the Electron-Phonon Interaction during Change of Topology of the Fermi Surface in Metals(Addis Ababa University, 1983-06) Habtetsion, SemerabThe necessary background material for the analysis of the electron phonon interaction with respect to·the absorption coefficient and change in incident phonon frequency is discussed in the first and second chapters of this thesis. At the end of the second chapter the Migdal-Kohn Bnomalies for a spherical Fermi surface is dis~ussed. Experimental varification and phisical sense of these anomalies is also presented here. An investigation of the change in the phonon spectrum due to the Migdal-Kohn anomalies for some important cases of change in topology of the Fermi surface in metals is done in chapter three. In general it is found that the anomalies in rand Aw depend on the changes of the Fermi surface topology caused at phase transition of order 21. Also it ia noted that the singularities in rand Aw ~re interdependent as can be predicted by the Kramer's and Kronig relationsItem Peculiarities of the Electron-phonon Interaction During Change of Topology of the Fermi Surface in Metals(Addis Ababa University, 1983-06) Habtetsion, Semereab; Dr . V. DavydovThe necessary background material for t h e a na lys is of the electon phonon in te r ac t i on v it h respect t o the abs o r pt i on c o ef fi c i e n t a nd c ha nge i n in c i de nt p ho non f r e qu e ncy is d is c us s ed i n the fir st and s ec o nd chapte r s o f t hi s thesisItem Electroop'l'ical Method of Dt'ermina'l'ion of the Permanent Dipole Moment of Coli,Oidal Particles(Addis Ababa University, 1984-06) Feleke, Abraham; A.A. Spartakov (PhD)~qO tYges of rectangular electric fields (Rl - and R2~field) are produced by a specially constructed generator. IHhen Rl ~ field acts on the caracitor plates between ~Ihich is the solution to be investigated, the colloidal particles rotate and modulate the intensity of light that passes through the solutioIl. The electric dipole moment is given by the expression 6KTT ~n{ (~ - 1) + 2 1 t(~· .- 1) 11 FT o R2-field is used for the determination of the time of relaxation T. '['he electric field E is choosen and the para~ meters b and TO are measured. Although specimens of diffe~ rent chemical and physical nature are investigated the dipole moment per tmit area \.1 0 is almost the same for all specimens \.I lies in the ranae (1.4 - 2.0) x 10-4 CGSEItem Investigation of Photoconductivity in Cadmium Sulfide(Addis Ababa University, 1984-06) Asfaw, LetemeskelIn this thesis the photoconductivity of polycrystalline cadmium sulfide was investigated theoretically and experimentally. The theory shows that both a change in carrier conent~ ration and mobility can contribute to the variation in conduc~" tivity under illumination depending on the doping level, trap concentration and light intensity. Thin-film polycrystalline layers of CdS were prepared by the chemical bath deposition technique. Doping with lithium was possible. X-ray investigation of the layers indicated that the layers are made up of very small crystallites. Annealing enhanced recrystallization increasing the crystallite dimension. Besides polycrystalline CdS, monocrystalline and pressed CdS were used for photoconductivity measurements. The annealed layers showed a spectral photoresponse similar to the monocrystalline CdS with an absorption edge at 2.4e'1. In order to measure the lifetime of the charge carriers, the photoconductive decay process was used. The lifetime was found to have a spectral dependenceItem Motion of Plasma Particles Located in an Electromagnetic Filed of Mode TE 111 Perpendicular to a Magnftic filed of special Configuration(Addis Ababa University, 1984-06) Workalemahu, BantikassegnMotion of charqec1 part.icles in magnetic and/or electric fields (from simple to cOInnlex fonfigurations) is discussed in chapter one as a necessary backaround for the understanding of the orbit theory of particles in a special confiqura~· tion presented in the last chapter. Fundamental concepts regarding- confinina and heating of plasma and the energy irlterchange bet\~een waves and plasma particles have been dealt ~lith in chapters blo and three. I>lith the help of circularly polarized fields and a coordinate system that rotates with E, the nature of the averaqeforce and pseudoj1otential, instantantaneous rate of energy gain ane. its dependence on angle X have been inves·tiqated in chapter fourItem Theoretical and Experimental Study of the Photovoltaic Effect In Thin Films(Addis Ababa, 1985-06) Hiwet, Gebre; uAhka, P. Hr (PhD)In the pres ent 8tud~ tho th eory o f ph ot ovo ltaic , n, rgy conv ersi on is pres ented. 8 ~ 8ic f actors affecting oonversion capability of phot ovolt ai c devic es aro di8CU 8 8 ~d . Goner l f ormula of the minority carri er distribution and current density across p-n junctions are r e vis ed and fu rther deu,loped t o arrive ~t the over all c ollection effi ienoy expre ssion which is valid f or any thin f ilm phot ovo ltaic c e lls. POCU8S is put on the main s o lar cell p ~ r a m 6 t e r 8 like conversion e fficienc y and spectral response . To thB end some exper imental works on a sing!, orystal solar cell (FD-K) a r ~ made. EMphasis is put on establishing circuits capable of measuring various Bolar cell parameters r anging f r om Si - eingLe ~YDt a L c~LL o f tow efficiGncy. The resuLts of tho measur ement ar e prasanted in tho fo rm of tabL es and graphs . Conclusions ara also ~a d e on thG results obtained.Item Energy Band Structure of Chromium by the Slater-Koster Interpolation Scheme(Addis Ababa University, 1985-06) Seifu, Dereje; Mikusik, Peter(PhD)The matrix elements of tho Hauiltonian between nine localized 110.VC functions in tiGht-bindinf; fOrlJaliGlil are derived. The syml:letry adapted wave-functions and the secular equations are formed by the t,roup theory method for hign sy~~etry points in the Brillouin Zone. h set of intero.ction integraln is chosen on physical grounds and fitted via tL 0 Slater -Koster interpolation schBlfie to the abinitio bund structure of chromium calculated by the Green's function method. Then the energy band structure of chromiUla is interpolated and extrapolated in the Brillouin Zone. '1'hese rosul ts L1ay be directly used fGr cOInputation of the cOulplex energy band structure at any point of the Brillouin ~ono and density of staten of cllromiul:l,Item Depth Profiles of the Top and Wheel Side of Fe40 Ni40Si4 B16 (Glassy Metal) By X~RAY Photoelectron Spectroscopy(Addis Ababa University, 1985-06) Bililign, Solomon; Mikusik, Peter(PhD)X-ray photoelectn:>n spectroscopy i~l ar1pIi<;Kjtotl:e:st'Jc1.y 'of. " rr.etallic ( ;::':- -( .., '[ - (; ~ ; glass Fe4~Ni40Si4B16 prepared by melt spinnir".g)t1e';:liod;', b'j:jeCt~ 6f the sample ~lere taken els91'lhere by l'SCA 3 HARK nspeptJ;'q[~t;er ,~Il ,~e top 1l{de , and ~iheel side, in its as recieved form, after sputtering for 5, 15 and 30 minutes respectively and when the sample crystallizaCJ by heating to 580"C. Q <> Ulese spectra \ifere recorded for tiro detection angles 15 and 55 from the surface normal. 'l\1e CX)r9 level and valence band spectra are interpreted, and the surface concentration of the top and the \'Ihool sides are calculated after eac:h sample treatment. It is found t.hat the surface is highly contaminated with oxygen' and Car'ron and these contaminants form rather complicated c:hemical CO'lt1pounds ~Iith the matrix elements. Surface conposition after all treatn",nts is discu.."lSed and conclusiOn concerning col1C0ntration c:h(l1)ges are dra~m, ego it has been obsetved that the surface is enric:hed by Boron and Iron after Sputtering. 'Ihe electronic structures of the amorphou.s and mystalline sal1\ples are found to be similarItem Drift of Charged Particles in High Frequency Fields(Addis Ababa, 1985-06) Kelati, Ghebregaziher; Brauer, Andreas (PhD)The non- relativistic equntions of motion fo r a chnrged par t icle , an electron , in a wave of slowly varying amplitude aro examined . The ',/ilv e , whistle r wave , is supposed to be propagating at an arbitr ary but small angle to a uniform background magnetic field , in nn infinite collisionless plasma . Approximate solutions f or t he equations of motion of particles in cyclotron resonance with the shistler wave are evaluated by method of ave r aging . An expr ession for the period of trapped par t icles i n a lIpotential well" and an integral of motion in the space of phase difference are der ived . ,Item Theoritcal and Experimental Study of the Photovolta ic Ef'fect in Thin Films(Addis Ababa University, 1985-06) Hiwot, GebreIn the present study the theory of photovoltaic energy conversion is presented. Basic factors affecting conversion capability of photovoltaic devices are discussed. General formula of the minority carrier distribution and current density across p-n junctions are revised and further develop to arrive at the over all collection efficiency expression w is valid for any thin film photovoltaic cells. Focuss is put the main so lar ce II parame -cers like conversion efficiency an spectral response. To the end some experimental works on a single crystal solar cell (FD-K) are made. Emphasio is put on establishing circuits capable of measuring various solar cel pm'wneters ranging from Si--single crystal cell of lou) effici The results of the measurement are presented in the form Of tables and graphs. Conclusions are also made on the re8ults obtainedItem The Analysis and interpretatlon of the Anomalies Transition impurity diffusion in aluminium(Addis Ababa University, 1985-06) Mammo, YewondwossenAnalysis of the existing interpretations on the anomalous of transition imnurity dlffusion At is made, A synthes.izing simple theoretical model is developed, assuming dislocations decor a tee, by segregation phases, which made it possible to interpret theItem Determination of Size Distribution Function (SDF) by Electpooptical Method(Addis Ababa University, 1985-06) Abay, Teshome; Dr . A. SpartakovWhen particles. Are in polare medi.um the molecules of the liquid'Will ahsorb on the surfaces. of the particles.