Physics

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Evaluation of Reaction Cross-Section for Deuteron Induced Radioisotope [125I,62ZN,15o and 103PD] at Different Energy Ranges Using the PACE 4 CODE
(Addis Ababa University, 2024-06) Anteneh Getachew; Tilahun Tesfaye
This thesis work emphasize on theoretical evaluating reaction cross sections of deuteron induced nuclear reactions for the production of therapeutic radionuclide using PACE4 statistical model code , which is a code based on the statistical model of nuclear reactions. PACE4 statistical model code is used to calculate the theoretical nuclear cross section in the production processes of 125I, 62Zn, 15O and 103Pd, while experimentally decoded nuclear cross sections data of these radionuclide were taken from ENDF(Evaluated nuclear data file) IAEA database, to compute a reliable result, PACE4 statistical model code performed at level density parameter(K=8, K=10 and K=12 ) and the number of cascades(events in monte carlo calculation) is set at 100,000. The target radioisotopes are 124T, 63Cu, 14N and 103Rh are taken for the production of medical useful radioisotope 125I, 62Zn, 15O and 103Pd respectively. Deuteron energies ranging from 4.5MeV to 20MeV were considered for the production of 125I, 17MeV to 35MeV for the production of 62Zn, 1MeV to 20MeV for the production of 15O and energy range from 6.5MeV to 23.5MeV were considered for the production of 103Pd, and then experimental and theoretical outputs of nuclear cross sections of these radionuclide production were analyzed and compared. The maximum experimental and theoretical nuclear cross section computed at different energy range is stated below respectively: for 124T (d,n)125I reaction the maximum cross section at deuteron incident energy of 9.0MeV was 232 mb and 555 mb at 9.5MeV ( at K=12), for 63Cu(d,3n)62Zn reaction 50.5 mb at 33MeV and 63.9 mb at 31.5MeV ( at K=8), for the reaction 14N(d,n)15O the maximum cross section was 213 mb at 3.5MeV and 214 mb at 12.5MeV ( at K=12) and for the reaction 103Rh(d,2n)103Pd the maximum cross section was 1056 mb at 13.5MeV and 1390 mb at 18.5MeV ( at K=12). The PACE4 code slightly gives good agreement with ENDF determined excitation function at some computed radionuclide production considered under this study,while the rest results are unfitted with the ENDF data. It has been observed that complete fusion, incomplete fusion and pre-equilibrium emission processes play important roles in heavy ion reactions at these energies. The observed disagreement may be credited to the contribution from the incomplete fusion reaction, pre-equilibrium emission processes and light particle reaction is not well taken into account by PACE4 statistical model code.
The Effect of Anisotropy Field on the Dispersion Relation and Thermodynamic Properties of Antiferromagnetic Materials : Employing the Quantum Field theory
(Addis Ababa University, 2024-08) Desalegne Tefera; Chernet Amente
In this thesis, we look at the complex dynamics of spin waves in a two-sublattice antiferromagnetic (AFM) system, with an emphasis on spin interactions and the magnon dispersion relation. The main purpose of this study was to examine spin wave interaction and how anisotropy field influence on dispersion relation and characteristics of (AMF) systems. The theoretical framework is based on the Heisenberg Hamiltonian model, which was specifically built to manage a uniaxial anisotropy field within an antiferromagnetic system. To overcome the problem, we employ quantum field theory, namely the double-time temperature-dependent Green function technique to achieve magnon dispersion. A random phase approximation is used to decouple and diagonalize higher order components. The discovery of a relationship between the anisotropy field and the dispersion relation for the wave vector k at low temperatures is particularly interesting. The findings indicate that as the anisotropic field becomes stronger, the magnon dispersion progressively shifts from a curved trajectory to linearity, finally adopting a sinusoidal form with further expansion into the first Brillouin zone. Furthermore, we investigate the thermodynamic parameters of magnetization and heat capacity within the uniaxial symmetric AFM crystal lattice, concentrating on excitation temperature at low temperatures and utilizing the long-wavelength approximation. The results show that AFM magnetization and heat capacities are sensitive to anisotropic fields, with magnetization trending upward and the greatest peak of heat capacity dropping as anisotropy increased. The findings provide understanding of the complicated relationship between anisotropy and exchange fields in antiferromagnetic systems, indicating their significant impact on magnetization, heat capacity, and other thermodynamic parameters. Furthermore, this model gives information on the variations in susceptibility and heat capacity between transition metal antiferromagnetic fluorides. Further investigation may be necessary in this situation.
Measurement of Radioactivity Concentrations and Analysis of Radiation Hazards for Environmental and Industrial Samples Collected from Different Parts of Ethiopia
(Addis Ababa University, 2025-01) Yared Birhane; Tilahun Tesfaye
In this study, the activity concentrations of 238U, 226Ra, 232Th, and 40K in various environmental and industrial product samples were determined using a gamma detection system. The industrial samples analyzed included cement raw materials and finished products, while the environmental samples comprised soil samples and medicinal plants. The measured mean activity concentrations of 226Ra, 232Th, and 40K in the cement raw materials and products were found to be 21.1 ± 0.995, 53.2±2.9, and 304±13.8Bqkg−1, respectively. For soil samples from Mekelle City, the corresponding mean activity concentrations were 25.035±1.788, 53.091±4.22, and 371.34±14.26Bqkg−1, respectively. The mean specific activity concentrations of 238U, 232Th, and 40K in soil samples from the districts ofMenge, Sherkole, Assosa, and Bambasiwere determined as follows: for Menge, 24±1.2, 36.15±2, and 275.5±13.3Bqkg−1; for Sherkole, 35.14±1.77, 47.3±2.7, and 146±7.2Bqkg−1; for Assosa, 45.2±2.3, 70±3.8, and 238.8±11.6Bqkg−1; and for Bambasi, 61±3.2, 89.2±5.3, and 237.7±12.7Bqkg−1. Regarding the medicinal plants, the mean activity concentrations of 238U, 232Th, and 40K were found to be 7.82±0.04, 28.67±2.66, and 579.4±1.37Bqkg−1, respectively. The study also estimated the absorbed dose rate (D(nGyh−1)), the annual effective dose rate (E (mSvy−1)), the gamma index (Iγ), the hazard indices (Hex and Hin), and the excessive lifetime cancer risk (ELCR). Notably, the specific activity concentration of 40K in Moringa oleifera exceeded the recommended safe limit. Meanwhile, the measured mean radioactivity concentrations in the Mekelle soil, Messebo cement raw materials, and cement products were below the safe values of 35, 30, and 400 Bqkg−1 for 226Ra/238U, 232Th, and 40K, respectively. However, the mean concentrations in soil samples from the Assosa, Bambasi, Menge, and Sherkole districts exceeded these safe values. Consequently, such elevated concentrations pose potential health risks, and continuous monitoring is recommended.
Investigating the Doping Effects of Pb Concentration on the Optical & Electrical Properties of CdS Colloidal Quantum Dots
(Addis Ababa University, 2024-08) Henock Tadele; Fekadu Gashaw
In the present study, the doping effect of lead (Pb) atoms on the optoelectronic properties of cadmiumsulfide (CdS) colloidal quantumdots is investigated. The concept of quantum confinement has been explored, emphasizing the role of QuantumMechanics and the effective mass approximation in understanding confinement energy. Experimental synthesis of CdS colloidal quantumdots was performed using a modified method of chemical bath deposition technique. The resulting quantum dots exhibited a bright yellow vibrant color. UV-Vis and PL studies revealed a redshift followed by a blueshift at increased Pb concentrations. Tauc plot analysis determined the bandgap values to be 2.70eV, 2.67eV, 2.72eV, 2.74eV and 2.77eV for pure, 0.10%, 0.15%, 0.20% and 0.25% doped samples respectively. This increase in bandgap was attributed to the Burstein-Moss effect. FTIR characterization showed shifts and intensity changes in peaks of the fingerprint region, indicating variations in molecular vibrations and stretching due to Pb doping. Optical analysis provided insights into the refractive index, dielectric constant, and linear optical susceptibility, which decreased with increasing bandgap. The electrical characterization showed decrease in resistivity and augmented conductivity by upto 7 times from the undoped sample with higher Pb concentrations. Moreover, the IV curve exhibited an ohmic nature, suggesting the samples resemble metallic conductor properties.
Impact of Ocean-Atmosphere Interaction on Weather and Climate
(Addis Ababa University, 2025-02) Seyied Muhe; Yitagesu Elfagd
In this project we have reviewed the impact of ocean-atmosphere interaction on weather and climate. We considered ocean-atmosphere interaction and exchange of energy by sensible heat, latent heat, wind stress, precipitation heat ux, and surface energy budget of the surface ocean mixed layer. In our work the mass exchanges between ocean-atmosphere boundary layers by the methods fresh water, precipita- tion, runo_, melting of sea ice, evaporation, inert and sparingly soluble gases in sea water. The radiation transfer at ocean and atmosphere boundary layer interrelations of micro wave and infrared radiation uxes. The solar radiation by net shortwave ir- radiance, reection at the sea surface, and absorption of solar radiation in the ocean. Terrestrial radiation occurs in two ways longwave emission from the sea surface and radiative transfer in the lower atmosphere. To analyzed and identi_ed the impact of ocean-atmosphere interaction on weather and climate, those e_ects described by the following methods, air-sea feedback, their global distribution, the common practices to diagnose, ocean surface salinity budget, the planetary boundary layer, and the dynamical implications of air-sea interactions.
Tailoring Aggregation of Thiophene-Based Polymers Using Solvent and Solvent Additives
(Addis Ababa University, 2024-11-15) Werkitu Geremew; Newayemedhin Aberra
With an emphasis on P3HT and P1TI, this thesis examines how H and J aggregation affects the photophysical characteristics and charge production mechanisms in donor-acceptor (D-A) copolymers. Because of their promising charge transport and exciton mobility properties, these polymers are especially interesting for organic optoelectronic devices, such as organic photovoltaics (OPVs) and organic lightemitting diodes (OLEDs). But there is still a lack of thorough knowledge on how aggregation behavior affects their optical and electrical characteristics, especially when it comes to the effects of solvent conditions and high boiling point additives on the aggregation mechanisms of H and J. The copolymers were produced and deposited as thin films on cleaned glass substrates using thiophene-based derivatives as donor components and isoindigo as acceptor. Several solvents, including 1,2-dichlorobenzene (o-DCB), were used to create the films. chloroform (CF), selected according to their polarity and refractive indices.Higher A00/A01 and I00/I01 ratios in both P3HT and P1TI demonstrated that o-DCB promoted J-aggregation, according to experimental results. This led to better chain ordering and exciton delocalization, both of which are advantageous for charge transfer in OPVs. On the other hand, CF encouraged H-aggregation, which resulted in less exciton mobility and more localized exciton states. It was discovered that adding the high boiling point additive DIO improved charge separation, decreased H-aggregation, and increased J-aggregation—all of which are essential for increasing device efficiency. Additionally, the study discovered that P1TI displayed greater crystallinity whereas P3HT displayed a larger Stokes shift, suggesting increased disorder in the excited states of P3HT. This implies that P1TI might work better in applications that benefit from lower reorganization energy. These findings provide important information about how to modify solvent conditions and additives to regulate aggregation behavior, which optimizes material characteristics for organic electron.
Exploring Non-Equilibrium Thermodynamics and Quantum Fluctuations: Perspectives from Spin-1 Systems in Nmr
(Addis Ababa University, 2024-12-20) Mohammed Mahmud; Mulugeta Bekela
This dissertation explores the non-equilibrium thermodynamics of quantum systems, specifically focusing on spin-1 nuclei and the dual influences of external perturbations and quadrupolar interactions. We first analyze the dynamic responses of these nuclei to external perturbations, utilizing principles from quantum and statistical mechanics. By manipulating a work parameter and treating work as a random variable, we collect data from finite-duration cyclic processes to compute the generated work distribution. We then extend our investigation to the contributions of quadrupolar interactions, comparing their effects with those of external perturbations. Through this comprehensive analysis, we derive key equilibrium quantities, such as the free energy difference between initial and final states, while deepening our understanding of work distribution properties. Overall, this research enhances our insights into the complex dynamics of non-equilibrium quantum thermodynamics and sets the stage for future explorations of quantum systems under varying conditions.
Aggregation-Dictated Photophysics of Conjugated Polymers
(Addis Ababa University, 2025-01-30) Eninges Asmare; Newayemedhin Aberra
Improving the PCE in OPVs is among the pioneering researches to satisfy the world energy demand. Recently PCEs of above 19% are recorded by improving morphology of the active layer in OSCs. Molecular aggregation, which was _rst developed by Kasha, and Jelly and Schiebe, plays a role on the morphology of conjugated polymers. In this work, we study the aggregation photophysics of three copolymers dividing into two objectives. We used three methods - Franck- Condon (FC) analysis, HR factor evolution with temperature, and relative QY calculation - to determine the aggregates types in a benzodithiophene-isoindigo-based (PBDTI-DT) copolymer which show that both H- and J-aggregation types present, and the QY calculation clearly indicates dominance of H-aggregates. As a second work the e_ect of backbone conformation on the aggregation photophysics of isoindigo-based copolymers, namely, P2TI and P2TITT is studied. P2TI was systematically tuned by inserting TT into the former resulting in modi_cation of the backbone and was found to a_ect the planarity due to reduced steric hindrance between the donor and the acceptor units, which was evidenced from the di_erence in oscillator strength of the _rst excited state transition. Temperature-dependent PL of the two polymers was well reproduced using two FC progressions, indicating the formation of both H- and J-type aggregates. This was supported by the presence of two emission lifetimes obtained from time-resolved uorescence measurements. The evolution of the _rst two vibronic peaks with temperature clearly showed stronger interchain interaction in P2TITT.
Computational Study of the Electronic Structure of Nitrogen Doped H-Borophene
(Addis Ababa University, 2024-08) Gezahegn Gizachew; Chernet Amente
In this study,we explore the effects of nitrogen doping on hexagonal borophene, a two-dimensional material composed of boron atoms arranged in a hexagonal structure, known for its unique electronic properties. Using density functional theory (DFT), we examine how varying nitrogen concentrations alter and enhance the material’s structural and electronic characteristics. Our findings reveal that nitrogen doping induces significant changes, particularly at a concentration of x=0.38, where the band gap begins to open, transforming h-borophene from a metallic to a semiconducting state. As the concentration increases to x=0.44, the band gap widens, resulting in a direct band gap at the Γ−Λ symmetry point. These insights suggest that nitrogen- doped h-borophene holds great potential for applications in transistors, photodetectors, and other electronic devices.
The Effect of Surface Plasmonic Resonances and Enhancement of the Optical Response on Magneto-Plasmonic Fe3O4@Ag Spherical Core-Shell Nanoparticles
(Addis Ababa University, 2024-06) Kinde Yeneayehu; Teshome Senbeta; Belayneh Mesfin
In this work, the optical properties of Fe3O4@Ag core/shell spherical nanostructures embedded in a dielectric host matrix are investigated theoretically. The theoretical analysis is carried out based on the electrostatic approximation and Maxwell-Garnet effective medium theory to obtain the effective electric permittivity and magnetic permeability, electric polarizability, refractive index, absorbance, as well as the corresponding scattering and absorption cross-sections. Moreover, for a fixed size of NPs (of radius r2 = 30 nm) numerical analysis is carried out to see the effect of varying the metal fraction (_), the filling fraction (f), and the permittivity ("h) of the host matrix on the optical properties of the nanostructures. The results show that graphs of real and imaginary parts of polarizability, refractive index, absorbance, extinction cross-sections as a function of wavelength possess two sets of resonance peaks in the UV and visible regions. These sets of peaks arise due to the strong couplings of the surface plasmon oscillations of silver with the semiconductor/dielectric at the inner (Fe3O4/Ag) and outer (Ag/host) interfaces. Moreover, the two set of resonance peaks are found to be enhanced with an increase of _, f, or "h; keeping two of these parameters constant at a time. On the other hand for the case of absorption and extinction cross-sections, as _ increases, the absorption and scattering cross-sections are blueshifted in the first peak and red shifted in the second set of peaks. Similarly, as "h increases or as _ decreases, the sets of resonance peaks for extinction cross-section get enhanced. The results obtained might be utilized in a variety of applications that are designed to integrate plasmonic effects of noble metals with magnetic semiconductors in a core/shell nanostructure ranging from UV to Visible spectral regions.
Unravelling Heating and Light Induced Degradation Mechanisms in Fullerene and Nonfullerene Acceptor Based Organic Solar Cells
(Addis Ababa University, 2025-06-12) Yissa Abdie; Newayemedhin Aberra; Genene Tessema
Organic solar cells (OSCs) have emerged as a promising alternative to expensive silicon-based solar cells. Over the past few years, these devices have achieved remarkable advancements, with power conversion efficiencies (PCE) surpassing 20 %, comparable to commercially available thin-film solar cells. However, under continuous illumination, OSCs are susceptible to thermal and photo-induced degradation. Addressing the challenges of thermal and photostability is essential for their industrial application. To enable widespread commercialization, a comprehensive understanding of the degradation mechanisms caused by exposure to light, heat, or humidity is crucial. This thesis examines how different acceptors influence the thermal degradation of thin-film OSCs under a controlled environmental condition. Poly(3-hexylthiophene) (P3HT), a commonly utilized donor polymer, was used to fabricate the bulkheterojunction (BHJ) organic solar absorber. Changes in the optical and structural characteristics of the polymer film provided clear signs of degradation. Additionally, data collected from various characterization techniques demonstrated that the extent of degradation is heavily influenced by the type of acceptor molecules present in the polymer matrix. Notably, solar absorber films blended with PC60BM acceptors exhibited greater stability compared to those based on 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene (ITIC). This difference was reflected in the measured device parameters, such as short-circuit current density (Jsc) and open circut voltage (VOC ), which showed poorer performance in P3HT:ITICbased devices. Furthermore, a 50% drop in open-circuit voltage was observed in ITIC-based solar cells within one hour of thermal degradation. Additionally, impact of non-electron-withdrawing unit copolymerization on the photostability of fullerene-based OSCs was examined using two donor polymers: benzodithiophene-4,8-dione (BDD) copolymerized with α-quaterthiophene-thiophene (4T) (PBDD4T) and P3HT. Optical and electrochemical characterizations revealed that PBDD4T had a deeper highest occupied molecular orbital (HOMO) and broader absorption compared to P3HT, attributed to BDD copolymerization. This enhanced its power conversion efficiency (PCE), as evidenced by higher VOC and JSC values. The photostability study showed that PBDD4T-based devices retained 86% of their initial PCE after seven hours of irradiation, whereas P3HT-based devices experienced a 48% reduction. Further analysis of the differences in photostability suggested that BDD copolymerization suppressed photo-oxidation and recombination induced by irradiation in PBDD4T-based devices, leading to improved stability. Conversely, P3HT:PC71BM-based solar absorbers exhibited bimolecular recombination due to photo-aging, which adversely affected their stability. This reduction in device stability was evixvident in the diminished photogenerated current, attributed to decreased charge mobility and increased surface roughness.
Study of Novel Properties of Graphene-Zno Hetrojunction Interface Using Density Functional theory
(Addis Ababa University, 2023-03) Hailu Diro; Kenate Nemera (PhD)
Studies of the structural, electronic, and optical characteristics of the interfaces between graphene and ZnO polar surfaces is carried out using first-principles simulations. At the interface, a strong van der Waals force is present, and because of the different work functions of graphene and ZnO, charge transfer takes place. Graphene’s superior conductivity is not impacted by its interaction with ZnO, since its Dirac point is unaffected despite its adsorption on ZnO. In hybrid systems, excited electrons with energies between 0 and 3 eV (above Fermi energy) are primarily accumulated on graphene. The calculations offer a theoretical justification for the successful operation of graphene/ZnO hybrid materials as photocatalysts and solar cells. ZnO semiconductor is found to be a suitable material with modest band gap, (_ 3 eV), having high transparency in visible region and a high optical conductivity.
Measuring the Electrical Property and Infrared Light Sensitivity of Pre Ionized 24 Hour Treated Breast Cancer Cells Using Laser Trapping Techniques
(Addis Ababa University, 2023-09) Yetwale Alemu; Endries Muhammed (PhD)
A study was conducted to introduce a novel method utilizing laser trapping techniques for measuring the electric charge and coefficient of the laser trap for breast cancer cells treated continuously for 24 hours. The 4T1 breast cancer cells used in this study were treated with a compound called 2-Dodecyl-6-methaxycyclohexa-2, 5-diene-1, 4-dione (DMDD). A high-power infrared laser operating at 1064nm was utilized to trap individual 4T1 cells from the group treated continuously for 24 hours. The measured values for the spring constant (k) ranged from 0.05 μN/m to 1.11 μN/m, with an average value of 0.38 μN/m. The data showed a high correlation, as indicated by an R-square value of 0.98. The charge developed on each of the 24-hourly treated breast cancer cells was quantified relative to the charge of an electron. On average, the cells exhibited a charge of -2249.55 ± 1983.89 units. It was observed that the charge developed on the cell surface was influenced by the size of the cells. As the cells moved closer to the laser trap, their charge increased, while their velocity, acceleration, and momentum decreased. After determining the electrostatic force and trapping force, a homogeneous second-order differential equation was solved to further analyze the system. This study provides valuable insights into the relationship between charge development, spring constant, and cell size in continuously treated breast cancer cells using laser trapping techniques. Velocity and acceleration decreases as the cells approaches to the trap and spring constant and mass have positive correlation to the charge developed on the cells
Verification of Einstein General theory of Relativity with Gravitational Waves
(Addis Ababa University, 2021-07-11) Habtie, Abel; Reshid, Remudin (PhD)
Gravitational wave science is one of direct observation of the waves predicted by Einstein’s general theory of relativity and opening the exciting new field of gravitational wave astronomy. In this thesis work we study gravitational waves and we also present some of the general relativity test of gravitational wave such as linear approximation of Einstein field equation which is Einstein equation for a weak gravitational field simply _h__ = 0, thus, the metric perturbations satisfy the flat space wave equation and the solutions can therefore be interpreted as gravitational waves polarization(plus and cross polarization). In this thesisWe also found that gravitational wave emites when BBHs are spiraling with each other. We suggested that high amplitude of gravitational waves are formed around merger of BBHs, the amplitude of GWs large for high masses and also the amplitude fails when the waves moves away from the source like standard siren’s of h / 1 r . We also checked that SEOBNR and IMRPhenom models are matched with pridiction of GR simulated by NR and the waveform observed from LIGO. These waveform comparison tells us Einstein general theory of relativity passes the test of GW.
Size Dependent Optical Properties of Spherical ZnO@Cu and ZnO@Au Core/Shell Nanostructures
(Addis Ababa University, 2022-02-19) Gizat, Tesfahun; Mesfin, Belayneh (PhD)
In this work, we studies the effect of size and thickness variation on the optical properties of a system that consists of spherical ZnO@Cu and ZnO@Au core-shell composite nanostructures embedded in a dielectric host matrix. The effective dielectric function, refractive index, and absorbance of the composite nanostructures are determined using the Maxwell-Garnett effective medium theory within the framework of the electrostatic approximation. The numerical simulation using nanoinclusions of radii 30 nm shows interesting behavior in the optical responses of the ensemble. In particular, it is shown that for different values of volume fraction and filling factor the refractive index and optical absorbance of the ensemble exhibited two sets of resonance peaks; the first set located around 515 nm and 490 nm and the second set found above 635 nm and 605 nm spectral regions for a system of ZnO@Cu and ZnO@Au nanoparticles, respectively. These peaks are attributed to the surface plasmon resonance of copper and gold at the core@metal and metal@host-matrix interface. Moreover, when the Cu and Au shell thickness is increased, the observed resonance peaks are enhanced; accompanied with slight red shifts for the first set of peaks and a blue shifts for the second set of peaks. In brief, it is seen that the optical properties of spherical ZnO@Cu and ZnO@Au core-shell nanoinclusions embedded in vacuum can be tuned by varying the shell thickness, filling factor, and/or volume fraction of the nanocomposites. The results obtained may be used in various applications such as sensors and nano-optoelectronics devices in optimizing material parameters to the desired values.
The Quantum Analysis of the Light Produced by Coherently Driven Degenerate Three-Level Atom in a Cavity Containing Parametric Amplifier and Coupled to a Vacuum Reservoir
(Addis Ababa University, 2022-04-18) Mekete, Antigegn; Hirpo, Deribe (PhD)
In this thesis, we analyze the statistical and squeezing properties of the light produced by a degenerate three-level atom, whose top and bottom levels are coupled by coherent light, and available in a cavity containing degenerate parametric amplifier and coupled to a vacuum reservoir via a port-mirror. Employing the master equation for the system under consideration, we obtain the equations of evolution for the expectation value of atomic operators and the quantum Langevin equation for the cavity mode operator. Using the steady-state solutions of these equations and the large time approximation, we have determined the mean and variance of photon number, the power spectrum of cavity mode, quadrature variance and quadrature squeezing. We observe that the increase of the amplitude of the driving coherent light and the presence of the parametric amplifier enhance the mean and variance of the photon number. We have also established that the maximum quadrature squeezing is 61% for _ = 0.03 and 70% for _ = 0.06 below the vacuum-state level. Thus, we note that the presence of parametric amplifier has positive impact on the quadrature squeezing.
Physics of Cloud and Precipitation
(Addis Ababa University, 2022-04-11) Kuchi, Nigatu; Elfagd, Yitagesu (PhD)
In this project we present a review of the physics of clouds and precipitation in the atmosphere. Thunderstorms are a global phenomenon in the mid-latitudes and tropics. They form where and whenever the ingredients for their formation come together: instability, moisture and lift. Especially upon interaction with vertical wind shear, they may develop in to wellorganized systems that produce hazards such as large hail, severe winds, heavy precipitation, and tornadoes. We must look in to the processes by which the clouds are formed and precipitation is produced in order to the meaning of clouds they related to weather. We will see how clouds are classified and, named and what kinds of precipitation certain types of clouds produce. And also in this project we study how to clouds form and precipitation develop in the atmosphere must be saturated with moisture. As a cold air passes over warm water, rapid evaporation takes places and the saturation is quickly reached. Lifting of air, and the resulting adiabatic expansion, is the most important cooling method. The lifting may be accomplished by thermal orographic or frontal action. It produces most of the clouds and precipitation.
Degenerate Three-Level Atom Driven by Coherent Light and in a Cavity Coupled to Squeezed Vacuum Reservoir
(Addis Ababa University, 2022-04-18) Gizachew, Abebaw; Hirpo, Deribe (PhD)
In this thesis, we analyze the squeezing and statical properties of light produced by degenerate three-level atom in a cavity coupled to squeezed vacuum reservoir via a port-mirror. The three-level atom available in the cavity is driven by coherent light from the bottom to the top level. Employing the master equation we obtain the differential equation of the atomic and cavity mode operators. Applying the large time approximation to the time evolution of cavity mode operator and using steady-state solutions of the expectation values of cavity mode and atomic operators, we obtain the mean of the cavity photon number, power spectrum, quadrature variance and quadrature squeezing of the cavity light.We have seen that the amplitude of the coupling coherent light, the squeezing parameter, and the stimulated emission decay constant have the effect of increasing both the global and local mean photon number. Moreover, we find that the quadrature squeezing of the cavity light increases with the increase of the amplitude of the driving coherent light, the rate of the stimulation decay constant, and squeeze parameter. The squeeze parameter and the amplitude of the driving coherent light have the effect of enhancing the quadrature squeezing, with maximum squeezing of 58% for r = 0.5 and 32% for r=0.
Generation of Squeezed Light by Optically Pumped Two-Level Atom in a Cavity Containing Parametric Amplifier and Coupled to Squeezed Vacuum Reservoir
(Addis Ababa University, 2022-04-18) Desta, Mulu; Hirpo, Deribe (PhD)
In this thesis, we have analyzed the quantum properties of light generated by coherently driven two level atom in a cavity containing a parametric amplifier and coupled to a squeezed vacuum reservoir. The equations of evolution for the expectation values of cavity mode and atomic operators are determined with the aid of the system’s master equation. Applying the large time approximation to the cavity mode quantum Langiven equation, we obtain the steady-state solutions for the expectation values of cavity mode and atomic operators. Utilizing these solutions, we calculate the mean photon number, the power spectrum, second-order correlation function, quadrature variance and squeezing of the cavity mode. Our results indicate that the two-level atom has larger probability of being found in the lower level than being found in the upper level and the photons of the fluorescent light produced by the two-level atom are found to be anti-bunched. Moreover, the cavity mode is observed to be squeezed, with squeezing being occurring in the plus quadrature. In addition, the squeezing increases as the amplitude of driving coherent light increases; with a maximum squeezing of 60% for (_ = 0.1) and 50% in the absence of parametric amplifier. And the degree of squeezing enhances with the increase of stimulated emission decay constant and reaches a maximum value of 70% below the vacuum state level.
The Study of the Electronic Thermal Conductivity of Superconducting Magnesium Dlboride (MgB2)
(Addis Ababa University, 2005-06) Beyoro, Zeleke; Singh, P.(Prof.)
For magnes ium diboride (MgB2)' some of th e superconducting pmperlies that have been studied are summari zed. The energy di spersion relation is determined and it is used to determ ine the electmnic thermal conductivity of MgB2. From that energy functi on. the , , expression for the elec tronic heat capac ity of magnesium diboride in normal state has be~n determ·ined. ·Tile general ex pression of the electmnic thermal conducti vity for MgB ~ in normal state i ~ fo und. Then, by taking th e energy gap parameter in to account the electmnic then;lal conductivity has been computed for the superconducting state of our material ; that is belO\'-\ tbe transition temperatu re. Then, th e electroni c thermal conductivit) of magnesium diboride has been plotted as a function of tempe ratu re with in the superconducting state. Moreover, the electrical conducti vity of MgB2 is calcu lated and the Wiedemann-F ranz law is checked fo r normal sta te of a material. Finally. the general expression for electronic thermal conducti vity of MgB2 is determined in K - Space Key Words: Magnesium chloride. thermal conductivity. superconducting state

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