Theses and Dissertations

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Open Access
Broadband Solar Irradiance and Photometric Illuminance at the Tropical Station in Ileife Nigeria
(2015-04-30) Okogbue, Emmanuel Chilekwu
The main objectives of this research were to investigate the diurnal variations of the solar radiation fluxes and the associated solar radiation ratios with a view to characterising the sky conditions over Ile-lfe, Nigeria and establishing models for estimating the radiation fluxes at the station. Hourly solar radiation flux densities (global and diffuse) and ambient temperature measured at the rooftop of the Physics Department Building, Obafemi Awolowo University (OAU), Ile-Ife, Nigeria, between 1992 and 2002 and photometric illuminance measured between 1992 and 1996 were utilized for the study. Additional solar radiation data measured during the Nigerian Micrometeorological Experiments (NIMEX-1, 2 and 3) at OAU during the months of February and March of 2004, 2005 and 2006 were also utilized. The solar radiation ratios (the clearness index, the cloudiness index, and the luminous efficacy) computed from the measured solar fluxes and relevant astronomical relationships were investigated for diurnal and seasonal variations. These ratios (which are sky conditions indicators) were also used to characterize the local sky conditions over Ile-lfe and to develop statistical models for estimating the solar irradiance (global and diffuse) and photometric illuminance at the station. Very strong diurnal variations in the solar input and solar radiation ratios were observed resulting from the influence of the intervening atmosphere such that on particular days in August and December 1993 only about 45% and 530/0 respectively, of the total solar radiation arriving at the edge of the atmosphere at local noon actually got to the surface. The local sky conditions at the station were almost devoid of clear skies (clear skies occurred for only about 3.5% of the time). Overcast skies were also very scarce (overcast skies occurred for only about 4.8% of the time). The sky conditions were rather predominantly cloudy (cloudy skies occurred for above 72% of the time) all the year round. Daylight availability at Ile-Ife in terms of luminous efficacy was as low as 35 lm/W and as high as 115 lm/W and varied seasonally. The probability of having daylight at Ile-Ife with luminous efficacies more than 100 Im/W was about 24%.of the time on hourly and 33% of the time on daily bases. Empirical models for estimating diffuse solar radiation and photometric illuminance from the more readily measured global solar radiation were established for Ile-Ife. Models for estimating global solar radiation from the more readily measured ambient temperature were also established for the station. Inter comparison of the models using mean bias error (MBE), root mean square error (RMSE) and t-statistic showed that for any of the models, estimated values were not significantly different from their measured counterparts. The t-values ranged between t = 0.22, P > 0.05 and t = 0.88, P > 0.05. The models therefore predicted the measured values accurately. It was concluded that the local sky conditions over Ile-Ife were predominantly cloudy all the year round and almost devoid of clear skies and overcast skies and that the models predicted the measured values accurately.
Open Access
Development of a Meteorological Database Algorithm for Radio Channel Evaluation
(2015-04-02) Ajileye, Oluwaseun Olasunmbo
This study developed an instrumentally and computationally efficient linkage between a meteorological database' and the performance of a radio communication channel by determining the effect of meteorological conditions on the range of frequencies suitable for radio waves under varying meteorological conditions. It also developed an algorithm for evaluating radio channels from meteorological data with a view to predicting the emerging radio communication characteristics. Radio meteorological data, including net radiation, were extracted from the meteorological database of an experiment conducted at the campus dam site of the Obafemi Awolowo University, Ile-Ife, by the micrometeorology group of the Physics Department in October/November, 1998. The values of motivation of net radiation were estimated and used in calculating the equivalent earth radius factor (K) using the market paradigm. The hourly minimum, maximum, median and average values of K were subsequently evaluated. The results showed that the variation of the equivalent earth radius factor (K) with time had a direct application in describing the propagation properties of radio waves in terms of "diffraction", "reflection", "refraction", "extinction", "attenuation': and "ducting" modes. The median values of K evaluated were applicable in the description of climate types and weather conditions. The hourly-average values of K were found suitable in describing and predicting the real-time channel evaluation of the range of frequencies suitable for radio wave propagation. The statistical distributions of the values of K were found to be a random function of time. The study concluded that the meteorological database algorithm (MEDAL) developed was suitable for carrying out the real time channel evaluation of radio communication frequencies and in the estimation of the equivalent earth radius factor (K).
Open Access
Work-Hardening and Recovery Studies of Pure Aluminium.
(Obafemi Awolowo University, 1985) Ojediran, Surajudeen Oluwafemi; Ajaja., O.
The effects of work-hardening and recovery on the strength of pure aluminium have been investigated. The modes of interaction of these two processes during creep deformation were closely examined. The Bailey-Orowan equation was derived without recourse to a mechanical equation of state. This new method of derivation clearly showed that the Bailey-Orowan equation is applicable only to steady-state but not to transient creep deformation. The results of recovery tests performed on prestrained samples showed that the flow stress decreased with recovery time, eventually approaching an asymptotic value which was appreciably higher than the flow stress of the annealed sample. It was demonstrated that the recovery rate was not a unique function of the instantaneous dislocation density. Stress increment and stress removal (state recovery) tests performed on the creeping samples showed the generation of appreciable instantaneous plastic strains during the stress hike, and high strain rates following recovery. Both of these observations are consistent with the promise that creep is recovery-controlled in this material.
Open Access
Re-association Kinetics of the DNA of the Reptile, Agama Agama Agama (L).
(Obafemi Awolowo University, 1987) Ighavini, Bulex Oroghekowho; Adegoke, J.A.
The re-association kinetics of the Agama agama agama DNA and some of the characteristics of the highly repetitive DNA sequence were investigated on hydroxyapatite column with the specific objectives of determining the re-association profile at 60°C for this organism and also determining the amount and nature of the highly repetitive DNA sequences. The re-association curve showed that the genome consists of the three components characteristic of eukaryotic genomes. These components are highly repetitive, intermediate repetitive and single or unique copy sequences which form 18%, 8% and 74% of the total genome respectively. A Cot 1/2 of 370 was obtained for the genome, and this is a reflection of a high proportion of unique sequences in this animal and also indicates a fairly complex genome. Thermal elution studies on the total DNA, highly repetitive DNA and on mouse DNA (for comparison) were carried out on HA, and melting profiles deduced from the results. Two peaks (a minor and a major) were obtained for both the native DNA and highly repetitive. The minor peak formed about 3.6% of the native genome and about 9.6% of the highly repetitive DNA sequences. It elutes at 65°C to 75°C in both cases, and this indicates that it is AT-rich. The major peak of the highly repetitive DNA has a melting temperature of 89. 5°C, giving a base composition of 49. 5% G + C. The results suggest that repetitive sequence is localised on the chromosomes, while the bulk may be dispersed throughout the genome. The native DNA shows a Tm of 85.60C which gives a base composition of 40. 2% G + C. This value does not vary from a general recently evolved eukayotic pattern, and the totality of the results obtained for the DNA of Agama shows that the animal is evolutionarily advanced.
Open Access
Generation of the Basis States for the Calculation of the Effects of Core Excitations on the Low-lying Negative Parity States of 90 Zr.
(Obafemi Awolowo University, 1985) Jegede, Oluwagbemiga Olawale; Amusa, A.
From the various theoretical studies reported on the low-lying levels in 90 Zr, it has been established that the spectrum is rather anomalous in that it has attributes of a simple two-proton coupling and some collectivity, notably with the 21+, 22+ and 31- low-lying states. The basis states necessary for the inclusion of core excitations in the low-lying negative parity states (J<7-) in 90 Zr are generated in this work. It is hoped that the eventual inclusion of core excited states in manner specified by Lawson in the study of the low-lying positive parity states for 18 O would lead to reproducing the experimental energy levels for these low-lying states better than was obtained with the previous models.

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