UISpace
Welcome to UISpace, The University of Ibadan Institutional Repository. A collection of theses, articles, books, videos, images, lectures, papers, data sets and all types of digital content originating from the University of Ibadan Nigeria. This repository is managed by the Kenneth Dike Library University of Ibadan, Nigeria.
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"Evaluation of soil thermal diffusivity algorithms at two equatorial sites in West Africa"
(2021) Otunla, T.A.; Oladiran, E. O.
This study presents comparisons between six algorithms used in the calculation of apparent thermal diffusivity (Kh ) of the topsoil during measurement campaigns conducted at two equatorial sites. It further investigates the effects of transient and seasonal variations in soil moisture content (i) on the estimation of Kh. The data used comprise soil temperatures (T) measured at depths of 0.05 m and 0.10 m, and i within the period of transition from the dry season to the wet season at Ile Ife (7.55° N, 4.55° E), and for the peak of the wet season at Ibadan (7.44° N, 3.90° E). The thermal diffusivity, Kh, was calculated from six algorithms, of: harmonic, arctangent, logarithmic, amplitude, phase, and conduction-convection. The reliability of these algorithms was tested using their values to model T at a depth of 0.10 m, where direct measurements were available. The algorithms were further evaluated with statistical indices, including the empirical probability distribution function of the differences between the measured and modeled temperatures (DT). The maximum absolute values of DT for the six algorithms investigated were: 0.5°C, 0.5°C, 0.5°C, 1°C, 1°C and 1°C, respectively. Kh showed an increasing trend as i increased from the dry season to the peak of the wet season, with R2 = 0.70 for the harmonic algorithm. The accuracy of all of the algorithms in modeling T reduced with transient variations of i. The harmonic, arctangent and logarithmic algorithms were the most appropriate for calculating Kh for the region of study. The empirical relation between i and Kh and the values of Kh obtained in this study can be used to improve the accuracy of meteorological and hydrological models.
Nigerian surgical outcomes – Report of a 7-day prospective cohort study and external validation of the African surgical outcomes study surgical risk calculator
(Elsevier Ltd., 2019) Osinaike, B.; Ayandipo, O.; Onyeka, T.; Alagbe-Briggs, O.; Mohammed, A.; Oyedepo, O.; Nuhu, A.; Asudoh, F.; Akanmu, O.; Nwokorie, C.; Mohammed, A.; Edubiol, M.; Izuoram, K.; Mohammed, R.; Nweze, O.; Efu, M.; Eguma, S.; Jasper, A.; Ewah, R.; Akhideno, I.; Nnaji, C.; Adov, S.; Ogboli-Nwasor, E.; Atiku, M.; Salisu, I.; Adinoyi, Y.|; Aguz, E.; Desalu, I.; Samuel, L.; Olorode, Y.; Fatungase, O.; Akinwonmia, O.; Faponle, F.; Idowu, O.; Isamade, E.; Aliyu, A.; Buba, S.; Hamza, G.; Onajin-Obembe, B.; Amanor-Boadu, S.
Background: Surgical outcomes study for individual nations remains important because of international differences in patterns of surgical disease. We aimed to contribute to data on post-operative complications, critical care admissions and mortality following elective surgery in Nigeria and also validate the African Surgical
Outcomes Study (ASOS) surgical risk calculator in our adult patient cohort.
Materials and methods: We conducted a 7-day, national prospective observational cohort study in consented consecutive patients undergoing elective surgery with a planned overnight hospital stay following elective surgery during a seven-day study period. The outcome measures were in-hospital postoperative complications, critical care admissions and in-hospital mortality censored at 30 days. Also, we identified variables which significantly contributed to higher ASOS surgical risk score. External validation was performed using area under the receiver operating characteristic curve (ROC) for discrimination assessment and Hosmer–Lemeshow test for calibration.
Results: A total of 1,425 patients from 79 hospitals participated in the study. Postoperative complications occurred in 264(18.5%, 95% CI 16.6–20.6), 20(7.6%) of whom were admitted into the ICU and 16(6.0%) did not survive. Total ICU admission was 57 (4%), with mortality rate of 23.5% following planned admission and overall in-hospital death was 22(1.5%, 95% CI 0.9–2.2). All prognostic factors in the ASOS risk calculator were significantly associated with higher ASOS score and the scoring system showed moderate discrimination (0⋅73, 95% CI 0.62–0.83). Hosmer–Lemeshow χ2 test revealed scale was well calibrated in the validation cohort.
Conclusion: NiSOS validates the findings of ASOS and the ability of the ASOS surgical risk calculator to predict risk of developing severe postoperative complications and mortality. We identified failure-to-rescue as a problem in Nigeria. Furthermore, this study has provided policy makers with benchmarks that can be used to monitor
programmes aimed at reducing the morbidity and mortality after elective surgery. We recommend the adoption of the ASOS surgical risk calculator as a tool for risk stratification preoperatively for elective surgery.
Estimation of daily solar radiation at equatorial region of West Africa using a more generalized Angström‑based broadband hybrid model
(2020) Otunla, T.A.
A well-calibrated simple and economical viable Ȧngström–Prescott model has long been accepted to be more accurate than other surface meteorological data-based models. The major limitation is that it is site dependent. This study exploited the appropriateness of a more generalized Ȧngström-based broadband hybrid model in the estimation of solar radiation at seven stations in equatorial region of West Africa. This model features parametric equations that explicitly and accurately account for clear-sky damping processes in the atmosphere. It empirically estimates cloudy sky radiation extinctions using relative sunshine duration. A new cloud transmittance calibration curve that followed the cloud cover patterns of the region of study was also tried. The result indicated that the new cloud transmittance could be unique to equatorial region of West Africa. The performance of the hybrid model, after modification using the new cloud transmittance equation, was tested using mean bias error and root mean squared error. The performance was found to be comparable to the site-dependent, locally calibrated, Ȧngström–Prescott model at the calibration stations, and even better at validation stations. The same performance test comparisons with the original version of the hybrid model, and four other site-independent models: globally calibrated, FAO-recommended Ȧngström–Prescott models, Hay and Gopinathan models indicated the modified version of the hybrid model as better
Estimates of clear-sky solar irradiances over Nigeria
(2019) Otunla, T.A.
This study attempts to circumvent the problem of paucity of input data required in climatology mapping of clear-sky solar irradiance in Nigeria by computing beam normal (Ebn) and diffuse (Ed) irradiances using a high performance broadband radiative model in the country climate zones. Air temperature, relative humidity and global datasets of ozone thickness and angstrom turbidity were used as input parameters. The biases in the Ebn estimates with NASA datasets across Nigeria (11e25%) are of similar magnitudes with NASA observations with ground measurements. The estimates show persistent negative biases that increased from tropical savannah to semi-arid climate zones (_8 to _24%). The bias in the Ed estimates is only of similar magnitude with NASA in semi-arid climate zone (10%). The Ed estimates show persistent negative biases that increase from semi-arid to tropical savannah across Nigeria (_7 to _54%). Also, the estimates in each climate zone correspond to the expected climatology of water vapour, aerosol turbidity and absolute optical mass. Lastly, the response of Ebn to water vapour absorption and aerosol extinction signals is mostly active in monsoon zone while the response to the signals by Ed are active in all the zones.
"Assessment of Wind Speed Distributions and Turbine Characteristics in Equatorial West Africa"
(2026-03) Otunla, T.A.
Wind nullity, low wind, and bi- or multi-modality are common characteristics at high temporal resolution, especially in Equatorial regions. The traditional two-parameter Weibull (Weibull) distribution function (DF) is not designed to capture such peculiarities. Hourly mean wind speed data for eight locations that cut across different climate zones in an Equatorial region of West Africa have been analyzed using Weibull and Maximum Entropy Principle-based (MEP) distribution functions (DFs). Wind characteristics, such as power density, null wind speed, and modal distributions, together with turbine efficiency, capacity, and availability factors, were also assessed at a wind turbine hub height of 73 m using standard statistical tools. The results indicated that null wind speed and/or bimodality were present in the wind distributions at Abuja, Akure, Akungba, Nsukka, Makurdi, and Yola. The results of the assessments of the two DFs show that the MEP DF generated much better results across all time scales (R2: 0.83 - 0.98; RMSE: 0.0037 - 0.0109 m/s2) than the Weibull DF (R2: 0.47 - 0.98; RMSE: 0.0038 - 0.0191 m/s2), especially for locations where null wind speed and bimodality were prominent in the wind data distribution. MEP DF results further indicated that annual and rainy season periods were better modeled than the dry season in all the locations. The overall effect of all the turbine characteristics on annual and seasonal scales is that sufficient winds were available (Availability factor: 0.733 - 0.97; Capacity factor: 0.350 - 0.778) at the rated power for energy production in all the climate zones.