Scholarly works

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A review of the bulk layer pollutant transfer over Nigeria during the harmattan season
(2007) Oladiran, E. O.,; Nymphas, F. F.
A review of the results of the bulk characteristics of the harmattan dust is presented to facilitate ease of reference and regional comparison where similar local effects exist. The meteorological interconnections are dealt with. The transport properties are presented, and are found to agree with the plume model for cascaded continuous sources on a 1km x 1km gnd point system. The wind profile is found to be consistent with turbulent electrode model of Willet.
A statistical approach to estimate wind speed distribution in ibadan, nigeria
(2016) Rauff, K.O; Nymphas, E.F.
In this paper, the wind energy potential in Ibadan is statistically analyzed using daily wind speed data for 10 years (1995-2004) obtained from the International Institute of Tropical Agriculture (IITA) and 1 year (2006) obtained from Nigeria Micro-scale Experimental (NIMEX) Ibadan,Nigeria. The statistical wind data set was analyzed using Weibull distributions in order to investigate the Weibull shape and scale parameters. The daily, monthly, seasonal, and yearly wind speed probability density distributions were modeled using Weibull Distribution Function. The measured annual mean wind speed was found to be 0.76 m/s and the total extractable wind power has been estimated as 0.33 kW at IITA while the annual mean wind speed ranged between 0.74 m/s, 1.02 m/s, 1.16 m/s and 1.34 m/s at (3 m, 6 m, 12 m and 15 m) respectively at NIMEX. The maximum extractable annual wind power density value of 0.90W /m2 for the whole year at IITA and 5.61W / m2 at the highest height of 15 m at NIMEX indicated that, Ibadan can be classified as a low wind energy region and it belongs to the wind power class 1, since the density is less than 100W /m2 . It is concluded that at both sites, the highest wind speed that prevailed in Ibadan is March and the location can be explored for wind power.
An algoritm for solving electromagnetic field equations by finite element method
(Medwell Journals, 2007) Adetoyinbo, A. A.; Adewole, O. O.
Describing the behaviour of electromagnetic frequency responses from vertically inhomogenous and anisotropic earth of 2-Dimensional structures energized finite sources is computationally laborious. Differential equations were derived and their numerical solutions also sought for the desired components of electric and magnetic fields. Also, expressions for the impedance and apparent conductivity were stated. An algorithm based on the finite element method for computing approximate numerical solutions for these problems were dealinated.
An artificial neural network estimation of global solar radiation at Ibadan, Nigeria using meteorological data
(2020) Nymphas, E.F.; Udomboso, C.G.
This paper estimates global solar radiation (Rs) from routinely measured meteorological parameters in the city of Ibadan, Nigeria, using artificial neural network method. Six combinations were used to estimate Rs namely (i) daily mean air temperature (T) and day of the year as inputs and global solar radiation as output, ((ii) daily mean relative humidity (RH) and day of the year as inputs and Rs as output (iii) daily mean T, daily mean RH and day of the year as inputs and Rs as output (iv) daily mean minimum relative humidity (RHmin) and day of the year as inputs and Rs as output, (v) daily mean minimum temperature (Tmin), daily RHmin and day of the year as inputs and Rs as output (vi) daily mean maximum temperature (Tmax), daily mean Tmin, daily mean RHmin, daily maximum relative humidity (RHmax) and day of the year as inputs and Rs as output. The neural network was trained with 3653 measured data between 1995 and 2004 and tested with data for 731 days between 2003 and 2004. The data for testing the neural network were not used for the training. The results obtained showed that the combination of RHmin, RHmax and day of the year gave the best estimate of Rs with MSE of 3.4124. This is followed by RHmin and day of the year with MSE of 3.4424. Daily mean air temperature and day of the year could not mimic the measured Rs; it gave MSE of 5.3345. It is concluded that Rs can be estimated for locations where only temperature and relative humidity data are available.
Analysis of data on net longwave, shortwave, and global radiation during a transition period in a tropical station in southwestern Nigeria
(2009) Ogolo, E.O. Ph.D,; Falodun,S.E.; Oluyanmo,S.S.; Nymphas, E.
This paper examines the distribution of the surface radiation balance components measured during the Nigerian Micrometeorological Experiment (NIMEX-1), a field study conducted to measure surface heat fluxes in the boundary layer during the transition period which marks the end of dry season and the onset of wet season (February 15 and March 10, 2004) in the southwestern part of Nigeria. Regression equations were obtained using the daily average values and hourly mean values between net shortwave and net longwave radiation, respectively, with the global radiation. Higher correlations with low standard error of measurement were obtained for daily mean values than the hourly mean. It was also observed that the peak values of each type of radiation during the period occurred, on average, two hours after noon when it was expected to occur.
Analysis of heavy metals concentration in sediments and water samples of selected functional dams in Oyo State, Southwestern Nigeria
(2008) Adegoke, J. A.; Sunmonu, L. A.; Ojeniyi, O. S.
"The quality as well as the quantity of clean water supply is of vital significance to the welfare of mankind particularly in the developing countries. Therefore, knowing the concentration of heavy metals present in Dams can help us to ascertain the health safety of the populace using the water for drinking and domestic purposes. Ten Dams at Oyo State in the Southwestern Nigeria were studied for the heavy metals concentration contained in the sediments and water of the selected Dams. Bottom sediments and water were collected from the selected dams for analysis. Analysis of both the water and sediments to determine the concentration of each heavy metal was evaluated. The result obtained shows that, the concentration of Manganese (Mn) ranges from 14.8 mg/kg to 332.96 mg/kg followed by Zinc (Zn) which ranges between 6.18 mg/kg and 52.53 mg/kg which spread across all locations., Lead (Pb) was not detected in virtually all the locations except in Ilora which has a concentration of 0.87 mg/kg and this may be as a result of the activities of motor mechanics and vulcanizers around the dam. In the water samples, the result showed that the concentration of heavy metals is very low which is far below the limit specified by World Health Organization (WHO). Zn has the highest concentration ranging from 0.049mg/kg to 0.729mg/kg, followed by Mn which has concentration between 0.011mg/kg and 0.344mg/kg. Pb, Cadmium (Cd) and Cobalt (Co) were not detected at all in all the water samples. The variation in the concentrations may be due to geological nature of the ground, solubility, an ion exchange and human activities. "
Assessing the Performance of Global Solar Radiation Empirical Models at a Sahelian Site, Sokoto, Nigeria
(The Nigerian Association of Mathematical Physics, 2015) Otunla, T.A.; Kolehaje, O. T.
In the region where solar radiation data are scarce, the next alternative method is to use solar radiation models to estimate the data needed for some applications such as simulation of crop performance and the design of solar energy conversion devices. In this paper, the validations of fifteen models for estimating monthly mean daily global solar radiation on the horizontal surfaces were conducted at a location in salielian region where there is great potential for solar energy utilization in electricity generation and irrigation. Evaluations of these models were carried out by using the Mean Bias Error (MBE), Root Mean Square Error (RMSE), Mean Percentage Error (MPE) and t-test. Three of these statistical performance indicators were combined to generate rank score for each model. Temperature based models made the rank of the best three during the wet season. On the annual scale and in the dry season, temperature variations and humidity were combined with sunshine duration to get the best rank of I to 3.
Assessing Wildfire Occurrence in West Africa with Atmospheric Co₂ Removal
(2025-06) Uzoma E.K.; Otunla T. A.; Nymphas E. F.; Ogunsola O. E.; Adeniyi M. O.
The increase in wildfire occurrence is one of the consequences of the recent global temperature rise. Understanding wildfire occurrence in West Africa under atmospheric carbon dioxide removal is significant because of its implications on climate systems, ecosystems, agriculture, and socioeconomic development. This study projected the impacts of atmospheric carbon dioxide removal on fire occurrence in West Africa by analyzing the CNRM ESM1 C1 model output for the Carbon Dioxide Removal Model Inter-comparison Project (CDRMIP). Four climatological periods–1990–2019 (reference period), 2040 – 2069, 2070–2099 and 2100-2129 were analyzed using four fire indices. The periods 2040–2069, 2070–2099, and 2100–2129 have 42%, 45.9%, and 49.4% of “No Fire” category among other categories, respectively, with the Lebanese Index. With Mark 4 Grassland Fire Danger Index, a low category of fire risk is also predominant at 95.6%, 96.4%, and 66.1% for 2040–2069, 2070–2099, and 2100–2129, respectively. None of the indices projected a case of high, very high, or extreme risk in any period. “Low risk” category is predominant with all indices, particularly in Cote D’Ivoire, Ghana, Burkina Faso, Togo, Benin, and Nigeria. The low-risk category for fire occurrence during carbon dioxide removal in West Africa suggests a favorable outcome for the region’s ecosystems, agriculture, and communities. The study highlights the potential benefits of CDR beyond carbon removal, such as enhanced resilience, sustained productivity, and reduced vulnerability to climate-induced hazards like wildfires.
Assessment of Air Quality Conditions in an Area in the Gulf of Guinea, Ibadan, Using Low-Cost Sensors
(2025) Otunla, T.A.
Air quality monitoring is essential for the determination of the potentialnegative impacts of air pollution on humans and the environment. This study investigated the contribution of particulate matter (PM 2.5 and 10) to air quality in an area in the Gulf of Guinea, far south of Sahara. The study used the hourly data of PM 2.5 and 10 concentrations and other auxiliary data in 2021 from the PurpleAir sensors. These PM concentration data were first converted into Air Quality Index (AQI) using appropriate method of aggregation. Subsequently, the AQI was used to categorize the ambient air into six classes that range between “Good" to "Severe" conditions. Results indicated higher prevalence of "Good “to “Satisfactory" AQI conditions during the peak of the rainy season (June, July and August), characterized by low PM concentrations, whereas the harmattan season (December, January and February) exhibited a higher prevalence of "Very Poor" to "Severe" conditions, characterized by high PM concentrations. High AQI and PM concentrations were attributable to organic PM Saharan dust in the harmattan season, while low AQI and PM concentrations in the rainy season were associated with localized anthropogenic sources. Thus, the low-cost sensor PurpleAir was able to capture the expected seasonal patterns peculiar to the study region.
Assessment of building failure within and around quarries
(2019-07) Adetoyinbo, A. A.
The substructures of various engineering structures that were erected on the earth are being were been supported by the soil. Hence, the nature of the soil supporting these structures becomes an important issue. Quarry blasting peak particle velocity (QBPPV) is not sufficient to ascertain the causes of foundation failure, therefore, the physical parameters governing the competency of the soil supporting engineering structures need to be determine. This work investigated the possible causes of foundation failure of buildings within the vicinity of quarries. The investigation was done by carrying out Vertical Electrical Sounding (VES) and Radial Vertical Electrical Sounding (RVES) using Campus omega terrameter. The results show that buildings found within this area have shallow foundation and their foundations founded on sandy clay which can still support foundation The values of the degree of fracturing was found not to exceed 1.53 in this region which was not the case with the previous radial vertical electrical soundings, 1.94 was calculated as the highest degree of fracturing for RVES 1 while 1.83 was calculated for RVES 2. In all the RVES, degree of fracturing ranges between 1.02 to 1.94.
Assessment of ground water pollution in Itagunmodi, South-West, Nigeria
(2012-02) Adetoyinbo, A. A.; Bello, A. K; Hammed, O. S.
Some investigations have been earned out on geochemical characteristics of soil samples that embedded the ore deposits. Physiochemical analysis of water collected within gold mining area and the water consumed in the town of Itagunmodi was earned out to determine their hygienic conditions. The major objective of this study was to determine the suitability of the available water consumed in the town based on the Physiochemical analysis test carried out. In this regards, four major sources of water were analyzed. Analysis shows that the water within the town of Itagunmodi was hygienic with the inclusion of water within the mining site. The analysis includes; conductivity test, the pH test and others. It was noticed that the pH of the sample from the gold mining site was also suitable for drinking according to the World Health Organization standard. For a safe drinking water, the pH should be between (6.5 -8.5).
Assessment of groundwater quality in unconsolidated sedimentary coastal aquifer in Lagos State, Nigeria
(Academic Journals, 2009-04) Adebo, B. A; Adetoyinbo, A. A.
This study assesses the quality of ground water from nine different borehole locations in Lagos State, Nigeria. Borehole water samples were carefully collected for physico - chemical analyses. Calcium, magnesium, iron, zinc, copper, manganese, aluminium, and silver, Nitrate, phosphate, fluoride, chloride, pH, conductivity, total dissolved solid, total suspended solid, hardness, summation of ions as well as the temperature and colour were assessed among the entire samples collected. The results show that: temperature ranges from 26.6 - 27.8°C, pH (7.27), average conductivity (462.2 ps/cm), TDS (204.73 mg/l), Total hardness (18.48 - 297.70 mg/l) and Chloride concentration (343.3 mg/l). However, a high value of chloride, 343.3 mg/l, was recorded in one of the water sample collected but, this is higher and above the limit of WHO guidelines of portable water (250 mg/i). This may be due to the proximity of the area where the sample was collected to the sea. Five samples of the water are is soft, that is, hardness was within a range of 0 - 75 mg/l recommended for safe drinking water, one is moderately hard while three samples are hard. Also, the presence of metals such as zinc, manganese, sodium, copper and magnesium were also observed. Results show that not all the water samples are safe for drinking purposes.
Assessment of Soil Thermal Properties in a Tropical Environment: Ile Ife and Ibadan
(Journal of Faculty of Science, University of Ibadan, Ibadan, Nigeria., 2011) Otunla T.A.; Oladiran E.O.
Soil thermal properties are crucial parameters that affect soil heat flux. Time series of soil temperature, soil moisture content, and rainfall and soil heat flux were measured at two tropical locations in West Africa during the transition from dry to wet season, and at the peak of rainy season in July. The data were analyzed to estimate soil thermal diffusivity, thermal inertia and volumetric heat capacity. The thermal properties were clearly related to soil moisture (and thus rainfall) throughout the measurement period. The modeled soil heat flux using the soil thermal properties compared favorably with the measured soil heat flux.
"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.
Behavior of multiple lightning dischargers under a tropical thundercloud
(2010) Nymphas. E.F.; Adeniyi, M.O.; Oladiran, E.O.
Lightning discharges on ground depend on the electrostatic charges, nature of vegetation, topography and dynamics of the turbulent layer. In designing lightning protectors, one major consideration is the highest point in the surrounding that lightning is directed. The effects of ambient dischargers on lightning protectors were investigated. to determine both the discharge behavior and performance. The starting potential of the discharger configuration increased with clearance of tip of the central discharger from surrounding dischargers, instead of increasing with the average spacing between dischargers. The point of strike of lightning discharge depended on the line of least stress rather than the height clearance from the cloud: which determined the charge structure and dynamics of the cloud particulates
A case study of the depth of fresh/ Salt water interface using values of freshwater heads in groundwater of variable density
(2012) Adegoke, J. A.; Owoeye, O. I.; Ozebo, V. C.
"Almost two thirds of the world's population lives within 400 km of the ocean shoreline; just over half live within 200 km, an area only taking up 10% of the earth's surface. As the world's population continues to grow at an alarming rate, fresh water supplies are constantly being depleted, bringing with it issues such as saltwater intrusion and increasing the importance of groundwater monitoring, management, and conservation. Constant monitoring of the fresh/salt water interface is necessary for proper management of ground water resources. This work studies the variation in the depth of fresh/salt water interface using different values of freshwater heads extracted from heads in coastal groundwater system near The Hague, Netherlands along sections P-DD. Results showed that high density difference between freshwater and saltwater has little effect on the depth of fresh/saltwater interface."
Characteristics of total solar radiation in an urban tropical environment
(2012) Adeniyi M. O.,; Nymphas E. F.; Oladiran, E. O.
The maximum total solar radiation in Ibadan (7.38° N, 3.93° E), Nigeria occurred around 13 and 14h local time (LT) and it varied from an average value of 584.3±10.9 Wm-2 in the wet season (April to October) to 642.5±10.8 Wm-2 in the dry season (November to March) throughout the period of 1997 to 2001. Maximum total solar radiation had two peaks, one in March/April/May with value 750.3±41 Wm-2 and the other in October/November with value 633.1±63.5 Wm-2. The minimum was in July/August with the value 404.8±54 Wm-2. Diurnal total solar radiation had a similar variation with mean day total solar radiation; the latter had its maxima and minimum values to be 564.7±19, 488±36 and 308.4±40 respectively. The annual trend of solar radiation was positive throughout the period considered, which revealed global brightening. The values of total solar radiation observed in Ibadan compared well with those obtained at Ife (7.55° N, 4.56° E) a nearby tropical station. A time lag of about 3 h between the peak of the diurnal temperature and solar radiation was observed. During the month of July or August as the case may be, there was little or no time lag between the time of maximum total solar radiation and maximum diurnal temperature. Significant intra-annual solar radiation cycles (at 0.05 significant level) of 360 to 370 days (1 per year); 180 to 200 days (2 per year), 90 to 121 days (3 per year), 45 to 70days (5 per year); 20 to 35 days (10 per year), 4 to 16 days (20 per year) were obtained for all the years (1997 to 2001).
Characteristics of worst hour rainfall rate for radio wave propagation modelling in Nigeria
(springer, 2019) Osita I.; Nymphas E.F.
Radio waves especially at the millimeter-wave band are known to be attenuated by rain. Radio engineers and designers need to be able to predict the time of the day when radio signal will be attenuated so as to provide measures to mitigate this effect. This is achieved by characterizing the rainfall intensity for a particular region of interest into worst month and worst hour of the day. This paper characterized rainfall in Nigeria into worst year, worst month, and worst hour. It is shown that for the period of study, 2008 and 2009 are the worst years, while September is the most frequent worst month in most of the stations. The evening time (LT) is the worst hours of the day in virtually all the stations.
Characterization of tropical rainfall structure for some selected locations in Nigeria
(2021) Osita, I.; Nymphas,E.F.
Rainfall rate for any location is required for rain attenuation modeling for the region of interest. The characteristics of tropical rainfall structure in Nigeria have been investigated. The data was collected from the Tropical Data Acquisition network (TRODAN) set up by the Center for Atmospheric Research (CAR) in Nigeria. The rainfall rates were measured at 5-minutes integration time. The results were then compared with those predicted by the ITU-R model, and those from other tropical locations. The results revealed that the ITU-R model performs best only in the Southern Guinea Savannah (SGS) region of the country. In other geographical locations, the ITU-R model either under-estimates or over-estimates rainfall rates. The Cumulative Distribution Functions (CDFs) at the 0.01% time of exceedence showed that the percentage difference in the measured rain rate and the ITU-R estimates varied from a minimum of 4.89% in SGS to a maximum of 22.93% in the Derived Savannah (DS). At the 0.001% of time, these differences varied from a minimum of 11.90% to a maximum of 38.80% in these respective regions. These results and others from the tropics suggest the need for the modification of the ITU-R model for predicting rain attenuation in the tropical region to take into account the peculiar characteristics of rainfall in the region.
Characterizing buried metallic objects in porous media from attenuation fluctuations
(Academic Journals Inc, 2013) Akinyemi, O. D.; Adegoke, J. A.; Salam, M. A.; Badmus, B. S.; Awokola, S. O.
"Study of attenuation characteristics of electromagnetic signals passing through porous media is becoming increasing relevant in providing important insights into the physical properties of the medium and objects that are buried therein. Laboratory experiments have been carried out in this work to determine the relationship between Q-factor of the electromagnetic signal passing through buried metals and the porosity of the surrounding sediments. Sediments were obtained from Erinle River in Ilobu, Southwestern Nigeria and Iron, Silver and Copper plates of similar dimensions were buried inside box-filled sediment in succession. Electromagnetic signal was passed through metal, sediments and sediments with buried metals while lissajous figures generated at different frequencies were analyzed to assess the impacts of buried objects. Results showed that Q-factor decreased as the porosity of riverbed sediments increased. Of the metals buried inside the sediments, Iron had the most attenuation effect while Silver plates had the least, except at frequency 400Hz where Copper had the least and at 600Hz where there were some overlaps between Silver and Copper. Q-factor increased, for all metals and at all signals frequencies, up to a maximum value at the porosity of 0.24 and thereafter decreased. Knowledge of Q- factor from attenuated signals is therefore, a useful way to characterize and identify buried materials "