FACULTY OF SCIENCE
Permanent URI for this communityhttps://repository.ui.edu.ng/handle/123456789/266
Browse
363 results
Search Results
Item 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).Item Impact of the total solar eclipse of 29 March 2006 on the surface energy fluxes at Ibadan,Nigeria(2012) Nymphas,E.F.; Otunla,T.A.; Adeniyi,M.O.; Oladiran, E.O.This paper document the impact of the total solar eclipse (97.4%) of 29 March 2006 on the surface energy fluxes at Ibadan, Nigeria (longitude4.561E, latitude7.551N), a tropical location. The surface energy (determined by the BREB method) was found to be grossly affected by the eclipse. The latent heat and net radiation (Rn) lagged the sensible heat by 11 min in totality. The sensible heat lagged the latent heat and Rn by 6 min before it start to increase after the totality phase of the eclipse while global radiation (Rg) lagged Rn by 7 min. The sensible heat reversed sign reaching a value of _1.02 Wm_2 during the total phase of the eclipse while the latent heat dropped by 89.7%. All the radiation fluxes (global radiation, Rg, net radiation Rn, temperature and soil heat flux) measured during the eclipse event were significantly affected by the sudden ‘cutoff’of the solar irradiation.There was a 95% decrease in Rg, while Rn dropped from 354.3Wm_2 to _11.7 Wm_2.Item Estimation of bare soil surface temperature from air temperature and soil depth temperature in a tropical station(2011) Adeniyi, M.O.; Nymphas,E.F.Soil surface temperature has critical influence on climate, agricultural and hydrological activities since it serves as a good indicator of the energy budget of the earth’s surface. Two empirical models for estimating soil surface temperature from air temperature and soil depth temperature were developed. The coefficient of determination (R2) of soil surface temperature from the air temperature model ranged from 0.92 - 0.99, while the mean absolute error (MAE) and root mean squared error (RMSE) ranged from 0.5 - 2.48 and 0.77 - 2.630C respectively. For the soil depth model, the R2 value ranged from 0.75 - 0.96, MAE ranged between 1.05 and 4.94, while RMSE ranged from 1.28 - 5.25. Both models performed well on days of year (DOYs), under similar prevailing weather conditions during the model training period.Item On the environmental effects on a point discharger(2011) Nymphas E.F.; Oladiran E. O.The environmental effect on a point discharger has been investigated. It was found that the magnitude of point-discharge current (Ip) measured from a discharger is strongly affected by the presence of other dischargers, particularly when they are very close to the discharger through which Ip is measured. The starting potential depends on the tip clearance of the central discharger rather than the separation of the points. At higher tip clearances the compound discharger exhibits a stepped-leader like process. Atmospheric contaminants also affect the magnitude of Ip.Item 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 particulatesItem Determination of rainfall attenuation at millimeter wave band for the design of 5g and higher bandwidth radio equipment for terrestrial paths in the tropical region(2020) Osita, I.; Nymphas, E. F.Millimeter Wave (mmW) radio systems operating at 30 to 300GHz band provides higher bandwidth, frequency reuse and communications security. With the available wide bandwidth, millimeter wave equipment is capable of achieving 10 Gbps full duplex capacities. The mean annual 1-minute RR (mm/hr) ranged from 87.25 in the coastal region to 51.0mm/hr in semi-arid region. The ITU-R predicted RR ranged from 109.10mm/hr in the coast to 91.90mm/hr in the semi-arid region. The ITU-R overestimated the rain rate by 23.83% in the semi-arid region while at the coastal region, it was over-estimated by 12.47%. The highest value of specific attenuation (R g) at horizontal polarization (Hp) and vertical polarization (Vp) for the two regions occurred at 120 and 150GHz MWFs and R P g H > R P g V. The clear signal band at 20km Path length were estimated to be 40 and 45GHz across the regions, while the predicted value by ITU-R is also 40GHz. However, the ITU-R over predicted the value of attenuation at this frequency band by 13.16% and 35.29% at the coastal and semi-arid locations respectively. included 150GHz which overlaps with 45GHz band. The path attenuation across the regions at 40GHZ ranged from 112.58dB to 164.14dB while at 45GHZ, it ranged from 122.02dB to 175.57.45dB. The range of the ITU predicted value of path attenuation at 40GHz and 45GHz were 170.20dB to 192.18dB and 181.83 dB to 204.43dB respectively.Item Transformer and transmission of power(Ibadan university press, 2013) Nymphas, E.F.Item Global warming(springer, 2010) Ibe,O.; Nymphas,E.F.Item TLC phytochemical screening in some Nigerian loranthaceae(Academic Journals, 2010-07) Wahab, O. M.; Ayodele, A. E.; Moody, J. O.The phytochemical screening of specimens of the family Loranthaceae collected from the field was carried out with a view to ascertaining chemical constituents present and determining their importance in the taxonomic delimitation of the taxa. Thirty field collections from various localities were screened for secondary metabolites such as alkaloids, anthraquinones, terpenoids and ketones using thin layer chromatography (TLC). Most of the samples tested slightly positive for alkaloids, anthraquinone-related compounds, terpenoids and terpenoidrelated compounds but ketonic compounds were of rare occurrence in all the samples. The chemical profile was useful in separating the collections of Phragmanthera from the other two genera while the collections of Globimetula were found embedded in Tapinanthus. The secondary metabolites obtained however showed the relative affinity of the Nigerian species of Tapinanthus. It is concluded that chemical characters may only be used as supporting evidence in the identification and delimitation of the taxa.Item Scanning electron microscopy of fruits in the West African polygonaceae(Institute of Botany, Chinese Academy of Sciences, 2010) Ayodele, A. E.; Zhou Z.The fruit morphology of 18 taxa representing seven genera of the family Polygonaceae in West Africa was investigated using scanning electron microscopy. The achenes are trigonous, lenticular, globose, subglobose, heart shaped, ovoid, or cone like. Sizes range from 0.12 × 0.10 cm2 in Polygonum plebeium to 7.87 × 0.58 cm2 in Afrobrunnichia erecta. Colors are brown to black. The cells are isodiametric in P. plebeium, irregular in A. erecta, Antigonon leptopus, and Harpagocarpus snowdenii, and polygonal in other species. The walls are straight, curved, or undulate and are either raised or depressed. Afrobrunnichia erecta is characterized by deeply sinuate lateral walls. The cell surface may be smooth or tuberculate or fibrillate in the family, usually covered with wax deposits. The combination of these characters is mainly taxonomically useful at the tribal level and rarely at the specific or infraspecific level for the delimitation of the taxa.