Scholarly works

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INITIAL STAGES AND SOME CHARACTERISTICS OF WEST AFRICAN LINE SQUALLS
(1983-03) ADEDOYIN, J. A.
A review of West African synoptic weather pattern reveals that the sub-region experiences a special kind of atmospheric disturbance -the line squall - whenever the south-westerlies cover, approximately, the whole of Nigeria. Various methods that have been used to study the squalls (i.e. observational investigations, satellite investigations and modelling) have not been very successful in isolating the trigger mechanism of the phenomenon. It is been proposed that line squalls are initiated through the amplification (with time) of any wave-like perturbation along the surface of discontinuity between the south-westerlies and the north-easterlies. The amplifying perturbations could block the 650 mb. mid-tropospheric jet which further distorts the 'bump' formed by the undulating perturbation. This distortion forces the southwesterlies further up and they could condense. The precipitates fall into the underlying, dry jet and some of them evaporate; the latent heat of evaporation being supplied by the jet. The jet, now cooler, sinks. On sinking, the jet could hit the surface of the earth on which it forms the squall front and crawls; thereby lifting the south-westerlies ahead of it. The cycle of condensation, evaporation and sinking then continunes. A gravity-wave model of this mechanism is presented through the solution of a frequency equation with the aid of a two-layer atmospheric model. The solution is an eigenvalue problem from which many modes of different growth rates and phase velocities could be obtained. Some of these phase velocities will be complex - the real part representing the phase velocity while the imaginary part represents the amplification. Waves with the largest amplifications (i.e. the largest imaginary part) are those that could possibly block the 650 mb. mid-tropospheric jet and trigger off line squalls. Among others, this proposal on the trigger mechanism of line squalls is able to explain: (i) the preference of highlands as places of origin of line squalls, (ii) the close association between the speeds of propagation of line squalls and the mid-tropospheric jet and (iii) the observed overturning of the atmosphere after the passage of line squalls.
SPIN COMPLEXES IN FERROMAGNETISM
(1988-11) AGBOOLA, A. I.
The spin-wave theory in Heisenberg model of ferromagnetism is investigated with the Holstein - Primakoff transformation and with emphasis on the spin wave interactions. The temperature Tₒ below which the concept of magnons is valid is determined. By a special expansion formalism of operator (l-a+a/2S)1/2 which yields 1+(1-(1-1/2S)1/2 )a+a it is shown that quantized spin waves which behave like spin 1 quasiparticles (with dispersion relation ω~ k2 ) called magnons at temperatures T < Tₒ, are Bosons with an effective (negative) electrochemical potential µ that varies as T in the wave-wave interaction approximation. The various coefficients of Tv in the expression of the spontaneous magnetization M(T)/M(o) = l-(C1T3/2+C2T5/2+C3T7/2+C4T4) as well as the specific heat for some ferromagnets are calculated. The results are remarkably close to the experimental values obtained by other investigators. The method used enables one to deal especially with regimes of small spin values S for which µ differs substantially from zero. The influence of the chemical potential on some thermodynamic quantities are found for ferromagnets with Hexagonal-close-packed structures, as well as for cubic crystals, The existence of the spin wave interactions and hence of non-zero effective chemical potential is shown to give rise to a lowering of the thermodynamic internal energy with the implication that spin waves, on the average, form bound states called spin complexes. The kinematical as well as the dynamical interactions on the thermodynamic quantities are also found for some ferromagnets, by subjecting the magnons to intermediate statistics. The influence of the spin-wave-spin-wave-spin-wave interactions on the coefficients of Tv in the expression of the spontaneous magnetization of some ferromagnets are found to be negligible in comparison with wave-wave interactions. An attempt is made to extend the above calculations to spin complexes in antiferromagnetism, a phenomenon which seems to be relevant to high temperature superconductivity.
Modelling effective rheologies for viscoelastic porous media with application to silt, and medium coarse sand
(Nanjing Institute of Geophysical Prospecting, 2004) Olowofela, J. A.; Adegoke, J. A.
A modification of Biot's poroelastic differential equations is made to include matrix-fluid interaction mechanisms which assume a solid-fluid relaxation function coupling coefficient. Values of physical properties of sediments are incorporated into equations which define phase velocity and attenuation for porous media which are dependent on the composite densities of various media (silt, and medium and coarse sand). The results enable us to compare the attenuation and velocities of waves in these media. We observed that the density of coarse sand is greater than that of medium sand and this in turn is greater than that of silt-the same holds-for the velocities of P-waves in these media but the situation is converse for shear waves in the same given media. As the densities of the media increase, their attenuation decreases as it was found that the attenuation of silt is the highest and that of coarse sand lowest for the media considered.
Contemporary aspects of Monte Carlo methods and simulation in physics
(Faculty of Science, University of Abuja, 2004) Olowofela, J. A; Adegoke, J. A; Adewumi, O. P; Kamiyole, I. C.
"This article introduces Monte Carlo methods which are different from conventional numerical methods and show how some of the methods can be applied in Physics to stimulate or solve physical problems, through computer programmes (written in FORTRAN in this case) by using a few examples touching modern and classical physics showing its usefulness. A functional approach to probability and statistics is described for the purpose of this work instead of complete treatment. The importance of good sequence of random numbers with large periods is demonstrated and the methods, in same instance are compared with conventional type and differences pointed out. "
Effects of clay content and porosity on wave velocities in unconsolidated media wing empirical relations
(Nanjing Institute of Geophysical Prospecting, 2004) Olowofela, J. A.; Kamiyole, I. C.; Adegoke, J. A.
"Wave velocities in sandstones are greatly influenced by porosity and clay contents. We formulated new empirical relations for the velocities Vp and Vs in these media which take into account the porosity and clay contents. These relations are Vp=5.57 - 6.47ø - 2.27C1 ø and Vx=3.41 - 4.44ø - 2.23C1 ø, and can be used to compute velocitiesfor various porosities and clay contents. The result compare favourably with those of other works. "
The nigerian micrometeorological experiment (nimex-1): an overview
(2004) Jegede, O.O.; Mauder, M.; Okogbue, E.C.; Foken, T.; Balogun, E.E.; Adedokun, J.A.; Oladiran, E.O.; Omotosho, J.A.; Balogun, A.A.; Oladosu, O.R.; Sunmonu, L.A.; Ayoola, M.A.; Aregbesola , T.O.; Ogolo, E.O.; Nymphas, E.F.; Adeniyi, M.O.; Olatona, G.L.; Ladipo, K.O.; Ohamobi, S.I.; Gbobaniyi, E.O.; Akinlade, G.
The first phase of the Nigerian Micrometeorological Experiment (NIMEX-1) was concluded between 15 February and 10 March 2004, at an agricultural site within the campus of Obafemi Awolowo University in Ile-Ife, Nigeria (7°33’N, 4°33’E). The multi-institutional project was aimed at determining the surface energy balance of a tropical wet and dry location in West Africa. The field observations made fell within a transition from the dry to wet season in the area, and as such, the surface conditions varied in extremes. An integrated measurement system comprising of various micrometeorological sensors was deployed to record the mean and turbulence parameters in the surface layers separately. A number of methodologies viz: the eddy covariance (EC), Bowen ratio energy balance (BREB), and modified Bowen ratio (MBR) systems, used to determine magnitudes of the surface fluxes; sensible and latent heats, were compared. Generally, there is a consistency of their diurnal trends but the BREB method overestimated the surface fluxes up to about 30%. The radiation balance indicated that the incoming shortwave is dominant during daytime and is mainly responsible for the surface forcings. The nonclosure of the energy balance obtained at the surface, typically, was less than 25%.
Soil Thermal Properties at Nimex-1 site
(2004) Oladosu, O.R.; Ayoola, M.A.; Nymphas, E.F.
Lightning signature as an index for the determination of the beginning of the Planting season in Nigeria
(2004) Nymphas, F..F.; Adeniyi. M.O.; Ogolo, E.O.; Oladiran, L.O.
The discharge characteristics of a Franklin rod and a compound discharger with an insolated central point and surrounding points (a modified Franklin rod) has been investigated in the Laboratory and in the open atmosphere with a view to determine their effectiveness as lightning protectors. Analysis of the data showed that the compound discharger is about two and half times more effective as lightning protectors as compared to a typical Franklin rod with multiple ends. An aperiodic relationship between in (At V.. :/AVf) and m (dn/dt) has been observed instead of the speculated linear relationship. Investigation of the environment effects reveals that point- discharge current measurement from a point in a built discharge is an under-estimate.
A laboratory study of the effects of porosity and bed tilting on the discharge rate of groundwater
(Springer India, 2005) Olowofela, J. A.; Adegoke, J. A.
The study of movement of underground water helps to predict the extent of flow in as much as we can determine the volume rate among other things. Sand samples from river bed were used as porous media, a laboratory experiment was set up to look at longitudinal dispersion in term of volume of liquid flowing across a unit cross sectional area per unit time in these materials. Water was made to flow through a cylindrical pipe drilled sideways at intervals. Values of pressure were taken at regular interval and using appropriate basic equations, the volume flux rate was determined at various angles of tilt, from which volume rate of flow was also determined. A graph of volume rate of flow against angle of tilt gives the value of volume rate of flow as 1.00 ' 10-10 m3/s irrespective of porosity and permeability of the medium provided that the angle of tilt is 1.42°
The characteristics of positive ground discharges of tropical thunderstorms at Ibadan, Nigeria
(2006) Oladiran. E.O.; Nymphas, F.F.; Akpan U. F.; Israelsson, S
Positive ground lightning discharges were continuously recorded over a period of three years at Ibadan to supplement earlier composite records from 1987 by adapting the earlier design of Oladiran. et al (1988a) using the shape of the radiation field signatures and the frequency components of positive discharges (Oladiran and Israelsson. 1990). We recorded 92% discrimination between negative and positive ground flashes. The positive ground flashes were recorded at VLF and 17.3kHz, 3Db attenuation and yielded an average 13 and 11.6% ratios for (+CG)/(-CG) respectively. Compared to our results of 1988, the flash-rate characteristics for positive ground flashes are not significantly different from those of negative ground flashes and it does not show any seasonal preference. This leads to the conclusion that the occurrence of positive and negative ground flashes depends only on the cloud charge structure. Its dynamics and the ground conditions.
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.
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.
Effect of porosity on surface of drawndown in an unsteady state drainage in porous material. I
(2007) Olowofela, J. A .; Adegoke, J. A; Bejide, F. A.; Okeyode, I. C.
"This work considered the unsteady state drainage of fluid from a vertical column of porous material of varying porosities in an attempt to verify variation of drawndawn surface with porosity and time using riverbed sand. Kerosene was used as the flowing fluid. Mathematical assumptions ware made in connection with Darcy's law. The result showed that the experiment which was designed from the theoretical framework agreed with the theory to a large extent, However, this is not in perfect agreement with an earlier experiment which was performed using well rounded beads in which glycerine was used as the flowing fluid. A FORTRAN program was written to study the variation theoretically and this was compared with the experimental result. There exists, a degree of discrepancy between theory and experiment indicating that, the mathematical formulations did not perfectly agree with the complex earth system as compared with the bead model that was initially used. There is a need for the modification of the mathematical formulations; nonetheless, an unsteady drawndown, pattern was attained with different porosity even in medium with very complex geometry. "
Modification of Darcy's law for turbulent flow in saturated porous media
(Medwell, 2007) Popoola, O. I.; Adegoke, J. A; Alabi, O.
"Darcy's law is an essential equation in determining the permeability of porous media which is vital tool in seepage and drainage control in soils. However, whenever the aggregate sizes of the porous media and hydraulic gradient are large, the flow in drains will be semi-turbulent to turbulent. This research aims at modifying the true Darcy's permeability determined under small hydraulic gradients that ensure laminar or nearly laminar flow to allow for reduced efficiency caused by turbulence at greater hydraulic gradient and provide a relation between the maximum gradient for laminar flow and porosity of the porous media. A modeled experiment was set up using sand samples of different porosities from riverbed as porous media, which were packed in a vertical transparent cylinder tube of diameter 1.85x102m and relative permeabilities were determined for gradient ranging from 1.15-15.00. The result of the experiment shows that relative permeability increases with increasing porosity but decreases with increasing gradient. The maximum (or limiting) hydraulic gradient for laminar flow decreases with increasing porosity. Also, the vertical fluid flow in any porous medium is laminar or nearly laminar as much as hydraulic gradient is less than or equal to 1.04. "
Monitoring the effect of water pollution in twelve selected water dams in Osun State of SouthWestern Nigeria
(2007) Adegoke, J. A.; Sunmonu, L. A.; Lateef, T. A.
"The level of water pollution by heavy metals (Cu, Zn,Co, Ni, As, Mn, Cd, Cr, Pb) in twelve selected water Dams in Osun state were determined in order to know their distribution and possible source into the dams. Their bottom sediment and water were collected for analysis. The result in sediment showed that the concentration of manganese is high in all the dams with values ranging from 21, 27-775.99mg/kg and it spreads across all the locations. Cobalt was detected only at one location with concentration of 3.01md/kg. The result in water analysis showed that the concentration of zinc is more than that of manganese, almost in all the dams. The values detected were between 0.0618lng/kg and 0.5068mg/kg while that of manganese was between 0.011 2mg/kg and 0.1887 mg/kg. Cobalt and cadmium were not detected in all the dams. The variation in the concentration of these metals in sediment and water may be due to chemical factors such as solubility, ion exchange ratio and electrochemical deposition. The concentrations of all metals detected were below the standard limit for the heavy metals in surface water according to Regulatory authority Specification. Meanwhile, bioaccumulation of these metals in tissue of the body may be toxic to human health. "
Study of permeability of saturated homogeneous and heterogeneous porous media
(Duncan Science Company, 2008) Popoola, O. I.; Adegoke, J. A.; Alabi, O. O.
Many practical seepage and drainage problems can be studied by constructing flow nets for section with a single permeability, however, many natural soil deposits are more or less stratified, often with horizontal bedding that make horizontal permeabilities much greater than the vertical. Three different types of heterogeneous media from five soil sample of different porosities were considered: with constant-head permeameter to determine the saturated hydraulic conductivity for each. The result shows that least permeable medium dominates in the permeability of heterogeneous medium than layered heterogenous medium. However, fluid flow in homogeneous porous media is generally faster than that of heterogeneous medium of similar geometry and grains packing. Therefore, the effect of least permeable unit in heterogeneous medium must be considered in selecting a proper filter for seepage control.
Variability of permeability with diameter of conduit
(Indian Academy of Sciences, 2008) Adegoke, J. A.; Olowofela, J. A.
"An entry length is always observed before laminar flow is achieved in fluid flowing in a conduit. This depends on the Reynolds number of the flow and the degree of smoothness of the conduit. This work examined this region and the point where laminar flow commences in the context of flow through conduit packed with porous material like beads, of known porosity. Using some theoretical assumptions, it is demonstrated that permeability varies from zero at wall-fluid boundary to maximum at mid-stream, creating a permeability profile similar to the velocity profile. An equation was obtained to establish this. We also found that peak values of permeability increase with increasing porosity, and therefore entry length increases with increasing porosity with all other parameters kept constant. A plot of peak permeability versus porosity revealed that they are linearly related. "
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. "
Radiogenic heat production distribution of soil samples from Idi Omo, Akinyele LGA, Oyo State, Nigeria
(Creative Commons Attribution, 2009) Adegoke, J. A.; Layade, G. O.; Popoola, O. I.
The NaI(TI) gamma-ray spectrometer was employed to determine the concentration of naturally occurring Potassium(K-40). Uraniurn (U-238) and Thorium (Th-232) vis-à-vis the radiogenic heat production in soil samples from Idi-Omo farmland area of Akinyele, Local Government area o f Oyo state. The farmland which is at Latitude 07° 30’ 26.3" and Longitude 003° 57' 21.9" covers an area of about 80,000 square metre, and is at an average elevation of 240m above mean sea level (msl). The samples were pulverized, sealed and activities of the radiogenic isotopes in them were measured for an accumulating period of 7 hours (25200s). The elemental concentrations were determined from the gamma ray spectra. The radiogenic heat determined from activity concentrations on samples from the locality for 40k has on the average 92.86±0.02p W/Kg, while 238U has 251.26±0.61pW /Kg and 232Th has 77.210±0.03pW/Kg. The mean radiogenic heat calculated from the three radionuclides for the whole area under study is 421.3.3±0.66pW/Kg. 238U contributes 60% to the total heat production, 40K contributes 22% and 232Th contributes 18%. This makes Uranium to be the highest contributor to the total heat production in the area. However observed that the radiogenic heat production distribution in the area is low.
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.