F. N. Okeke

Department of Physics & Astronomy, University of Nigeria, Nsukka

Abstract. From the analysis and study of abnormal quiet days (AQDs) at mid and low latitudes locations, it was found that there is difference between the characteristics of phase variability Sq (H) of the low latitude locations. This suggests that the origin and cause of AQDs are of different sources in the two latitude regions. The AQDs events are independent of local time and could be of extra-terrestrial origin. The lunar contribution as seen from the analysis carried out has insignificant effects on the AQDs in both latitudes.

F. N. Okeke and A. B. Rabiu

Abstract. The latitudinal geomagnetic variation of the element H, D, and Z at eight Indian Observatories from about 0° to 22⁰ dip latitude have been studied. It is observed that the day-day variability of Sq (H), Sq (D) and Sq (Z) exhibit latitudinal variation. The latitudinal variation is found to be dependent on the position of the station from the equator. The latitudinal variation peaking around the dip equator suggests that one of the possible causative factors is the electrojet strength at the station near the dip equator. The latitudinal variation is independent of local time.

E. S. Falodun and L. B. Kolawole

Department of Physics, Federal University of Technology, Akure

e-mail: [email protected]

Abstract. Studies of tropospheric refraction of long and short wavelength radio signals have been carried out in the coastal and savannah areas of Nigeria using meteorological data collected by radiosondes in Lagos (3⁰ 45' E, 6⁰ 28' N) and Kano (8⁰ 30' E, 12⁰ 2'N). Daily mean values of the initial refractivity gradients, dN/dh, were computed for the two zones and the results obtained have been used to classify the refractivity profiles as sub-refractive, normal, super-refractive and ducting. The refraction of radiowaves in the lower atmosphere is considered to be normal whenever the refractivity gradient is —40N/km. Between about — 41N/km and —156.9N/km, the atmosphere is super-refractive and when the refractivity gradients become equal to, or more negative than —157N/km ducting occurs. The modified refractive index was also computed for the two zones. A negative gradient of M is a useful indicator as to the occurrence of ducting. The refractivity values obtained show that the propagation conditions are super-refractive at the coastal region, especially during the rainy season. At Oshodi, the surface layer is super-refractive 75% of the time with 38% probability of occurrence of ducting. The surface layer at Kano, on the other hand, is sub-refractive 88% of the time with the probability of occurrence of ducting being only 3.5%.

Moses oludare Ajewole and Adeseye Muyiwa Arogunjo

Department of Physics, Federal University of Technology, Akure, Nigeria

Abstract. Results of propagation measurements are often required to improve the coverage of Medium Frequency (MF) broadcast transmitters. To achieve this, ground electrical conductivity measurement is one of the parameters often determined. In this study, ground conductivity has been measured around MF radio transmitters in some parts of Western Nigeria, using the Vertical Electrical Sounding (VES) technique based on the Wenner Array geophysical prospecting method. Four of the radio transmitters belong to the Ondo State Radio Corporation (ODRC) and are located at Irese and Oba-Ile (both near Akure), Okitipupa, and Ido-Ani, while one each belongs to the Ekiti State Broadcasting Service (ESBS) at Ifaki-Ekiti, and the Osun State Broadcasting Corporation at Osu. The mean ground electrical conductivity obtained in this study ranged from mS/m at Okitipupa to mS/m at Ido-Ani. Investigation shows that the penetration depth at the frequency of transmission of each station varies from a minimum of m at Ido-Ani at a transmitting frequency of 1035 kHz to a maximum of m at Okitipupa at a transmitting frequency of 765 kHz.

Sam. B. Adejuyigbe and S. P. Ayodeji

Abstract. This paper investigates the use of soybean oil as alternative cutting fluid to soluble oil in machining a mild steel material. Soybean oil and soluble oil (Standard) are used as cutting fluid when machining a mild steel material and their effect on the mild steel material was observed for 70 days. The results of the study shows that the use of soybean oil lead to a slight corrosion of the mild steel than that of the soluble oil used in the time past. The inability of soybean performance at 100% level to that of soluble oil may be due to racidity (decomposition) of soybean oil on the mild steel material, and the heat generated during machining. Although soybean shows a very high correlation (r) (0.782 and 0.730) on the rate of corrosiveness of the metal samples and looked more stable than soluble oil (fig.1) but still needs a further work. The result obtained by using chi-square (x²) also confirmed the above assertion by having soybean (B₁) and soluble oil (S₁) as not significant and soybean (B₂) and soluble (S₂) as significant.

M.O. Osiele¹, I. A. Fuwape² I. A. Ashaolu³

1,2Department of Physics, Federal University Of Technology, Akure
³Department of Physics, Ogun State University, Ago -Iwoye

Abstract. In the jellium model, for electron-positron annihilation to take place, the positron must overcome the screened potential of the valence electrons. In this paper, we develop electron-positron screened pseudopotential to explain positron annihilation rate in metals. The results obtained show that there is a trend in the variation of the screened pseudopotential for metals in the same group in the periodic table and also that the higher the positron annihilation rate in a metal the higher the screened pseudopotential experienced before annihilation.

S. O. Alao¹ and S. F. A. Akande²

1Department of Science Technology, Federal Polytechnic Bauchi, Bauchi
²Department of Physics, University of Jos, Jos

Abstract. Measurements of relative field strength were carried out on the FM Broadcasting frequency of 94.57 MHz of a 20kW transmitter of the Bauchi Radio Corporation. Measurements were taken at regular intervals up to a distance of 70 km along five different routes starting from Bauchi (10.25° N, 9.75° E) in each case. There was a rapid deterioration of the field strength with distance owing to factors such as shadowing or diffraction and meteorological conditions in the lower atmosphere. Coverage gaps existed in shadowed valleys. Fill-in stations are required in regions of poor service to provide limited local coverage. Even when the transmitting antenna has adequate terrain clearance listeners can help improve their own reception by sitting their antenna to minimise local shadowing losses.

A.O. Ologunleko and L. B. Kolawole

Department of Physics, Federal University of Technology, Akure, Nigeria

Abstract. The study of low-latitude electron density profiles has been carried out on a semi-empirical basis with the International Reference Ionosphere (IRI-90) and the CCIR models. Electron density profiles are computed using the median values of ionospheric data routinely scaled from ionograms at Ibadan (7.4⁰N, 3.9⁰E) and Tsumeb (19.2⁰S, 17.7⁰E) for different scalar activities and times of the day. The results of this study revealed the possibility of using analytic semi-empirical models to produce representative electron density profiles of the equatorial and low-latitude ionospheres. The importance of incorporating results of studies on the equatorial anomaly into the IRI-90 model and further comparisons with additional sets of electron density profiles under different solar-geophysical conditions are highlighted. The need for additional ionosonde stations in the African sector in order to incorporate the results of studies on equatorial anomaly into the models is emphasized.