Plastic buckling of ring-stiffened conical shells under external hydrostatic pressure

The paper describes experimental tests carried out on three ring-stiffened cones that were tested to destruction under external hydrostatic pressure. The cones were carefully machined from EN1A Steel. All three cones failed by plastic non-symmetric bifurcation buckling in a mode commonly known as general instability. In this mode the entire ring-shell combination buckles bodily.The paper also provides a design chart using the results obtained from these three vessels, together with the results of six other vessels obtained from other tests. The design chart allows the possibility of obtaining a plastic knock down factor, so that the theoretical buckling pressures, based on elastic theory, can be divided by the plastic knockdown factor, to give the predicted buckling pressure. This method can also be used for the design of full-scale vessels.     

The acquistion and application of basic land use data in urban growth analysis: A case study of Metropolitan Lagos

Basic to the study of urban growth is information on population and land use changes. These basic data are generally lacking in Nigeria. This paper examines and assesses the growth of urban land use of Lagos (the Federal Capital of Nigeria) through a systematic utilization of sequential serial photographs (taken in 1962 at a scale of 1:40,000, and in 1974, at a scale of 1:20,000) and computer techniques. The land use data resulting are then used in evaluating the population growth of Lagos. The resulting population estimate is then compared with the available population data. The study concludes by recommending the use of remote sensing, especially aerial photography for the acquisition of basic urban data not only in Nigeria but also in other developing countries lacking in such data.     

Preliminary Results from the Magnetic Field Measurements Using MAGDAS at Ilorin, Nigeria

MAGDAS, the Magnetic Data Acquisition System, was successfully installed at the University of Ilorin, Nigeria—an equatorial station—in August 2006. MAGDAS is an important component of the International Heliophysical Year, IHY. We examined the preliminary results obtained from the analysis of the geomagnetic data obtained from the MAGDAS measurement. Diurnal variations of the solar quiet daily variation in the three geomagnetic elements, H, D, Z were studied. The obtained signatures of the magnetic field variations were discussed in the context of the literature. The day-to-day variability of the horizontal and vertical intensities as well as the declination of the geomagnetic field were examined. The study justified the need for a partner magnetic field observatory along same meridian as Ilorin, north or south of it, to facilitate synthesis of the equatorial electrojet effect.     

Micrometeorological measurements in Nigeria during the total solar eclipse of 29 March, 2006

The total solar eclipse of 29 March, 2006 which was visible at Ibadan (7.55°N, 4.56°E), south-western Nigeria was utilized to document atmospheric surface-layer effects of the eclipse for the first time in Nigeria. The meteorological parameters measured are global radiation, net radiation, wind speed (at different heights), atmospheric pressure and soil temperature (5, 10 and 30 cm), moisture and heat flux and rainfall. The results revealed remarkable dynamic atmospheric effects. The observations showed that the incoming solar radiation, net radiation and air temperature were significantly affected.There was an upsurge of wind speed just before the first contact of the eclipse followed by a very sharp decrease in wind speed due to the cooling and stabilization of the atmospheric boundary layer. The atmospheric pressure lags the eclipse maximum by 1 h 30 min, while the soil temperature at 5 and 10 cm remain constant during the maximum phase of the eclipse.     

A brief note on remote sensing activities in Nigeria

Abstract

Orbital photography from the Space Shuttle missions (1981–88) and earlier manned spaceflight programs (1962–1975) allows remote sensing time series to be constructed for observations of environmental change in selected portions of the global tropics. Particular topics and regions include deforestation, soil erosion, supersedimentation in streams, lacustrine, and estuarine environments, and desertification in the Greater Amazon, Tropical Africa and Madagascar, South &; Southeast Asia, and the Indo‐Pacific archipelagoes.     

Electron density distribution at fixed heights N(h): Gaussian distribution test

Occurrence probability distribution (Gaussian distribution) test was carried out at selected fixed heights on the electron density profile, N(h), for selected hours around midday and midnight from representative months within 1995 and 1999/2000. The main objective of this work is to investigate the normality of the frequency distribution of the data sets around the mean value. Although the distribution is not perfectly symmetrical about the mean value, the results show that the percentage of data within ±1 standard deviation of the mean is at least 69% between 100 km and the F2 peak height around midday and midnight for all the selected hours and for the two years investigated.     

Assessing the link between Atlantic Niño 1 and drought over West Africa using CORDEX regional climate models

The skill of Coordinated Regional Climate Downscaling Experiment (CORDEX) models (ARPEGE, CCLM, HIRHAM, RACMO, REMO, PRECIS, RegCM3, RCA, WRF and CRCM) in simulating the climate (precipitation, temperature and drought) of West Africa is determined using a process-based metric. This is done by comparing the CORDEX models’ simulated and observed correlation coefficients between Atlantic Niño Index 1 (ATLN1) and the climate over West Africa. Strong positive correlation is observed between ATLN1 and the climate parameters at the Guinea Coast (GC). The Atlantic Ocean has Niño behaviours through the ATLN indices which influence the climate of the tropics. Drought has distinct dipole structure of correlation with ATLN1 (negative at the Sahel); precipitation does not have distinct dipole structure of correlation, while temperature has almost a monopole correlation structure with ATLN1 over West Africa. The magnitude of the correlation increases with closeness to the equatorial eastern Atlantic. Correlations between ATLN1 and temperature are mostly stronger than those between ATLN1 and precipitation over the region. Most models have good performance over the GC, but ARPEGE has the highest skill at GC. The PRECIS is the most skilful over Savannah and RCA over Sahel. These models can be used to downscale the projected climate at the region of their highest skill.     

Variability of Horizontal Magnetic Field Intensity Over Nigeria During Low Solar Activity

Magnetic field intensity of the horizontal component (H) data measured from Magnetic Data Acquisition System (MAGDAS) at Ilorin (geographic latitude: 8.47°N, geographic longitude: 4.68°E, geomagnetic latitude: 1.82°S, geomagnetic longitude: 78.6°S), Nigeria in the year 2009 (a low activity year) was used to study the diurnal, monthly-median and standard deviation of the solar quiet of the horizontal component (S _q H). The diurnal variation of S _q H and its corresponding monthly median variation (MS _q H) shows minima values at pre-sunrise hours between 0500 and 0600 LT. The S _q H value shows a daytime maximum variation range between 20 and 91 nT and a nighttime minimum variation range from 1 to 4 nT. The occurrences of daytime maxima of the S _q H values that were observed in all the months are between the hours of 1000 and 1200 LT. The daytime maximum of the MS _q H values from the entire months were seen at 1100 LT with exceptions of January and December. The month of October has the highest value (61 nT) and the lowest value was observed in December (35 nT). It is clearer that the range in maximums of S _q H and MS _q H variations during the daytime period in all the months is greater than the range in minimums observed at nighttime period (post-sunset and pre-sunrise). The monthly standard deviation (STD) depicts the index of variability of all the day-to-day variations in each month. Counter electrojet (CEJ) events were observed in the morning and as well during the evening hours. The magnitudes and frequencies of CEJ events during the evening hours are greater than that of the morning hours. CEJ seen during the morning period around 0500–0600 LT is the consequence of late reversals of nighttime westward currents to daytime eastward currents. A semi-annual variation with peak values during March, April, September and October was observed. Seasonal variation that was characterized with CEJ was also investigated.     

Variability of daily precipitation over Nigeria

This study identified coherent daily precipitation regions in Nigeria by analyzing the spatial and temporal homogeneity of daily precipitation; investigating the dependence of wet day amount (WDAMT) and percentage of wet day (PWD) on latitude, longitude, elevation and distance from the ocean and finally regionalizing the daily precipitation stations. Non-parametric spatial homogeneity test was carried out on daily precipitation over 23 stations in Nigeria between 1992 and 2000 while the temporal analysis was done from 1971 to 2000. Regression analysis was used to determine the dependence of WDAMT and PWD on latitude, longitude, elevation and distance from the ocean. Principal component and cluster analyses were conducted to regionalize the precipitation stations. Seven homogeneous groups of stations were identified. Elevation explains 19.9 and 4.8 % of the variance in WDAMT and PWD, respectively, while latitude explains 76.2 % of variance in PWD. Eight principal components that explain 63.1 % of the variance in the daily precipitation data were retained for cluster analysis. Precipitation in the six daily precipitation regions that emerged from the cluster analysis is influenced by the Inter-tropical Convergence Zone, latitude, distance from ocean and southwesterlies while the northern region alone is influenced by the African Easterly Wave. In addition, precipitation in all the regions is influenced by topography. Low to medium spatial coherence exists in the precipitation regions. The spatial variations of PWD and WDAMT have implications for agricultural productivity and water resources in different parts of the country.