Thomas J. Afullo

The effect of electromagnetic radiation in the mobile phone range on the behaviour of the rat.

Electromagnetic radiation (EMR) is emitted from electromagnetic fields that surround power lines, household appliances and mobile phones. Research has shown that there are connections between EMR exposure and cancer and also that exposure to EMR may result in structural damage to neurons. In a study by Salford et al. (Environ Health Perspect 111:881–883, 2003) the authors demonstrated the presence of strongly stained areas in the brains of rats that were exposed to mobile phone EMR. These darker neurons were particularly prevalent in the hippocampal area of the brain. The aim of our study was to further investigate the effects of EMR. Since the hippocampus is involved in learning and memory and emotional states, we hypothesised that EMR will have a negative impact on the subject’s mood and ability to learn. We subsequently performed behavioural, histological and biochemical tests on exposed and unexposed male and female rats to determine the effects of EMR on learning and memory, emotional states and corticosterone levels. We found no significant differences in the spatial memory test, and morphological assessment of the brain also yielded non-significant differences between the groups. However, in some exposed animals there were decreased locomotor activity, increased grooming and a tendency of increased basal corticosterone levels. These findings suggested that EMR exposure may lead to abnormal brain functioning.

RAINDROP SIZE DISTRIBUTION MODELING FOR RADIO LINK DESIGN ALONG THE EASTERN COAST OF SOUTH AFRICA

A study of the raindrop size distribution along the eastern coast of South Africa (Durban) is presented. The Biweight kernel estimator based on distometer measurement is used to determine the best estimate of the measured raindrop size probability distribution function (pdf). The best kernel estimator, which results in the lowest integral square error (ISE), is used to measure the closeness of the estimated lognormal and gamma pdf of raindrop size to the measured raindrop size distribution. It is established that the optimised lognormal pdf slightly outperforms the optimised gamma pdf in terms of the mean ISE and the RMSE values, with mean ISE values of 0.026 for lognormal and 0.04 for gamma distributions, respectively, and corresponding mean RMSE values of 0.073 and 0.081, respectively. The method-of-moments gamma and lognormal distributions are observed to be worse estimators of the measured pdf than the two optimized distributions. The N(D) distributions using the optimised lognormal and gamma distributions for the region are compared with those for difierent tropical regions, namely, India, Singapore, Nigeria, Indonesia, and Brazil. While the Indian lognormal N(D) model gives the highest peak for low raindrop sizes for all rain rates, Durbans gamma and lognormal models exhibit the widest raindrop size spread over all rain rates ranging from 1{120mm/h. Finally, the speciflc attenuation due to rain using the Durban models are compared against the ITU-R models and actual measurements over a 19.5GHz LOS link; the results indicate a need for further work involving both distrometer and radio link measurements for rain rates exceeding 30mm/h in the eastern coast of South Africa.

Seasonal Distribution Modeling and Mapping of the Effective Earth Radius Factor for Microwave Link Design in South Africa

In this paper we present seasonal results of the efiective earth radius factor distribution in South Africa using recently (2007{ 2009) acquired radiosonde data from the South African Weather Service (SAWS) for seven locations in South Africa. Two data modeling methods are used to formulate the solution for the distribution of the efiective earth radius factor. The seasonal efiective earth radius factor statistics obtained from the radiosonde measurements are then interpolated, gridded and presented in contour maps to cover the rest of the country for the four seasons deflned by ITU-R recommendation P.453-10. The Integral of Square Error is used to check the performance of the data modeling techniques while the Root Mean Square Error is used to compare the performance of the difierent interpolation methods used.

Characteristics of rainfall queues for rain attenuation studies over radio links at subtropical and equatorial Africa

Attenuation due to precipitation remains an important design factor in the future deployment of terrestrial and earth-space communication radio links. Largely, there are concerted efforts to understand the dynamics of precipitation in attenuation occurrence at subtropical, tropical, and equatorial region of Africa. In this deliberate approach, rainfall spikes pertaining to rain cells are conceptualized as distinct rain spike traffic over radio links, by applying queueing theory concepts. The queue distributions at Durban (29°52′S, 30°58′E) and Butare (2°36′S, 29°44′E)—respectively, of subtropical and equatorial climates—are investigated from distrometer measurements. The data sets at both sites are observed over four rain regimes: drizzle, widespread, shower, and thunderstorm. The queue parameters of service time and inter-arrival of rain spikes traffic at both regions are found to be Erlang-k distributed (Ek) and exponentially distributed (M), respectively. It is established that the appearance of rain rates over radio links invariably follows a First Come, First Served (FCFS), multi-server (s), infinite queue, and semi-Markovian process, designated as M/Ek/s/∞/FCFS discipline. Modeled queue parameters at both regions are found to vary significantly over different regimes. However, these queue parameters over the entire data set suggest similar queue patterns at both sites. More importantly, power law relationships describing other queue-related parameters are formulated. The paper concludes by demonstrating an application of queueing theory for rainfall synthesis. The proposed technique will provide an alternative method of estimating rain cell sizes and rain attenuation over satellite and terrestrial links.

THREE - PARAMETER RAINDROP SIZE DISTRIBUTION MODELING FOR MICROWAVE PROPAGATION IN SOUTH AFRICA

This paper considers the estimation of the three-parameter raindrop size distributions in Durban, South Africa. The two models- modified gamma and lognormal distribution models compare reasonably well with the measured data and are both suitable for the modeling of raindrop size distributions in the region and for computation of specific attenuation. The method of moments is adopted for the estimation of the parameters. The models are compared with the ITU-R model at frequencies of 2-150 GHz. From the performance analysis of the estimated error, the deviations of the models from the measured data are minimal. The three-parameter lognormal distribution model however gives a better performance when compared with the modified gamma distribution model and the ITU-R.

Path reduction factor modeling for terrestrial links based on rain cell growth

A new path length reduction factor that accounts for the growth and occurrence of multiple rain cells along a propagation path of a given terrestrial link is introduced in this work. In addition, the mathematical and empirical derivations that were used to come up with this new factor are outlined. This model is investigated by comparing it to other well-known models by utilizing attenuation statistics from a 19.5 GHz terrestrial link experiment carried out in Durban, South Africa. The predicted and measured attenuation values are then compared for the three models. Evaluation of the three models is then carried out by calculating their attenuation percentage error values. It is seen that the proposed model performs well over the ITU-R model in the terrestrial link thus validating it as a good model for rain attenuation predictions in the Southern Africa region.

Rain attenuation prediction along terrestrial paths in South africa using existing attenuation models

Different rain attenuation prediction models proposed by different authors on terrestrial paths are presented. These models are used to estimate the rain attenuation in different climatic rain zones in South Africa. In our previous paper, four new climatic rain zones N, M, P and Q are proposed from the locally observed data as against the ITU-R zones of C, D, E, K and N. The specific rain attenuation gammaR (dB/km) for frequencies up to 50 GHz is computed using a 1-minute integration time rain rate exceeded for 0.01% of the time for these 4 different climatic rain zones from an available 5-year local rain rate data. Finally, the rain attenuation A0.01 (dB) exceeded for 0.01% of the time is estimated and predicted for different geographical locations that are within these climatic rain zones based on the comparison of the different existing attenuation models at different frequencies for path lengths not exceeding 22 km.

Use of spatial interpolation technique for determination of geoclimatic factor and fade depth calculation in Southern Africa

Different authors have adopted various techniques to resolve the clear-air radio-propagation effect problems. These authors have presented different modeling techniques based on the radio propagation variables of the region in question. These variables are determinable from the local radio propagation data of the region in question. This paper uses the radiometeorological data collected in Durban, South Africa and in Maun, Botswana to determine the geoclimatic factor (K) variable. This is then used in implemented link designs to calculate the fade depth and worst month for these two locations.

Effective Earth radius factor characterization for line of sight paths in Botswana

The ITU has adopted new methods for predicting the deep-fading distribution due to multipath propagation for the average worst month over UHF and SHF terrestrial line-of-sight links. These methods employ refractivity gradient statistics available from world maps, and are recommended for application in all regions of the world. In this regard, significant progress in the global climatological modeling of the main propagation effects in clear-air and precipitation conditions have been reported (Olsen, R.L. and Tjelta, T., IEEE Trans. Anten. and Propag., vol.47, no.1, 1999; Olsen, Proc. 3rd Regional Workshop on Radio Communications in Africa, 1999), with an attempt to relate the results to the African continent. D.C. Baker and A.J. Palmer (see Trans. SAIEE, vol.93, 2002) have proposed a model for the cumulative distributions of the fraction of times of occurrence for certain values of the k-factor for South Africa. They have assumed, based on earlier reports, that a normal distribution for the pdf of the k-factor is appropriate. We develop an empirical model for the k-factor distribution based on radiosonde data for Botswana. We model the distribution for the months of February, May, August and November, as per ITU-R practice, at height ranges of 0-500 m and 0-200 m above ground level

The Critical Diameters for Rainfall Attenuation in Southern Africa

This paper investigates the in∞uence of critical raindrop diameters on the speciflc rain attenuation in Durban (29 - 52 0 S, 30 - 58 0 E), South Africa. The total rainfall attenuation is evaluated by integrating over all the raindrop sizes and the difierential change in the attenuation is observed over a given range of drop size diameters. The major contribution to the speciflc attenuation for the drop size distribution (DSD) models considered is created by the raindrop diameters not exceeding 2mm especially at higher frequencies. The three parameter lognormal and gamma distribution models are employed for the purpose of analysis. For the DSD models considered in this work, the total percentage fraction created by raindrops in the diameter range 0:5mmD • 2:5mm and 1mmD • 3mm to the total speciflc attenuation is found to be critical for the overall and seasonal rainfall attenuation at 2.5GHz{ 100GHz in Durban. It is observed that the total speciflc attenuation increases with increased frequencies and a higher rainfall rate produces high rain attenuation. In this paper, both the overall and seasonal values of R0:01 determined for Durban are used.