BPSK subcarrier intensity modulated free-space optical communications in atmospheric turbulence

Free-space optical communications (FSO) propagated over a clear atmosphere suffers from irradiance fluctuation caused by small but random atmospheric temperature fluctuations. This results in decreased signal-to-noise ratio (SNR) and consequently impaired performance. In this paper, the error performance of the FSO using a subcarrier intensity modulation (SIM) based on a binary phase shift keying (BPSK) scheme in a clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the probability density function (pdf) of the received irradiance after traversing the atmosphere is modelled using the gamma-gamma distribution while the negative exponential distribution is used to model turbulence in the saturation region and beyond. The effect of turbulence induced irradiance fluctuation is mitigated using spatial diversity at the receiver. With reference to the single photodetector case, up to 12 dB gain in the electrical SNR is predicted with two direct detection PIN photodetectors in strong atmospheric turbulence

BER and outage probability of DPSK subcarrier intensity modulated free space optics in fully developed speckle.

In this paper a differential phase shift keying (DPSK) subcarrier intensity modulated (SIM) free space optical (FSO) link is considered in negative exponential atmospheric turbulence environment. To mitigate the scintillation effect, the selection combining spatial diversity scheme (SelC) is employed at the receiver. Bit error rate (BER) and outage probability (Pout) analysis are presented with and without the SelC spatial diversity. It is shown that at a BER of 10-6, a maximum diversity gain 25 dB is predicted. And about 60 dBm signal power is required to achieve an outage probability of 10-6, based on a threshold BER of 10-4

Effects of Some Selected Macro-Economic Indicators on Exchange Rates (1986-2019)

Background: The foreign exchange market plays a significant role in the development of a country and the stability of her currency in recent years. Objectives: This article reports the effect of macro-economic indicators on foreign exchange parallel markets for a period between 1986 – 2019. Methods: The macro-economic indicators used were inflation rate, demand for money, the supply of money, OPEC crude oil and the real GDP growth with the dependency of the foreign exchange market. The data for this project was extracted from the publication of the Statistics Unit of the Central Bank of Nigeria in recent years. Multiple Linear Regression was used with special attention on Multicollinearity, Serial Correlation and Heteroscedasticity. The coefficient of determination value of 0.740 shows that the demand for money, the supply of money, OPEC crude oil and the real GDP growth accounted for over 74 percent of the variation in the exchange rate in Nigeria between the years 1986 and 2019. Results: It was discovered from the findings that, money supply into the circulation determines the foreign exchange rate. And it was also discovered that the money supply has a high dependency ratio on the exchange rate among other macro-economic indicators. Thus, the reduced model is a result of the insignificancy of other variables while only variable two (supply of money) is significant. Conclusions: The use of a flexible exchange rate had eliminated the over-valuation of the naira. The parallel market premium has also been narrowed from 600 percent in 1986 to about 11.0 percent in 2018. These were attributed to the weak and import-dependent production structure of the economy. The suggested solution was articulated towards increasing foreign exchange inflows, reducing demand, as well as reforming the foreign exchange market to evolve a more realistic exchange rate for the naira.  Keywords: Multiple Linear Regression, Macro-Economic Indicators, Exchange Rate, Multicollinearity, Serial Correlation and Heteroscedasticit

Atmospheric channel effects on terrestrial free space optical communication links

Abstract. This paper illustrates the challenges imposed by the atmospheric channel on the design of a terrestrial laser communication link. The power loss due to scattering effect is described using the Kim/Kruse scattering model while the effect and the penalty imposed by atmospheric turbulence is highlighted by considering the bit error rate (BER) of an On-Off Keying modulated link in an optical Poisson channel. The power loss due to thick fog can measure over 100 dB/km while snow and rain result in much lower attenuation. We show that non-uniformity in the atmospheric temperature also contributes to performance deterioration due to scintillation effect. At a BER of 10-4, for a channel with a turbulence strength of>0.1, the penalty imposed by turbulence induced fading is over 20 photoelectron counts in order to achieve the same level of performance as a channel with no fading. The work reported here is part of the EU COST actions and EU projects.

Sino-Africa Trade Relations

This paper briefly covers the economic relations between China and Africa as China’s amazing economic growth dramatically increases its dependence on fuel and raw materials - readily (and cheaply) available in developing countries, such as those in the African continent

Integrity of offshore structures

Corrosion and fatigue have been dominant degradation mechanisms in offshore structures, with the combination of the two, known as corrosion fatigue, having amplified effects in structures in the harsh marine environments. Newer types of structure are now being developed for use in highly dynamic, harsh marine environments, particularly for renewable energy applications. However, they have significantly different structural details and design requirements compared to oil and gas structures, due to the magnitude and frequency of operational and environmental loadings acting on the support structures. Therefore, the extent of corrosion assisted fatigue crack growth in these structures needs to be better understood. In this research, fatigue crack growth in S355J2+N steel used for offshore wind monopile fabrications was investigated in air and free corrosion conditions. Tests were conducted on parent, HAZ and weld materials at cyclic load frequencies similar to what is experienced by offshore wind monopile support structures. The seawater used for testing was prepared according to ASTM D1141 specifications and was circulated past the specimens through a purpose designed and built corrosion rig at a rate of 3 l/min, at a temperature of 8-100C and at a pH of 7.78-8.1. A new crack propagation method accompanied by constant amplitude loading was used. Crack growth rates in parent, HAZ and weld materials were significantly accelerated under free corrosion conditions, at all the stress ratios used compared to in air environment. However, in free corrosion conditions, crack growth rates in the parent, HAZ and weld materials were similar, particularly at a lower stress ratio. The results are explained with respect to the interaction of the loading condition, environment and the rate of material removal by corrosion in the weldments. A new model was developed to account for mean stress effects on crack growth rates in air and in seawater, and was found to correlate well with experimental data as well as with the other mean stress models tested

Soil nitrogen fluxes and root uptake in the boreal forest

Nitrogen (N) is essential for growth and net primary production of plants. However, N acquisition by plants is influenced by movement of soil N compounds from bulk soil to plant roots and uptake of N by roots. This thesis is aimed at deepening our knowledge on these key processes involved in plant N acquisition in the N-limited boreal forest. To address this aim, a novel, non-invasive microdialysis technique was employed. Amino acids dominated N fluxes in the boreal forest soils. Further, plant roots were shown to have the capacity to absorb organic and inorganic N present in the measured soil fluxes, but these soil fluxes, rather than root uptake, may limit plant N acquisition. The microdialysis technique was further developed to enable simultaneous estimation of diffusion and mass flow of N in soil. Applying this refinement of the technique in the field showed that mass flow significantly increased flux rates of soil N in the boreal forest ecosystem, and that it also altered the chemical composition of the N fluxes. The results from the studies presented in this thesis highlight the potential of the microdialysis technique to improve our understanding of the intrinsic processes involved in N acquisition by plant roots. They also suggest that amino acids might comprise an important source of N for plants in the boreal forest ecosystem. The results suggest that mass flow plays an important role for plant N acquisition in the boreal forest, and mass flow might increase the share of nitrate, particularly in nutrient-rich ecosystems. This finding opens a discussion on the role of transpiration in plant N nutrition, with implications for our understanding of how plant N nutrition will be affected by, among other things, elevated CO2, increased temperatures, and N fertilization

Impact of Poor Reading Culture among Selected Secondary School Students in Owo Local Government Area of Ondo State, Nigeria

The study identified reading as the ability to obtain meaning from words. Reading culture refers to habitual and regular reading of books and information materials. Hence, the study investigated the effects and remedies of poor reading culture among secondary school students in Owo Local Government Area of Ondo State. This study was a descriptive survey design which involved the use of questionnaire to obtain information from teachers and students from four selected secondary schools in Owo Local Government Area of Ondo State, Nigeria. The population of the study was one hundred and twenty while the sample of twenty five students was randomly selected from the students and twenty teachers were also selected from four secondary schools in Owo Local Government Area of Ondo State, Nigeria. The data collected were analyzed quantitatively using simple percentage. Results of the findings of the study indicated that majority of the respondent were of the opinion that students from educated home read fluently than students from uneducated home, it also revealed that 80% of the respondent believed that parent’s inability to set high standard for students affects their reading performance, it also indicated that students do not read as much as they are expected to read, and also students do not have well-equipped libraries to aid effective reading performance. The study confirmed that reading habit has influence on academic performance and there is a relationship between reading culture and academic performance. In view of this, the study recommended among others that parents should be active and establish libraries at home where early reading culture can begin and also set high standard of reading for their children and also motivate them to read on daily basis, government should equip the libraries in the secondary schools and stock them with up-to-date books, particularly on reading, provision of more public libraries in all nooks and crannies of the country where reading can take place. Keywords: Poor Reading, Culture, Students, Secondary Schools