Showing papers in "International Journal of Physical Sciences in 2018"

Green synthesis of silver monometallic and copper-silver bimetallic nanoparticles using Kigelia africana fruit extract and evaluation of their antimicrobial activities

Abstract: Aqueous extract of Kigelia africana fruits have been utilized in the syntheses of silver nanoparticles (AgNPs) and copper-silver bimetallic nanoparticles (Ag-CuNPs). The synthesized nanoparticles have been characterized using UV-vis, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), x-ray diffration (XRD) and transmission electron microscopy (TEM). The antimicrobial activities have been evaluated against both Grams-negative and Grams-positive strains of bacteria and fungus. The UV-vis and FTIR techniques revealed the formation of nanoparticles and the active components were adsorbed on the surface of the particles thereby stabilizing the nanoparticles. The SEM reveals uniform microspheres of AgNPs and anisotropic particles for AgCuNPs. TEM shows a particle size of 10 nm. The nanoparticles inhibit the growth of both Grams-negative and Grams-positive bacteria. The present nanoparticles synthesized from aqueous extract of K. africana fruits inhibits Klebsiella pneumoniae more than any of the antibiotics tested in this study. It competes very well with augmentin against Pseudomonas aeruginosa and with meropenem against Candida albicans with inhibition zones of 23 and 25 mm, respectively. The bimetallic nanoparticles have demonstrated effectiveness against Staphylococcus aureus, with maximum inhibition zone of 27 mm. Key words: Green synthesis, bioreduction, nanoparticles, bimetallic particles, Kigelia africana, antimicrobial activities.

Theoretical models for prediction of methane production from anaerobic digestion: A critical review

Abstract: This work presents a critical analysis for three models group of methanogen potential prediction. The first group allows determination of the methane productivity of substrates, through three models (BMPthCOD, BMPthAtC and BMPthOFC). The BMPthCOD is suitable for a first approximation calculation. BMPthAtC and BMPthOFC are more accurate; however, require a complex characterization of substrates. The second models group predicts the cumulative methane production using seven models. The analysis shows that the Artificial Neuron Network (ANN) is more accurate; moreover, it allows carrying out an optimization of the cumulative methane production. The third group of models is particularly involved in the determination of daily flow of methane by a biodigester. The Hashimoto model, which uses the operating parameters, has been identified as the most suitable. Key words: Biochemical methane potential (BMP), anaerobic digestion, kinetics, methane production, artificial neuron network (ANN), substrate.

Assessment of outdoor radiation levels and radiological health hazards in Emene Industrial Layout of Enugu State, Nigeria

Abstract: A study to assess the outdoor Background Ionizing Radiation (BIR) levels in Emene Industrial Layout of Enugu State, Nigeria has been conducted. An in-situ measurement of BIR exposure rate in mRh-1 for 30 locations was done using a well calibrated portable GQ GMC-320 PLUS nuclear radiation detector at an elevation of 1.0 m above ground level with a geographical positioning system (GPS) for geographical location. The measured BIR exposure rates were used to evaluate the radiological health hazards and radiation effective doses to different body organs using well established radiological relations. The obtained values were compared with recommended permissible limits to ascertain the radiological health status of the environment. The mean values of BIR exposure levels (0.015±0.001 mRh-1), absorbed dose rates (126.15±5.10 ηGyh-1) and excess lifetime cancer risk (0.541±0.032×10-3) are higher than their recommended safe limits of 0.013 mRh-1, 84.0 ηGyh-1, 0.29×10-3 respectively as recommended by ICRP and UNSCEAR. The mean annual effective dose equivalent (0.155±0.006 mSvy-1) is within recommended permissible limits of 1.00 mSvy-1 for general public exposure. Also, the effective doses to different body organs are all below the recommended limits of 1.0 mSvy-1. Generally, the study shows that Emene Industrial Layout is radiologically contaminated due to industrial activities taking place. However, the contamination does not constitute any immediate radiological health effect on resident of the area but there is the potential for long-term health hazards in the future such as cancer due to accumulated doses. Key words: BIR exposure level, effective dose, industrial activities, Emene Industrial Layout.

Study of the performance of a system for dry cleaning dust deposited on the surface of solar photovoltaic panels

Abstract: This study was carried out at the International Center for Training and Research in Solar Energy (CIFRES) and its main purpose was to study the performance of a solar module cleaning system. To handle this work, a measuring platform consisting of two polycrystalline (pc-Si) PV modules was designed. The modules were connected to a waterless cleaning system on the surface of the solar panels. The platform also contained a temperature sensor on the surface of the module, a pyranometer, shunt resistors (for current measurement), and an acquisition unit. This platform was exposed under real conditions and measurements of the parameters were taken in increments of ten seconds. Only one of the two modules was cleaned daily, and an evaluation of the degradation rate of the short-circuit current (Isc) of the dust module with respect to the cleaned module was carried out. After one month of exposure, the analysis of the results showed a degradation rate of 17.13% of the short circuit current (Isc) of the dirty module compared to the clean module. Compared to the initial conditions under the standard test conditions, a degradation of 10.16 and 24.09%, respectively for the clean module and the dirty module was obtained. This work also showed that a polynomial relation exists between the degradation rate and the dust deposition density with a coefficient of determination of 0.9933. Key words: Photovoltaic modules, dust, short-circuit current, impact, automatic cleaning without water, degradation.

Noise exposure levels and health implications on daily road side petty traders at some major roundabouts in Ibadan, Nigeria

Abstract: The level of noise exposure to daily road side traders at five major roundabouts in Ibadan metropolis was assessed. Noise measurements were made using a precision multi-function sound level meter. Measurements were made at three different periods of the day; morning (7:30 to 11:30 a.m.), afternoon (12:00 to 3:00 p.m.) and evening (4:00 to 5.00 p.m.) for a consecutive period of ten days. The highest mean maximum noise levels of 87.19 dBA (evening), 87.14 dBA (morning) and 87.35 dBA (afternoon) were obtained at Ojo, Iwo road and Dugbe roundabouts respectively while all the lowest mean minimum noise level for the periods of measurements were obtained at Sango roundabout. The results obtained were within the safe recommended 90 dBA for an 8 h exposure noise level by Occupational Safety and Health Administration. However, longer periods beyond 8 h may portend deleterious acoustic effects to these traders given the peculiar nature of the daily road side business activities and also being close to sources of noise from vehicles at these roundabouts Key words: Noise exposure level, roundabout, noise health effects, road side petty traders.

Seven-dimensional space-time and its objects: Arbitrary spin state, electromagnetic fields, mirror symmetry and superconductivity

Abstract: To form the basis spin states of a field, vector states of the multicomponent wave function to the four coordinates of Minkowski space that determine the position of the local observer have been added by angular extra dimensions that determine the orientation of the local observer. The generators of the Poincare group in the angular representation have been obtained. The Dirac equation (generalized for any spin) and Maxwell’s equation have been designed from these generators. In the framework of transformations of the Lorentz group in angular representation united with its transpose representation, the transformations of the (generalized) Dirac equations that is similar to the Heaviside-Larmor transformations for Maxwell’s equations have been performed. As a result, the Dirac equation for the Dirac monopole, which corresponds to a particle with mirror symmetry have been obtained. Indication of a low probability of the existence of the Dirac monopole had been obtained. Key words: Spinor representation of the Poincare group, seve¬n dimensions of space-time, mirror symmetry.

Mineralogical and geochemical properties of clay deposits in parts of Southeastern Nigeria

Abstract: The rocks underlying many parts of Southeastern Nigeria had undergone extensive alterations to form considerable clay deposits. The mineralogical compositions of some of these clay deposits were evaluated with the X-Ray Diffraction (XRD) method to ascertain the suitability of the deposits as raw materials. Results of the analyses indicated that kaolinite (Al2Si2O5 (OH)4) is the dominant clay mineral. Traces of bentonite and dickite were also observed, while the identified non-clay minerals were quartz and iron. Chemical analysis of the clays revealed the predominance of SiO2, Al2O3, Fe2O3 and TiO with values ranging from 31.70 to 56.45%, 19.30 to 29.30%, 3.11 to 29.42% and 2.21 to 7.04%, respectively, while the compositions of CaO, MgO, Na2O, and MnO in the analyzed samples were relatively lower with values ranging from 0.19 to 0.29%, 0.13 to 0.19%, 0.11 to 0.70% and 0.01 to 0.03%, respectively. The Al2O3/TiO2 ratio (3.7 to 13.5) of the studied clays indicated a mafic to intermediate igneous rock origin. Binary plots of TiO2 versus Al2O3 to distinguish between granitic and basaltic sourced clays indicated basalt-rhyolite/granite provenances. The high chemical index of alteration (95.8%), chemical index of weathering (98.3%) and low contents of alkali and alkali earth elements (averaging 0.11%) of the clay-rich sediments, is indicative of a relatively intense weathering source area. The SiO2-K2O/Na2O plots suggested that the sediments in the study area were deposited between passive and active continental margins. In comparison with other reference clays and standard specifications, the clay deposits in the study area possess characteristics satisfactory for economic and some engineering purposes. Key words: Chemical, clay, deposits, economic, mineralogical, potentials, provenance.

Comparative study of commercial gas with biogas produced from co-digestion of corn cob, rice chaff, goat and dog dungs

Abstract: Investigations were conducted to compare gas produced from co-digestion of corncob, rice chaff, goat dung and dog dung with commercial gas. The study was carried out anaerobically at a temperature of 29.5 to 33°C (mesophilic condition) in a mini laboratory digester (bioreactor) fabricated using guage 16 metal sheets with 80-L capacity for a 90-day retention time. The shredded corn cob and rice chaff were mixed with water at ratio 4:1 (waste to water) and 3:1 (waste to water) respectively and mixed with goat and dog dungs at ratio 2:1 (waste to water). The control sample collected from a domestic cooking gas cylinder contained 56.12% CH2, 0.14% NH3, 0.22% CO, 0.23% H2S and 43.20% CO2. The result obtained for the biogas analysis shows that Sample E (75:25) contains 63.54% CH4, 0.93% NH3, 0.84% CO, 0.54% H2S, 34.12% CO2. The value recorded for sample E represented the highest value obtained among the samples. Also the gas composition shows a good substitute for commercial gas. Key words: Corn cob, rice chaff, goat dung, dog dung, biogas, commercial gas, bioreactor and digestates.

Magnetosphere convection electric field (MCEF) time variation from 1964 to 2009: Investigation on the signatures of the geoeffectiveness coronal mass ejections

Abstract: The signatures of the geoeffectiveness solar disturbed events on the Magnetosphere Convection Electric Field (MCEF) universal time variation from 1964 to 2009 are investigated. Here, attention is focused our on the periods concerned by the whole shock activity and by the different types of the geoeffectiveness Coronal Mass Ejections (CMEs) which are one-day-shock, two-days-shock and three-days-shock. The investigation is made with respect to the orientation of the Interplanetary Magnetic Field (IMF). The MCEF time profiles show three different trends except for one-day-shock activity and for three-days-shock activity where we have four trends and one trend, respectively. The MCEF time profiles of the whole disturbed activity, the all shock activity and the one-day-shock activity present the initial phase where the Interplanetary Magnetic Field (IMF) is southward. During the two-days-shock activity, the initial phase of the MCEF shows a non-sensitive trend to the change of the direction of the IMF z-component while for the three-days-shock activity, the MCEF always exhibits the signature of the northward IMF. The last trend of the MCEF time profile shows the southward IMF signature except for the one-day-shock and the three-days-shock activities where that of the northward IMF was seen. Key words: Magnetosphere convection electric field, interplanetary magnetic field, shock activity, coronal mass ejections (CMEs).

Gross alpha and beta activity concentrations in soil and some selected Nigerian food crops

Abstract: Gross alpha and beta activity concentrations in soil, cassava and fluted pumpkin (leaf and stem) were investigated using a gas flow proportional counter. The gross alpha activity concentrations for the fluted pumpkin were between 3.55 and 13.95 Bq/Kg and 3.53 and 3.61 Bq/Kg for the leaves and stems, respectively. The gross alpha activity concentrations for cassava and soil samples ranged from 0.07 to 0.60 Bq/Kg and 0.35 to 0.53 Bq/Kg, respectively while the gross beta activity concentrations ranged from 0.43 to 0.89 Bq/Kg and 0.46 to 1.04 Bq/Kg for the cassava and soil samples, respectively. The gross alpha and beta activity concentrations in cassava, fluted pumpkin and soils samples have been determined using alpha/beta spectroscopy. The result of thestudy showed that the Iva-valley coal mine area has lower gross alpha and beta activity concentrations compared to other areas of the country. This shows that the coal mining activities in the area may not have increased the radiation burden of the area. Key words: Gross, alpha, beta, concentration, activity, food, crop.

Simulation of the impact of climate change on peanut yield in Senegal

Abstract: This paper treats the impacts of climate change on peanut yield in Ziguinchor (Southwest of Senegal) during the near future (2021 to 2050) and the far future (2071 to 2100). The Decision Support System for Agrotechnology Transfer (DSSAT) crop model was run using daily weather data (maximum and minimum surface temperature, rainfall and solar radiation) of four (4) regional climate models (RCMs) of the Coordinated Regional Climate Downscaling Experiment (CORDEX). Two climate change scenarios (RCP4.5 and RCP8.5) are used to assess the climate change impact on peanut yield. First of all, the DSSAT crop model is calibrated and validated for peanut using relevant observed data: peanut yield and meteorological data. Compared to the reference period (1976 to 2005), the RCMs exhibit some disparities in the projected rainfall during the near and the far future. The ensemble mean of the models (Ens/RCMs) predict a strong decrease of rainfall under the RCP4.5 scenario and a slight decrease under the RCP8.5 scenario during both periods. A gradual increase in mean temperature is predicted by all models. However, this increase is stronger for the RCP8.5 scenario. Analysis of the yield change during the near future shows a decrease for all RCMs except RACMO22T model under the two considered scenarios. During the far future, all RCMs predict a decrease of the peanut yield. Moreover, this decrease is stronger for the RCP8.5 scenario. These results indicated that the peanut crop could be negatively affected by the climate change and adaptation strategies are needed to protect this sector. Key words: Climate change, Regional Climate Models, Coordinated Regional Climate Downscaling Experiment (CORDEX), Decision Support System for Agrotechnology Transfer (DSSAT), peanut.

Comparative analysis of physical and chemical characteristics of selected clays deposits found in Kebbi State, Nigeria

Abstract: The intent of this paper was to explore the physical and chemical characteristics of clays in Kebbi State, Nigeria, and the clays were compared with standard clay which is considered with highest quality standard in casting. Clay’s deposits from Dukku River along River Rima, Jega River which is the tail end of River Niger and Yauri were investigated for their potentials as raw materials used for casting and ceramic industries. Samples were collected from three local governments’ areas at the bank of the Rivers. Chemical analyses of individual clay were determined by employing four different techniques as follows; Complexiometric Titration, Atomic Absorption Spectrophotometer (AAS), X-Ray Diffraction (XRD), and X-Ray Fluorescence (XRF). The data collected from the analyses revealed that the structures of clay minerals were mainly kaolinite, Smectite (bentonite), and illite, and non-clay minerals for the three places were mainly quartz, feldspars and gibbsite. The results obtained revealed high silicate clays and moderate alumina content with trace elements of oxides (Fe2O3, CaO, K2O, TiO2, MgO, MnO, Na2O) also present within acceptable limits. Physical tests results at 900°C and 1300°C were used to determine firing shrinkage, colour, and modulus of rupture, bulk modulus, apparent density, crack formation, apparent porosity, water absorption, and bulk densities. The modulus of rupture, bulk densities, and fired linear shrinkage of all the samples increase with increasing firing temperature. The findings of this work revealed that the clays minerals from Dukku and Yauri had the necessary properties for the foundry work and refractory applications, but clays from Jega, can be exploited for commercial purposes after beneficiation by reducing the level of iron, quartz and other impurities. Key words: Clay minerals, chemical analysis, firing characteristics, oxides.

A comparative study of maximum power point tracker approaches based on artificial neural network and fuzzy controllers

Abstract: The performances of a photovoltaic (PV) module connected to a load through a conversion stage (chopper, inverter) are linked to the average electricity output including the delivered power. Nevertheless, the efficiency depends on atmospheric parameters as temperature, irradiance, and wind speed. To make electrical power available, Maximum Power Point Trackers (MPPT) algorithms are developed to keep up the PV module at optimal operating point with regard to climatic variations. This paper proposes an assessment of Artificial Neural Networks model based on MultiLayer Perceptron (MLP) and Radial Basis Function (RBF). A comparative study with an Adaptive Neuro-Fuzzy Inference System and a hybrid neural network RBF/MLP is done using measured data to optimize the maximum power point of a photovoltaic generator. Key words: Multilayer perceptron, radial basis function, maximum power point trackers, neuro-fuzzy.

Energy and exergy analysis of a solar photovoltaic module performance under the Sahelian Environment

Abstract: This work focuses on the performance study of a photovoltaic solar module based on energy and exergy analysis. The experimental data were obtained by precise measurements during a clear sky day March 20, 2018 and a cloudy day March 27, 2018 in the Laboratory of Chemistry and Materials Physics (LCPM) at the Assane Seck University of Ziguinchor, Senegal (12° 34 N, 16° 16 E). Exergy, energy and power conversion efficiency were evaluated for the two days based on measured parameters such as solar intensity, ambient temperature and module temperature. We find that the exergy efficiency varies between 4.5 and 8.93%, the energy efficiency varies between 11.08 and 14.50% and the power conversion efficiency varies between 7.98 and 10.49% throughout the day in the clear sky. While for the cloudy day the exergy efficiency varies between 2.00 and 9.45%, the energy efficiency ranges from 12.41 and 14.5% and the power conversion efficiency varies between 8.93 and 10.46%. Key words: Exergy, energy, photovoltaic module, performance analysis, efficiency, thermal exergy.

Correlation of geotechnical parameters with geological formations in a basement complex and its implications on civil structure foundation

Abstract: Geotechnical tests were carried out on twenty subsoil samples obtained from ten locations at the depth of 1 and 2 m within Federal University of Technology, Akure, Nigeria. The area is typical of basement complex. The test include; Natural Moisture Content, Grain Size Analyses, Specific Gravity, Atterberg Limits, Compaction, California Bearing Ratio (CBR), and Unconfined Compression Tests. The ten locations where the soil samples were collected were selected across the geological classification of the area. ArcGIS 10.1 software was used to generate maps showing the geotechnical parameters distribution across four geological formations within the area at 1 and 2 m depth. It was observed that the distribution of each geotechnical parameter correlates with the composition of the weathering end-product of the geology. The rocks underlain the area includes; Migimatite Gneiss, Quartzite, Charnockite and Biotite Granite. The poorest geotechnical parameters were obtained within subsoil underlain by Charnockite, hence are most unsuitable soil to host the foundation of civil engineering structures, while the area underlie by weathering end-product of quartzite rock is of good geotechnical parameters and most suitable soil to host the foundation of civil engineering structures. The weathering end-products of Charnockite, Migimatite and Granite rocks give relatively high shear strength than that of quartzite, indicating low cohesive nature of the weathering end-product of quartzite. Key words: Geological classification, geotechnical parameter, weathering, road base.

Improvement of the homotopy perturbation method to nonlinear problems

Abstract: This paper proposes an effective improvement of the homotopy perturbation method (HPM) by using Jacobi and He's polynomials to solve some nonlinear ordinary differential equations. With this method, the source terms of ordinary differential equations can be expanded in series of shifted Jacobi polynomials. Numerical results are given in this paper to illustrate the reliability of this method with nonlinear ordinary differential equations. Key words: Homotopy perturbation method (HPM), shifted Jacobi polynomials, nonlinear ordinary differential equations.

Radionuclide concentration: The coal ash effect

Abstract: Radionuclide concentrations in coal ash, soil mixed with coal ash and soil were determined using the gamma spectroscopic method. The average activity concentrations of 226Ra, 232Th, and 40K in coal ash samples were found as 35.0, 5.8, and 109.4 Bq/kg, respectively. The average activity concentrations of 226Ra, 232Th and 40K in soil mixed with coal ash samples varied from 21.2 to 30.8, 48.6 to 82.7, and 162.5 to 180.1 Bq/kg, respectively. The activity concentrations of radionuclides from the non-mixed soil area, which serves as a control to this study ranged from 123.95 to 128.82, 16.33 to 18.38, and 46.63 to 50.30 Bq/kg, respectively for radionuclides 40K, 226Ra, and 232Th, respectively. From the radiological calculations, it was found that the use of coal ash as a soil additive contributed slightly to the radionuclide concentrations of the area under study. Key words: Radionuclide, coal ash, radium equivalent, external and internal hazard index.

Investigation of gravity anomalies in parts of Niger Delta Region in Nigeria using aerogravity data

Abstract: Gravity anomalies in parts of the Niger Delta region, Nigeria, were investigated through the interpretation of aerogarvity data with the objectives to determine the thickness of the sedimentary basin, establish the basement topography, density contrasts and the geological models which will give information about variation of geological structures. Four sheets of digital airborne gravity data were used for the study. Source parameter imaging (SPI), Standard Euler deconvolution and forward and inverse modeling techniques were employed in quantitative interpretation. The Bouguer anomaly of the study area varied from -20.0 to 37.7 mGal, while the residual Bouguer anomaly varied from -19.6 to 25.7 mGal. The SPI gave depth values ranging from -539.7 to -4276.0 m for shallow and deep lying gravity anomalous bodies. The windowed Euler-3D for Bouguer gravity result revealed the depth range of 1355.5 to -1518.1 m for structural index of one; 2384.5 to -3283.2 m for structural index of two and 2426.0 to -5011 m for structural index of three. The forward and inverse modeling gave the density values for the modeled profiles 1, 2, 3, 4 and 5 as 1.820, 2.410, 0.720, 2.310 and 2.100 gcm-3, respectively, with their respective depths of 3872, 4228, 4880, 3560 and 2527 m. The results from this study have shown that the depth to basement and density contrast have influence on the petroleum/hydrocarbon accumulation. Key words: Aerogravity, basement, density contrast, sedimentary.

Feasibility analysis of hybrid electricity generation system by HOMER for Mauritanian northern coast

Abstract: The reported work was motivated by the energy needs in the Mauritania region and the utility of the search features of a software system, named HOMER (Hybrid Optimization of Multiple Energy Resources), for feasibility analysis of a hybrid power generation system (HS) for the Mauritanian northern coast. This study analyzed a sample of the available wind resources to meet the energy needs of these localities, using the HOMER software with the aim to search for the best possible configuration. A configuration was sought through this work which is considered with less intermittence in the system. In addition, given the relationship noted in the study between the influence of the average wind speed and the price of diesel in liters, it was also suggested to highlight configurations that exclude storage or that may decrease the size of the fuel. This, as a supplementary feature, also allowed, for example, to justify the additional cost generated by the insertion of the diesel group. In this context, five (5) values are given for the study of the price sensitivity of the liter of diesel; these values are proposed as follows: 1.05 $/L (current), 1.08, 1.1, 1.2 and 1.5 $/L (Maximum price). In another way, to carry out the sensitivity analysis through simulations that take into account the average wind speed, the values retained (4, 5, 6, 7 and 8 m/s (maximum speed)) to deepen the study of the behavior of configurations by HOMER software. Finally, we must remember the number of kilowatt-hours produced that may seem insignificant to the country's energy production capacity, but these few tens or hundreds of kilowatt-hours can revive all the hope of the localities of the Mauritanian northern coast. In short, we report here some interesting findings as a result of the search carried out of resources using the HOMER system. Key words: HOMER software, hybrid system, wind, kilowatt-hours (kWh) price, sensitivity analysis.

A comparative study of Nigerian GNSS Reference Networks Global Positioning System (NIGNETs-GPS) vertical Total Electron Content (vTEC) measurements with the International Reference Ionosphere - Total Electron Content (IRI-TEC) predictions over Calabar, Nigeria

Abstract: A study of the vertical Total Electron Content (vTEC) values as measured by the Nigerian GNSS Reference Network’s (NIGNET’s) GPS receiver in Calabar with geographic coordinates: 4.95°N, 8.32°E and geomagnetic coordinates: 6.46°N, 81.59°E has been carried out for some selected days in the year 2013. The results obtained are compared with the corresponding predictions of the three topside options for the TEC predictions (NeQuick, IRI01-cor, and the IRI 2001) of the International Reference Ionosphere (IRI) model (version 2012) over Calabar region. Despite some gaps in the measured vTEC values by the GPS receiver in Calabar, the results of this research shows high hourly and diurnal correlation of about 0.9 with the IRI-vTEC predictions for the days examined; thus supporting the viability of the receiver as a vTEC measuring device. The NeQuick option gives the best topside representation for the region. Key words: Nigerian GNSS Reference Network’s – Global Positioning System (NIGNET’s-GPS) Receiver, vertical Total Electron Content (vTEC), International Reference Ionosphere (IRI)-Model.

Mathematical modeling and numerical simulation for the formation process of nanofilms

Abstract: This study applied a generalized model to describe and optimize the formation process of nanofilms from their polymeric solutions. Through this model, one can optimize the concentration of the solvent in the polymeric solution, the appropriate geometric dimensions as well as the nanofilm formation speed. A comparison of this model with experimental data has revealed some similarities and differences in the solidification and evaporation processes of the solvent. The yield strength and plasticity were deeply studied using numerical simulation for polypolymer nanofilms when subjected to a tensile deformation along the direction. Key words: Polypolymer, linear polymers, rheological equation of state, tensile deformation, polymer nanofilm.

Optical and structural performance of polymer/fullerene thin film based on Poly (3-hexylthiophene)/1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C61 [(P3HT)/PCBM] after post-annealing

Abstract: The polymer solar cell is a promising candidate for the next-generation solar cells because of its light weight, flexibility and easy fabrication. Poly (3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61(PCBM) are, to date, the most-studied active materials around the world for bulk-heterojunction structure. Recent power-conversion efi¬ciencies are reported up to approximately 13%. This research investigates the optical and morphological properties of P3HT, PC61BM, and P3HT:PC61BM blend thin films deposited on glass substrate by spin-coating technique. Optical absorbance and transmittance measurements were recorded by using a single beam spectrophotometer. Morphological characterization was carried out with scanning electron microscope. Samples were pre-heated at 60°C for 30 min to evaporate the solvent. The samples deposited on the substrate were then annealed at 70 and 80°C for 30 min respectively. Optical properties of thin films were obtained. The sample annealed at 80°C has the highest absorption of photon energy in the visible region of the spectrum for the P3HT: PCBM blend thin film. Observation shows that as the annealing temperature increases, there is increase in absorption of photon energy for PC61BM and P3HT:PC61BM blend films and a reduction for P3HT thin film. Observation of surface morphology shows that: as the temperature increases the surface of the sample roughness increases. This is due to increase in grain size with increase in annealing temperature. It has been demonstrated in the study that gradual thermal annealing, in a controlled manner reveals a more stable and efficient control in tuning the P3HT–based thin film. Furthermore, this work has revealed the significance of employing thermal annealing strategies in control of the bulk of active layer of organic thin film. The results of the study can be used to develop a guideline for improving the design and fabrication of organic solar cells. It is expected that this result will lead to improvement in performance and stability of organic solar cells. Key words: Organic thin film, conjugated polymer, morphology, Poly (3-hexylthiophene) (P3HT), 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 (PCBM), post-annealing.

High-latitude thermospheric zonal winds during low solar activity period

Abstract: Changes resulting from the cyclical nature of the sun’s energy output result to variations in thermosphere-ionosphere system parameters. The prolonged low solar activity period of solar cycle 23 provides an opportunity to study the thermosphere-ionosphere system parameters when the sun was at its ground state. The CHAMP satellite has provided wind data that can be used for investigation of neutral thermospheric parameters such as zonal winds and density. Using zonal wind data from 2006 to 2008 generated from CHAMP accelerometer readings using an iterative algorithm, the diurnal variation of averaged zonal thermospheric winds in the high latitudes (70 - 80°N) has been investigated. In the analysis we grouped the data into four seasons; the March and September equinoxes, and the June and December solstices. The wind data is binned into local time bins and averaged to find the hourly mean speeds. The results reveal maximum eastward and westward wind speeds going above 150 m/s for each of the seasons considered. Of particular interest is the observation that despite the expected complex behavior resulting from the expected magnetospheric inputs, the diurnal patterns are similar to those obtained in the mid-latitudes in an earlier study with data from this algorithm. Due to likely errors arising from the longitudinal effects of mixing composite solar times, there is need for simultaneous measurements in the high latitudes. Key words: CHAMP satellite, high latitude, solar activity, thermosphere.

Interpretation of aeromagnetic data over some parts of Mambilla Plateau, Taraba State

Abstract: The data covering Mayo Daga and Gashaka areas of Taraba State has been interpreted by applying source parameter imaging (SPI) and forward and inverse modeling methods. From the quantitative method of interpretation, it was found out that the magnetic intensity within the study area ranges from -129.9 to 186.6 nT in which the area is noticeably marked by both low and high magnetic signatures which may be as a result of several factors such as; susceptibility, degree of strike, difference in magnetic variation in depth and difference in lithology. From the quantitative interpretation, depth estimates obtained when SPI is employed shown minimum to maximum depth to anomalous source that ranges from 400.7 to 2119.2 m. Forward and inverse modeling estimated depths for profiles P1, P2, P3, and P4 were 2372, 2537, 1621 and 1586 m, respectively, with susceptibility values of 0.0754, 0.0251, 0.0028, and 0.001 respectively, suggesting that the bodies causing the anomaly are typical of igneous rocks; basalt and olivine, intermediate igneous rock; granites, and rocks mineral (quartz). Key words: Aeromagnetic data, source parameter imaging (SPI), qualitative and quantitative interpretation

Effect of annealing temperature on the optical properties of Sb-ZnO thin films prepared using co-sputtering technique

Abstract: Transparent conducting oxide thin films of Sb-ZnO were prepared on optically flat quartz by radio-frequency (RF) sputtering method. The scan electron microscope was used to characterize the topological morphology of the surface of the as-prepared and annealed films at (300, 400, 470, and 525°C) for 4 h in air. The optical properties of the films were deliberated using their reflectance and transmittance spectra at normal incident light. The optical energy band gap energy (Eop ) values were found to increase by elevating the annealing temperatures. The dispersion curves of the refractive index of Sb-ZnOthin films were found to follow the single oscillator model. Optical parameters such as refractive index, real and imaginary parts of the dielectric constant, and optical conductivity were investigated. Key word: Sputtering, thin film, Sb-ZnO, optical gap, refractive index.

A compact and sensitive avalanche photodiode-based gamma detection and spectroscopy system

Abstract: This research presents the design of a simple and compact yet sensitive gamma detection system which finds optimal utility in student research and demonstration purposes. The design is based on an Avalanche Photodiode (APD), a compact solid-state device. It was argued that, by the virtue of its concise size, simplicity and lower cost, an APD based gamma detection system is a better alternative in these applications as compared to the high-cost and complex Photomultiplier (PMT) based detector systems. This paper provides the basic working details of our design and preliminary test results. Key words: Avalanche photodiode (APD), gamma spectroscopy, scintillator.

Investigating influence of the phases of solar activity cycle 23 on coronal mass ejections transit time

Abstract: It has been established that Coronal Mass Ejections (CMEs) follow the phase of solar activity cycle. CMEs are known to be the major cause of geomagnetic storms which have devastating effects on earth atmosphere. Predicting their arrival times has been a major issue in space weather forecast. Influence of the phases solar activity cycle 23 on CMEs transit time were investigated using fast CMEs data with initial speed ≥ 900 kms-1 that were associated with intense geomagnetic storm obtained from Large Angle Spectrometric Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO) for solar cycle 23. Empirical Coronal Mass Ejections Arrival (ECA) model equations of Ojih-Okeke modified model, Gopalswamy 2000 model (G2000), Gopalswamy 2001 model (G2001), and Vrsnak and Gopalswamy 2002 model (VG2002) were applied to the data points. Scatter plots of CMEs transit time as function of CMEs initial speed and solar wind speed were generated. Linear correlation coefficients were obtained. The significance of the correlation was tested at 0.05 level of significant. Linear correlation coefficients obtained for solar maximum period of solar cycle 23 for Ojih-Okeke model, VG2002 model, G2001 model and G2000 model were -0.63, -0.82, -0.78 and -0.79 respectively and those obtained for declining phase of solar cycle 23 were -0.93, -0.80, -0.80 and -0.86 respectively. There is no significant difference between the correlations obtained for solar maximum phase and the declining phase of solar cycle 23. The findings depict that phases of solar activity cycle has no significant influence on CMEs transit time. Key words: Coronal mass ejections, solar activity cycle, transit time, phase, geomagnetic storm.

Deriving an expression for electron-reflection-coefficient at metal-semiconductor-interface of dye-sensitized solar cells

Abstract: This work aims to derive an expression to describe the reflection coefficient of an escape electron from metal-semiconductor interface of DSSC. The derivation was obtained by analytically solving electron diffusion equation with assumptions of steady state DSSC and negligible current flow at the outer most part of the film. The derived corrected Richardson-Dushman equation including a reflection of electron wave at potential barrier is inserted into current-voltage (JV) characteristic equation. We showed that voltage loss at various temperature and current densities do not vary with and without reflection coefficient. However, the reflection coefficient is shown to be insignificant to JV characteristics with respect to potential barriers. Our results confirm the effect of potential barrier through which an electron must be accelerated in order to gain sufficient energy necessary for high power conversion efficiency. Key words: DSSC, drift-diffusion, metal-semiconductor, reflection coefficient.

Quantification and correction of the Thomsens Delta Anisotropy for improved quantitative seismic interpretation in AMFO Field, Western Niger Delta

Abstract: The Niger Delta is a sedimentary deposit with continuing sediment deposition to date. In a stratified earth, seismic waves tend to propagate faster along layers than across layer boundaries. Shales, due to the clay minerals they contain, exhibit similar behavior. As a result, velocities derived from surface seismic are often faster than well-derived velocities, causing depths of structures from surface seismic interpretations to be much shallower than their true depths. Reservoir characterization workflows such as amplitude-versus offset (AVO) analysis, seismic inversion and pore pressure prognosis, which make use of seismic velocities to accurately delineate and define exploration targets, would be seriously impacted if velocity anisotropy is not quantified and the seismically-derived velocities corrected. Accurate quantification and correction of velocity anisotropy requires the use of offset vertical seismic profile (VSP) data to aid the estimation of the Thomsen’s anisotropic parameters, and . Unfortunately, such data are rarely acquired in many exploration projects and when they are available, they are often limited in areal coverage. In this study, an integrated approach using well and seismic data, based on the degree to which check shot and stacking interval velocity trends diverge with increasing depths, was utilized to quantify and correct seismically-derived velocity in AMFO field for improved quantitative seismic interpretation. Estimated anisotropy is between 2 and 22%, and becomes apparent at about 1,100 m true vertical depth subsea (TVDss). Key words: Velocity anisotropy, interval velocity, vertical seismic profile (VSP), anisotropic parameters, well velocity.