Background:A germicide like Izal is chemical agent used for reducing and preventing microbial loads in systems for treating water as well as other industries like agriculture and aquaculture.The environmental impact o...Background:A germicide like Izal is chemical agent used for reducing and preventing microbial loads in systems for treating water as well as other industries like agriculture and aquaculture.The environmental impact of germicide is often more than the target intended by those who use them.The purpose of the current study was to ascertain the toxicity levels and behavioral alterations of Juvenile African catfish,Clarias gariepinus,subjected to Izal exposure.Methods:The stock solution was created from the 100 mL by mixing 1 mL of the Izal with 99 mL of water.After that,different nominal concentrations of Izal were prepared using the stock solution by diluting the toxin with tap water in determined amounts(10 L).The fish were exposed to acute concentrations of 1.0,1.5,2.0,2.5 and 3.0 mg/L of Izal had a control that served as a reference point.Results:The lethal concentration of Izal(24 h LC50)was found to be 2.4136 mg/L(95%confidence interval=2.1707–2.6838)for test fish under a semi-static system showing that Izal is moderately poisonous to the species in a dose-dependent manner and time(duration).The highest mortality was recorded in the highest concentration(3.0 mg/L)of Izal while the least mortality was observed in the 1.5 mg/L group.Izal-exposed fish had aberrant behavior,including hyperactivity,gasping of air,respiratory distress,attempts to jump out of the water,erratic swimming,refusal to feed,lethargic movement,and slow response to feed,loss of balance and depigmentation.The severity of the abnormal behavior decreased after 24 h,but remained mildly to moderately high at 2.0 and 2.5 mg/L of Izal.It was found that the death rate increased with Izal concentration and duration.Conclusion:The present study revealed that Izal was moderately toxic to Claris gariepinus juveniles and should be used prudently in the environment to guard against toxicological effect on non-target organisms such as fish.For this reason,the use of the germicides should be with caution especially near water bodies.展开更多
A 30-m TeraHertz（THz） radio telescope is proposed to operate at 200 μm with an active primary surface.This paper presents sensitivity analysis of active surface panel positioning errors with optical performance in ...A 30-m TeraHertz（THz） radio telescope is proposed to operate at 200 μm with an active primary surface.This paper presents sensitivity analysis of active surface panel positioning errors with optical performance in terms of the Strehl ratio.Based on Ruze＇s surface error theory and using a Monte Carlo simulation,the effects of six rigid panel positioning errors,such as piston,tip,tilt,radial,azimuthal and twist displacements,were directly derived.The optical performance of the telescope was then evaluated using the standard Strehl ratio.We graphically illustrated the various panel error effects by presenting simulations of complete ensembles of full reflector surface errors for the six different rigid panel positioning errors.Study of the panel error sensitivity analysis revealed that the piston error and tilt/tip errors are dominant while the other rigid errors are much less important.Furthermore,as indicated by the results,we conceived of an alternative Master-Slave Concept-based（MSC-based） active surface by implementating a special Series-Parallel Concept-based（SPC-based） hexapod as the active panel support mechanism.A new 30-m active reflector based on the two concepts was demonstrated to achieve correction for all the six rigid panel positioning errors in an economically feasible way.展开更多
The motion of a test particle within the context of the restricted four-body problem(R4BP)driven by a new kind of potential,called the generalized Manev potential,with perturbations in the Coriolis and centrifugal for...The motion of a test particle within the context of the restricted four-body problem(R4BP)driven by a new kind of potential,called the generalized Manev potential,with perturbations in the Coriolis and centrifugal forces is considered in this study.The system possesses eight libration points which were distributed on its plane of motion in different manner from those of the usual Newtonian potential.Unlike the case of the perturbed R4BP under Newtonian potential,where two of these librations are stable,all of them are unstable in linear sense under Manev potential.We found that a gradual perturbation in the centrifugal force causes the trajectories of motion to drift inward but the Coriolis force was proven to have no effect on the location of the libration points of the system.Using first order Lyapunov characteristic exponents,the dynamical behavior of the system is found irregular.We experimented with a high velocity stellar system(82 G.Eridani)to establish the applicability of the model in astrophysics.展开更多
This study focuses on the stepwise procedure involved in the development of a numerical model of a bi-propellant hypergolic chemical propulsion system using key features and performance characteristics of existing and...This study focuses on the stepwise procedure involved in the development of a numerical model of a bi-propellant hypergolic chemical propulsion system using key features and performance characteristics of existing and planned (near future) propulsion systems. The study targets specific impulse of 100</span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">N delivery performance of thrust chambers which is suitable for primary propulsion and attitude control for spacecraft. Results from numerical models are reported and validated with the Rocket Propulsion Analysis (RPA) computation concept. In the modelling process, there was proper consideration for the essential parts of the thruster engine such as the nozzle, combustion chamber, catalyst bed, injector, and cooling jacket. This propulsion system is designed to be fabricated in our next step in advancing this idea, using a combination of additive manufacturing technology and commercial off the shelf (COTS) parts along with non-toxic propellants. The two non-toxic propellants being considered are Hydrogen Peroxide as the oxidiser and Kerosene as the fuel, thus making it a low-cost, readily available and environmentally-friendly option for future microsatellite missions.展开更多
This study investigates the variability and periodicity of minimum temperature, maximum temperature and sunspot number—a solar activity index in selected synoptic stations across Nigeria from 1946 to 2010. Annual and...This study investigates the variability and periodicity of minimum temperature, maximum temperature and sunspot number—a solar activity index in selected synoptic stations across Nigeria from 1946 to 2010. Annual and semiannual effect of solar activity on minimum temperature was observed in all the six stations. This was indicated in the occurrence of modal periodicities of 6-month and 12-month observed across the six synoptic stations. The synoptic stations are Sokoto (13.01°N, 5.15°E), Ilorin (8.29°N, 4.35°E), Ikeja (6.35°N, 3.20°E), Enugu (6.28°N, 7.33°E), Port-Harcourt (4.51°N, 7.01°E) and Maiduguri (11.51°N, 13.05°E). Similarly, the trends of inter-decadal va-riability of minimum and maximum temperature show a non-uniformity increase over the analyzed period with a slight decrease before 1960. The long term behavior of minimum and maximum temperature shows a warming rate which ranges from 0.1°C/decade to 0.2°C/ decade across the six stations except for maximum temperature at Ilorin and minimum temperature at Sokoto which is at -0.2°C/decade and 0.3°C/decade respectively.展开更多
There has been an increasing global and local interest in developing renewable, clean, and cheap energy towards achieving Goal number 7 of the Sustainable Development Goals (SDG). However, decisions involving suitable...There has been an increasing global and local interest in developing renewable, clean, and cheap energy towards achieving Goal number 7 of the Sustainable Development Goals (SDG). However, decisions involving suitable and sustainable locations for renewable energy projects remain an important task. This study employed Geographic Information System (GIS) and Multi-Criteria Decision Analysis (MCDA) to spatially analyze and model wind farm site suitability in Nasarawa State. The aim is to integrate the environmental, social, and economic aspects of decision-making for identifying sustainable wind farm sites. The study distinguished between two sets of decision criteria: decision constraints and decision factors. The former defined the exclusion zones while the latter were standardized based on fuzzy logic to depict varying degrees of suitability across the State. The MCDA applied the weighted linear combination method, with relative weights generated through pairwise comparisons of the analytic hierarchy process to analyze three policy scenarios: equal weights, environmental/social priority, and economic priority scenario. A combination of resulting composite maps from the constraints and the factors gave the final suitability maps. The resulting suitability index (SI) for the respective policy scenario describes the degrees of suitability: Ideal locations were denoted by one (1) and the not suitable locations by zero (0), with values in-between depicting varying degrees of wind farm site suitability. Based on the SI, priority locations indicating areas with good prospects, in addition to the most suitable parcels of land, were identified and delineated. The composite decision constraint revealed that wind farm projects would not be viable in more than half (57.58%) of the State. Wind speed was the major constraint and accounted for the exclusion of 46.25%, with a mean fuzzy membership value of 0.2008 indicating low suitability across the State. Also, the average acceptable wind farm location for the three-policy scenario was 33.33% of the entire study area. Lafia, Obi, Keana, Awe, Nasarawa-Eggon, Wamba and Kokona LGAs were the identified priority Local Government Areas (LGAs). However, only Lafia, Obi, and Nasarawa-Eggon were consistent with changes in the policy objectives. All the priority LGAs have one or more of the most suitable parcels within their administrative boundaries except for Wamba. Despite the severe limitations of wind speed, substantial parts of Nasarawa State still provide great development potentials for wind energy. The “most suitable” locations in Lafia, Nasarawa-Eggon, and Obi LGAs should have first consideration for the development of wind energy in the State.展开更多
As interest in the use and launching of spacecraft for communications,earth observation,scientific experiment and navigation purposes increases and manned missions to the Moon and Mars intensify,there is need for the ...As interest in the use and launching of spacecraft for communications,earth observation,scientific experiment and navigation purposes increases and manned missions to the Moon and Mars intensify,there is need for the design of efficient and highfidelity relative motion dynamics to reduce spacecraft collisions and increase return on investment.The main aim of this work is to develop new approximate solution of spacecraft relative motion in elliptical orbit via power series method.Advantage of this method is that it does not involve evaluating complex integral I as employed for developing approximate solutions of linearized Tschauner–Hempel equations.Cauchy product,used for the discrete convolution of power series,is employed for the development of power series solutions of the approximated nonlinear spacecraft relative motion.Application of Cauchy criterion shows that the new solutions are convergent making them useful for spacecraft formation flying,proximity and rendezvous mission analysis.展开更多
In this paper,approximated nonlinear spacecraft relative motion model is developed via Euler Lagrange approach using local vertical-local horizontal frame attached to the chief spacecraft.Harmonic balance analysis app...In this paper,approximated nonlinear spacecraft relative motion model is developed via Euler Lagrange approach using local vertical-local horizontal frame attached to the chief spacecraft.Harmonic balance analysis approach,a powerful technique for approximating nonlinear equation and generating periodic solutions,is applied to the approximated nonlinear relative motion for the development of new linear harmonic balance approximation model and investigation of its periodic solutions.Using power series method,power series approximate solutions of the harmonically balanced model of the relative motion are developed.Furthermore,the computational algorithm employed for the orbit propagation of nonlinear,harmonic balance and Clohessy-Wilshire models is presented.Using MATLAB ODE45 integrator,the relative motion models are numerically integrated and propagated.The numerical results show that harmonic balance model gave a better approximation of the nonlinear model.展开更多
Nonlinear time-varying system,such as a spacecraft formation flying system with chief spacecraft in elliptical orbit and under the effect of perturbation forces,is difficult to analyze,design,and control based on the ...Nonlinear time-varying system,such as a spacecraft formation flying system with chief spacecraft in elliptical orbit and under the effect of perturbation forces,is difficult to analyze,design,and control based on the presence of time-varying parameters.The proper functioning of aerospace systems and their ability to be able to achieve the designed mission objectives depend largely on proper understanding of their nonlinear time-varying nature,dynamics,and ability to keep them in the required mission operation configurations through high-fidelity optimal control strategy.This paper presents nonlinear dynamics and optimal control of J_(2)perturbed spacecraft formation flying.Via Euler–Lagrange approach,the nonlinear J_(2)perturbed motion dynamics was approximated into a time-varying nonlinear form,having periodic coefficients and time-varying parameters,suitable for designing fuel efficient control strategies,spacecraft formation flying,relative motion,and rendezvous mission analysis.Through the application of State-Dependent Riccati Equation(SDRE)approach,the approximated model was converted into a non-unique,pseudo-linear state-dependent coefficient(SDC)form.The numerical simulations confirmed that the SDRE controllers,developed using SDC parameterized systems,are maximally robust and able to return the system to the desired radial,along-track,and cross-track positions.展开更多
Monsoon driven water mass exchange between the Bay of Bengal(Bo B) and Arabian Sea(AS) is the common experience. However, it is not yet firmly confirmed that the exchange pathway is either passing through southern tip...Monsoon driven water mass exchange between the Bay of Bengal(Bo B) and Arabian Sea(AS) is the common experience. However, it is not yet firmly confirmed that the exchange pathway is either passing through southern tip of Sri Lanka or Palk Strait. Local circulation patterns impact the pathways followed by the East Indian Coastal Currents(EICC) that drive exchange, thereby modulating mixing and water mass transformation in the Bay of Bengal around Sri Lanka. In this study, observations from surface drifters were incorporated with the satellite derived data to understand the monsoonal impact on circulation patterns in the Indian Ocean. This was the first multi-national scientific effort which was conducted in the Bo B and AS during 2013 to 2015 to understand the monsoonal impact on circulation patterns in the complex region. The results indicated that seasonally reversing monsoonal currents of southern Sri Lanka, traced by the wintertime freshwater export pathways of the EICC. The deflection of monsoon currents running along the east coast of Sri Lanka by forming cyclonic and anti-cyclonic eddies, which influence the mixing and stirring associated with these flows. Results further indicate the low salinity cold water flows from the Bo B to AS along the western boundary of the Bo B during northeast monsoon. In the same way, reverses the phenomena during southwest monsoon, transporting high salinity warm water from AS to the Bo B. This maintain the bay status which occurred due to freshwater influx from large rivers and high saline water from AS. However, no evidences were observed for the exchange through Palk Strait during the study.Also, there are some mis-matches in in-situ and remotely sensed measurements which imply the necessity of systematic observation system for the complex region as an alternative approach.展开更多
The aim of this study was to develop an efficient and realistic response surface optimization technique for the design of V-belt drive for optimum power output of the drive in machinery design. Optimization mathematic...The aim of this study was to develop an efficient and realistic response surface optimization technique for the design of V-belt drive for optimum power output of the drive in machinery design. Optimization mathematical model of the V-belt drive was constructed. The power output of the belt drive was modeled and optimized by the Response Surface Methodology (RSM). Analysis of variance was used to evaluate the extent of influence of each independent variables on the power output response of the belt drive. A RSM optimization process was proposed to calculate optimal power output for V-belt drive given a set of pulley diameter for the drive employed in a tilling machine. The analysis showed that optimum power output of the drive for workshop light operation machinery could be obtained at driving and driven pulley radius range of 550 - 900 mm and 250 - 500 mm. An optimum power output of 1418.76 kW was obtained at driving and driven pulley radius of 846 and 486 mm respectively for a farm tilling machine.展开更多
We present interesting application of artificial intelligence for investigating effect of the COVID-19 lockdown on 3-dimensional temperature variation across Nigeria(2°-15°E,4°-14°N),in equatorial ...We present interesting application of artificial intelligence for investigating effect of the COVID-19 lockdown on 3-dimensional temperature variation across Nigeria(2°-15°E,4°-14°N),in equatorial Africa.Artificial neural networks were trained to learn time-series temperature variation patterns using radio occultation measurements of atmospheric temperature from the Constellation Observing System for Meteorology,Ionosphere,and Climate(COSMIC).Data used for training,validation and testing of the neural networks covered period prior to the lockdown.There was also an investigation into the viability of solar activity indicator(represented by the sunspot number)as an input for the process.The results indicated that including the sunspot number as an input for the training did not improve the network prediction accuracy.The trained network was then used to predict values for the lockdown period.Since the network was trained using pre-lockdown dataset,predictions from the network are regarded as expected temperatures,should there have been no lockdown.By comparing with the actual COSMIC measurements during the lockdown period,effects of the lockdown on atmospheric temperatures were deduced.In overall,the mean altitudinal temperatures rose by about 1.1℃ above expected values during the lockdown.An altitudinal breakdown,at 1 km resolution,reveals that the values were typically below0.5℃ at most of the altitudes,but exceeded 1℃ at 28 and 29 km altitudes.The temperatures were also observed to drop below expected values at altitudes of 0-2 km,and 17-20 km.展开更多
Theoretical frameworks used to explain the location of services include central place theory, aspects of industrial location theory and spatial diffusion theory. They are all described as normative theories which opti...Theoretical frameworks used to explain the location of services include central place theory, aspects of industrial location theory and spatial diffusion theory. They are all described as normative theories which optimize with respect to defined criteria operating in prescribed environmental conditions (Rushton, 1979). However, recent advancement in geospatial technologies has led to several applications in geographically orientated challenges, hence, the adoption of an effective decision tool like Geographic Information System (GIS), high resolution products of satellite remote sensing as well as the Global Positioning System (GPS) in solving the rather challenging task of optimal location for facilities with respect to necessary criteria. Minna metropolis is being affected adversely by the problem of appropriate location of public facilities. These facilities are either too far from their market zone or they are too congested in a particular location and in some cases, political consideration to the siting of these facilities dominate without given considerations to the necessary criteria for demands and public interest. The study is an investigation into the “optimal determination of the locations of some public facilities in Minna metropolis of Niger State, using geospatial techniques”. The fusion of remote sensing, geographic information system (GIS) and GPS techniques was explored. Geodata base of existing facilities was created and Euclidean-distance geometry used to spatially analyze the appropriate locations with regards to the set of standard criteria. The results showed the haphazard and uncontrolled pattern of development of schools location. However, petrol stations met the evaluated criteria and optimal location indexes.展开更多
Three gram negative bacteria isolated from infected koi carp, Cyprinus carpio L. and screened for sensitivity to thirty antibiotics by the Bauer disc diffusion method. Bacteria evaluated were Aeromonas hydrophila, Pse...Three gram negative bacteria isolated from infected koi carp, Cyprinus carpio L. and screened for sensitivity to thirty antibiotics by the Bauer disc diffusion method. Bacteria evaluated were Aeromonas hydrophila, Pseudomonas aeruginosa and Edwardseilla tarda. A. hydrophila was resistant to ampicilin, cephalothin, sulphatriad, cefpodoxime and cefoxitin. Highest sensitivity was recorded to Colistin methane sulphonate and Ceftriaxone. High resistance was observed for P. aeruginosa in Kanamysin, Cephalothin, Sulphatriad, Colistin methane sulphonate, Tobramysin, Nitro Furantoin, Cefpodoxime, Cefoxitin and Aztreonam. Highest sensitivity recorded with Moxifloxacin. High resistance was observed in Co-trimoxamole and higher sensitivity performed for E. tarda by Tetracyclin, Cephotaxime, Ciprofloxacin, Norfloxacin, Ofloxacin, Moxifloxacin, Gatifloxacin and Levofloxacin. Out of that highest sensitivity recorded with Moxifloxacin High sensitivity was recorded for Moxifloxacin, Ciprofloxacin, Gatifloxacin, Levofloxacin. By means of antibiotic sensitivity test highest resistance was recorded to P. aeruginosa （MAR index-0.3） and least resistant was recorded to E, tarda （MAR index- 0.033）.展开更多
The urban environment has continued to experience changes from increasing impervious surfaces, which alters the proper functioning of the ecological zones and impairs water quality in the watershed. Impervious cover i...The urban environment has continued to experience changes from increasing impervious surfaces, which alters the proper functioning of the ecological zones and impairs water quality in the watershed. Impervious cover is predominantly used as an indicator to assist in understanding and forecasting the impact of human actions and other related activities on aquatic resources. In this study, the rate of change in land uses using the impervious surface as an indicator, and the percentage of imperviousness on the effect on water quality in the urban watershed were assessed. Ile-Ife was delineated as an urban watershed, and the percentage of imperviousness from 2008 to 2016 and the effect of imperviousness on water bodies were assessed. The study utilized ASTERDEM, Worldview (0.46 m), IKONOS (1.4 m), Landsat (30 m) for 2008 and 2016, GPS and Drone (10 cm). Water sampling was carried out in selected locations as generated by the impervious surface analyst tool, (ISAT). The percentage (%) of impervious surfaces accounted for 59.4% (4567.1/7691.5ha) in 2008 and 70.3% (5408.2/7691.5ha) in 2016, from the total number of lands investigated. The turbidity values from low to high regions were 32.3, 55.9 and 82.4 NUT. Changes in LULC of the watershed led to increased surface temperature, impermeable surfaces, and decreased vegetation, which exposes the area to flooding and reduced water quality. This study emphasized the importance of GIS and its integration into urban changes and water quality assessment.展开更多
The importance of Remote Sensing and Geographic Information System in map making cannot be overemphasized because of its ability to integrate spatial data with non-spatial data and also communicate the resulting infor...The importance of Remote Sensing and Geographic Information System in map making cannot be overemphasized because of its ability to integrate spatial data with non-spatial data and also communicate the resulting information in a way that everyone would understand. Several works have taken advantage of the abilities of these technologies to produce street maps using High Resolution Images. The increase in development in Ile Ife, Osun State, Nigeria, has brought about navigation challenge and associated difficulties. This work intends to produce a street map that will ease navigation within the study area and help in road network analysis, site suitability analysis etc. Aerial Photographs, captured in the year 2009 and GeoEye1 Satellite Image of 2011 were used to extract the road network of Ife Metropolis. The image was imported into ArcGIS environment, where the database was created having feature datasets such as roads and special features. To have all the elements in vector format, the image was digitized. The street names collected from the field work was inputted into the database and then subjected to cartographical processes. 512 Roads were captured within four classes of Road Network namely Express road (5), Secondary Road (25), Primary Roads (22) and Street Road (460). This field work revealed that a larger percentage of the roads were not paved, while most of the paved ones have deteriorated and the newly constructed ones were not documented. It also showed that some of the roads were not named according to the standard and some were not named at all. From this study, we recommend that the naming system should be standardized across the study area. It is also recommended that provision should be made for street map revision on a yearly basis so as to account for changes.展开更多
This study employed Geographic Information System (GIS) and remote sensing approach to analyze the flood vulnerability areas in the Okoko basin area of Osogbo in Osun state, Southwestern Nigeria. High-resolution image...This study employed Geographic Information System (GIS) and remote sensing approach to analyze the flood vulnerability areas in the Okoko basin area of Osogbo in Osun state, Southwestern Nigeria. High-resolution imageries, a Topographic map of the study area and a TCX software program (Version 2.0) were integrated using ArcGis (10.7). Some of the causative factors for flooding in the watershed were taken into account which are: Land use, Distance of buildings to drainage, Digital Elevation Model, and Slope. This study aimed at mapping the flood-vulnerable areas along the Okoko basin of Osogbo. In developing a flood risk/flood hazard map of the study area, and determining the level of expected disaster, a multi-criteria analysis was utilized. The factors considered were ranked in five classes with the highly vulnerable areas having the highest score of “5”. These factors were weighed according to the estimated significance of causing flooding. The study revealed that the study area has an estimated area of 17.85 km<sup>2</sup> of which 14.2 km<sup>2</sup> falls within the vulnerable areas while 3.6 km<sup>2</sup> is on the least vulnerable areas. Moreover, out of 16,829 buildings in the study area, 8204 buildings were found susceptible to flood disasters. This research attempts to equip decision-makers to make accurate decisions and also serves as a mitigation measure for flood disaster management.展开更多
A process capability study is performed for the turning process on a general purpose center lathe in order to verify the process performance and machine ability to perform within specified tolerance limit. The process...A process capability study is performed for the turning process on a general purpose center lathe in order to verify the process performance and machine ability to perform within specified tolerance limit. The process and machine capability indices were measured to determine the process and machine adequacy for industrial application. The tolerance limits were obtained from the given nominal size of the shaft, using the basic hole system and 90 sample shafts were turned on the lathe machine to specification for varying spindle speed and feed rate of the lathe. Three (3) samples were randomly selected for the turning process of a combination of the spindle speed and feed rate as a subgroup size for a total subgroup of thirty (30). The diameters (representing the quality characteristics) were used to generate control charts and capability histogram for the process. The process is within statistical control but found incapable of meeting up to specification because the capability index (C<sub>p</sub>) measured was less than 1 and the machine capability for industrial application is not adequate.展开更多
Over the years,the African continent has been importing used gasoline and diesel vehicles including ones that are 10 years old.Such vehicles emit carbon dioxide,which is the leading cause of greenhouse gases(GHGs)that...Over the years,the African continent has been importing used gasoline and diesel vehicles including ones that are 10 years old.Such vehicles emit carbon dioxide,which is the leading cause of greenhouse gases(GHGs)that are driving the climate change.In Rwanda,for example,road transport contributes to 13 percent of the country’s greenhouse emissions,according to the Rwanda Environment Management Authority(REMA).Africa as a developing continent continues to pollute air,partly due to the use of second-hand cars from developed countries.展开更多
This study examines the prenoon-postnoon asymmetrical behaviour and latitudinal dependence of Sq （solar quiet） current system using data of quiet-time daily variations of the geomagnetic field intensity from twelve ...This study examines the prenoon-postnoon asymmetrical behaviour and latitudinal dependence of Sq （solar quiet） current system using data of quiet-time daily variations of the geomagnetic field intensity from twelve geomagnetic observatories along the African Meridian. The dataset of each month during 2009 （noted for empirically low solar activity with average sunspot number Rz = 3.1） was treated for non-cyclic correction. From a blend of spatial contour maps and graphical analyses, our results show that Sq current system exhibits in the daytime unstable tendency. A consistent diurnal variation of solar quiet variation in the horizontal component of earth magnetic field （SqH） was observed which exhibits synoptic pre-noon and post-noon mean values of 59 nT and 33 nT with ranges of 33 nT and 24 nT, respectively. The centre of circulation of overhead electric current is observed to exhibit both pre-noon and post-noon epoch＇s asymmetric variations. This is noted to indicate the dynamic heterogeneous genesis of the mechanism responsible for the observation. The spatial contour mapping result depicts SqH behaviour switch twice a year around March and September with similar spatial distribution in January up to March and then October up to December. A similar distribution was noted for the months of April to September. Prenoon values of SqH have higher magnitudes across the latitudes in comparison with the post noon values just as is the case at noontime.展开更多
文摘Background:A germicide like Izal is chemical agent used for reducing and preventing microbial loads in systems for treating water as well as other industries like agriculture and aquaculture.The environmental impact of germicide is often more than the target intended by those who use them.The purpose of the current study was to ascertain the toxicity levels and behavioral alterations of Juvenile African catfish,Clarias gariepinus,subjected to Izal exposure.Methods:The stock solution was created from the 100 mL by mixing 1 mL of the Izal with 99 mL of water.After that,different nominal concentrations of Izal were prepared using the stock solution by diluting the toxin with tap water in determined amounts(10 L).The fish were exposed to acute concentrations of 1.0,1.5,2.0,2.5 and 3.0 mg/L of Izal had a control that served as a reference point.Results:The lethal concentration of Izal(24 h LC50)was found to be 2.4136 mg/L(95%confidence interval=2.1707–2.6838)for test fish under a semi-static system showing that Izal is moderately poisonous to the species in a dose-dependent manner and time(duration).The highest mortality was recorded in the highest concentration(3.0 mg/L)of Izal while the least mortality was observed in the 1.5 mg/L group.Izal-exposed fish had aberrant behavior,including hyperactivity,gasping of air,respiratory distress,attempts to jump out of the water,erratic swimming,refusal to feed,lethargic movement,and slow response to feed,loss of balance and depigmentation.The severity of the abnormal behavior decreased after 24 h,but remained mildly to moderately high at 2.0 and 2.5 mg/L of Izal.It was found that the death rate increased with Izal concentration and duration.Conclusion:The present study revealed that Izal was moderately toxic to Claris gariepinus juveniles and should be used prudently in the environment to guard against toxicological effect on non-target organisms such as fish.For this reason,the use of the germicides should be with caution especially near water bodies.
基金the National Natural Science Foundation of China (Grant Nos. 10973025 and 10833004)
文摘A 30-m TeraHertz（THz） radio telescope is proposed to operate at 200 μm with an active primary surface.This paper presents sensitivity analysis of active surface panel positioning errors with optical performance in terms of the Strehl ratio.Based on Ruze＇s surface error theory and using a Monte Carlo simulation,the effects of six rigid panel positioning errors,such as piston,tip,tilt,radial,azimuthal and twist displacements,were directly derived.The optical performance of the telescope was then evaluated using the standard Strehl ratio.We graphically illustrated the various panel error effects by presenting simulations of complete ensembles of full reflector surface errors for the six different rigid panel positioning errors.Study of the panel error sensitivity analysis revealed that the piston error and tilt/tip errors are dominant while the other rigid errors are much less important.Furthermore,as indicated by the results,we conceived of an alternative Master-Slave Concept-based（MSC-based） active surface by implementating a special Series-Parallel Concept-based（SPC-based） hexapod as the active panel support mechanism.A new 30-m active reflector based on the two concepts was demonstrated to achieve correction for all the six rigid panel positioning errors in an economically feasible way.
文摘The motion of a test particle within the context of the restricted four-body problem(R4BP)driven by a new kind of potential,called the generalized Manev potential,with perturbations in the Coriolis and centrifugal forces is considered in this study.The system possesses eight libration points which were distributed on its plane of motion in different manner from those of the usual Newtonian potential.Unlike the case of the perturbed R4BP under Newtonian potential,where two of these librations are stable,all of them are unstable in linear sense under Manev potential.We found that a gradual perturbation in the centrifugal force causes the trajectories of motion to drift inward but the Coriolis force was proven to have no effect on the location of the libration points of the system.Using first order Lyapunov characteristic exponents,the dynamical behavior of the system is found irregular.We experimented with a high velocity stellar system(82 G.Eridani)to establish the applicability of the model in astrophysics.
文摘This study focuses on the stepwise procedure involved in the development of a numerical model of a bi-propellant hypergolic chemical propulsion system using key features and performance characteristics of existing and planned (near future) propulsion systems. The study targets specific impulse of 100</span></span><span><span><span style="font-family:""> </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">N delivery performance of thrust chambers which is suitable for primary propulsion and attitude control for spacecraft. Results from numerical models are reported and validated with the Rocket Propulsion Analysis (RPA) computation concept. In the modelling process, there was proper consideration for the essential parts of the thruster engine such as the nozzle, combustion chamber, catalyst bed, injector, and cooling jacket. This propulsion system is designed to be fabricated in our next step in advancing this idea, using a combination of additive manufacturing technology and commercial off the shelf (COTS) parts along with non-toxic propellants. The two non-toxic propellants being considered are Hydrogen Peroxide as the oxidiser and Kerosene as the fuel, thus making it a low-cost, readily available and environmentally-friendly option for future microsatellite missions.
文摘This study investigates the variability and periodicity of minimum temperature, maximum temperature and sunspot number—a solar activity index in selected synoptic stations across Nigeria from 1946 to 2010. Annual and semiannual effect of solar activity on minimum temperature was observed in all the six stations. This was indicated in the occurrence of modal periodicities of 6-month and 12-month observed across the six synoptic stations. The synoptic stations are Sokoto (13.01°N, 5.15°E), Ilorin (8.29°N, 4.35°E), Ikeja (6.35°N, 3.20°E), Enugu (6.28°N, 7.33°E), Port-Harcourt (4.51°N, 7.01°E) and Maiduguri (11.51°N, 13.05°E). Similarly, the trends of inter-decadal va-riability of minimum and maximum temperature show a non-uniformity increase over the analyzed period with a slight decrease before 1960. The long term behavior of minimum and maximum temperature shows a warming rate which ranges from 0.1°C/decade to 0.2°C/ decade across the six stations except for maximum temperature at Ilorin and minimum temperature at Sokoto which is at -0.2°C/decade and 0.3°C/decade respectively.
文摘There has been an increasing global and local interest in developing renewable, clean, and cheap energy towards achieving Goal number 7 of the Sustainable Development Goals (SDG). However, decisions involving suitable and sustainable locations for renewable energy projects remain an important task. This study employed Geographic Information System (GIS) and Multi-Criteria Decision Analysis (MCDA) to spatially analyze and model wind farm site suitability in Nasarawa State. The aim is to integrate the environmental, social, and economic aspects of decision-making for identifying sustainable wind farm sites. The study distinguished between two sets of decision criteria: decision constraints and decision factors. The former defined the exclusion zones while the latter were standardized based on fuzzy logic to depict varying degrees of suitability across the State. The MCDA applied the weighted linear combination method, with relative weights generated through pairwise comparisons of the analytic hierarchy process to analyze three policy scenarios: equal weights, environmental/social priority, and economic priority scenario. A combination of resulting composite maps from the constraints and the factors gave the final suitability maps. The resulting suitability index (SI) for the respective policy scenario describes the degrees of suitability: Ideal locations were denoted by one (1) and the not suitable locations by zero (0), with values in-between depicting varying degrees of wind farm site suitability. Based on the SI, priority locations indicating areas with good prospects, in addition to the most suitable parcels of land, were identified and delineated. The composite decision constraint revealed that wind farm projects would not be viable in more than half (57.58%) of the State. Wind speed was the major constraint and accounted for the exclusion of 46.25%, with a mean fuzzy membership value of 0.2008 indicating low suitability across the State. Also, the average acceptable wind farm location for the three-policy scenario was 33.33% of the entire study area. Lafia, Obi, Keana, Awe, Nasarawa-Eggon, Wamba and Kokona LGAs were the identified priority Local Government Areas (LGAs). However, only Lafia, Obi, and Nasarawa-Eggon were consistent with changes in the policy objectives. All the priority LGAs have one or more of the most suitable parcels within their administrative boundaries except for Wamba. Despite the severe limitations of wind speed, substantial parts of Nasarawa State still provide great development potentials for wind energy. The “most suitable” locations in Lafia, Nasarawa-Eggon, and Obi LGAs should have first consideration for the development of wind energy in the State.
文摘As interest in the use and launching of spacecraft for communications,earth observation,scientific experiment and navigation purposes increases and manned missions to the Moon and Mars intensify,there is need for the design of efficient and highfidelity relative motion dynamics to reduce spacecraft collisions and increase return on investment.The main aim of this work is to develop new approximate solution of spacecraft relative motion in elliptical orbit via power series method.Advantage of this method is that it does not involve evaluating complex integral I as employed for developing approximate solutions of linearized Tschauner–Hempel equations.Cauchy product,used for the discrete convolution of power series,is employed for the development of power series solutions of the approximated nonlinear spacecraft relative motion.Application of Cauchy criterion shows that the new solutions are convergent making them useful for spacecraft formation flying,proximity and rendezvous mission analysis.
文摘In this paper,approximated nonlinear spacecraft relative motion model is developed via Euler Lagrange approach using local vertical-local horizontal frame attached to the chief spacecraft.Harmonic balance analysis approach,a powerful technique for approximating nonlinear equation and generating periodic solutions,is applied to the approximated nonlinear relative motion for the development of new linear harmonic balance approximation model and investigation of its periodic solutions.Using power series method,power series approximate solutions of the harmonically balanced model of the relative motion are developed.Furthermore,the computational algorithm employed for the orbit propagation of nonlinear,harmonic balance and Clohessy-Wilshire models is presented.Using MATLAB ODE45 integrator,the relative motion models are numerically integrated and propagated.The numerical results show that harmonic balance model gave a better approximation of the nonlinear model.
文摘Nonlinear time-varying system,such as a spacecraft formation flying system with chief spacecraft in elliptical orbit and under the effect of perturbation forces,is difficult to analyze,design,and control based on the presence of time-varying parameters.The proper functioning of aerospace systems and their ability to be able to achieve the designed mission objectives depend largely on proper understanding of their nonlinear time-varying nature,dynamics,and ability to keep them in the required mission operation configurations through high-fidelity optimal control strategy.This paper presents nonlinear dynamics and optimal control of J_(2)perturbed spacecraft formation flying.Via Euler–Lagrange approach,the nonlinear J_(2)perturbed motion dynamics was approximated into a time-varying nonlinear form,having periodic coefficients and time-varying parameters,suitable for designing fuel efficient control strategies,spacecraft formation flying,relative motion,and rendezvous mission analysis.Through the application of State-Dependent Riccati Equation(SDRE)approach,the approximated model was converted into a non-unique,pseudo-linear state-dependent coefficient(SDC)form.The numerical simulations confirmed that the SDRE controllers,developed using SDC parameterized systems,are maximally robust and able to return the system to the desired radial,along-track,and cross-track positions.
文摘Monsoon driven water mass exchange between the Bay of Bengal(Bo B) and Arabian Sea(AS) is the common experience. However, it is not yet firmly confirmed that the exchange pathway is either passing through southern tip of Sri Lanka or Palk Strait. Local circulation patterns impact the pathways followed by the East Indian Coastal Currents(EICC) that drive exchange, thereby modulating mixing and water mass transformation in the Bay of Bengal around Sri Lanka. In this study, observations from surface drifters were incorporated with the satellite derived data to understand the monsoonal impact on circulation patterns in the Indian Ocean. This was the first multi-national scientific effort which was conducted in the Bo B and AS during 2013 to 2015 to understand the monsoonal impact on circulation patterns in the complex region. The results indicated that seasonally reversing monsoonal currents of southern Sri Lanka, traced by the wintertime freshwater export pathways of the EICC. The deflection of monsoon currents running along the east coast of Sri Lanka by forming cyclonic and anti-cyclonic eddies, which influence the mixing and stirring associated with these flows. Results further indicate the low salinity cold water flows from the Bo B to AS along the western boundary of the Bo B during northeast monsoon. In the same way, reverses the phenomena during southwest monsoon, transporting high salinity warm water from AS to the Bo B. This maintain the bay status which occurred due to freshwater influx from large rivers and high saline water from AS. However, no evidences were observed for the exchange through Palk Strait during the study.Also, there are some mis-matches in in-situ and remotely sensed measurements which imply the necessity of systematic observation system for the complex region as an alternative approach.
文摘The aim of this study was to develop an efficient and realistic response surface optimization technique for the design of V-belt drive for optimum power output of the drive in machinery design. Optimization mathematical model of the V-belt drive was constructed. The power output of the belt drive was modeled and optimized by the Response Surface Methodology (RSM). Analysis of variance was used to evaluate the extent of influence of each independent variables on the power output response of the belt drive. A RSM optimization process was proposed to calculate optimal power output for V-belt drive given a set of pulley diameter for the drive employed in a tilling machine. The analysis showed that optimum power output of the drive for workshop light operation machinery could be obtained at driving and driven pulley radius range of 550 - 900 mm and 250 - 500 mm. An optimum power output of 1418.76 kW was obtained at driving and driven pulley radius of 846 and 486 mm respectively for a farm tilling machine.
文摘We present interesting application of artificial intelligence for investigating effect of the COVID-19 lockdown on 3-dimensional temperature variation across Nigeria(2°-15°E,4°-14°N),in equatorial Africa.Artificial neural networks were trained to learn time-series temperature variation patterns using radio occultation measurements of atmospheric temperature from the Constellation Observing System for Meteorology,Ionosphere,and Climate(COSMIC).Data used for training,validation and testing of the neural networks covered period prior to the lockdown.There was also an investigation into the viability of solar activity indicator(represented by the sunspot number)as an input for the process.The results indicated that including the sunspot number as an input for the training did not improve the network prediction accuracy.The trained network was then used to predict values for the lockdown period.Since the network was trained using pre-lockdown dataset,predictions from the network are regarded as expected temperatures,should there have been no lockdown.By comparing with the actual COSMIC measurements during the lockdown period,effects of the lockdown on atmospheric temperatures were deduced.In overall,the mean altitudinal temperatures rose by about 1.1℃ above expected values during the lockdown.An altitudinal breakdown,at 1 km resolution,reveals that the values were typically below0.5℃ at most of the altitudes,but exceeded 1℃ at 28 and 29 km altitudes.The temperatures were also observed to drop below expected values at altitudes of 0-2 km,and 17-20 km.
文摘Theoretical frameworks used to explain the location of services include central place theory, aspects of industrial location theory and spatial diffusion theory. They are all described as normative theories which optimize with respect to defined criteria operating in prescribed environmental conditions (Rushton, 1979). However, recent advancement in geospatial technologies has led to several applications in geographically orientated challenges, hence, the adoption of an effective decision tool like Geographic Information System (GIS), high resolution products of satellite remote sensing as well as the Global Positioning System (GPS) in solving the rather challenging task of optimal location for facilities with respect to necessary criteria. Minna metropolis is being affected adversely by the problem of appropriate location of public facilities. These facilities are either too far from their market zone or they are too congested in a particular location and in some cases, political consideration to the siting of these facilities dominate without given considerations to the necessary criteria for demands and public interest. The study is an investigation into the “optimal determination of the locations of some public facilities in Minna metropolis of Niger State, using geospatial techniques”. The fusion of remote sensing, geographic information system (GIS) and GPS techniques was explored. Geodata base of existing facilities was created and Euclidean-distance geometry used to spatially analyze the appropriate locations with regards to the set of standard criteria. The results showed the haphazard and uncontrolled pattern of development of schools location. However, petrol stations met the evaluated criteria and optimal location indexes.
文摘Three gram negative bacteria isolated from infected koi carp, Cyprinus carpio L. and screened for sensitivity to thirty antibiotics by the Bauer disc diffusion method. Bacteria evaluated were Aeromonas hydrophila, Pseudomonas aeruginosa and Edwardseilla tarda. A. hydrophila was resistant to ampicilin, cephalothin, sulphatriad, cefpodoxime and cefoxitin. Highest sensitivity was recorded to Colistin methane sulphonate and Ceftriaxone. High resistance was observed for P. aeruginosa in Kanamysin, Cephalothin, Sulphatriad, Colistin methane sulphonate, Tobramysin, Nitro Furantoin, Cefpodoxime, Cefoxitin and Aztreonam. Highest sensitivity recorded with Moxifloxacin. High resistance was observed in Co-trimoxamole and higher sensitivity performed for E. tarda by Tetracyclin, Cephotaxime, Ciprofloxacin, Norfloxacin, Ofloxacin, Moxifloxacin, Gatifloxacin and Levofloxacin. Out of that highest sensitivity recorded with Moxifloxacin High sensitivity was recorded for Moxifloxacin, Ciprofloxacin, Gatifloxacin, Levofloxacin. By means of antibiotic sensitivity test highest resistance was recorded to P. aeruginosa （MAR index-0.3） and least resistant was recorded to E, tarda （MAR index- 0.033）.
文摘The urban environment has continued to experience changes from increasing impervious surfaces, which alters the proper functioning of the ecological zones and impairs water quality in the watershed. Impervious cover is predominantly used as an indicator to assist in understanding and forecasting the impact of human actions and other related activities on aquatic resources. In this study, the rate of change in land uses using the impervious surface as an indicator, and the percentage of imperviousness on the effect on water quality in the urban watershed were assessed. Ile-Ife was delineated as an urban watershed, and the percentage of imperviousness from 2008 to 2016 and the effect of imperviousness on water bodies were assessed. The study utilized ASTERDEM, Worldview (0.46 m), IKONOS (1.4 m), Landsat (30 m) for 2008 and 2016, GPS and Drone (10 cm). Water sampling was carried out in selected locations as generated by the impervious surface analyst tool, (ISAT). The percentage (%) of impervious surfaces accounted for 59.4% (4567.1/7691.5ha) in 2008 and 70.3% (5408.2/7691.5ha) in 2016, from the total number of lands investigated. The turbidity values from low to high regions were 32.3, 55.9 and 82.4 NUT. Changes in LULC of the watershed led to increased surface temperature, impermeable surfaces, and decreased vegetation, which exposes the area to flooding and reduced water quality. This study emphasized the importance of GIS and its integration into urban changes and water quality assessment.
文摘The importance of Remote Sensing and Geographic Information System in map making cannot be overemphasized because of its ability to integrate spatial data with non-spatial data and also communicate the resulting information in a way that everyone would understand. Several works have taken advantage of the abilities of these technologies to produce street maps using High Resolution Images. The increase in development in Ile Ife, Osun State, Nigeria, has brought about navigation challenge and associated difficulties. This work intends to produce a street map that will ease navigation within the study area and help in road network analysis, site suitability analysis etc. Aerial Photographs, captured in the year 2009 and GeoEye1 Satellite Image of 2011 were used to extract the road network of Ife Metropolis. The image was imported into ArcGIS environment, where the database was created having feature datasets such as roads and special features. To have all the elements in vector format, the image was digitized. The street names collected from the field work was inputted into the database and then subjected to cartographical processes. 512 Roads were captured within four classes of Road Network namely Express road (5), Secondary Road (25), Primary Roads (22) and Street Road (460). This field work revealed that a larger percentage of the roads were not paved, while most of the paved ones have deteriorated and the newly constructed ones were not documented. It also showed that some of the roads were not named according to the standard and some were not named at all. From this study, we recommend that the naming system should be standardized across the study area. It is also recommended that provision should be made for street map revision on a yearly basis so as to account for changes.
文摘This study employed Geographic Information System (GIS) and remote sensing approach to analyze the flood vulnerability areas in the Okoko basin area of Osogbo in Osun state, Southwestern Nigeria. High-resolution imageries, a Topographic map of the study area and a TCX software program (Version 2.0) were integrated using ArcGis (10.7). Some of the causative factors for flooding in the watershed were taken into account which are: Land use, Distance of buildings to drainage, Digital Elevation Model, and Slope. This study aimed at mapping the flood-vulnerable areas along the Okoko basin of Osogbo. In developing a flood risk/flood hazard map of the study area, and determining the level of expected disaster, a multi-criteria analysis was utilized. The factors considered were ranked in five classes with the highly vulnerable areas having the highest score of “5”. These factors were weighed according to the estimated significance of causing flooding. The study revealed that the study area has an estimated area of 17.85 km<sup>2</sup> of which 14.2 km<sup>2</sup> falls within the vulnerable areas while 3.6 km<sup>2</sup> is on the least vulnerable areas. Moreover, out of 16,829 buildings in the study area, 8204 buildings were found susceptible to flood disasters. This research attempts to equip decision-makers to make accurate decisions and also serves as a mitigation measure for flood disaster management.
文摘A process capability study is performed for the turning process on a general purpose center lathe in order to verify the process performance and machine ability to perform within specified tolerance limit. The process and machine capability indices were measured to determine the process and machine adequacy for industrial application. The tolerance limits were obtained from the given nominal size of the shaft, using the basic hole system and 90 sample shafts were turned on the lathe machine to specification for varying spindle speed and feed rate of the lathe. Three (3) samples were randomly selected for the turning process of a combination of the spindle speed and feed rate as a subgroup size for a total subgroup of thirty (30). The diameters (representing the quality characteristics) were used to generate control charts and capability histogram for the process. The process is within statistical control but found incapable of meeting up to specification because the capability index (C<sub>p</sub>) measured was less than 1 and the machine capability for industrial application is not adequate.
文摘Over the years,the African continent has been importing used gasoline and diesel vehicles including ones that are 10 years old.Such vehicles emit carbon dioxide,which is the leading cause of greenhouse gases(GHGs)that are driving the climate change.In Rwanda,for example,road transport contributes to 13 percent of the country’s greenhouse emissions,according to the Rwanda Environment Management Authority(REMA).Africa as a developing continent continues to pollute air,partly due to the use of second-hand cars from developed countries.
文摘This study examines the prenoon-postnoon asymmetrical behaviour and latitudinal dependence of Sq （solar quiet） current system using data of quiet-time daily variations of the geomagnetic field intensity from twelve geomagnetic observatories along the African Meridian. The dataset of each month during 2009 （noted for empirically low solar activity with average sunspot number Rz = 3.1） was treated for non-cyclic correction. From a blend of spatial contour maps and graphical analyses, our results show that Sq current system exhibits in the daytime unstable tendency. A consistent diurnal variation of solar quiet variation in the horizontal component of earth magnetic field （SqH） was observed which exhibits synoptic pre-noon and post-noon mean values of 59 nT and 33 nT with ranges of 33 nT and 24 nT, respectively. The centre of circulation of overhead electric current is observed to exhibit both pre-noon and post-noon epoch＇s asymmetric variations. This is noted to indicate the dynamic heterogeneous genesis of the mechanism responsible for the observation. The spatial contour mapping result depicts SqH behaviour switch twice a year around March and September with similar spatial distribution in January up to March and then October up to December. A similar distribution was noted for the months of April to September. Prenoon values of SqH have higher magnitudes across the latitudes in comparison with the post noon values just as is the case at noontime.
