SOUTHERN JOURNAL OF SCIENCES

Background: MQ-series gas sensors belong to the metal oxide semiconductor (MOS) family of sensors that can sense the presence of many gases. These sensors find their application in gas alarm systems as key components. While necessary sensor circuit output voltage value for alarm point in a stand-alone gas alarm system is desirable, but what exact combination of the sensor circuit parameters is required? Hitherto, the determination of these circuit parameters has not been given much attention in the research community. Aim: the purpose of this work is to explore a structured graphical approach of determination of MQ series gas sensor circuit parameters for a stand-alone gas alarm system that yields desired sensor circuit output voltage value for the alarm point; the main objective of the study was to develop mathematical model equations that relate the: (i) sensor resistance (RS) with the gas concentration (x) and the sensor resistance at standard calibration concentration of the sensor base gas in the clean air (Ro) and (ii) sensor circuit output voltage (VRL), load resistance (RL) and sensor resistance (RS). It is expected from the model equations developed that graphical correlations of the sensor circuits parameters will be generated. Using these graphs for a particular case of an MQ-4 gas sensor under the influence of LPG, the parameters that yield desired sensor circuit output voltage of 2V for 1000 ppm of LPG alarm point will be determined. Methods: Model equations were developed for the sensor dynamics, and based on these model equations, graphs for the determination of required sensor parameters were plotted for a case of MQ-4 gas sensor response to LPG. Results and Discussion: The results yielded optimal values for R_O,R_S and R_L of 20 kΩ, 30 kΩ and 20 kΩ respectively, for alarm settings of 1000 ppm and a desired sensor circuit output voltage of 2 V. Based on determined parameters, the calibration equation for determination of best concentration value for a given value of emulated LPG concentration was developed. Using the method proposed in this study makes the process of determining the MQ-series gas sensor circuit parameters less cumbersome as their value can easily be obtained from the resulting graphs. Conclusions: a structured graphical approach for determination of MQ-series gas sensor circuit parameters for alarm points in a stand-alone gas alarm system showed that using MQ-4 gas sensor and LPG as the target gas, and for a sensor circuit output voltage of 2 V for alarm point at 1000 ppm of LPG, the corresponding value of R_O, R_S and R_L obtained were 20 kΩ, 30 kΩ, and 20 kΩ respectively. Hence, a structured graphical approach is suitable for determining MQ series gas sensor circuit parameters for a stand-alone gas alarm system under the influence of its associated gases.

Background: The desire to create a database of research documents providing information about the tracts of gold deposits across the local geological province provides the impetus for a study of the kind being considered here. Geospatial identification of built-up structures within Phase I Development along the Kazaure-Karaukarau-Kushaka-Ilesha Schist Belt, trending through Minna town and its outlying districts, constitutes the veritable reference material desired in this regard. Methods: This study began by segmenting the area of study for ground-based and remotely sensed attribute mapping, using the key reference map from a previous study as the area-of-study guide. A handheld Garmin GPSmap78® global positioning system unit and a standard smartphone with a built-in camera were the key equipment used for the fieldwork. Polygonal-format georeferenced coordinate information was collected at conveniently detached buildings, beginning with the cluster of residential homes at the Staff Quarters, for the ground-based survey. Result: Nine of the ten built-up structure clusters on the path of the Belt in Phase I Development were mapped for this study, as well as six neighborhoods in the Minna built-up area beyond Phase I. The nine clusters occupy almost 40% of the circa 2 km2 areal extent of the Phase I Development. The belt's trend and structures were north-northeast. Discussion: The nine cluster structures in Phase I and the six neighborhoods of Minna identified in this study have been determined to align with the path of the belt. Conclusion: Having now determined that the trace of the belt exits the Campus at the northern sector of the Gidan Kwano village and trends in a long arc beyond the town, this study becomes the desired reference material to be archived and consulted for information relating to gold exploitation in the Minna Area geological province.

In order to investigate the antioxidant activity of Salvia nemorosa L. collected from Ahar and Urmia regionsin Iran at different growth stages, aerial parts of sage after collecting were dried, and for measurement, the abilityof scavenge DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) radical in different concentrations (0.025, 0.05, 0.07,0.1, 0.2, 0.04 and 0.6) of methanolic extracts were prepared. The result showed that the ability to scavenge DPPHradical and amount of inhibition percent of vegetative stage leaves, flowering stage leaves, and flowers increasedwith increasing concentrations of methanolic extracts from 0.25 to 0.6 mg/mL. In the region of Urmia, the highestamount of DPPH inhibition there was in vegetative stage leaves, and the lowest amount of DPPH inhibition wasseen in flowers. In Ahar regions, unlike the Urmia region, the highest amount of DPPH inhibition there was inflowers, but the lowest of DPPH inhibition was seen in flowering stage leaves. Also, the content of inhibition ofDPPH in Ahar and Urmia regions similarly increased between two phenological stages (vegetative stage leaves,flowering stage leaves, and flowers) in 0.4 mg/mL and 0.6 mg/mL concentrations.