There is a substantial amount of literature dealing with many aspects of synthesis and characterization of pure and doped binary compounds including Mn-doped ZnO which has been widely studied due to its superb properties as a dilute magnetic semiconductor (DMS). Aspects concerning doping limits for these compounds is an important stage in the search for new materials. Samples of Zn1-xMnxO nanocrystal were synthesized at temperatures of 180 °C and 200 °C using wet or liquid phase synthesis method. Dopant concentrations x=0.5, 1, 1.5, 2, 2.5, 5, 10, 20, 30, 40 and 50 per cent were studied. Powder x-ray diffraction (PXRD) patterns of the samples were analyzed with a view to determining the onset of secondary phases and hence the solubility limit of the dopant. The solubility limit for Mn in ZnO samples synthesized at temperature of 200 °C is realized at x <20%. For samples synthesized at temperature of 180 °C, the solubility limit is x <0.5%.
The paper outlines three approaches which were used to study the frictional properties of explosive substances. The techniques involved sliding (i) single crystals on single crystals, (ii) single crystals on glass and (iii) glass surfaces over thin films of the explosive which were deposited on glass substrates. The latter technique in conjunction with the adhesion model of friction is shown to be capable of predicting accurately the coefficients of friction in the other two cases within certain ranges of load. Data are also presented on the hardness of certain explosive materials. The paper concludes by speculating the likely effects of temperature and sliding velocity on the friction of single-crystal contacts.
IntroductionIt is generally thought that countries that experience extended periods of sunshine might better enjoy the benefit of solar energy. Nevertheless, the performance of photovoltaic (PV) devices is critically dependent on the ambient temperature and the operating temperature of a given device. Also, irradiance, relative humidity and harmattan dust particles, and several other parameters such as wind speed, wind chill and direction, seasonal variation of sunrise and sunset, rainfall, and how the module is installed (rooftop, ground system, orientation, etc.) can be expected to influence the performance of a solar panel.Generally, sunny climates are most often hot, with a large variation in relative humidity, ranking from dry to humid. It is necessary, therefore, to carry out in situ studies of the parameters of PV devices under controlled and varying conditions. Such a study of the seasonal variation of the operating temperature of solar PV panels was undertaken in Southern Ghana.Ghana's climate depends on three types of air masses. Consequently, Ghana has three distinct types of climate (Varley and White 1958, 34-50):
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