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  • Author or Editor: A. M. Gomaa x
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A pot trial was carried out in the greenhouse of the National Research Centre during the summer season of 1999 to investigate the combined impact of Bradyrhizobium sp. (vigna) and Azotobacter vinelandii in the presence of various doses of chemical fertilizers, i.e. 25%, 50% and 100% of the recommended dose of NPK, on nodulation, growth parameters, seed yield and its components, and seed contents of protein, phosphorus and potassium of a local (Kawmy-1) and three exotic (VC-4, VC-9 and King) varieties of mungbean. The results indicated that there were no significant differences between the different varieties for nodule number per plant, while significant variations were obtained between both varieties and biofertilization treatments. The plants of the Kawmy-1 variety gave the shortest period of growth, the highest number of pods per plant and the highest values of harvest index and seed protein content. The King variety had the longest period of growth and the highest values for number of branches, seed yield, biological yield, seed index and seed phosphorus content. The inclusion of Azotobacter vinelandii significantly augmented various tested parameters, with the exception of seed yield, biological yield and potassium content, in comparison with Bradyrhizobium. Insignificant differences were found owing to the interaction between varieties, various levels of mineral fertilizers and types of biofertilizers with the exception of harvest index and seed phosphorus content.

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The electrical conductivity of pure and Co-doped MgAl2O4 spinels was measured at 700–1100 K. The results of both pure and doped spinels were found to be fitted with an exponential expression with two different activation-energy parameters, in two ranges of temperature. The effect of -irradiation on the electrical conductivity of pure and doped spinels was also studied. The kinetic parameters of the isothermal annealing of the induced irradiation damages in the spinels were determined. All the results were found to be consistent with the ionic conduction which was suggested to be due to the motion of the cation vacancy.

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Vegetation in natural desert and agro-ecosystems was investigated in the middle sector of Egypt. The vegetation was classified by the Two Way Indicator Species Analysis technique (TWINSPAN) into nine vegetational groups representing seven habitat types: desert, fallow land, winter crops of old cultivated land, summer crops of old cultivated land, Citrus orchards, winter crops of reclaimed land, and summer crops of reclaimed land. Detrended Canonical Correspondence Analysis (DCCA) demonstrates that soil factors especially soil texture, CaCO3, organic carbon and electric conductivity contribute significantly to the distribution of species. In all habitat types, species diversity is higher in winter than in summer season. The weed species diversity is greater in the reclaimed areas compared to the old cultivated land and in winter crops than in summer ones.

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Using the positron annihilation lifetime technique, the annihilation parameters have been measured for epoxy and high density polyethylene (HDPE) as a function of AC electric field strength and the exposure time. The lifetime spectra have been resolved into three components, the longest component (I3 3) is attributed to the pick-off annihilation of o-Ps in the amorphous regions. The intermediate one (I2 2) is due to the annihilation of free positrons, while the shorter component (I1 1) stems from self annihilation of p-Ps. In HDPE, the o-Ps parameters 3 andI 3 are measured as a function of electric field strengths in the range from 10 to 100 kV/cm exposed for 24 hours. A decrease inI 3 of 8% is observed from zero to 50 kV/cm followed by an increase of the same order from 50 to 100 kV/cm. By investigating the effect of the exposure time from 2 to 24 hours at 16 and 50 kV/cm, the effect is confirmed and is attributed to the inhibition of o-Ps formation at lower field strength. In epoxy, the effect or exposure time onI 3 at 166 and 133 kV/cm shows a similar behavior as in HDPE. At 133 kV/cmI 3 decreases by only 2.5%. On the other hand, the changes in 3 occur at short exposure times. Again at large times the saturation is obtained. These effects are attributed to the expansion of free volume (increase of 3) competing at longer exposure times with other phenomena, such as liberation of free radicals, which reduce the o-Ps intensityI 3 through the conversion to p-Ps. The reactions between o-Ps and free radicals might also lead to free positrons, which could explain the increase ofI 2 and the decrease of 3 at longer exposure times.

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