A.S.M. Hajar
Using the random quadrat method, a one year ecological study on the vegetation of a traditionally protected and a continuously grazed parts of hema Sabihah was conducted. This was undertaken by recording the:
a) Flora of the study area (72 species of 32 family were recorded).
b) Plant height (The height of the important palatable plant Cymbopogon schoenanthus (L.) spreng was decreased by 59% in the area open for grazing of it's height in the protected part).
c) Importance Value Index (IVI) for every species found in the random quadrats, and from that the Total IVI was calculated (e.g. the total IVI in Autumn was 354.5 & 245.7 for the protected and the grazed areas respectively).
d) plant dry biomass gm/m^2
e) chemical and physical properties of the soil
Results of a, b, c, d, & e showed that the protected part maintained higher species diversity, and palatable plants, e.g., C. Schoenanthus (IVI 486.1). Such high plant diversity played a major role in soil conservation. The area open for grazing has a low cover, and consists mainly of a non-palatable species, e.g. Asphodelus fistulosus L. (IVI 212.4) and Psiadia punctulata D.C. (IVI 208.5). The palatable species are severely destroyed in this part, and represented, if found by their rhizomes.
This resulted in severe soil erosion, and Cross soil texture. The average soil water soluble nitrogen (N) was higher in this part (2.17 µg/g dry soil) than that of the protected part (1.03 µg/g dry soil). However similarities between some of the soil properties were found e.g. the average soil: water content (2%). pH (8), organic matter (8%) and the water soluble P, Ca, and K, and the electrical conductivity (µm ho/cm). The present study shows both the ecological and economical important of such hema system.
A.A. Joraide
This paper deals with the effect of Se impurity, grain size, and the anisotropic state on the energy gap for a pressed powder alloy of p- type semiconductor (Bi2Te3)25- (Sb2Te3)75. The D.C. four probe technique was used to measure the temperature variations of the electrical resistivity over the temperature range 120- 700K. The samples were doped with Se of concentrations 0, 0.1, 0.3, 0.5, 0.9 and 1.3 wt%, and were possessed grain sizes (L) in the range 30 > L > 20 µm, 15 > L > 10 µm, 10 > L > 5 µm and L < 5 µm. From the resistivity results the energy gaps were obtained.
The results indicate the anisotropic state of the alloy, grain size, and Se concentration all affect the energy gap.