Kajian terhadap struktur komuniti tumbuhan Periuk Kera di Hutan Pendidikan Alam, Universiti Kebangsaan Malaysia, Bangi, Selangor Darul Ehsan

Two species of pitcher plants namely Nepenthes gracilis Korthals and . mirablis (Loureiro) Druce were recorded in the plot with an area of 0.1 hectare. The former species differed from the later species lJy its angular stem, sessile leaves, very thin peristome (~ 1 mm thick), under surface of pitcher lids were sparsely glandular, inner surface of the pitcher cavities were partly covered with exposed type of digestive glands whereas the later species have cylindrical stem, petiolate leaves, thick peristome (;? 1 mm thick), under surface of pitcher lids were densely glandular, inner surface surface of the pitcher cavities were partly covered with overarched type of digestive glands. The population density of N. gracilis is greater than that of N. mirabalis, each contained 147 and 15 individuals respectively. The low density of the former species was attributed to its strong tendency to grow in wet soil particularly in temporary and permanent inundated secondary vegetation. The population dispersion pattern of seedlings, saplings and matured plants of N. gacilis and N. gracilis were significantly aggregated

Modelling of stark effect in InAs-AlGaSb multi-quantum wells

The Stark effectina (20)InAs­(6)As-(6)Al0.1Ga0.9 Sb multi-quantum well structure was theoretically modelled using the electric-field-perturbed formulation of the empirical pseudopotential method. An external electric field of up to 4.0 x 1()5 V cm-! was applied along the axis of the multi-quantum well structure and its effect on the energy level, localisation and optical transition of the lowest electron and hole states were investigated. The perturbation pro­duced Wannier-Stark localisation and a red Stark shift for this type II semiconductor heterostructure. The calculated optical gap decreased down to 10 meV with the corresponding principal momentum matrix elements, along x polarisation, remain basically constant at a.u.(atomic unit). This property makes the III-V semiconductor heterostructure poten­tially attractive for use as a field-tunable device in the infrared spectra of 10-100µm

Effective mass of band edges in a (20)InAs-(6)Al0.1Ga0.9Sb superlattice

The curvature method and the f-sum rule are used to calculate the effective mass of electrons and holes at the Brillouin zone band edges of a (20)InAs(6)Al0.1Ga0.9Sb superlattice. The electronic and optical parameters used in the calculations for this type II semiconductor superlattice are derived from the relativistic empirical pseudopotential method. In this superlattice system the calculated effective masses for the carriers are anisotropic and differ from those of the various reported semiconductor heterostructures. These results indicate that the carrier effective masses are dependent on certain factors such as polarisation, constituent layer composition and layer length. The calculated effective masses of electrons in this III- V semiconductor heterostructure are found to be larger than those in Hg1-xCdxTe alloys with similar band gaps corresponding to cutoff wavelengths near 10 μm. This makes the InAs-AlGaSb superlattice system a potential competitor to the present standard material of HgCdTe for far infrared applications