Atomic Effective Pseudopotentials for Semiconductors

We derive an analytic connection between the screened self-consistent effective potential from density functional theory (DFT) and atomic effective pseudopotentials (AEPs). The motivation to derive AEPs is to address structures with thousands to hundred thousand atoms, as given in most nanostructures. The use of AEPs allows to bypass a self-consistent procedure and to address eigenstates around a certain region of the spectrum (e.g., around the band gap). The bulk AEP construction requires two simple DFT calculations of slightly deformed elongated cells. The ensuing AEPs are given on a fine reciprocal space grid, including the small reciprocal vector components, are free of parameters, and involve no fitting procedure. We further show how to connect the AEPs of different bulk materials, which is necessary to obtain accurate band offsets. We derive a total of 20 AEPs for III-V, II-VI and group IV semiconductors and demonstrate their accuracy and transferability by comparison to DFT calculations of strained bulk structures, quantum wells with varying thickness, and semiconductor alloys.Comment: 10 pages, 5 figures, submitted to PR

Forster signatures and qubits in optically driven quantum dot molecules

An interesting approach to achieve quantum gate operations in a solid state device is to implement an optically driven quantum gate using two vertically coupled self-assembled quantum dots, a quantum dot molecule (QDM). We present a realistic model for exciton dynamics in InGaAs/GaAs QDMs under intense laser excitation and applied electric fields. The dynamics is obtained by solutions of the Lindblad master equation. A map of the dressed ground state as function of laser energy and applied electric field exhibits rich structure that includes excitonic anticrossings that permit the identification of the relevant couplings. The optical signatures of the dipole-dipole Forster energy transfer mechanism show as splittings of several (spatially) indirect excitonic lines. Moreover, we construct a model for exciton qubit rotations by adiabatic electric field cyclic sweeps into a Forster-tunneling regime which induces level anticrossings. The proposed qubit exhibits Rabi oscillations among two well defined exciton pairs as function of the residence time at the anticrossing.Comment: Paper presented in the International Conference on Electronic Properties of Two-dimensional Systems and Modulated Semiconductor Structures Genova Magazzini del Cotone, July 15-20 200

The Movement Of Soil Moisture Under A Government Subsidy House

Conference: First Southern African Geotechnical Conference, At Sun CityThe South African government's attempts to provide affordable, subsidised housing for the very poor has suffered from a large number of structural failures, many due to heaving foundations. These houses are particularly susceptible to damage by heaving clay because they are exceptionally light and clay can lift them very easily. Rational design requires knowledge of the pattern of heave which will occur under the foundation. The pattern of heave depends on the pattern of moisture movement. Currently available methods of rational design rely on assumptions about the shape of the mound which will develop due to moisture movement under the foundation. The shape assumed is largely guided by measurements made on test foundations. Instrumentation has been installed under a Government Subsidy house in the Free State and moisture movement is being monitored. The actual pattern of moisture movement observed is substantially different to what is normally assumed and could point to more reliable estimates of the heave which needs to be designed for

Jamming Transition In Non-Spherical Particle Systems: Pentagons Versus Disks

We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on experiments with monodisperse photoelastic particles with static friction coefficient μ≈1. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, Znr, reaches 3, and the dependence of Znr on the packing fraction ϕ changes again when Znr reaches 4. (2) Though the packing fractions ϕc1 and ϕc2 at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of ϕc1 and ϕc2 for pentagons are around 1% smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution

Carrier relaxation mechanisms in self-assembled (In,Ga)As/GaAs quantum dots: Efficient P -> S Auger relaxation of electrons

We calculate the P-shell--to-S-shell decay lifetime \tau(P->S) of electrons in lens-shaped self-assembled (In,Ga)As/GaAs dots due to Auger electron-hole scattering within an atomistic pseudopotential-based approach. We find that this relaxation mechanism leads to fast decay of \tau(P->S)~1-7 ps for dots of different sizes. Our calculated Auger-type P-shell--to-S-shell decay lifetimes \tau(P->S) compare well to data in (In,Ga)As/GaAs dots, showing that as long as holes are present there is no need for an alternative polaron mechanism.Comment: Version published in Phys. Rev.

Jamming Transition In Non-Spherical Particle Systems: Pentagons Versus Disks

We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on experiments with monodisperse photoelastic particles with static friction coefficient μ≈1. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, Znr, reaches 3, and the dependence of Znr on the packing fraction ϕ changes again when Znr reaches 4. (2) Though the packing fractions ϕc1 and ϕc2 at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of ϕc1 and ϕc2 for pentagons are around 1% smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution

Investigating the Effect of Withania somnifera, Selenium and Hydrocortisone on Blood Count and Bronchial Lavage of Experimental Asthmatic BALB/c Mice

The murine asthmatic Balb/c mouse model was used to investigate the effect of W. somnifera L., the  antioxidant selenium, W. somnifera and selenium in combination and hydrocortisone as positive control  on the number of white blood cells in blood smears and bronchial lavage smears as well as the platelet  distribution of asthmatic Balb/c mice. The mice were sensitised, nebulized and treated over a period of  43 days and blood smears were made of each individual animal and bronchial lavage was performed by  injecting 0.3ml of saline into the trachea of the mice, both on the day of termination. Light microscopy  analysis of the bronchial lavage revealed a significant decrease in the number of eosinophils counted in the  asthmatic and the different treatment groups. In the asthmatic group, numerous platelet clumps were found  distributed between white blood cells. Platelets were also found in the other treatment groups but are not  as prevalent as in the asthmatic group. Results from the blood smears showed the same trends, where cell  counts in control and hydrocortisone blood smears were decreased compared to that of the asthma group. It  is concluded that W. somnifera and W. somnifera combined with selenium significantly decreased the white  blood cells in both bronchial lavage as well as blood smears, suggesting that W. somnifera indeed has an  anti-inflammatory potential and it, in combination with an anti-oxidant like selenium, might successfully  be used in the treatment of asthma.

Kennis en houding van verpleegstudente aangaande VIGS in drie opleidingsinstansies in die, Wes-Kaap

A survey was done by means of a questionnaire to obtain information on the knowledge and attitudes of 297 nursing students from three training institutions in the Western Cape regarding HIV-infection and AIDS-patients