Site-controlled quantum dots fabricated using an atomic-force microscope assisted technique

An atomic-force microscope assisted technique is developed to control the position and size of self-assembled semiconductor quantum dots (QDs). Presently, the site precision is as good as ± 1.5 nm and the size fluctuation is within ± 5% with the minimum controllable lateral diameter of 20 nm. With the ability of producing tightly packed and differently sized QDs, sophisticated QD arrays can be controllably fabricated for the application in quantum computing. The optical quality of such site-controlled QDs is found comparable to some conventionally self-assembled semiconductor QDs. The single dot photoluminescence of site-controlled InAs/InP QDs is studied in detail, presenting the prospect to utilize them in quantum communication as precisely controlled single photon emitters working at telecommunication bands

Anisotropic Confinement, Electronic Coupling and Strain Induced Effects Detected by Valence-Band Anisotropy in Self-Assembled Quantum Dots

A method to determine the effects of the geometry and lateral ordering on the electronic properties of an array of one-dimensional self-assembled quantum dots is discussed. A model that takes into account the valence-band anisotropic effective masses and strain effects must be used to describe the behavior of the photoluminescence emission, proposed as a clean tool for the characterization of dot anisotropy and/or inter-dot coupling. Under special growth conditions, such as substrate temperature and Arsenic background, 1D chains of In0.4Ga0.6 As quantum dots were grown by molecular beam epitaxy. Grazing-incidence X-ray diffraction measurements directly evidence the strong strain anisotropy due to the formation of quantum dot chains, probed by polarization-resolved low-temperature photoluminescence. The results are in fair good agreement with the proposed model

On the phenomenon of vortex street breakdown

A von Kármán vortex street generated in the usual way was subjected to a deceleration, thereby changing the ratio of longitudinal to lateral spacing between the vortices. Distortion of the individual vortices followed which resulted in annihilation of concentrated vortex regions and creation of a stationary wake flow. This wake flow was itself dynamically unstable and developed into a new vortex street of a different frequency from the initial one. The breakdown of the initial vortex street is qualitatively explained by considering the convection of a concentrated vortex region due to the motion imposed by all the other vortices

Identification, Antifungal Susceptibility and Phylogenetic Comparison of Fungi in Poultry Environment in Nigeria

Objective: This study was conducted to investigate the fungal community structure in Nigerian poultry environments. Materials and Methods: In ten (layer and broiler) farms, samples were collected from drinkers, doors, feeders, floors, poles, roofs, walls and window nets. Fungal isolation was done on Sabouraud dextrose agar (SDA) followed by identification using morphological and microscopic features. The fungal identities were confirmed by sequencing the internal transcribed spacer region, followed by phylogenetic analysis. Antifungal susceptibility testing was done using nystatin (100 μg mL–1), fluconazole (25 μg mL–1) and voriconazole (1 μg mL–1). Results: A total of 244 fungi were identified in all the locations. In the layers farm, 112 fungal isolates were identified, while 132 isolates were identified in the broiler farm. In all the poultry farms, Aspergillus and Candida species had the highest occurrence of 32.4 and 24.6%, respectively while other fungi (Dematiaceous, Rhizopus, Penicillium, Mucor and Rhodotorula) had 43% occurrence. For the locations, poles and window nets had the highest isolation frequency of 15.2% each. The roofs, feeders and floors had 14.3 and 13.1%, while other locations had 27% isolation rate. Phylogenetic comparison of the isolates showed that closely related fungi from different countries formed separate clades. Candida species were sensitive to the three antifungal agents with the zone of inhibition diameter ranging from 19.08-25.36 mm. All the Aspergillus species were resistant to fluconazole but were sensitive to nystatin and voriconazole. Conclusion: Different fungi were identified in this study and they were all susceptible to nystatin antifungal agent