Photoluminescence of tetrahedral quantum-dot quantum wells

Taking into account the tetrahedral shape of a quantum-dot quantum well (QDQW) when describing excitonic states, phonon modes, and the exciton-phonon interaction in the structure, we obtain within a nonadiabatic approach a quantitative interpretation of the photoluminescence spectrum of a single CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW is bright, in contrast to the dark ground state for a spherical QDQW. The position of the phonon peaks in the photoluminescence spectrum is attributed to interface optical phonons. We also show that the experimental value of the Huang-Rhys parameter can be obtained only within the nonadiabatic theory of phonon-assisted transitions.     

A sparse octree gravitational N-body code that runs entirely on the GPU processor

We present the implementation and performance of a new gravitational N-body tree-code that is specifically designed for the graphics processing unit (GPU).¹ All parts of the tree-code algorithm are executed on the GPU. We present algorithms for parallel construction and traversing of sparse octrees. These algorithms are implemented in CUDA and tested on NVIDIA GPUs, but they are portable to OpenCL and can easily be used on many-core devices from other manufacturers. This portability is achieved by using general parallel-scan and sort methods. The gravitational tree-code outperforms tuned CPU code during the tree-construction and shows a performance improvement of more than a factor 20 overall, resulting in a processing rate of more than 2.8 million particles per second.