University of Stuttgart

About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.

Imperfect shadow maps for efficient computation of indirect illumination

Abstract: We present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow maps---low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.

Numerical investigation of the three-dimensional development in boundary-layer transition

Abstract: A numerical method for solving the complete Navier-Stokes equations for incompressible flows is introduced that is applicable for investigating three-dimensional transition phenomena in a spatially growing boundary layer. Results are discussed for a test case with small three-dimensional disturbances for which detailed comparison to linear stability theory is possible. The validity of our numerical model for investigating nonlinear transition phenomena is demonstrated by realistic spatial simulations of the experiments by Kachanov and Levchenko1 for a subharmonic resonance breakdown and of the experiments of Klebanoff et al.2 for a fundamental resonance breakdown.

Model for electronic transport in Cu(In,Ga)Se2 solar cells

Abstract: Temperature-dependent measurements of the current–voltage characteristics and of the junction admittance of ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells are presented, together with numerical modelling of these experimental results. We explain the cross-over between dark and illuminated current–voltage characteristics currently observed for this type of device by the impact of the defect chalcopyrite layer at the surface of the Cu(In,Ga)Se2 absorber. Our model assumes an illumination-dependent voltage drop across a defect layer with a thickness of 15 nm to explain the cross-over. The voltage drop results from the electrical dipole made up of donor-like states at the interface between the defect layer and CdS and deep acceptor states in the defect layer itself. The illumination dependence of this voltage drop is explained by photogenerated holes trapped by the deep acceptor states in the defect layer. Numerical simulations have been carried out using the program SCAPS-1D in order to verify our model assumptions. From our model, indirect conclusions are derived concerning the maximum conduction band offsets between CdS and the defect layer and between CdS and ZnO. Copyright © 1998 John Wiley & Sons, Ltd.