Karlsruhe Institute of Technology

About: Karlsruhe Institute of Technology is a education organization based out in Karlsruhe, Germany. It is known for research contribution in the topics: Computer science & Catalysis. The organization has 37946 authors who have published 82138 publications receiving 2197068 citations. The organization is also known as: KIT & University of Karlsruhe.

Tunable two-dimensional photonic crystals using liquid crystal infiltration

Abstract: The photonic band gap of a two-dimensional photonic crystal is continuously tuned using the temperature dependent refractive index of a liquid crystal. Liquid crystal $E7$ was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 $\ensuremath{\mu}$m and a band gap wavelength range of 3.3--5.7 \ensuremath{\mu}m. After infiltration, the band gap for the H polarized field shifted dramatically to 4.4--6.0 \ensuremath{\mu}m while that of the E-polarized field collapsed. As the sample was heated to the nematic-isotropic phase transition temperature of the liquid crystal $(59\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}),$ the short-wavelength band edge of the H gap shifted by as much as 70 nm while the long-wavelength edge was constant within experimental error. Band structure calculations incorporating the temperature dependence of the liquid crystal birefringence can account for our results and also point to an escaped-radial alignment of the liquid crystal in the nematic phase.

JavaParty – transparent remote objects in Java

Abstract: Java’s threads offer appropriate means either for parallel programming of SMPs or as target constructs when compiling add-on features (e.g. forall constructs, automatic parallelization, etc.) Unfortunately, Java does not provide elegant and straightforward mechanisms for parallel programming on distributed memory machines, like clusters of workstations. JavaParty transparently adds remote objects to Java purely by declaration while avoiding disadvantages of explicit socket communication, the programming overhead of RMI, and many disadvantages of the message-passing approach in general. JavaParty is specifically targeted towards and implemented on clusters of workstations. It hence combines Java-like programming and the concepts of distributed shared memory in heterogeneous networks.

Highly resolved large-eddy simulation of separated flow in a channel with streamwise periodic constrictions

Abstract: High-resolution large-eddy simulation is used to investigate the mean and turbulence properties of a separated flow in a channel constricted by periodically distributed hill-shaped protrusions on one wall that obstruct the channel by 33% of its height and are arranged 9 hill heights apart. The geometry is a modification of an experimental configuration, the adaptation providing an extended region of post-reattachment recovery and allowing high-quality simulations to be performed at acceptable computing costs. The Reynolds number, based on the hill height and the bulk velocity above the crest is 10595. The simulated domain is streamwise as well as spanwise periodic, extending from one hill crest to the next in the streamwise direction and over 4.5 hill heights in the spanwise direction. This arrangement minimizes uncertainties associated with boundary conditions and makes the flow an especially attractive generic test case for validating turbulence closures for statistically two-dimensional separation. The emphasis of the study is on elucidating the turbulence mechanisms associated with separation, recirculation reattachment, acceleration and wall proximity. Hence, careful attention has been paid to resolution, and a body-fitted, low-aspect-ratio, nearly orthogonal numerical grid of close to 5 million nodes has been used. Unusually, the results of two entirely independent simulations with different codes for identical flow and numerical conditions are compared and shown to agree closely. Results are included for mean velocity, Reynolds stresses, anisotropy measures, spectra and budgets for the Reynolds stresses. Moreover, an analysis of structural characteristics is undertaken on the basis of instantaneous realizations, and links to features observed in the statistical results are identified and interpreted. Among a number of interesting features, a distinct ‘splatting’ of eddies on the windward hill side following reattachment is observed, which generates strong spanwise fluctuations that are reflected, statistically, by the spanwise normal stress near the wall exceeding that of the streamwise stress by a substantial margin, despite the absence of spanwise strain.