Simulations, models, and testbeds: A mutual catalysis

Recent developments in the area of decentralized and infrastructureless systems opened avenues for novel applications. Along with these new technologies, new questions regarding their operational bounds in terms of e.g. scalability and security arose. Due to the sparse presence of real-world decentralized and infrastructureless systems, new protocols and applications have to be scrutinized by means of simulation, in (small-scale) testbeds, and by analytical models. In this paper, we discuss challenges of evaluating security mechanisms for mobile ad hoc networks and peer-to-peer systems. We focus on harmonizing predictions of analytical models and results obtained from simulation studies and testbed experiments.     

Automated compensation of misalignment in phase retrieval based on a spatial light modulator

In this paper, the issue of misalignment in phase retrieval by means of optical linear filtering is discussed. The filtering setup is based on a 4f configuration with a spatial light modulator (SLM) as an active element, located in the Fourier domain. From the analysis, crucial parameters for the alignment procedure of the setup's optical axes and the center of the SLM are identified. Furthermore, a method to automatically as well as electronically compensate such effects by modifying the phase pattern displayed on the SLM is introduced. Experimental results are presented that validate the compensation approach.     

Particle‐Based Synthesis of Peptide Arrays

High‐density peptide arrays with solid amino acid particles: Intermittent “freezing” of activated amino acid derivatives within solid particles allows a laser printer or a chip to spatially address these “postal packages”. Subsequent parallel coupling is started simply by melting a whole layer of 20 different amino acid particles, freeing the hitherto immobilized amino acids and resulting in the coupling of all 20 different amino acids to the support in a single coupling step.

     

Multigrid methods for discrete elliptic problems on triangular surfaces

We construct and analyze multigrid methods for discretized self-adjoint elliptic problems on triangular surfaces in ${\mathbb{R}^3}$ . The methods involve the same weights for restriction and prolongation as in the case of planar triangulations and therefore are easy to implement. We prove logarithmic bounds of the convergence rates with constants solely depending on the ellipticity, the smoothers and on the regularity of the triangles forming the triangular surface. Our theoretical results are illustrated by numerical computations.     

Nondestructive mechanical release of ordered polymer microfiber arrays from porous templates

The fabrication of one-dimensional (1D) nanostructures and microstructures inside the pores of porous templates is intensively investigated. The release of these structures is commonly accomplished by etching and destroying the templates. The 1D nanostructures and microstructures tend to condense because of the occurrence of capillary forces during drying of the specimens. It is shown that highly ordered arrays of polymer microfibers can be easily detached from silanized porous templates by mechanical lift-off. This procedure leaves the templates intact, thus allowing their recycling, and does not involve the use of solutions or solvents, thus circumventing condensation. Therefore, mechanical lift-off may enable the up-scaling of template-based approaches to the fabrication of highly ordered assemblies of 1D nanostructures and microstructures.     

Performance and stability of poly(phenylene vinylene) based polymer light emitting diodes with caesium carbonate cathode

We have studied the phenomena resulting from the combination of a hole-conducting poly(phenylene vinylene) (PPV) based light emitting polymer with a highly efficient electron injection layer of caesium carbonate (Cs₂CO₃) in light emitting diodes. A strong dependence between the thickness of the applied Cs₂CO₃ and the electro-optical performance of the diodes is detected and already with ultrathin Cs₂CO₃ layers high efficiency diodes are achieved. The Cs₂CO₃ is shown to diffuse into the polymer layer leading to an increased electron density but also quenching of both electro and photoluminescence when the amount of applied Cs₂CO₃ is increased. During electrical stressing the electron density decreases assumably through degradation of the n-doping and quenching Cs₂CO₃ species inducing an unusual increasing luminescence behavior.     

Catalysts Based Upon Organoclay with Tunable Polarity and Dispersion Behavior: New Catalysts for Hydrogenation, C–C Coupling Reactions and Fluorous Biphase Catalysis

Spherical Pd nanoparticles (2–8 nm) were immobilized on the nanometer-scaled platelets of montmorillonite (MMT) by means of cation exchange of Pd²⁺ for Na⁺ followed by chemical reduction. The resulting Pd catalysts were readily dispersible in water and polar solvents. Polarity design and thus, variation of the dispersion behavior was achieved by subsequent organophilic MMT modification involving cation exchange with N-alkyl and N-perfluoroalkylethyl pyridinium cations. This allowed for easy catalyst dispersion in a wide range of organic solvents. According to characterization by TEM, EDXS, AAS and WAXS the nanoparticle formation did not destroy the superstructure of unmodified and organophilic MMT. Catalysts were applied to hydrogenation, Suzuki–Miyaura C–C coupling and fluorous biphase catalysis. The tunable dispersion behavior of MMT catalysts was successfully employed to guarantee easy catalyst recovery and recycling.