Mathematical analysis and numerical simulation of multi-phase multi-component flow in heterogeneous porous media

Multi-phase multi-component flow processes are fundamental to engineering applications in hydrocarbon and geothermal reservoirs but also to many classical geological processes. This review will highlight recent developments in the mathematical modelling and numerical simulations of the underlying physical processes from the pore- to the reservoir scale. Many modern approaches now rely on integrating numerical and analytical methods and incorporate results across the different length scales. This provides new insights into the fundamental properties of multi-phase multi-component flow and helps to mitigate some of the inherent difficulties in quantifying them in subsurface reservoirs.     

4D solid-state NMR for protein structure determination

Solid-state NMR offers the chance to extend structural studies to proteins that are otherwise difficult to study at atomic resolution, such as protein fibrils, membrane proteins or poorly diffracting crystals. As two-dimensional spatial correlation NMR spectra of proteins suffer from severe resonance overlap, we analyze in this perspective article the potential of higher-dimensional (3D and 4D) proton-detected experiments, which have an increased number of identifiable and assignable distance restraints for solid-state structural studies. We discuss practical considerations for the NMR measurements and the preparation of suitable protein samples and show results of structure calculations from 4D solid-state NMR spectra.     

Flexible planar microfluidic chip employing a light emitting diode and a PIN-photodiode for portable flow cytometers

Detection of fluorescence particles is a key method of flow cytometry. We evaluate the performance of a design for a microfluidic fluorescence particle detection device. Due to the planar design with low layer thicknesses, we avoid optical components such as lenses or dichroic mirrors and substitute them with a shadow mask and colored film filters. A commercially available LED is used as the light source and a PIN-photodiode as detector. This design approach reduces component cost and power consumption and enables supplying the device with power from a standard USB port. From evaluation of this design, we obtain a maximum particle detection frequency of up to 600 particles per second at a sensitivity of better than 4.7 × 10(5) MESF (molecules of equivalent soluble fluorochrome) measured with particles for FITC sensitivity calibration. Lowering the flow rate increases the instrument sensitivity by an order of magnitude enabling the detection of particles with 4.5 × 10(4) MESF.     

Synthesis and characterization of propylene and butylene bridged fac-tricarbonylrhenium(I) biscarbene complexes

Nine new complexes of the type fac-[(CO)(3)ReBr(L)], where L represents a chelating bis-NHC ligand consisting of two alkylene (propylene and butylene) bridged (R') N-substituted (R) imidazoline moieties (1,1'-di-R-3,3'-R'-diimidazolin-2,2'-diylidene), were synthesized. Spectroscopic methods, elemental analysis, mass spectrometry and X-ray crystallography were employed to characterize the complexes both in solution and in solid state. The complexes were compared to the analogous complexes with smaller bridge lengths in order to reveal differences and similarities. Depending on the bridge length and the ligand size in some cases dinuclear complexes were obtained as small scale side products.     

Obtaining communities with a fitness growth process

The study of community structure became an important topic of research over the last years. But, while successfully applied in several areas, the concept lacks of a general and precise notion. Facts like the hierarchical structure and heterogeneity of complex networks make it difficult to unify the idea of community and its evaluation. The global functional known as modularity is probably the most used technique in this area. Nevertheless, its limits have been deeply studied. Local techniques as the one by Lancichinetti et al. (2009) [1] arose as an answer to the resolution limit and degeneracies that modularity has.     

An Optimal p-Refinement Strategy for Dynamic Iteration of Ordinary and Differential Algebraic Equations

Multiphysical simulation tasks are often numerically solved by dynamic iteration schemes. Usually, this demands the efficient and stable coupling of existing simulation software for the contributing physical subdomains or subsystem. Since the coupling is weakened by such a simulation strategy, iteration is needed to enhance the quality of the numerical approximation. By the means of error recursions, one obtains estimates for the approximation order and the reduction of error per iteration (convergence rate). It is know that the first iterations can be coarsely sampled (in time), but the last iterations need to be refined (h-refinement) to obtain the accuracy gain of latter iterations (‘sweeps’). In this work we discuss an optimal choice of the approximation order p used in the time integration with respect to the iteration ‘sweep’ count. It is deduced from the analytical error recursion and yields a p-refinement strategy. Numerical experiments show that our estimates are sharp and give a precise prediction of the correct convergence. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)