The analytical solution of two interesting hyperbolic problems as a test case for a finite volume method with a new grid refinement technique

A finite volume method with grid adaption is applied to two hyperbolic problems: the ultra-relativistic Euler equations, and a scalar conservation law. Both problems are considered in two space dimensions and share the common feature of moving shock waves. In contrast to the classical Euler equations, the derivation of appropriate initial conditions for the ultra-relativistic Euler equations is a non-trivial problem that is solved using one-dimensional shock conditions and the Lorentz invariance of the system. The discretization of both problems is based on a finite volume method of second order in both space and time on a triangular grid. We introduce a variant of the min-mod limiter that avoids unphysical states for the Euler system. The grid is adapted during the integration process. The frequency of grid adaption is controlled automatically in order to guarantee a fine resolution of the moving shock fronts. We introduce the concept of “width refinement” which enlarges the width of strongly refined regions around the shock fronts; the optimal width is found by a numerical study. As a result we are able to improve efficiency by decreasing the number of adaption steps. The performance of the finite volume scheme is compared with several lower order methods.     

Non‐uniform nanosecond gate‐delay of hybrid pixel detectors

A simple experiment to characterize the gating properties of X‐ray area detectors using pulsed X‐ray sources is presented. For a number of time‐resolved experiments the gating uniformity of area detectors is important. Relative gating delays between individual modules and readout chips of PILATUS2 series area X‐ray detectors have been observed. For three modules of a PILATUS 300K‐W unit the maximum gating offset between the modules is found to be as large as 30 ns. On average, the first photosensor module is found to be triggered 15 ns and 30 ns later than the second and the third modules, respectively.     

Decorrelation of networked communication flow via load-dependent routing weights

Clever assignments of link weights are able to change communication routes in such a way that loads are distributed almost evenly across a network. This is achieved by weight assignments based on the link load. As demonstrated for scale-free as well as synthetic Internet networks, they decorrelate the loads of the nodes and links from the network structure and increase the transport capacity of the network. For various Internet scans the increase of transport capacity amounts to a factor of around five when compared to shortest-path routing.     

Precursors of biological cofactors from ultraviolet irradiation of circumstellar/interstellar ice analogues

Biological cofactors include functionalized derivatives of cyclic tetrapyrrole structures that incorporate different metal ions. They build up structural partnerships with proteins, which play a crucial role in biochemical reactions. Porphyrin, chlorin, bacteriochlorin, and corrin are the basic structures of cofactors (heme, chlorophyll, bacteriochlorophyll, siroheme, F 430, and vitamin B12). Laboratory and theoretical work suggest that the molecular building blocks of proteins (alpha-amino acids) and nucleic acids (carbohydrates, purines, and pyrimidines) were generated under prebiotic conditions. On the other hand, experimental data on the prebiotic chemistry of cofactors are rare. We propose to search directly for the pathways of the formation of cofactors in the laboratory. Herein we report on the detection of N-heterocycles and amines in the room-temperature residue obtained after photo- and thermal processing of an interstellar ice analogue under high vacuum at 12 K. Among them, hexahydro-1,3,5-triazine and its derivatives, together with monopyrrolic molecules, are precursors of porphinoid cofactors. Hexahydropyrimidine was also detected. This is the first detection of these compounds in experiments simulating circumstellar/interstellar conditions. Except for 2-aminopyrrole and 2,4-diaminofuran, which were only found in 13C-labeled experiments, all the reported species were detected in both 12C- and 13C-labeled experiments, excluding contamination. The molecules reported here might be present in circumstellar/interstellar grains and cometary dust and could be detected by the Stardust and Rosetta missions.     

Structure and dynamics of electrostatically interacting magnetic nanoparticles in suspension

We investigate the structure and dynamics of charge-stabilized CoFe(2)O(4)-SiO(2) core-shell magnetic nanoparticles in suspensions. Small angle x-ray scattering and x-ray photon correlation spectroscopy allow us to analyze the intraparticle (core-shell) and interparticle structure of the suspension, as well as their dynamic and hydrodynamic behavior. Due to the weak magnetic interactions, the liquidlike structure is governed by screened Coulomb interactions. The hydrodynamic interactions of the measured systems are significantly stronger than predicted by current theories.     

Bromine is an endogenous component of a vanadium bromoperoxidase

On the basis of EXAFS and MS/MS experimental results and a reinterpretation of the electron density map obtained by X-ray crystallography, we describe a new post-translational modification, that is, a 3,5-dibromotyrosine residue that is incorporated in the polypeptide chain of a vanadium haloperoxidase.     

Vibrational spectrum of m-benzyne: a matrix isolation and computational study

m-Benzyne (2) was generated in low-temperature matrices and IR spectroscopically characterized from four different precursors. To assign the IR absorptions, the perdeuterated derivative 2-d(4) was also investigated. By comparison with CCSD(T) calculations all vibrations between 200 and 2500 cm(-)(1) with a predicted relative intensity >2% could be assigned. All experimental and theoretical results are in accordance with a biradicaloid structure for 2, while there is no evidence for a bicyclic closed-shell structure. While benzyne 2 is stable under the conditions of matrix isolation at low temperature, flash vacuum pyrolysis at high temperatures or UV irradiation results in the rearrangement to cis-enediyne. A mechanism involving ring opening accompanied by hydrogen migration is proposed.