Potential-controlled filtering in quantum star graphs

We study the scattering in a quantum star graph with a Fülöp–Tsutsui coupling in its vertex and with external potentials on the lines. We find certain special couplings for which the probability of the transmission between two given lines of the graph is strongly influenced by the potential applied on another line. On the basis of this phenomenon we design a tunable quantum band-pass spectral filter. The transmission from the input to the output line is governed by a potential added on the controlling line. The strength of the potential directly determines the passband position, which allows to control the filter in a macroscopic manner. Generalization of this concept to quantum devices with multiple controlling lines proves possible. It enables the construction of spectral filters with more controllable parameters or with more operation modes. In particular, we design a band-pass filter with independently adjustable multiple passbands. We also address the problem of the physical realization of Fülöp–Tsutsui couplings and demonstrate that the couplings needed for the construction of the proposed quantum devices can be approximated by simple graphs carrying only δ$\delta$ potentials.     

Modulation of self-assembly and magnetism of Cu(II) grids in solution

Depending on the Cu(II)/ligand molar ratio, a pyrimidine-based ligand generates a tetranuclear grid (1/1) or a dinuclear stick (2/1). EPR, MS and visible spectroscopy studies suggest that dilution produces partial dissociation of the grid in solution. Replacement of 2-H-pyrimidine by a 2-phenyl-triazine unit prevents the dissociation of the grid. All these factors influence the magnetic properties of the architectures herein involved.     

X-ray structure of a novel histidine-copper(II) complex

A new crystal structure of the dichloro(L-histidine)copper(II) half-hydrate is reported. In this complex, histidine acts as a bidentate ligand to the copper(II) cation. The coordination sphere of the copper cation is created by the carboxyl oxygen and the amine nitrogen from main chain group of histidine. Two additional chloride anions complete the square coordination of the central Cu⁺² cation. In the crystal, the copper cations are additionally surrounded by two chloride anions from neighboring complex molecules, which are located in the distant axial position and fill up the stretched octahedral coordination sphere Cu⁺². In the presented complex, the histidine molecule exists as a zwitter ion with an unprotonated negatively charged carboxyl group and with double protonated positively charged imidazole ring. Crystallographic study was supported by IR measurements confirming the presence of water in the crystal structure.     

A curvature‐free multiphase flow solver via surface stress‐based formulation

In this note, we show the link between the classical continuous surface stress and continuous surface force approaches together with special finite element method techniques toward a fully implicit level set method. Based on a modified surface stress formulation, neither normals nor curvature has to be explicitly calculated. The method is space‐dimension independent. Prototypical numerical tests of benchmarking character for a rising 2D bubble are provided for validating the accuracy of this new approach. We show additionally that the explicit redistancing can be avoided using a nonlinear PDE so that a fully implicit and even monolithic formulation of the corresponding multiphase problem gets feasible.     

Monolithic Newton‐multigrid solution techniques for incompressible nonlinear flow models

We present special Newton‐multigrid techniques for stationary incompressible nonlinear flow models discretized by the high order LBB‐stable Q₂P₁ element pair. We treat the resulting nonlinear and the corresponding linear discrete systems by a fully coupled monolithic approach to maintain high accuracy and robustness, particularly with respect to different rheological behaviors and also regarding different problem sizes and types of nonlinearity. Here, local pressure Schur complement techniques are presented as a generalization of the classical Vanka smoother. The discussed methodology is implemented for the well‐known flow around cylinder benchmark configuration for generalized Newtonian as well as non‐Newtonian flows including non‐isothermal, shear/pressure dependent and viscoelastic effects.Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis of 5-substituted 1H-tetrazoles catalyzed by ytterbium triflate hydrate

Various 5-substituted 1H-tetrazoles were synthesized from aryl nitriles, alkyl nitriles, and vinyl nitriles reacting with sodium azide. The tetrazoles were recovered in high yield under mild conditions when the reaction was catalyzed by ytterbium triflate hydrate in dimethylformamide. Other rare-earth and post-transition metal catalysts were also investigated.     

Enzyme-modified electrolyte-insulator-semiconductor sensors

Field-effect capacitive enzyme biosensors for the detection of penicillin, organophosphorous pesticides, the cysteine sulphoxide alliin, and cyanide have been realized by means of immobilization of the respective enzymes (penicillinase, organophosphorous hydrolase, alliinase, and cyanidase) onto the gate surface of a pH-sensitive EIS (electrolyte-insulator-semiconductor) structure. The functional principle of these biosensors is based on the detection of a local pH change resulting from the particular catalytic reaction of the enzyme. As pH-sensitive transducer materials, thin films of Ta₂O₅, Si₃N₄ or Al₂O₃ have been utilized. For each type of enzyme biosensor, the composition and pH value of the buffer solution have been optimized in terms of a high sensitivity, a wide linear measuring range, and a low detection limit. Basic characteristics of the developed enzyme biosensors are summarized.     

Directly heated etching stand for electrochemical treatment of track detectors

The directly electrically heated etching stand has been developed for the electrochemical treatment of track detectors to avoid the time consuming overnight pre-heating and to simplify the procedure. The large plate electrode containing several heating elements on its rear side creates the main part of the etching stand. The temperature of the electrode connected to the control unit is variable within 30–70°C. Two types of etching stands were tested. The uniformity of the temperature distribution on the electrode surface, heating rate and stability of temperature were studied as the main parameters and the results are presented. The technical solution allows to construct smaller (even portable) devices for the electrochemical etching.     

Dehydration of isopropyl alcohol used as an indicator of the type and strength of catalyst acid centres

The subject of our studies was determination of the kind and strength of the catalyst acid centres on isopropyl alcohol conversion. The investigations were carried out for two groups of catalysts: typical Lewis acids γ-Al₂O₃ and ZrO₂ and Brønsted acids: H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀. Considerable differences between Lewis and Brønsted acids in the conversion of isopropyl alcohol were observed. The influence of Brønsted acid centres was studied for a group of catalysts with different strength: mixtures of two different heteropolyacids. It was observed that the increasing strength of Brønsted acids centres leads to higher catalytic activity but it does not significantly affect the activation energy of dehydration to propene.