Cation- and/or anion-directed reaction routes. Could the desolvation pattern of isostructural coordination compounds be related to their molecular structure?

The crystal and molecular structure of [Cu(ampf)(ClO₄)(MeOH)₂]ClO₄, (1), ampf = N,N′-bis(4-acetyl-5-methylpyrazol-3-yl)formamidine, determined by X-ray crystallography is described and compared with the structurally related copper(II) complexes, formed under similar experimental conditions, using Cu^II salts with different anions. The complex formation is discussed in view of the structures of cobalt(II) and nickel(II) complexes with the same organic ligand and different anions, also formed under similar reaction conditions. Solvent molecules coordinated to the central atom play an important role in biologic systems. To get a better insight into the desolvation mechanism, in this study the desolvation pattern of 1 is presented. As in literature little attention is paid to the desolvation mechanism of solvate complexes, the desolvation mechanism of three, potentially biologically active isostructural pairs of octahedral Ni^II and Co^II compounds with ampf and dmpc (3,5-dimethyl-1H-pyrazole-1-carboxamidine) ligands are evaluated and compared with the desolvation of 1. The results of the thermal data are discussed on the basis of structural features of the compounds. The minor differences in structures of the related compounds cannot be straightforwardly connected with the different solvent evaporation mechanism. To explain the differences found in desolvation pattern in isostructural Co^II and Ni^II complexes the Jahn-Teller effect is proposed.     

Velocity measurements of wake-induced unsteady flow in a linear turbine cascade

Extensive velocity measurements have been taken in a linear turbine cascade with unsteady oncoming wakes. The unsteady wakes were generated by moving cylinders on a squirrel cage device. The Reynolds number was 1.1 × 10⁵, and the Strouhal number varied from o to 7.36. The blade-to-blade flow and the boundary layers on the suction side were measured with a hot-wire anemometer. The results were obtained in ensemble-averaged form so that periodic unsteady processes can be studied. Of particular interest was the transition of the boundary layer. The boundary layer remained laminar in the case without wakes. The passing wakes caused transition, and the beginning of transition moves forward as the wake-passing frequency increases. Unlike in the flat plate study of Liu and Rodi (1991a) the boundary layer state hardly changed with time, although the turbulence level in the boundary layer showed clear periodic response to the passing wakes. The work reported here was sponsored by the German Federal Ministry of Research and Technology through program TURBOTHERM under contract no. 0326501D. The authors should like to thank Mr. D. Bierwirth for his excellent technician work on this project, Dr. N. H. Cho for his help with the preparation of the plots and Mrs. R. Zschernitz for her expert typing of the text.     

Search for spin canting in gadolinium iron garnet using the Mössbauer technique

We have studied the hyperfine interactions in GdIG in zero external magnetic field using⁵⁷Fe Mössbauer spectroscopy. Measurements were made at temperatures between 80 K and 310 K, whereby the region around the compensation point at 286 K was emphasized. The easy axis of magnetization was determined to be [111] at all the chosen temperatures. No indications of spin canting were found. The hyperfine parameters vary smoothly with temperature. The temperature dependences of the magnetization of the sublattices are deduced from the magnetic hyperfine fields.     

Identification of small molecule binding sites within proteins using phage display technology

Affinity selection of peptides displayed on phage particles was used as the basis for mapping molecular contacts between small molecule ligands and their protein targets. Analysis of the crystal structures of complexes between proteins and small molecule ligands revealed that virtually all ligands of molecular weight 300 Da or greater have a continuous binding epitope of 5 residues or more. This observation led to the development of a technique for binding site identification which involves statistical analysis of an affinity-selected set of peptides obtained by screening of libraries of random, phage-displayed peptides against small molecules attached to solid surfaces. A random sample of the selected peptides is sequenced and used as input for a similarity scanning program which calculates cumulative similarity scores along the length of the putative receptor. Regions of the protein sequence exhibiting the highest similarity with the selected peptides proved to have a high probability of being involved in ligand binding. This technique has been employed successfully to map the contact residues in multiple known targets of the anticancer drugs paclitaxel (Taxol), docetaxel (Taxotere) and 2-methoxyestradiol and the glycosaminoglycan hyaluronan, and to identify a novel paclitaxel receptor [1]. These data corroborate the observation that the binding properties of peptides displayed on the surface of phage particles can mimic the binding properties of peptides in naturally occurring proteins. It follows directly that structural context is relatively unimportant for determining the binding properties of these disordered peptides. This technique represents a novel, rapid, high resolution method for identifying potential ligand binding sites in the absence of three-dimensional information and has the potential to greatly enhance the speed of development of novel small molecule pharmaceuticals.     

Large Eddy Simulations and Experiments of Flow Around Finite-Height Cylinders

The paper presents experimental and numerical results for the flow around a surface-mounted circular cylinder at the two height-to-diameter ratios of 2.5 and 5. The Reynolds number based on approach flow velocity and cylinder diameter is 43,000 and 22,000 for these two cases and the boundary layer of the approach flow has a thickness of about 10% of the cylinder height. The experiments comprise both flow visualizations with dye and laser Doppler velocimeter measurements of all mean velocity and fluctuation components. The numerical study is performed by an elaborate large eddy simulation on a staggered Cartesian grid using the immersed boundary method. The instantaneous flow behaviour including the shedding is analysed with information based on animations. For the long cylinder alternating shedding is found to occur over most of the height while for the shorter cylinder the shedding is observed mainly near the ground where it is also mostly alternating but intermittently also symmetrical. The mean-flow behaviour is analysed with the aid of streamlines and contour plots of mean-velocity and fluctuation components in various planes and a detailed comparison of LES and LDV results is provided, showing generally good agreement. The LES with very fine resolution near the free end allow a detailed study of the complex flow in this region with owl-face topology on the end wall previously observed in experiments. Behind the cylinder, the longitudinal recirculation region, the downstream development of tip vortices and the emergence of trailing vortices further downstream are analysed. The sum of the results, together with those from previous studies that were reviewed extensively, provides a comprehensive picture of the very complex flow behaviour.     

Superconducting density of states and vortex cores of 2H-NbS2

Scanning tunneling microscopy and spectroscopy measurements in the superconducting dichalcogenide 2H-NbS2 show a peculiar superconducting density of states with two well-defined features at 0.97 and 0.53 meV, located, respectively, above and below the value for the superconducting gap expected from the single band s-wave BCS model (Delta=1.76k_(B)T_(c)=0.9 meV). Both features have a continuous temperature evolution and disappear at T_(c)=5.7 K. Moreover, we observe the hexagonal vortex lattice with radially symmetric vortices and a well-developed localized state at the vortex cores. The sixfold star shape characteristic of the vortex lattice of the compound 2H-NbSe2 is, together with the charge density wave order, absent in 2H-NbS2.     

Calculation of the Flow around a High-Pressure Turbine Blade with Cooling-Jet Injection from Slots at the Leading Edge

A fully vectorised, basically three-dimensional finite-volume multi-block method for flows with complex boundaries is applied in a stripped-down two-dimensional version for the investigation of the flow field in the leading-edge region of a high-pressure turbine blade with slot cooling-jet injection. The calculation results are compared with experiments and the numerical results of other investigators. The present method yields excellent agreement with the experiments for the isentropic Mach number distributions on the blade surface. All numerical results for the velocity field were found to be in very good agreement with each other and with experiments on the suction side, while the agreement is not as good on the pressure side.     

Direct Computations of Boundary Layers Distorted by Migrating Wakes in a Linear Compressor Cascade

A Direct Numerical Simulation (DNS) of flow in the V103 Low-Pressure (LP) compressor cascade with incoming wakes was performed. The computational geometry was chosen largely in accordance with the setup of the experiments performed by Hilgenfeld and Pfitzner (J Turbomach 126:493–500, 2004) at the University of the Armed Forces in Munich. The computations were carried out on the NEC-SX8 in Stuttgart using 64 processors and 85 million grid points. The incoming wakes stemmed from a separate DNS of incompressible flow around a circular cylinder with a Reynolds number of Re _d  = 3300 (based on mean inflow velocity and cylinder diameter). The boundary layer along the suction surface of the blade was found to separate and roll up due to a Kelvin–Helmholtz instability triggered by the periodically passing wakes. Inside the rolls further transition to turbulence was found to occur. The boundary-layer flow along the pressure surface did not separate, instead it underwent by-pass transition.