Particle-Laden Turbulent Channel Flow and Particle-Wall Interactions

The behavior of particle-laden gases in a turbulent channel flow is studied at moderate Reynolds number. Effects of the wallparticle interaction models on the velocity, statistics, and dispersion of the particles are presented. The results were obtained from a direct numerical simulation with particle feedback on the gas phase. The models were found to considerably influence the studied particle properties. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Forces acting on particles in separated wall‐bounded shear flow

Trajectories of solid particles in laminar and turbulent flow over a backward‐facing step (BFS) were numerically computed by integrating the equation of motion for particles. The various forces acting on the particles [5],[6] were calculated for a variety of flow Reynolds numbers and for different particle characteristics such as the Stokes number and the particle‐to‐fluid density ratio. The investigation was conducted for the distinct flow regimes of the BFS flow separately. Generally, the drag and gravitation were found to be the most significant forces. The lift and history force were the next most important, mostly two orders of magnitude smaller, but in some cases closing up to the other two in importance. The pressure and virtual mass effects were very small for the majority of cases. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A molecular oyster: a neutral anion receptor containing two cyclopeptide subunits with a remarkable sulfate affinity in aqueous solution

An artificial anion receptor is presented, in which two cyclohexapeptide subunits containing l-proline and 6-aminopicolinic acid subunits in an alternating sequence are connected via an adipinic acid spacer. This compound was devised to stabilize the 2:1 sandwich-type anion complexes that are observed when the two cyclopeptide moieties are not covalently connected and to obtain a 1:1 stoichiometry for these aggregates. Electrospray ionization mass spectrometry and NMR spectroscopic investigations showed that the bridged bis(cyclopeptide) does indeed form defined 1:1 complexes with halides, sulfate, and nitrate. ROESY NMR spectroscopy and molecular modeling allowed a structural assignment of the sulfate complex in solution. The stabilities of various anion complexes were determined by means of NMR titrations and isothermal titration microcalorimetry in 50% water/methanol. Both methods gave essentially the same quantitative results, namely stability constants that varied in the range 105-102 M-1 and decreased in the order SO42- > I- > Br- > Cl- > NO3-. This order was rationalized in terms of the size of the anions with the larger anions forming the more stable complexes because they better fit into the cavity of the host. The ability of sulfate to form stronger hydrogen bonds to the NH groups of the receptor, in addition to its slightly larger ionic radius with respect to iodide, causes the higher stability of the sulfate complex. No significant effect of the countercation on complex stability was observed. Furthermore, complex stability is enthalpically as well as entropically favored. A comparison of the iodide and sulfate complex stabilities of the ditopic receptor with those of a cyclopeptide that forms 1:1 anion complexes in solution showed that the presence of a second binding site increases complex stability by a factor of 100-350.     

Potentiometric determination of chlorides with an "Air-Gap" cyanide sensor

A new electroanalytical method for determining chloride ions with an Air-Gap cyanide sensor system is described. The method is based on the reaction of chloride with mercury(II) cyanide in dilute sulphuric acid. This reaction leads to hydrogen cyanide which can be determined with an Air-Gap cyanide sensor. Optimum concentrations of mercury(II) cyanide and sulphuric acid were established and an analytical curve was prepared for 1 x 10(-1)-1 x 10(-5)M Cl(-). The slope of the calibration curve was equal to 62.8 mV/log C. The correlation coefficient (R) was equal to 0.9992. The method can determine chloride with good results in high saline solutions and in the presence of surfactants, which is in contrast to direct potentiometry with a chloride electrode. The method was applied for chloride determination in fuses used for initiating explosions. The chlorides were determined both in the raw materials used to prepare the fuse braids and in the other fuse components. Chloride was also determined in drinking water and river water. In dependence of source, chloride amount analyzed in drinking water was in the range 2.18-182.6 mg/l. and 25.8 mg/l. in river water. A comparative analysis was carried out. In the first case, chloride was determined by a turbidimetric method, whereas in the second one by potentiometric titration against a chloride-ISE.     

Polyphenols Content,Antioxidant Properties and Allergenic Potency of Organic and Conventional Blue Honeysuckle Berries

Blue honeysuckle berries are a rich source of polyphenols with strong antioxidant properties. The purpose of this research was to determine the effect of organic and conventional cultivation on the polyphenols, antioxidant and allergenic potency of blue honeysuckle berry cultivars: ‘No 30’, ‘Jolanta’ and ‘Indygo’ in two growing seasons. Identification of individual polyphenols was performed using the HPLC method; the total polyphenols content and antioxidant activity were determined by spectrophotometric methods. The determination of allergic potency was tested by ELISA. In the second year of the study the total polyphenols were significantly higher in organic blue honeysuckle than in the conventional blue honeysuckle. In both growing seasons, the ‘Indygo’ cv. was characterized by the highest concentration of all bioactive compounds 3241.9 mg and 3787.2 mg per 100 g⁻¹ D.W. A strong correlation was found between the polyphenol content and the antioxidant activity for organic fruit in both years, as well as for allergenic potency. Contrary to the best bioactive properties was ‘Indigo’ cv., with the highest allergenic potency (108.9 and 139.2 ng g⁻¹ D.W.). The lowest content of specific allergens was found in the ‘No 30’ cv. Since honeysuckle is still a new cultivated plant, information about its allergenic potency is insufficient.     

Surface Properties of Saponin—Chitosan Mixtures

The surface properties of saponin and saponin-chitosan mixtures were analysed as a function of their bulk mixing ratio using vibrational sum-frequency generation (SFG), surface tensiometry and dilational rheology measurements. Our experiments show that saponin-chitosan mixtures present some remarkable properties, such as a strong amphiphilicity of the saponin and high dilational viscoelasticity. We believe this points to the presence of chitosan in the adsorption layer, despite its complete lack of surface activity. We explain this phenomenon by electrostatic interactions between the saponin as an anionic surfactant and chitosan as a polycation, leading to surface-active saponin-chitosan complexes and aggregates. Analysing the SFG intensity of the O-H stretching bands from interfacial water molecules, we found that in the case of pH 3.4 for a mixture consisting of 0.1 g/L saponin and 0.001 g/L chitosan, the adsorption layer was electrically neutral. This conclusion from SFG spectra is corroborated by results from surface tensiometry showing a significant reduction in surface tension and effects on the dilational surface elasticity strictly at saponin/chitosan ratios, where SFG spectra indicate zero net charge at the air–water interface.     

Two-particle correlations in 360 GeV/cp p interactions

Two particle correlations of hadrons produced in 360 GeV/cpp interactions are investigated in the transverse plane and in rapidity. The data were obtained at the European hybrid spectrometer equipped with a rapid cycling bubble chamber. The observed transverse and rapidity correlations are compared with the one string LUND-and a two string dual parton-model. These models predict in general stronger correlations in the transverse plane and much weaker correlations in rapidity than found in the data. The LUND-FRITIOF-and multichain dual parton models provide a better reproduction of the data, although the agreement is not yet satisfactory. Only the UA5 cluster model GENCL shows agreement with the data.     

A new mesogenic fluorene derivative: 2,7-bis(4-pentylphenyl)-9,9-diethyl-9H-fluorene

The title compound, 2,7-bis(4-pentylphenyl)-9,9-diethyl-9H-fluorene, is a new mesogenic compound containing the fluorene moiety. It exhibits a monotropic nematic liquid crystalline behaviour, with isotropisation temperature of 53°C. The compound is also polymorphic in the solid state, with one crystal phase melting at 103°C and another one melting at 71°C. The crystal and molecular structure of the high melting solid phase have been determined from single crystal X-ray diffraction analysis. Crystals are monoclinic, with cell dimensions a = 16.649(6) Å, b = 8.305(3) Å, c = 24.598(7) Å, β = 111.60(2)?, space group P2₁/c and four molecules in the unit cell. Refinement leads to R = 0.0558. The two terminal alkyl chains and one phenyl ring are disordered over two split positions. The imbricated molecular packing observed in the solid state seems to resemble that of the nematic phase that is formed upon cooling the melt.