On image pre-processing for PIV of single- and two-phase flows over reflecting objects

A novel image pre-processing scheme for PIV of single- and two-phase flows over reflecting objects which does not require the use of additional hardware is discussed. The approach for single-phase flow consists of image normalization and intensity stretching followed by background subtraction. For two-phase flow, an additional masking step is added after the background subtraction. The effectiveness of the pre-processing scheme is shown for two examples: PIV of single-phase flow in spacer-filled channels and two-phase flow in these channels. The pre-processing scheme increased the displacement peak detectability significantly and produced high quality vector fields, without the use of additional hardware.     

Self-focusing and defocusing of TEA CO2 laser radiation in NH3

We report on the observation of self-focusing and defocusing of TEA CO₂-laser pulses in NH₃. Self-focusing of the 9R(30) CO₂ laser line resulted in a significant spatial narrowing of the laser beam after propagating through a 100 cm long cell containing NH₃ at a relatively low pressure of 1 Torr. Spatial broadening, characteristics of self-defocusing, has been observed for the 9R(16) CO₂-laser line.     

Spectroscopy and photophysics of self-organized zinc porphyrin nanolayers. 2. Transport properties of singlet excitation

Exciton diffusion has been studied in 5-25-nm-thick films of zinc tetra-(p-octylphenyl)-porphyrin (ZnTOPP) spin-coated onto quartz slides by intentional doping with quenchers using steady-state as well as time-resolved fluorescence spectroscopy. The fluorescence spectra of the films are very similar to those of solutions, indicating emission from localized exciton states. From the dependence of the fluorescence quenching on the quencher concentration and fluorescence lifetime measurements, the exciton diffusion can be concluded to be quasi-one-dimensional with an exciton diffusion length of 9 +/- 3 nm and an intrastack energy-transfer rate constant of 10(11)-10(12) s(-1). From fluorescence anisotropy decay measurements, we conclude that neighboring stacks aggregate in a herringbone structure, forming ordered domains that are randomly oriented in the substrate plane. These measurements indicate an interstack energy-transfer rate constant of (7 +/- 2) x 10(10) s(-1).     

Catalytic conversions of diazosugars

Catalytic diazo decomposition chemistry was explored with novel diazoacetate functionalized carbohydrates. In both glucose and galactose derivatives, aromatic cycloadditions with the benzyl protecting groups proved to be most favorable reactions. Replacing the benzyl groups by methoxy groups in the glucose system led to formation of ‘carbene dimers’.     

Contributions to group IV organometallic chemistry: IX. The effect of ring size on silicon-29 NMR shifts in silicon heterocycles

Silicon-29 NMR shifts for a series of 2,2-diphenyl-1,3,2-dioxasilacycloalkanes are reported and reveal a clear dependence of shift on ring size for rings of 5–14 atoms.     

Inhibition of amyloid fibril formation of human amylin by N-alkylated amino acid and alpha-hydroxy acid residue containing peptides

Amyloid deposits are formed as a result of uncontrolled aggregation of (poly)peptides or proteins. Today several diseases are known, for example Alzheimer's disease, Creutzfeldt-Jakob disease, mad cow disease, in which amyloid formation is involved. Amyloid fibrils are large aggregates of beta-pleated sheets and here a general method is described to introduce molecular mutations in order to achieve disruption of beta-sheet formation. Eight backbone-modified amylin derivatives, an amyloidogenic peptide involved in maturity onset diabetes, were synthesized. Their beta-sheet forming properties were studied by IR spectroscopy and electron microscopy. Modification of a crucial amide NH by an alkyl chain led to a complete loss of the beta-sheet forming capacity of amylin. The resulting molecular mutated amylin derivative could be used to break the beta-sheet thus retarding beta-sheet formation of unmodified amylin. Moreover, it was found that the replacement of this amide bond by an ester moiety suppressed fibrillogenesis significantly. Introduction of N-alkylated amino acids and/or ester functionalities-leading to depsipeptides-into amyloidogenic peptides opens new avenues towards novel peptidic beta-sheet breakers for inhibition of beta-amyloid aggregation.     

Production and partial characterization of extracellular peroxidases produced bystreptomyces avermitilis UAH30

The effect of a number of environmental parameters (pH, temperature, carbon and nitrogen ratio of nutrient) on the production of extracellular peroxidase enzymes byStreptomyces avermitilis UAH30 was examined. Maximum specific peroxidase activity (0.12 U/mg of protein) was obtained after 72 hours of 1 incubation at 45‡C in a minimal salt medium (pH 7.5) containing 0.6% (w/v) yeast extract and 0.6% (w/v) xylan corresponding to a C:N ratio of 4 to 1. A study of the effect of incubation on peroxidase activity showed that the enzyme was stable and active for at least one hour after incubation at 50‡C while at higher temperatures the stability and activity of the peroxidase was reduced such that at 60‡C the peroxidase activity has a half life of 20 min while at 80‡C the half life was reduced to 5 min. The activation energy for deactivation as a result of thermal denaturation of the enzyme was calculated to be 80 ±7 kJ/mol. The optimum pH for the activity occurred between a pH range of 6.5–8.5 with pKa₁ and pKa₂ of 5.1 ±0.1 and 9.7 ±0.1, respectively. The K_m and V_max for the peroxidase activity were determined to be 1.45 mM and 0.31 unit per mg protein respectively using 2,4dicholorophenol (2,4-DCP) as a substrate. Characterization of the peroxidase activity revealed activity against L,3–4 dihydroxyphenylalanine and guaiacol, while no inhibition of peroxidase activity could be detected with the haem inhibitors such as potassium cyanide and sodium azide, suggesting the lack of haem component in the tertiary structure. Aspects of using the crude peroxidase preparation in the pulp and paper industry are discussed.     

Multidimensional time-dependent discrete variable representations in multiconfiguration Hartree calculations

In the multiconfiguration time-dependent Hartree (MCTDH) approach, the wave function is expanded in time-dependent basis functions, called single-particle functions, to increase the efficiency of the wave-packet propagation. The correlation discrete variable representation (CDVR) approach, which is based on a time-dependent discrete variable representation (DVR), can be employed to evaluate matrix elements of the potential energy. The efficiency of the MCTDH method can be further enhanced by using multidimensional single-particle functions. However, up to now the CDVR approach could not be used in MCTDH calculations employing multidimensional single-particle functions, since this would require a general multidimensional non-direct-product DVR scheme. Recently, Dawes and Carrington presented a practical scheme to implement general non-direct-product multidimensional DVRs [R. Dawes and T. Carrington, Jr., J. Chem. Phys. 121, 726 (2004)]. The present work utilizes their scheme in the MCTDH/CDVR approach. The accuracy is tested using the photodissociation of NOCl as example. The results show that the CDVR scheme based on multidimensional time-dependent DVRs allows for an accurate evaluation of the potential in MCTDH calculations with multidimensional single-particle functions.     

Spirastrellolide A,an antimitotic macrolide isolated from the Caribbean marine sponge Spirastrella coccinea

Sprirastrellolide A, a novel antimitotic macrolide, has been isolated from the Caribbean marine sponge Spirastrella coccinea. It has a 47-carbon linear polyketide backbone incorporated into a highly functionalized 38-membered lactone containing a tetrahydropyran and two spiro bispyran substructures embedded in the macrocycle and a side chain terminating in a carboxylic acid. Sprirastrellolide A's structure was elucidated by detailed spectroscopic analysis of its methyl ester 2. Spirastrellolide A methyl ester 2 shows potent activity in a cell-based assay that detects mitotic arrest, but it does not affect tubulin polymerization in vitro. It has the unusual biological property of being able to accelerate the entry of cells into mitosis from other cell-cycle stages, before it arrests them in mitosis.