Measurement and calculation of guide vane performance in expanding bends for wind-tunnels

 The design of guide vanes for use in expanding bends was investigated both experimentally and numerically. The primary application in mind is the use of expanding corners in wind-tunnels for the purpose of constructing compact circuits with low losses. To investigate the performance of guide vanes in realistic situations expansion ratios between 1 and 53 were tested in the experiments. These were carried out in an open wind-tunnel specially built for the present purpose. The experimental results demonstrated that suitably designed guide vanes give very low losses and retained flow quality even for quite substantial expansion ratios. For wind-tunnel applications expansion ratios around 1.3 seem appropriate, Optimization of a guide vane design was done using a two-dimensional cascade code, Mises. A new vane optimized for an expansion ratio of 43 gave a two-dimensional total pressure-loss coefficient as low as 0.041 for a chord Reynolds number of 200,000. Received: 7 April 1997/Accepted: 11 August 1997     

O-H and O-D stretching vibrations in isotopically dilute HDO molecules in some solid hydrates

Vibrational frequencies v_OH and v_OD have been measured for isotopically-dilute HDO molecules in eleven solid hydrates at 90 K. The results have been used to prepare a plot of the ratio v_OH/v_OD versus v_OH. The ratios fall on a smooth curve and decrease with decreasing frequencies v_OH. The anharmonicity constants ω_ex_e have been estimated. They were found to increase with decreasing v_OH.     

Three-Wave Interaction in Cold Semi-Infinite Plasmas

We have considered the theory for the resonant nonlinear interaction between three waves in a cold semi-infinite magnetized plasma and calculated the coupling coefficients.     

(γ, γ′) reactions in 89Y, 115In and 197Au at intermediate energies

The yields of isomeric states in ⁸⁹Y, ¹¹⁵In and ¹⁹⁷Au produced by the (γ, γ') reaction have been measured in the energy range 100–800 MeV by the activation method. From the yields the cross sections have been deduced. Large cross sections around the first pion resonance are found. The experimental results are compared to calculations based on the impulse approximation.     

Hydrogels from a water-soluble zwitterionic polythiophene: dynamics under pH change and biomolecular interactions observed using quartz crystal microbalance with dissipation monitoring

The water-soluble zwitterionic polythiophene, poly(3-((S)-5-amino-5-carboxyl-3-oxapentyl)-2,5-thiophene) hydrochloride (POWT), is a conjugated polyelectrolyte (CPE) with properties well suited for biochip applications. CPEs readily form hydrogels when exposed to water-based buffer solutions or biomolecule solutions. In this work, we used in situ quartz crystal microbalance with dissipation (QCM-D) monitoring to collect information on the interaction between POWT films exposed to buffers with different pH and POWT/DNA chains. Our data show that POWT swells significantly when exposed to low-pH buffers, such as pH 4 acetate, this is seen as an increase in thickness and decrease in viscosity obtained via a Voight-based modeling of combined f and D QCM-D measurements. The magnitude of thickness and viscosity change upon changing from a pH 10 carbonate buffer to pH 4 acetate is 100% increase in thickness and 50% decrease in viscosity. The response of the hydrogel under pH change is well correlated with fluorescence data from POWT films on glass. The state of the hydrogel is important during interaction with biomolecules; illustrated by the observation that a swollen CPE hydrogel adsorbs a higher amount of DNA than a compacted one. In agreement with previous results, the QCM-D data confirmed that the POWT/DNA hydrogel sense complementary DNA specifically and with negligible binding of noncomplementary DNA. These results are important for efficient constructions of biochips in water environments using this class of materials.     

Synthesis and characterisation of Gd2O3 nanocrystals functionalised by organic acids

Nanocrystals of Gd2O3 have been prepared by various methods, using, e.g., trioctylphosphine oxide (TOPO), diethylene glycol (DEG) or glycine. The crystalline particles were of sizes 5 to 15 nm. Different carboxylic acids, e.g., oleic acid or citric acid, were adsorbed onto the surface of the particles made with DEG. IR measurements show that the molecules coordinate to the Gd2O3 surface via the carboxylate group in a bidentate or bridging manner. The organic-acid/particle complexes were characterised by XRPD, TEM, FTIR, Raman, and XPS.     

Enzymatic degradation of model cellulose films

Enzymatic degradation of model cellulose films prepared by a spin-coating technique was investigated by ellipsometry. The cellulose films were prior to degradation characterized by ellipsometry, contact angle measurements, ESCA (electron spectroscopy for chemical analysis) and AFM (atomic force microscopy). At enzyme addition to preformed cellulose films an initial adsorption was observed, which was followed by a total interfacial mass decrease due to enzymatic degradation of the cellulose films. The degradation rate was found to be constant during an extended time of hours, whereafter the degradation leveled off. In parallel to the decreased interfacial mass, the cellulose degradation resulted in a thinner and more dilute interfacial film. At long degradation times, however, there was an expansion of the cellulose film. The enzyme concentration affected the degradation rate significantly, with a faster degradation at a higher enzyme concentration. The effects of pH, temperature, ionic strength and stirring rate in the cuvette were also investigated.     

Alpha-particle strengths from the 16O(6Li,d)20Ne reaction

The ¹⁶O(⁶Li, d)²⁰Ne reaction has been studied at bombarding energies of 20, 32 and 38 MeV. The α-particle spectroscopic strengths have been extracted for levels up to 12.15 MeV in excitation. Nondirect processes appear to contribute significantly to all levels at 20 MeV and to high spin levels (6⁺ and 8⁺) at 32 MeV. Strengths extracted for members of the ground state band assuming (sd)⁴ transfer are unequal at both 32 and 38 MeV, in marked contrast to theoretical predictions. To explain this, particle-hole correlations in ¹⁶O(g.s.), inelastic channel coupling in the reaction and perhaps other effects as well, have to be considered. Strengths extracted for members of excited bands and α-decay reduced widths compare poorly with each other and with simple SU(3) predictions.