Magnetic after-effect in magnetite below the verwey point

The fractional change in the initial magnetic susceptibility (Δx/x), shows a logarithmic time dependence below the Verwey point (T_V). Isochromes of the form 1n Δx/x=const?15 T/T_V, found just below T_V, suggest a five-parameter electron ordering.     

SITE-SELECTION SPECTROSCOPY OF CHLOROPHYLL b IN MEMBRANES OF LECITHIN VESICLES AND IN OTHER SOLVENTS

Abstract— Site-selection fluorescence spectra of chlorophyll b in membranes of lecithin vesicles and in the solvents ethanol, n -butanol, n -butyl acetate, 2-methyl tetrahydrofuran and toluene are presented. The spectra in vesicles display zero-phonon lines as pronounced as those in the best organic glasses. The characteristics of the distributions of O—O transition energies and of the electron-phonon couplings allow to infer the position of the chlorophyll molecule in the membrane of vesicles. It is thus found that the chromophore of chlorophyll b is situated in the layer formed by the ester moieties of the lecithins, i. e. close to the surface of the membrane but not in direct contact with the aqueous phase.     

Investigation of the interaction force between Cryptosporidium parvum oocysts and solid surfaces

Interaction force profiles between single Cryptosporidium parvum oocysts and positively charged, silane-coated silica particles were measured in aqueous solutions using an atomic force microscope. The oocysts were immobilized for the measurements by entrapment in Millipore polycarbonate membranes with 3 microm pore size. Experiments were performed in both NaCl and CaCl2 solutions at ionic strengths ranging from 1 to 100 mM. For both electrolytes, the decay length of the repulsive force profile was found to be nearly independent of the ionic strength and always much larger than the theoretical Debye length of the system. In addition, the magnitude of the force was found to be essentially the same for both electrolytes, suggesting that the long-range repulsive forces are primarily steric in nature. These results support the theory that the interaction force between oocysts and surfaces is controlled by an outer, weakly charged or uncharged carbohydrate layer. Measurements were also performed with oocysts that had been deactivated using either chemical (formalin) or heat treatment. The force profiles obtained with formalin-treated oocysts appear to be essentially the same as for the untreated oocysts, whereas the profiles measured with the heat-treated oocysts show a much stronger dependence on solution ionic strength. With either the heat-treated or formalin-treated oocysts, adhesion was observed much more frequently than with untreated oocysts, which is consistent with the increased deposition rate observed with treated oocysts by Kuznar and Elimelech (Kuznar, Z. A.; Elimelech, M. Langmuir 2005, 21, 710-716). These results also suggest that treated oocysts, especially ones that have been inactivated by heating, may not be good surrogates for viable oocysts in laboratory studies.     

Structuring of macroions confined between like-charged surfaces

We investigate the structuring of charged spherical nanoparticles and micelles (i.e., "macroions") between two surfaces as a function of bulk macroion concentration. Structuring is deduced from measured force profiles between a silica particle and a silica plate in the presence of an aqueous macroion (Ludox silica nanoparticle or sodium dodecyl sulfate micelle) solution, obtained with an atomic force microscope. We observe oscillatory force profiles that decay with separation. We find that the wavelength of the force profiles scales with the bulk number density as rho(-)(1/3), rather than with the effective macroion size. Only at very high silica nanoparticle concentration (above 10 vol %) in a low ionic strength solution does the wavelength become smaller than that predicted by the simple rho(-)(1/3) scaling; however, the original scaling is recovered upon the addition of a small amount of electrolyte. A comparison between the measured wavelength and the predicted spacing between the macroions in the bulk shows that the two variables differ in both magnitude and bulk density scaling. This finding suggests that confined macroions are more ordered than those in the bulk and the nature of this ordering is maintained over a relatively wide range of bulk concentration.     

Electric field-induced isomerization of azobenzene by STM

The electric field applied between the tip of a scanning tunneling microscope and a metallic surface is shown to induce the reversible trans-cis isomerization of single azobenzene derivatives adsorbed on a Au(111) surface. The investigated molecule is symmetrically equipped with four tert-butyl groups, which decouple the azobenzene core from the metallic surface, facilitating the formation of highly ordered islands. Due to the spatial extension of the electric field, it is possible to switch many molecules within the same island simultaneously.     

An Exact Navier-Stokes Solution for Three-Dimensional,Spanwise-Homogeneous Boundary Layers

The plane stagnation flow onto (Hiemenz boundary layer, HBL) and the asymptotic suction boundary layer flow over a flat wall (ASBL) are two boundary layer flows for which the incompressible Navier-Stokes equations are amenable to exact similarity solutions. The Hiemenz solution has been extended to swept Hiemenz flows by superposition of a third, spanwise-homogeneous sweep velocity. This solution becomes singular as the chordwise, tangential base flow component vanishes. In this limit, the homogeneous ASBL solution is valid, which however cannot describe the swept Hiemenz flow, because it does not contain any chordwise velocity. This work presents a generalized three-dimensional similarity solution which describes three-dimensional spanwise homogeneously impinging boundary layers at arbitrary wall-normal suction velocities, using a rescaled similarity coordinate. The HBL and the ASBL are shown to be two limits of this solution. Further extensions consist of oblique impingement or different boundary suction directions, such as slip or stretching walls. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Continuous coherent Lyman- alpha excitation of atomic hydrogen.

The 1S-2P transition in atomic hydrogen has been observed for the first time with almost natural linewidth. We employ a unique source of continuous coherent Lyman- alpha radiation based on four-wave mixing in mercury. The output of the source has been improved 40-fold to yield 20 nW. This demonstration shows that laser cooling and detection with continuous Lyman- alpha radiation has excellent prospects for future experiments with antihydrogen.