Air-dispersion measurement by second-harmonic heterodyne interferometry

Interferometers with long optical paths in air usually require knowledge and control of air dispersion. In addition, the measurements at several wavelengths and the dispersion properties of air allow errors caused by air turbulence to be compensated for. An innovative technique for air-dispersion measurement is described for long-baseline ground-based stellar interferometers. The technique combines second-harmonic interferometry and heterodyne detection to permit high-resolution measurement even for low optical powers. Experimental results show measurements of air dispersion in good agreement with the values predicted from the Edlén equation.     

Nonadiabatic superconductivity in fullerene-based materials

Fullerene compounds have phonon frequencies up to ω_max=0.2 eV and a Fermi energy of the order E_F=0.3 eV. It is, therefore, expected that the adiabatic parameter λω_ph/E_F (where λ is the electron-phonon coupling constant and ω_ph is a typical phonon frequency) is not a priori negligible and the conventional theory of phonon-mediated superconductivity is inapplicable in this case. Here, we discuss how the conventional theory is inconsistent with a number of experimental data and provide a generalization of the theory in order to include nonadiabatic electron-phonon effects. We show that the inclusion of nonadiabatic channels in the electron-phonon interaction is a key element for the high values of T_c in these materials. We make several predictions regarding the superconducting and normal-state properties of fullerene compounds that can be tested experimentally.     

Homogeneous ZnO Nanoparticles by Flame Spray Pyrolysis

Zinc oxide (ZnO) nanoparticles were made by flame spray pyrolysis (FSP) of zinc acrylate–methanol–acetic acid solution. The effect of solution feed rate on particle specific surface area (SSA) and crystalline size was examined. The average primary particle diameter can be controlled from 10 to 20nm by the solution feed rate. All powders were crystalline zincite. The primary particle diameter observed by transmission electron microscopy (TEM) was in agreement with the equivalent average primary particle diameter calculated from the SSA as well as with the crystalline size calculated from the X-ray diffraction (XRD) patterns for all powders, indicating that the primary particles were rather uniform in diameter and single crystals. Increasing the solution feed rate increases the flame height, and therefore coalescence and/or surface growth was enhanced, resulting in larger primary particles. Compared with ZnO nanoparticles made by other processes, the FSP-made powder exhibits some of the smallest and most homogeneous primary particles. Furthermore, the FSP-made powder has comparable BET equivalent primary particle diameter with but higher crystallinity than sol–gel derived ZnO powders.     

Scale-down of continuous protein purification by annular chromatography. Design parameters for the smallest unit

Theoretically, in fixed-bed chromatography an infinite separation time or volume is available. In annular chromatography the separation time is limited by the time required for a single rotation. In a chromatograph with a smaller annulus than the theoretical one, the equilibration zone will overtake the feed zone. The required separation time is determined by a number of steps such as equilibration, loading, washing, elution, regeneration and the retention of the solute. A mathematical model has been developed to estimate the minimum radius of an annular chromatograph. The minimal geometry of an annular chromatograph was calculated for a model system immunoglobulin and bovine serum albumin.     

Synthesis of functionalized ethynylphenothiazine fluorophores

Alkynylated and butadiynyl-bridged phenothiazines with variable functionalization can be synthesized in good yields by cross-coupling and condensation approaches. In addition, the structure of the diethynylated phenothiazine (7a) has been corroborated by an X-ray structure analysis. These oligofunctional heterocycles are fluorescent with modest quantum yields (Phi(f) = 20-35%) and represent suitable building blocks for novel photoexcitable molecular wires.     

'Hidden parameters' of infrared drying for determining low water contents in instant powders

Drying techniques are very frequently used and in many cases official methods for moisture determination. These methods, however, do not yield the water content as a result but a mass loss which is caused not only by the evaporation of water but by all substances volatile under the drying conditions, be they original components of the product or be they produced by decomposition reactions during the drying process. This mass loss varies therefore with the parameters applied like time, temperature, form of energy transfer, atmospheric pressure or surrounding humidity. To shorten determination times of many hours in common air ovens with convective heating, techniques with more efficient heating principles have been developed. One of these is infrared drying. With such methods, however, the danger of product decomposition and, consequently, of wrong results rises, particularly when the water content is low. It could be shown, however, that analyses are possible, even for beverage instant powders with very low water contents. Moreover, parameter sets could be found to match the infrared results exactly with the true water content determined by Karl Fischer titration. Another essential finding was that not only the parameters for the drying programme itself like time, temperature and end-point criterion are important, but also, and this to a surprisingly great extent, the number of consecutive measurements and the duration of the intervals between analyses. This effect again depends extremely on the type of apparatus.     

Accurate measurement of large optical frequency differences with a mode-locked laser

We have used the comb of optical frequencies emitted by a mode-locked laser as a ruler to measure differences of as much as 20 THz between laser frequencies. This is to our knowledge the largest gap measured with a frequency comb, with high potential for further improvements. To check the accuracy of this approach we show that the modes are distributed uniformly in frequency space within the experimental limit of 3.0 parts in 10(17) . By comparison with an optical frequency comb generator we have verified that the mode separation equals the pulse repetition rate within the experimental limit of 6.0 parts in 10(16).