Untersuchung von St?rke, Mehl, Teig und Backpulver

Ohne Zusammenfassung     

Study of temperature dependence of thermal diffusion in polystyrene/ethylbenzene by thermal field-flow fractionation

Using a special thermal field-flow fractionation apparatus capable of working over a broad temperature range, we have observed that retention in the polystyrene/ethylbenzene system decreases substantially as the cold wall temperature increases from 360 to 424 K. Polymers of four different molecular weights ranging from 20,000 to 160,000 were used to verify this conclusion. Based on our earlier work showing that thermal diffusion parameters could be calculated from retention data, we have used the present measurements along with earlier values to generate a compilation of thermal diffusion data over the temperature range from 270 to 424 K. These results are used to develop empirical expressions for the thermal diffusion factor and the thermal diffusion coefficient for polystyrene in ethylbenzene as a function of temperature and molecular weight. It is shown that these results have potential usefulness both in terms of the new physicochemical data obtained and in terms of the guidelines they provide for choosing experimental conditions for thermal field-flow fractionation experiments.     

Untersuchung von Stärke,Mehl, Teig und Backpulver

Analytical and Bioanalytical Chemistry -     

Breaking the far-field diffraction limit in optical nanopatterning via repeated photochemical and electrochemical transitions in photochromic molecules

By saturating a photochromic transition with a nodal illumination (wavelength, λ), one isomeric form of a small molecule is spatially localized to a region smaller than the far-field diffraction limit. A selective oxidation step effectively locks this pattern allowing repeated patterning. Using this approach and a two-beam interferometer, we demonstrate isolated lines as narrow as λ/8 (78 nm) and spacing between features as narrow as λ/4 (153 nm). This is considerably smaller than the minimum far-field diffraction limit of λ/2. Most significantly, nanopatterning is achieved via single-photon reactions and at low light levels, which in turn allow for high throughput.     

Microstructural analysis of neutron irradiated titanium and rhenium

The defect structure in α-titanium and rhenium irradiated with neutrons at 0.4T _m (T _m = absolute melting temperature) has been analyzed using transmission electron microscopy. In rhenium, the vacancies agglomerate into voids whereas in titanium, vacancy dislocation loops lying on the prism planes are the only vacancy type defects observed. In both metals, dislocation segments and network fragments are the main evidence of interstitial type defects. The presence of dislocation loops rather than voids in titanium irradiated at this temperature is an anamalous result when compared to results on other similarly irradiated pure metals. Possible explanations for the preferential formation of loops rather than voids in the titanium are discussed.     

Direct observation of laser filamentation in high-order harmonic generation

We investigate the spatial evolution of a laser pulse used to generate high-order harmonics (orders ranging from 45 to 91) in a semi-infinite helium-filled gas cell. The 5 mJ, 30 fs laser pulses experience elongated focusing with two distinct waists when focused with f/125 optics in 80 Torr of helium. Extended phase matching for the generation of harmonics occurs in the region between the double foci of the laser, where the laser beam changes from diverging to converging.