Molecular characterization and optimization of enzymes involved in glycosaminoglycan biosynthesis

Glycosaminoglycans are biological active polysaccharides composed of repeating disaccharides composed of a hexuronic acid and a hexosamine. They have various pharmaceutical applications and traditionally this type of molecule is isolated from animal tissue. Since extraction from animal derivatives has serious limitations for the production of a large variety of defined glycosaminoglycans, there is a general interest in developing alternative systems enabling a more tightly controlled synthesis. During this research project we explored alternative ways of controlled chemo-enzymatic synthesis ofmonodisperse and uniform glycosaminoglycans for pharmaceutical applications, with a main focus on heparin. Heparin is a highly sulfated and complex glycosaminoglycan which is worldwide used as an anticoagulant to prevent blood clotting during surgery.Upon closer investigation of the heparin biosynthesis the D-glucuronyl C5-epimerase was recognized as a key enzyme, as this is the only reaction that cannot be done chemically. Two alternative approaches were taken to get closer to an industrial applicable enzyme; improvement of the animal heparin sulfate D-glucuronyl C5-epimerase and identification and isolation of novel candidate C5-epimerases from prokaryotes. Both approaches gave functional production of C5-epimerases. </p

Dynamic Regimes in Films with a Periodic Array of Antidots

We have studied the dynamic response of Pb thin films with a square array of antidots by means of ac susceptibility chi(T,H) measurements. At low enough ac drive amplitudes h, vortices moving inside the pinning potential give rise to a frequency- and h-independent response together with a scarce dissipation. For higher amplitudes, the average distance travelled by vortices surpasses the pinning range and a critical state develops. We found that the boundary h*(H,T) between these regimes smoothly decreases as T increases whereas a step-like behavior is observed as a function of field. We demonstrate that these steps in h*(H) arise from sharp changes in the pinning strength corresponding to different vortex configurations. For a wide set of data at several fields and temperatures in the critical state regime, we show that the scaling laws based on the simple Bean model are satisfied.Comment: 7 pages, 5 figure

Dendritic flux penetration in Pb films with a periodic array of antidots

We explore the flux-jump regime in type-II Pb thin films with a periodic array of antidots by means of magneto-optical measurements. A direct visualization of the magnetic flux distribution allows to identify a rich morphology of flux penetration patterns. We determine the phase boundary $H^*(T)$ between dendritic penetration at low temperatures and a smooth flux invasion at high temperatures and fields. For the whole range of fields and temperatures studied, guided vortex motion along the principal axes of the square pinning array is clearly observed. In particular, the branching process of the dendrite expansion is fully governed by the underlying pinning topology. A comparative study between macroscopic techniques and direct local visualization shed light onto the puzzling $T-$ and $H-$independent magnetic response observed at low temperatures and fields. Finally, we find that the distribution of avalanche sizes at low temperatures can be described by a power law with exponent $\tau \sim 0.9(1)$

Subtitles in English-only TV commercials

Previous studies on the effects of subtitles in cross-national English spoken commercials have yielded contradictory results regarding young and highly educated viewers’ ad and brand attitudes. Most studies did not examine whether local-language subtitles are still necessary for older viewers to understand the English dialogues in the commercials. In a between-subjects experiment, we examined whether subtitles had a positive effect on (1) participants’ understanding of what the actors in commercials were saying to each other, and (2) participants’ attitudes towards commercials. Our sample (N = 188) consisted of viewers over age forty with different educational backgrounds living in a typical subtitling region. Our study showed that subtitles did not affect viewers’ attitudes towards the commercials. Local-language subtitles, however, increased participants’ understanding of what was said in the commercials, regardless of their educational level. Subtitles in English spoken commercials intended for an older and broad audience are, therefore, certainly not superfluous

Field-dependent Vortex Pinning Strength in a Periodic Array of Antidots

We explore the dynamic response of vortex lines in a Pb thin film with a periodic array of antidots by means of ac-susceptibility measurements. For low drive field amplitudes, within the Campbell regime, vortex motion is of intra-valley type and the penetration depth is related to the curvature of the pinning potential well, $\alpha$. For dc-fields below the first matching field $H_1$, $\alpha$ reaches its highest value associated with a Mott Insulator-like phase where vortex lines are strongly localized at the pinning sites. For $H_1<H_{dc}<H_2$, the response is mainly due to the interstitial vortices and $\alpha$ drops to smaller values as expected for this metallic-like regime. Strikingly, for $H_2<H_{dc}<H_3$, we observe that $\alpha$ reduces further down. However, for $H_3<H_{dc}<H_4$, a reentrance in the pinning strength is observed, due to a specific configuration of the flux line lattice which strongly restricts the mobility of vortices. We present a possible explanation for the measured $\alpha(H_{dc})$ dependence based on the different flux line lattice configurations.Comment: 5 pages, to be published in Phys. Rev.

Flux pinning properties of superconductors with an array of blind holes

We performed ac-susceptibility measurements to explore the vortex dynamics and the flux pinning properties of superconducting Pb films with an array of micro-holes (antidots) and non-fully perforated holes (blind holes). A lower ac-shielding together with a smaller extension of the linear regime for the lattice of blind holes indicates that these centers provide a weaker pinning potential than antidots. Moreover, we found that the maximum number of flux quanta trapped by a pinning site, i.e. the saturation number ns, is lower for the blind hole array.Comment: 6 figures, 6 page