Enantioselective Zinc‐Catalyzed Hydrosilylation of Ketones using Pybox or Pybim Ligands

The combination of ZnEt₂ and chiral pyridinebisoxazoline (pybox) or pyridinebisimidazoline (pybim) ligands catalyzed the asymmetric hydrosilylation of aryl, alkyl, cyclic, heterocyclic, and aliphatic ketones. Under mild conditions, high yields and good enantioselectivities were achieved. ESI measurements allowed for the characterization of the active catalyst.     

Structural Chemistry of Magnesium Acetates

Magnesium acetate solvates, Mg(OAc)₂ · nL, and their hydrates were prepared by crystallization of Mg(OAc)₂ · 4H₂O or Mg(OAc)₂ from different solvents (L = MeOH, EtOH, HOAc). Anhydrous Mg(OAc)₂ was obtained by thermal dehydration of the tetrahydrate at 150 °C. X‐ray single crystal diffraction mostly with the use of synchrotron radiation allowed the structure determination of Mg(OAc)₂(H₂O)₃(EtOH) ( I ), Mg(OAc)₂(HOAc)₂(H₂O)₂ ( II ), Mg₃(OAc)₆(MeOH)₆ ( III ), Mg₃(OAc)₆(HOAc)₂(H₂O)₂ · 2HOAc ( IV ), Mg(OAc)₂(HOAc) · 1.8(HOAc) ( V ), Mg(OAc)₂ · H₂O ( VI ), [Mg₃(OAc)₆(EtOH)₂] · 2EtOH ( VII ), and Mg(OAc)₂ ( VIII ). Structural data were discussed in terms of the number of neutral O‐donor ligands per magnesium atom, coordination environment of magnesium atoms, structural functions of acetate groups, and hydrogen bonding systems.     

Dynamic Data-Driven Genetic Algorithm for forest fire spread prediction

This work represents the first step towards a Dynamic Data-Driven Application System (DDDAS) for wildland fire prediction. Our main efforts are focused on taking advantage of the computing power provided by High Performance Computing systems and to propose computational data-driven steering strategies to overcome input data uncertainty. In doing so, prediction quality can be enhanced significantly. On the other hand, these proposals reduce the execution time of the overall prediction process in order to be of use during real-time crisis. In particular, this work describes a Dynamic Data-Driven Genetic Algorithm (DDDGA) used as steering strategy to automatically adjust highly dynamic input data values of forest fire simulators taking into account the underlying propagation model and real fire behaviour.     

Exposure of Arctic Field Scientists to Ultraviolet Radiation Evaluated Using Personal Dosimeters

During July 2000 we used an electronic personal dosimeter (X-2000) and a biological dosimeter (Deutsches Zentrum für Luft- und Raumfahrt: Biofilm) to characterize the UV radiation exposure of arctic field scientists involved in biological and geological fieldwork. These personnel were working at the Haughton impact structure on Devon Island (75 degrees N) in the Canadian High Arctic under a 24 h photoperiod. During a typical day of field activities under a clear sky, the total daily erythemally weighted exposure, as measured by electronic dosimetry, was up to 5.8 standard erythemal dose (SED). Overcast skies (typically 7-8 okta of stratus) reduced exposures by a mean of 54%. We estimate that during a month of field activity in July a typical field scientist at this latitude could potentially receive approximately 80 SED to the face. Because of body movements the upper body was exposed to a UV regimen that often changed on second-to-second time-scales as assessed by electronic dosimetry. Over a typical 10 min period on vehicle traverse, we found that erythemal exposure could vary to up to 87% of the mean exposure. Time-integrated exposures showed that the type of outdoor field activities in the treeless expanse of the polar desert had little effect on the exposure received. Although absolute exposure changed in accordance with the time of day, the exposure ratio (dose received over horizontal dose) did not vary much over the day. Under clear skies the mean exposure ratio was 0.35 +/- 0.12 for individual activities at different times of the day assessed using electronic dosimetry. Biological dosimetry showed that the occupation was important in determining daily exposures. In our study, scientists in the field received an approximately two-fold higher dose than individuals, such as medics and computer scientists, who spent the majority of their time in tents.     

Cavities in a visco-plastic material: A mesoscopic concept

In the present work we investigate the temporal development of arbitrarily distributed voids in a visco-plastic material under different loading regimes. A mesoscopic continuum model is used in order to take the microstructure of the material into account. In particular, we introduce a mesoscopic space representing an extension of the space-time domain of the continuum mechanical fields. This extended domain requires a reformulation of the classical balance equations as well as the consideration of additional constitutive quantities. Furthermore a mesoscopic distribution function can be introduced which follows an own balance. Assuming a special model of porous composites, the spherical shell model, all required steps are elaborated in order to describe load-induced void-growth in a metal-like matrix. We conclude with some exemplary results which show astonishing similarities with co-called LSW-theories. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)