@article{FleischhakerEversDey2010, author = {Fleischhaker, Robert and Evers, J{\"o}rg and Dey, Tarak N.}, title = {Phase modulation induced by cooperative effects in electromagnetically induced transparency}, series = {Physical Review A - Atomic, molecular, and optical physics}, volume = {82}, journal = {Physical Review A - Atomic, molecular, and optical physics}, number = {1}, publisher = {AIP Publishing}, address = {Melville, NY}, issn = {1050-2947}, doi = {10.1103/PhysRevA.82.013815}, pages = {013815}, year = {2010}, abstract = {We analyze the influence of dipole-dipole interactions in an electromagnetically induced transparency set up for a density at the onset of cooperative effects. To this end, we include mean-field models for the influence of local-field corrections and radiation trapping into our calculation. We show both analytically and numerically that the polarization contribution to the local field strongly modulates the phase of a weak pulse. We give an intuitive explanation for this local-field-induced phase modulation and demonstrate that it distinctively differs from the nonlinear self-phase-modulation that a strong pulse experiences in a Kerr medium.}, language = {en} } @article{FontivonArxGarciaGonzalezetal.2010, author = {Fonti, Patrick and von Arx, Georg and Garc{\´i}a-Gonz{\´a}lez, Ignacio and Eilmann, Britta and Sass-Klaassen, Ute G. W. and G{\"a}rtner, Holger and Eckstein, Dieter}, title = {Studying global change through investigation of the plastic responses of xylem anatomy in tree rings}, series = {New Phytologist}, volume = {185}, journal = {New Phytologist}, number = {1}, publisher = {Wiley-Blackwell}, address = {Oxford}, issn = {1469-8137 (Online)}, doi = {10.1111/j.1469-8137.2009.03030.x}, pages = {42 -- 53}, year = {2010}, abstract = {Variability in xylem anatomy is of interest to plant scientists because of the role water transport plays in plant performance and survival. Insights into plant adjustments to changing environmental conditions have mainly been obtained through structural and functional comparative studies between taxa or within taxa on contrasting sites or along environmental gradients. Yet, a gap exists regarding the study of hydraulic adjustments in response to environmental changes over the lifetimes of plants. In trees, dated tree-ring series are often exploited to reconstruct dynamics in ecological conditions, and recent work in which wood-anatomical variables have been used in dendrochronology has produced promising results. Environmental signals identified in water-conducting cells carry novel information reflecting changes in regional conditions and are mostly related to short, sub-annual intervals. Although the idea of investigating environmental signals through wood anatomical time series goes back to the 1960s, it is only recently that low-cost computerized image-analysis systems have enabled increased scientific output in this field. We believe that the study of tree-ring anatomy is emerging as a promising approach in tree biology and climate change research, particularly if complemented by physiological and ecological studies. This contribution presents the rationale, the potential, and the methodological challenges of this innovative approach.}, language = {en} } @article{DobbertinEilmannBleuleretal.2010, author = {Dobbertin, Matthias and Eilmann, Britta and Bleuler, Peter and Giuggiola, Arnaud and Graf Pannatier, Elisabeth and Landolt, Werner and Schleppi, Patrick and Rigling, Andreas}, title = {Effect of irrigation on needle morphology, shoot and stem growth in a drought-exposed Pinus sylvestris forest}, series = {Tree Physiology}, volume = {30}, journal = {Tree Physiology}, number = {3}, publisher = {Oxford University Press}, address = {Oxford}, issn = {1758-4469 (Online)}, doi = {10.1093/treephys/tpp123}, pages = {346 -- 360}, year = {2010}, abstract = {In Valais, Switzerland, Scots pines (Pinus sylvestris L.) are declining, mainly following drought. To assess the impact of drought on tree growth and survival, an irrigation experiment was initiated in 2003 in a mature pine forest, approximately doubling the annual precipitation. Tree crown transparency (lack of foliage) and leaf area index (LAI) were annually assessed. Seven irrigated and six control trees were felled in 2006, and needles, stem discs and branches were taken for growth analysis. Irrigation in 2004 and 2005, both with below-average precipitation, increased needle size, area and mass, stem growth and, with a 1-year delay, shoot length. This led to a relative decrease in tree crown transparency (-14\%) and to an increase in stand LAI (+20\%). Irrigation increased needle length by 70\%, shoot length by 100\% and ring width by 120\%, regardless of crown transparency. Crown transparency correlated positively with mean needle size, shoot length and ring width and negatively with specific leaf area. Trees with high crown transparency (low growth, short needles) experienced similar increases in needle mass and growth with irrigation than trees with low transparency (high growth, long needles), indicating that seemingly declining trees were able to 'recover' when water supply became sufficient. A simple drought index before and during the irrigation explained most of the variation found in the parameters for both irrigated and control trees.}, language = {en} } @article{EilmannBuchmannSiegwolfetal.2010, author = {Eilmann, Britta and Buchmann, Nina and Siegwolf, Rolf and Saurer, Matthias and Cherubini, Paolo and Rigling, Andreas}, title = {Fast response of Scots pine to improved water availability reflected in tree-ring width and δ13C}, series = {Plant, Cell and Environment}, volume = {33}, journal = {Plant, Cell and Environment}, number = {8}, publisher = {Wiley-Blackwell}, address = {Oxford}, issn = {1365-3040 (Online)}, doi = {10.1111/j.1365-3040.2010.02153.x}, pages = {1351 -- 1360}, year = {2010}, abstract = {Drought-induced forest decline, like the Scots pine mortality in inner-Alpine valleys, will gain in importance as the frequency and severity of drought events are expected to increase. To understand how chronic drought affects tree growth and tree-ring δ13C values, we studied mature Scots pine in an irrigation experiment in an inner-Alpine valley. Tree growth and isotope analyses were carried out at the annual and seasonal scale. At the seasonal scale, maximum δ13C values were measured after the hottest and driest period of the year, and were associated with decreasing growth rates. Inter-annual δ13C values in early- and latewood showed a strong correlation with annual climatic conditions and an immediate decrease as a response to irrigation. This indicates a tight coupling between wood formation and the freshly produced assimilates for trees exposed to chronic drought. This rapid appearance of the isotopic signal is a strong indication for an immediate and direct transfer of newly synthesized assimilates for biomass production. The fast appearance and the distinct isotopic signal suggest a low availability of old stored carbohydrates. If this was a sign for C-storage depletion, an increasing mortality could be expected when stressors increase the need for carbohydrate for defence, repair or regeneration.}, language = {en} } @article{EgliAyerPeteretal.2010, author = {Egli, Simon and Ayer, Fran{\c{c}}ois and Peter, Martina and Eilmann, Britta and Rigling, Andreas}, title = {Is forest mushroom productivity driven by tree growth? Results from a thinning experiment}, series = {Annals of Forest Science}, volume = {67}, journal = {Annals of Forest Science}, number = {5}, publisher = {Springer}, address = {Paris}, issn = {1286-4560 (Print)}, doi = {10.1051/forest/2010011}, pages = {509}, year = {2010}, abstract = {• Most of the edible forest mushrooms are mycorrhizal and depend on carbohydrates produced by the associated trees. Fruiting patterns of these fungi are not yet fully understood since climatic factors alone do not completely explain mushroom occurrence. • The objective of this study was to retrospectively find out if changing tree growth following an increment thinning has influenced the diversity patterns and productivity of associated forest mushrooms in the fungus reserve La Chan{\´e}az, Switzerland. • The results reveal a clear temporal relationship between the thinning, the growth reaction of trees and the reaction of the fungal community, especially for the ectomycorrhizal species. The tree-ring width of the formerly suppressed beech trees and the fruit body number increased after thinning, leading to a significantly positive correlation between fruit body numbers and tree-ring width. • Fruit body production was influenced by previous annual tree growth, the best accordance was found between fruit body production and the tree-ring width two years previously. • The results support the hypothesis that ectomycorrhizal fruit body production must be linked with the growth of the associated host trees. Moreover, the findings indicate the importance of including mycorrhizal fungi as important players when discussing a tree as a carbon source or sink.}, language = {en} } @article{RiglingEilmannKoechlietal.2010, author = {Rigling, Andreas and Eilmann, Britta and Koechli, Roger and Dobbertin, Matthias}, title = {Mistletoe-induced crown degradation in Scots pine in a xeric environment}, volume = {30}, number = {7}, publisher = {Oxford University Press}, address = {Oxford}, issn = {1758-4469 (Online)}, doi = {10.1093/treephys/tpq038}, pages = {845 -- 832}, year = {2010}, abstract = {Increasing Scots pine (Pinus sylvestris L.) mortality has been recently observed in the dry inner valleys of the European Alps. Besides drought, infection with pine mistletoe (Viscum album ssp. austriacum) seems to play an important role in the mortality dynamics of Scots pines, but how mistletoes promote pine decline remains unclear. To verify whether pine mistletoe infection weakens the host via crown degradation, as observed for dwarf mistletoes, we studied the negative effects of pine mistletoe infestation on the photosynthetic tissues and branch growth of pairs of infested and non-infested branches. Pine mistletoe infection leads to crown degradation in its host by reducing the length, the radial increment, the ramification, the needle length and the number of needle years of the infested branches. This massive loss in photosynthetic tissue results in a reduction in primary production and a subsequent decrease in carbohydrate availability. The significant reduction in needle length due to mistletoe infection is an indication for a lower water and nutrient availability in infested branches. Thus, mistletoe infection might lead to a decrease in the availability of water and carbohydrates, the two most important growth factors, which are already shortened due to the chronic drought situation in the area. Therefore, pine mistletoe increases the risk of drought-induced mortality of its host when growing in a xeric environment.}, language = {en} } @article{BragardSoltauThomasetal.2010, author = {Bragard, Michael and Soltau, N. and Thomas, S. and De Doncker, R. W.}, title = {The balance of renewable sources and user demands in grids : power electronics for modular battery energy storage systems}, series = {IEEE transactions on power electronics}, volume = {25}, journal = {IEEE transactions on power electronics}, number = {12}, publisher = {IEEE}, address = {New York}, issn = {0885-8993}, doi = {10.1109/TPEL.2010.2085455}, pages = {3049 -- 3056}, year = {2010}, abstract = {The continuously growing amount of renewable sources starts compromising the stability of electrical grids. Contradictory to fossil fuel power plants, energy production of wind and photovoltaic (PV) energy is fluctuating. Although predictions have significantly improved, an outage of multi-MW offshore wind farms poses a challenging problem. One solution could be the integration of storage systems in the grid. After a short overview, this paper focuses on two exemplary battery storage systems, including the required power electronics. The grid integration, as well as the optimal usage of volatile energy reserves, is presented for a 5- kW PV system for home application, as well as for a 100- MW medium-voltage system, intended for wind farm usage. The efficiency and cost of topologies are investigated as a key parameter for large-scale integration of renewable power at medium- and low-voltage.}, language = {en} } @article{DegeringEggertPulsetal.2010, author = {Degering, Christian and Eggert, Thorsten and Puls, Michael and Bongaerts, Johannes and Evers, Stefan and Maurer, Karl-Heinz and Jaeger, Karl-Erich}, title = {Optimization of protease secretion in Bacillus subtilis and Bacillus licheniformis by screening of homologous and herologous signal peptides}, series = {Applied and environmental microbiology}, volume = {76}, journal = {Applied and environmental microbiology}, number = {19}, publisher = {American Society for Microbiology}, address = {Washington, DC}, issn = {1098-5336 (E-Journal); 0003-6919 (Print); 0099-2240 (Print)}, doi = {10.1128/AEM.01146-10}, pages = {6370 -- 6378}, year = {2010}, abstract = {Bacillus subtilis and Bacillus licheniformis are widely used for the large-scale industrial production of proteins. These strains can efficiently secrete proteins into the culture medium using the general secretion (Sec) pathway. A characteristic feature of all secreted proteins is their N-terminal signal peptides, which are recognized by the secretion machinery. Here, we have studied the production of an industrially important secreted protease, namely, subtilisin BPN′ from Bacillus amyloliquefaciens. One hundred seventy-three signal peptides originating from B. subtilis and 220 signal peptides from the B. licheniformis type strain were fused to this secretion target and expressed in B. subtilis, and the resulting library was analyzed by high-throughput screening for extracellular proteolytic activity. We have identified a number of signal peptides originating from both organisms which produced significantly increased yield of the secreted protease. Interestingly, we observed that levels of extracellular protease were improved not only in B. subtilis, which was used as the screening host, but also in two different B. licheniformis strains. To date, it is impossible to predict which signal peptide will result in better secretion and thus an improved yield of a given extracellular target protein. Our data show that screening a library consisting of homologous and heterologous signal peptides fused to a target protein can identify more-effective signal peptides, resulting in improved protein export not only in the original screening host but also in different production strains.}, language = {en} } @article{ReisgenSchleserMokrovetal.2010, author = {Reisgen, Uwe and Schleser, Markus and Mokrov, Oleg and Ahmed, Essam}, title = {Uni- and bi-axial deformation behavior of laser welded advanced high strength steel sheets}, series = {Journal of materials processing technology}, volume = {210}, journal = {Journal of materials processing technology}, number = {15}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0924-0136}, doi = {http10.1016/j.jmatprotec.2010.08.003}, pages = {2188 -- 2196}, year = {2010}, abstract = {Bead-on-plate butt joints of 2.5 mm hot rolled DP600/DP600 and 1.2 mm cold rolled TRIP700/TRIP700 steel sheets were performed using 6 kW CO2 laser beam welding. The welding speed ranged from 1.5 to 3.0 and from 2.1 to 3.9 m/min in DP/DP and TRIP/TRIP steel weldments respectively. A top surface helium gas was used as a shielding gas at a flow rate of 20 l/min. Metallographic examinations and transverse tensile testing (DIN EN 895: 1995) were carried out to characterize the weldments. The formability of base metals and weldments were investigated by standard Erichsen test (DIN EN ISO 20482). It was found that the uniaxial plastic behavior of both DP600 and TRIP700 base metals was in agreement with Swift and modified Mecking-Kocks models respectively. In a perpendicular tensile test to the weld line, all specimens were fractured at the base metal however the strengths were somewhat higher than those of base metal. There was a significant reduction in formability caused by welding of both DP/DP and TRIP/TRIP steel weldments and the formability has been improved with the increase of the welding speed.}, language = {en} } @article{MukherjeePrahlBlecketal.2010, author = {Mukherjee, Krishnendu and Prahl, Ulrich and Bleck, Wolfgang and Reisgen, Uwe and Schleser, Markus and Abdurakhmanov, Aydemir}, title = {Characterization and modelling techniques for gas metal arc welding of DP 600 sheet steels}, series = {Materialwissenschaft und Werkstofftechnik}, volume = {41}, journal = {Materialwissenschaft und Werkstofftechnik}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1521-4052}, doi = {10.1002/mawe.201000692}, pages = {972 -- 983}, year = {2010}, abstract = {The objectives of the present work are to characterize the Gas Metal Arc Welding process of DP 600 sheet steel and to summarize the modelling techniques. The time-temperature evolution during the welding cycle was measured experimentally and modelled with the softwaretool SimWeld. To model the phase transformations during the welding cycle dilatometer tests were done to quantify the parameters for phase field modelling by MICRESS®. The important input parameters are interface mobility, nucleation density, etc. A contribution was made to include austenite to bainite transformation in MICRESS®. This is useful to predict the microstructure in the fast cooling segments. The phase transformation model is capable to predict the microstructure along the heating and cooling cycles of welding. Tensile tests have shown the evidence of failure at the heat affected zone, which has the ferrite-tempered martensite microstructure.}, language = {en} }