TY - JOUR AB - No catalyst required! A highly efficient, catalyst-free process to generate diimide in situ from hydrazine monohydrate and molecular oxygen for the selective reduction of alkenes has been developed. The use of a gas–liquid segmented flow system allowed safe operating conditions and dramatically enhanced this atom-economical reaction, resulting in short processing times. AU - Pieber, Bartholomäus AU - Martinez, Sabrina Teixeira AU - Cantillo, David AU - Kappe, C. Oliver ID - 11959 IS - 39 JF - Angewandte Chemie International Edition SN - 1433-7851 TI - In situ generation of diimide from hydrazine and oxygen: Continuous-flow transfer hydrogenation of olefins VL - 52 ER - TY - JOUR AB - It's not magic! The effects observed in microwave-irradiated chemical transformations can in most cases be rationalized by purely bulk thermal phenomena associated with rapid heating to elevated temperatures. As discussed in this Essay, the existence of so-called nonthermal or specific microwave effects is highly doubtful. AU - Kappe, C. Oliver AU - Pieber, Bartholomäus AU - Dallinger, Doris ID - 11960 IS - 4 JF - Angewandte Chemie International Edition SN - 1433-7851 TI - Microwave effects in organic synthesis: Myth or reality? VL - 52 ER - TY - JOUR AB - The use of high-temperature/pressure gas–liquid continuous flow conditions dramatically enhances the iron-catalyzed aerobic oxidation of 2-benzylpyridines to their corresponding ketones. Pressurized air serves as a readily available oxygen source and propylene carbonate as a green solvent in this radically intensified preparation of synthetically valuable 2-aroylpyridines. AU - Pieber, Bartholomäus AU - Kappe, C. Oliver ID - 11973 IS - 2 JF - Green Chemistry SN - 1463-9262 TI - Direct aerobic oxidation of 2-benzylpyridines in a gas-liquid continuous-flow regime using propylene carbonate as a solvent VL - 15 ER - TY - JOUR AB - Near-surface air temperature, typically measured at a height of 2 m, is the most important control on the energy exchange and the melt rate at a snow or ice surface. It is distributed in a simplistic manner in most glacier melt models by using constant linear lapse rates, which poorly represent the actual spatial and temporal variability of air temperature. In this paper, we test a simple thermodynamic model proposed by Greuell and Böhm in 1998 as an alternative, using a new dataset of air temperature measurements from along the flowline of Haut Glacier d’Arolla, Switzerland. The unmodified model performs little better than assuming a constant linear lapse rate. When modified to allow the ratio of the boundary layer height to the bulk heat transfer coefficient to vary along the flowline, the model matches measured air temperatures better, and a further reduction of the root-mean-square error is obtained, although there is still considerable scope for improvement. The modified model is shown to perform best under conditions favourable to the development of katabatic winds – few clouds, positive ambient air temperature, limited influence of synoptic or valley winds and a long fetch – but its performance is poor under cloudy conditions. AU - Petersen, Lene AU - Pellicciotti, Francesca AU - Juszak, Inge AU - Carenzo, Marco AU - Brock, Ben ID - 12642 IS - 63 JF - Annals of Glaciology KW - Earth-Surface Processes SN - 0260-3055 TI - Suitability of a constant air temperature lapse rate over an Alpine glacier: Testing the Greuell and Böhm model as an alternative VL - 54 ER - TY - JOUR AB - Parameterizations of incoming longwave radiation are increasingly receiving attention for both low and high elevation glacierized sites. In this paper, we test 13 clear-sky parameterizations combined with seven cloud corrections for all-sky atmospheric emissivity at one location on Haut Glacier d'Arolla. We also analyze the four seasons separately and conduct a cross-validation to test the parameters’ robustness. The best parameterization is the one by Dilley and O'Brien, B for clear-sky conditions combined with Unsworth and Monteith cloud correction. This model is also the most robust when tested in cross-validation. When validated at different sites in the southern Alps of Switzerland and north-western Italian Alps, all parameterizations show a substantial decrease in performance, except for one site, thus suggesting that it is important to recalibrate parameterizations of incoming longwave radiation for different locations. We argue that this is due to differences in the structure of the atmosphere at the sites. We also quantify the effect that the incoming longwave radiation parameterizations have on energy-balance melt modeling, and show that recalibration of model parameters is needed. Using parameters from other sites leads to a significant underestimation of melt and to an error that is larger than that associated with using different parameterizations. Once recalibrated, however, the parameters of most models seem to be stable over seasons and years at the location on Haut Glacier d'Arolla. AU - Juszak, I. AU - Pellicciotti, Francesca ID - 12643 IS - 8 JF - Journal of Geophysical Research: Atmospheres KW - Space and Planetary Science KW - Earth and Planetary Sciences (miscellaneous) KW - Atmospheric Science KW - Geophysics SN - 2169-897X TI - A comparison of parameterizations of incoming longwave radiation over melting glaciers: Model robustness and seasonal variability VL - 118 ER - TY - JOUR AB - Greater Himalayan glaciers are retreating and losing mass at rates comparable to glaciers in other regions of the world1,2,3,4,5. Assessments of future changes and their associated hydrological impacts are scarce, oversimplify glacier dynamics or include a limited number of climate models6,7,8,9. Here, we use results from the latest ensemble of climate models in combination with a high-resolution glacio-hydrological model to assess the hydrological impact of climate change on two climatically contrasting watersheds in the Greater Himalaya, the Baltoro and Langtang watersheds that drain into the Indus and Ganges rivers, respectively. We show that the largest uncertainty in future runoff is a result of variations in projected precipitation between climate models. In both watersheds, strong, but highly variable, increases in future runoff are projected and, despite the different characteristics of the watersheds, their responses are surprisingly similar. In both cases, glaciers will recede but net glacier melt runoff is on a rising limb at least until 2050. In combination with a positive change in precipitation, water availability during this century is not likely to decline. We conclude that river basins that depend on monsoon rains and glacier melt will continue to sustain the increasing water demands expected in these areas10. AU - Immerzeel, W. W. AU - Pellicciotti, Francesca AU - Bierkens, M. F. P. ID - 12640 IS - 9 JF - Nature Geoscience KW - General Earth and Planetary Sciences SN - 1752-0894 TI - Rising river flows throughout the twenty-first century in two Himalayan glacierized watersheds VL - 6 ER - TY - JOUR AB - We investigate the sensitivity of a distributed enhanced temperature-index (ETI) melt model, in order to understand which parameters have the largest influence on model outputs and thus need to be accurately known. We use melt and meteorological data from two Alpine glaciers and one glacier in the Andes of Chile. Sensitivity analysis is conducted in a systematic way in terms of parameters and the different conditions (day, night, clear-sky, overcast), melt seasons and glaciers examined. The sensitivity of total melt to changes in individual parameters is calculated using a local method around the optimal value of the parameters. We verify that the parameters are optimal at the distributed scale and assess the model uncertainty induced by uncertainty in the parameters using a Monte Carlo technique. Model sensitivity to parameters is consistent across melt seasons, glaciers, different conditions and the daily statistics examined. The parameters to which the model is most sensitive are the shortwave-radiation factor, the temperature lapse rate for extrapolation of air temperature, the albedo parameters, the temperature threshold and the cloud transmittance factor parameters. A parameter uncertainty of 5% results in a model uncertainty of 5.6% of mean melt on Haut Glacier d’Arolla, Switzerland. AU - Heynen, Martin AU - Pellicciotti, Francesca AU - Carenzo, Marco ID - 12641 IS - 63 JF - Annals of Glaciology SN - 0260-3055 TI - Parameter sensitivity of a distributed enhanced temperature-index melt model VL - 54 ER - TY - JOUR AB - When confronted with a large-field stimulus rotating around the vertical body axis, flies display a following behavior called "optomotor response." As neural control elements, the large tangential horizontal system (HS) cells of the lobula plate have been prime candidates for long. Here, we applied optogenetic stimulation of HS cells to evaluate their behavioral role in Drosophila. To minimize interference of the optical activation of channelrhodopsin-2 with the visual perception of the flies, we used a bistable variant called ChR2-C128S. By applying pulses of blue and yellow light, we first demonstrate electrophysiologically that lobula plate tangential cells can be activated and deactivated repeatedly with no evident change in depolarization strength over trials. We next show that selective optogenetic activation of HS cells elicits robust yaw head movements and yaw turning responses in fixed and tethered flying flies, respectively. AU - Haikala, Väinö AU - Maximilian Jösch AU - Borst, Alexander AU - Mauss, Alex S ID - 1304 IS - 34 JF - Journal of Neuroscience TI - Optogenetic control of fly optomotor responses VL - 33 ER - TY - JOUR AB - In the fly Drosophila melanogaster, photoreceptor input to motion vision is split into two parallel pathways as represented by first-order interneurons L1 and L2 (Rister et al., 2007; Joesch et al., 2010). However, how these pathways are functionally specialized remains controversial. One study (Eichner et al., 2011) proposed that the L1-pathway evaluates only sequences of brightness increments (ON-ON), while the L2-pathway processes exclusively brightness decrements (OFF-OFF). Another study (Clark et al., 2011) proposed that each of the two pathways evaluates both ON-ON and OFF-OFF sequences. To decide between these alternatives, we recorded from motionsensitive neurons in flies in which the output from either L1 or L2 was genetically blocked. We found that blocking L1 abolishes ON-ON responses but leaves OFF-OFF responses intact. The opposite was true, when the output from L2 was blocked. We conclude that the L1 and L2 pathways are functionally specialized to detect ON-ON and OFF-OFF sequences, respectively. AU - Maximilian Jösch AU - Weber, Franz AU - Eichner, Hubert AU - Borst, Alexander ID - 1305 IS - 3 JF - Journal of Neuroscience TI - Functional specialization of parallel motion detection circuits in the fly VL - 33 ER - TY - JOUR AB - We derive sufficient conditions for advection-driven backward motion of the free boundary in a chemotaxis model with degenerate mobility. In this model, a porous-medium-type diffusive term and an advection term are in competition. The former induces forward motion, the latter may induce backward motion of the free boundary depending on the direction of advection. We deduce conditions on the growth of the initial data at the free boundary which ensure that at least initially the advection term is dominant. This implies local backward motion of the free boundary provided the advection is (locally) directed appropriately. Our result is based on a new class of moving test functions and Stampacchia's lemma. As a by-product of our estimates, we obtain quantitative bounds on the spreading of the support of solutions for the chemotaxis model and provide a proof for the finite speed of the support propagation property of solutions. AU - Julian Fischer ID - 1308 IS - 3 JF - SIAM Journal on Mathematical Analysis TI - Advection-driven support shrinking in a chemotaxis model with degenerate mobility VL - 45 ER -