The impact of the spacecraft system SÄNGER on the composition of the middle atmosphere

A two-dimensional chemical model and physical considerations are used to estimate the impact of the spacecraft system SÄNGER on stratospheric and mesospheric ozone in relation to other spacecraft and other anthropogenic perturbations. Perturbations of middle atmospheric NOy H2O and H2 concentrations, and their impact on the radiative balance of the atmosphere, including contrail formation, are discussed. It is found, that in case of about 24 launches per year the perturbations due to SÄGER are about negligible on a global scale. However, if a SÄGER version would be used for a hypersonic fleet of commercial aircraft a serious ozone depletion is predicted. © 1992 by Wax Planck Society

Neural correlates of ‘pessimistic' attitude in depression

Background Preparing for potentially threatening events in the future is essential for survival. Anticipating the future to be unpleasant is also a cognitive key feature of depression. We hypothesized that ‘pessimism'-related emotion processing would characterize brain activity in major depression. Method During functional magnetic resonance imaging, depressed patients and a healthy control group were cued to expect and then perceive pictures of known emotional valences - pleasant, unpleasant and neutral - and stimuli of unknown valence that could have been either pleasant or unpleasant. Brain activation associated with the ‘unknown' expectation was compared with the ‘known' expectation conditions. Results While anticipating pictures of unknown valence, activation patterns in depressed patients within the medial and dorsolateral prefrontal areas, inferior frontal gyrus, insula and medial thalamus were similar to activations associated with expecting unpleasant pictures, but not with expecting positive pictures. The activity within a majority of these areas correlated with the depression scores. Differences between healthy and depressed persons were found particularly for medial and dorsolateral prefrontal and insular activations. Conclusions Brain activation in depression during expecting events of unknown emotional valence was comparable with activation while expecting certainly negative, but not positive events. This neurobiological finding is consistent with cognitive models supposing that depressed patients develop a ‘pessimistic' attitude towards events with an unknown emotional meaning. Thereby, particularly the role of brain areas associated with the processing of cognitive and executive control and of the internal state is emphasized in contributing to major depressio

Critical Phenomena at the Antiferromagnetic Phase Transition of Azurite

We report on high-resolution acoustic, specific-heat and thermal expansion measurements in the vicinity of the antiferromagnetic phase transition at T_N = 1.88 K on a high-quality single crystal of the natural mineral azurite. A detailed investigation of the critical contribution to the various quantities at T_N is presented. The set of critical exponents and amplitude ratios of the singular contributions above and below the transition indicate that the system can be reasonably well described by a three-dimensional Heisenberg antiferromagnet.Comment: 9 pages, 3 figures, proceedings of ICM 2012, JKP

Improved simulation of isoprene oxidation chemistry with the ECHAM5/MESSy chemistry-climate model: lessons from the GABRIEL airborne field campaign

The GABRIEL airborne field measurement campaign, conducted over the Guyanas in October 2005, produced measurements of hydroxyl radical (OH) concentration which are significantly higher than can be simulated using current generation models of atmospheric chemistry. Based on the hypothesis that this "missing OH" is due to an as-yet undiscovered mechanism for recycling OH during the oxidation chain of isoprene, we determine that an OH recycling of about 40–50% (compared with 5–10% in current generation isoprene oxidation mechanisms) is necessary in order for our modelled OH to approach the lower error bounds of the OH observed during GABRIEL. Such a large amount of OH in our model leads to unrealistically low mixing ratios of isoprene. In order for our modelled isoprene mixing ratios to match those observed during the campaign, we also require that the effective rate constant for the reaction of isoprene with OH be reduced by about 50% compared with the lower bound of the range recommended by IUPAC. We show that a reasonable explanation for this lower effective rate constant could be the segregation of isoprene and OH in the mixed layer. Our modelling results are consistent with a global, annual isoprene source of about 500 Tg(C) yr<sup>−1</sup>, allowing experimentally derived and established isoprene flux rates to be reconciled with global models

Impact across ecosystem boundaries-Does Bti application change quality and composition of the diet of riparian spiders?

Emerging aquatic insects link aquatic and adjacent terrestrial food webs by subsidizing terrestrial predators with high -quality prey. One of the main constituents of aquatic subsidy, the non-biting midges (Chironomidae), showed altered emergence dynamics in response to the mosquito control agent Bacillus thuringiensis var. israelensis (Bti). As riparian spi-ders depend on aquatic subsidy, they may be affected by such changes in prey availability. Thus, we conducted a field study in twelve floodplain pond mesocosms (FPMs), six were treated with Bti (2.88 x 109 ITU/ha, VectoBac WDG) three times, to investigate if the Bti-induced shift in chironomid emergence dynamics is reflected in their nutritional value and in the diet of riparian spiders. We measured the content of proteins, lipids, glycogen, and carbohydrates in emerged Chironomidae, and determined the stable isotope ratios of female Tetragnatha extensa, a web-building spi-der living in the riparian vegetation of the FPMs. We analysed the proportion of aquatic prey in spiders' diet, niche size, and trophic position. While the content of nutrients and thus the prey quality was not significantly altered by Bti, ef-fects on the spiders' diet were observed. The trophic position of T. extensa from Bti-treated FPMs was lower compared to the control while the aquatic proportion was only minimally reduced. We assume that spiders fed more on terrestrial prey but also on other aquatic organisms such as Baetidae, whose emergence was unaffected by Bti. In contrast to the partly predaceous Chironomidae, consumption of aquatic and terrestrial primary consumers potentially explains the observed lower trophic position of spiders from Bti-treated FPMs. As prey organisms vary in their quality the suggested dietary shift could transfer previously observed effects of Bti to riparian spiders conceivably affecting their populations. Our results further support that anthropogenic stressors in aquatic ecosystems may translate to terrestrial predators through aquatic subsidy

Concept of an ionizing time-domain matter-wave interferometer

We discuss the concept of an all-optical and ionizing matter-wave interferometer in the time domain. The proposed setup aims at testing the wave nature of highly massive clusters and molecules, and it will enable new precision experiments with a broad class of atoms, using the same laser system. The propagating particles are illuminated by three pulses of a standing ultraviolet laser beam, which detaches an electron via efficient single photon-absorption. Optical gratings may have periods as small as 80 nm, leading to wide diffraction angles for cold atoms and to compact setups even for very massive clusters. Accounting for the coherent and the incoherent parts of the particle-light interaction, we show that the combined effect of phase and amplitude modulation of the matter waves gives rise to a Talbot-Lau-like interference effect with a characteristic dependence on the pulse delay time.Comment: 25 pages, 5 figure

Magnetoelastic and structural properties of azurite Cu3(CO3)2(OH)2 from neutron scattering and muon spin rotation

Azurite, Cu3(CO3)2(OH)2, has been considered an ideal example of a one-dimensional (1D) diamond chain antiferromagnet. Early studies of this material imply the presence of an ordered antiferromagnetic phase below $T_N \sim 1.9$ K while magnetization measurements have revealed a 1/3 magnetization plateau. Until now, no corroborating neutron scattering results have been published to confirm the ordered magnetic moment structure. We present recent neutron diffraction results which reveal the presence of commensurate magnetic order in azurite which coexists with significant magnetoelastic strain. The latter of these effects may indicate the presence of spin frustration in zero applied magnetic field. Muon spin rotation, $\mu$SR, reveals an onset of short-range order below 3K and confirms long-range order below $T_N$.Comment: 5 pages, 4 figures, PHYSICAL REVIEW B 81, 140406(R) (2010

Uncertainties in atmospheric chemistry modelling due to convection parameterisations and subsequent scavenging

Moist convection in global modelling contributes significantly to the transport of energy, momentum, water and trace gases and aerosols within the troposphere. Since convective clouds are on a scale too small to be resolved in a global model their effects have to be parameterised. However, the whole process of moist convection and especially its parameterisations are associated with uncertainties. In contrast to previous studies on the impact of convection on trace gases, which had commonly neglected the convective transport for some or all compounds, we investigate this issue by examining simulations with five different convection schemes. This permits an uncertainty analysis due to the process formulation, without the inconsistencies inherent in entirely neglecting deep convection or convective tracer transport for one or more tracers. <br><br> Both the simulated mass fluxes and tracer distributions are analysed. Investigating the distributions of compounds with different characteristics, e.g., lifetime, chemical reactivity, solubility and source distributions, some differences can be attributed directly to the transport of these compounds, whereas others are more related to indirect effects, such as the transport of precursors, chemical reactivity in certain regions, and sink processes. <br><br> The model simulation data are compared with the average regional profiles of several measurement campaigns, and in detail with two campaigns in fall and winter 2005 in Suriname and Australia, respectively. <br><br> The shorter-lived a compound is, the larger the differences and consequently the uncertainty due to the convection parameterisation are, as long as it is not completely controlled by local production that is independent of convection and its impacts (e.g. water vapour changes). Whereas for long-lived compounds like CO or O<sub>3</sub> the mean differences between the simulations are less than 25%), differences for short-lived compounds reach up to ±100% with different convection schemes. <br><br> A rating of an overall "best" performing scheme is difficult, since the optimal performance depends on the region and compound

Cosmic multi-muon events observed in the underground CERN-LEP tunnel with the ALEPH experiment

Multimuon events have been recorded with the ALEPH-detector, located 140 m underground, in parallel with e$^+$e$^-$ data taking. Benefitting from the high spatial and momentum resolution of the ALEPH tracking chambers narrowly spaced muons in high multiplicity bundles could be analysed. The bulk of the data can be successfully described by standard production phenomena. The multiplicity distribution favors, though not with very high significance, a chemical composition which changes from light to heavier elements with increasing energy around the ``knee". The five highest multiplicity events, with up to 150 muons within an area of $\sim$ 8 m$^2$, occur with a frequency which is almost an order of magnitude above the simulation. To establish a possible effect, more of these events should be recorded with a larger area detector

Stratospheric dryness: model simulations and satellite observations

The mechanisms responsible for the extreme dryness of the stratosphere have been debated for decades. A key difficulty has been the lack of comprehensive models which are able to reproduce the observations. Here we examine results from the coupled lower-middle atmosphere chemistry general circulation model ECHAM5/MESSy1 together with satellite observations. Our model results match observed temperatures in the tropical lower stratosphere and realistically represent the seasonal and inter-annual variability of water vapor. The model reproduces the very low water vapor mixing ratios (below 2 ppmv) periodically observed at the tropical tropopause near 100 hPa, as well as the characteristic tape recorder signal up to about 10 hPa, providing evidence that the dehydration mechanism is well-captured. Our results confirm that the entry of tropospheric air into the tropical stratosphere is forced by large-scale wave dynamics, whereas radiative cooling regionally decelerates upwelling and can even cause downwelling. Thin cirrus forms in the cold air above cumulonimbus clouds, and the associated sedimentation of ice particles between 100 and 200 hPa reduces water mass fluxes by nearly two orders of magnitude compared to air mass fluxes. Transport into the stratosphere is supported by regional net radiative heating, to a large extent in the outer tropics. During summer very deep monsoon convection over Southeast Asia, centered over Tibet, moistens the stratosphere