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- ItemSimultaneous lidar observations of temperatures and waves in the polar middle atmosphere on the east and west side of the Scandinavian mountains: A case study on 19/20 January 2003(München : European Geopyhsical Union, 2004) Blum, U.; Fricke, K.H.; Baumgarten, G.; Schöch, A.Atmospheric gravity waves have been the subject of intense research for several decades because of their extensive effects on the atmospheric circulation and the temperature structure. The U. Bonn lidar at the Esrange and the ALOMAR RMR lidar at the Andøya Rocket Range are located in northern Scandinavia 250 km apart on the east and west side of the Scandinavian mountain ridge. During January and February 2003 both lidar systems conducted measurements and retrieved atmospheric temperatures. On 19/20 January 2003 simultaneous measurements for more than 7 h were possible. Although during most of the campaign time the atmosphere was not transparent for the propagation of orographically induced gravity waves, they were nevertheless observed at both lidar stations with considerable amplitudes during these simultaneous measurements. And while the source of the observed waves cannot be determined unambiguously, the observations show many characteristics of orographically excited gravity waves. The wave patterns at ALOMAR show a random distribution with time whereas at the Esrange a persistency in the wave patterns is observable. This persistency can also be found in the distribution of the most powerful vertical wavelengths. The mode values are both at about 5 km vertical wavelength, however the distributions are quite different, narrow at the Esrange with values from λz=2–6 km and broad at ALOMAR, covering λz=1–12 km vertical wavelength. In particular the difference between the observations at ALOMAR and at the Esrange can be understood by different orographic conditions while the propagation conditions were quite similar. At both stations the waves deposit energy in the atmosphere with increasing altitude, which leads to a decrease of the observed gravity wave potential energy density with altitude. The meteorological situation during these measurements was different from common winter situations. The ground winds were mostly northerlies, changed in the upper troposphere and lower stratosphere to westerlies and returned to northerlies in the middle stratosphere.
- ItemTowards closing the gap between hygroscopic growth and activation for secondary organic aerosol - Part 2: Theoretical approaches(München : European Geopyhsical Union, 2009) Wex, H.; Petters, M.D.; Carrico, C.M.; Hallbauer, E.; Massling, A.; McMeeking, G.R.; Poulain, L.; Wu, Z.; Kreidenweis, S.M.; Stratmann, F.We examine the hygroscopic properties of secondary organic aerosol particles generated through the reaction of α-pinene and ozone using a continuous flow reaction chamber. The water activity versus composition relationship is calculated from measurements of growth factors at relative humidities up to 99.6% and from measurements of cloud condensation nuclei activity. The observed relationships are complex, suggesting highly non-ideal behavior for aerosol water contents at relative humidities less than 98%. We present two models that may explain the observed water activity-composition relationship equally well. The first model assumes that the aerosol is a pseudo binary mixture of infinitely water soluble compounds and sparingly soluble compounds that gradually enter the solution as dilution increases. The second model is used to compute the Gibbs free energy of the aerosol-water mixture and shows that the aerosol behaves similarly to what can be expected for single compounds that contain a certain fraction of oxygenated and non-polar functional groups.
- ItemMagnetic quantum oscillations of diagonal conductivity in a two-dimensional conductor with a weak square superlattice modulation under conditions of the integer quantum Hall effect(Milton Park : Taylor & Francis, 2009) Gvozdikov, V.M.; Taut, M.We report on analytical and numerical studies of the magnetic quantum oscillations of the diagonal conductivity σxx in a two-dimensional conductor with a weak square superlattice modulation under conditions of the integer quantum Hall (IQHE) effect. The quantum Hall effect in such a system differs from the conventional IQHE, in which the finite width of the Landau bands is due to disorder only. The superlattice modulation potential yields a fractal splitting of the Landau levels into Hofstadter minibands. For rational flux through a unit cell, the minibands have a finite width and intrinsic dispersion relations. We consider a regime, now accessible experimentally, in which disorder does not wash out the fractal internal gap structure of the Landau bands completely. We found the following distinctions from the conventional IQHE produced by the superlattice: (i) the peaks in diagonal conductivity are split due to the Hofstadter miniband structure of Landau bands; (ii) the number of split peaks in the bunch, their positions and heights depend irregularly on the magnetic field and the Fermi energy; (iii) the gaps between the split Landau bands (and related quantum Hall plateaus) become narrower with the superlattice modulation than without it.
- ItemPlasma-oxidative degradation of polyphenolics – Influence of non-thermal gas discharges with respect to fresh produce processing(Prague : ČSAZV, 2009) Grzegorzewski, F.; Schlüter, O.; Ehlbeck, J.; Weltmann, K.-D.; Geyer, M.; Kroh, L.W.; Rohn, S.Non-thermal plasma treatment is a promising technology to enhance the shelf-life of fresh or minimaly processed food. An efficient inactivation of microorganisms comes along with a moderate heating of the treated surface. To elucidate the influence of highly reactive plasma-immanent species on the stability and chemical behaviour of phytochemicals, several polyphenolics were exposed to an atmospheric pressure plasma jet (APPJ). The selected flavonoids are ideal target compounds due to their antioxidant activity protecting cells against the damaging effects of reactive oxygen species such as singlet oxygen, superoxide, peroxyl radicals, hydroxyl radicals and peroxynitrite. Reactions were carried out at various radio-frequency voltages, using Ar as a feeding gas. Degradation was followed by reversed-phase high-performance liquid chromatography.
- ItemKelvin probe force microscopy of charged indentation-induced dislocation structures in KBr(Saarbrücken : Leibniz-Institut für neue Materialien, 2009) Egberts, Philip; Bennewitz, RolandThe incipient stages of plasticity in KBr single crystals have been examined in ultrahigh vacuum by means of Atomic Force Microscopy and Kelvin Probe Force Microscopy (KPFM). Conducting diamond-coated tips have been used to both indent the crystals and image the resulting plastic deformation. KPFM reveals that edge dislocations intersecting the surface carry a negative charge similar to kinks in surface steps, while screw dislocations show no contrast. Weak topographic features extending in <110> direction from the indentation are identified by atomic-resolution imaging to be pairs of edge dislocations of opposite sign, separated by a distance similar to the indenter radius. They indicate the glide of two parallel {110} planes perpendicular to the surface, a process that allows for a slice of KBr to be pushed away from the indentation site.
- ItemMomentum-resolved superconducting gap in the bulk of Ba1-xK xFe2As2 from combined ARPES and μSR measurements(Milton Park : Taylor & Francis, 2009) Evtushinsky, D.V.; Inosov, D.S.; Zabolotnyy, V.B.; Viazovska, M.S.; Khasanov, R.; Amato, A.; Klauss, H.-H.; Luetkens, H.; Niedermayer, Ch.; Sun, G.L.; Hinkov, V.; Lin, C.T.; Varykhalov, A.; Koitzsch, A.; Knupfer, M.; Büchner, B.; Kordyuk, A.A.; Borisenko, S.V.Here we present a calculation of the temperature-dependent London penetration depth, λ(T), in Ba1-xKxFe 2As2 (BKFA) on the basis of the electronic band structure (Zabolotnyy et al 2009 Nature 457 569, Zabolotnyy et al 2009 Physica C 469 448) and momentum-dependent superconducting gap (Evtushinsky et al 2009 Phys. Rev. B 79 054517) extracted from angleresolved photoemission spectroscopy (ARPES) data. The results are compared to the direct measurements of λ(T) by muon spin rotation (μSR) (Khasanov et al 2009 Phys. Rev. Lett. 102 187005). The value of λ(T = 0), calculated with no adjustable parameters, equals 270 nm, while the directly measured one is 320 nm; the temperature dependence λ(T) is also easily reproduced. Such agreement between the two completely different approaches allows us to conclude that ARPES studies of BKFA are bulk-representative. Our review of the available experimental studies of the superconducting gap in the new ironbased superconductors in general allows us to state that most of them bear two nearly isotropic gaps with coupling constants 2ΔkBTc = 2.5±1.5 and 7±2.
- ItemOut of Africa: High aerosol concentrations in the upper troposphere over Africa(München : European Geopyhsical Union, 2003) Heintzenberg, J.; Hermann, M.; Theiss, D.In the year 2000, six flights (three southbound and three northbound) of the CARIBIC project were conducted between Germany and two destinations in the southern hemisphere (Windhoek, Namibia and Cape Town, South Africa). In the present report, results on particle number concentrations are discussed in three size ranges (>4 nm, >12 nm, and >18 nm particle diameter) during the unique transequatorial Africa flights. The flights covered a total of about 80 h in May, July, and December. Thus, no claim can be made for long-term representativeness of the aerosol data. Nevertheless, they are the first upper systematic tropospheric transequatorial aerosol profiles over Africa. The average aerosol results show a broad maximum, roughly symmetrical to the equator, which compares well in latitudinal extent to a maximum of CO concentrations measured on the same flights. This export of continental surface aerosol to the upper troposphere will be dispersed on a global scale both with the easterly flow near the equator and with the westerlies in the adjacent subtropical regions. There was strong evidence of recent new particle formation before aerosol arrival at flight level, in particular during the time periods between 9:00 and 13:00 local time over Africa. Direct and indirect climate effects of the respective particulate matter remain to be investigated by future flights with the ongoing extension of the CARIBIC payload towards size-resolved measurements above 100 nm particle diameter. At the same time global chemical transport models and aerosol dynamics models need to be extended to be able to reproduce the CARIBIC findings over Africa.
- ItemAbsorption and photoemission spectroscopy of rare-earth oxypnictides(Milton Park : Taylor & Francis, 2009) Kroll, T.; Roth, F.; Koitzsch, A.; Kraus, R.; Batchelor, D.R.; Werner, J.; Behr, G.; Büchner, B.; Knupfer, M.The electronic structure of various rare-earth oxypnictides has been investigated by performing Fe L2, 3 x-ray absorption spectroscopy, and Fe 2p and valence band x-ray photoemission spectroscopy. As representative samples the non-superconducting parent compounds LnFeAsO (Ln=La, Ce, Sm and Gd) have been chosen and measured at 25 and 300 K, i.e. below and above the structural and magnetic phase transition at ~150 K. We find no significant change of the electronic structure of the FeAs layers when switching between the different rare-earth ions or when varying the temperature below and above the transition temperatures. Using a simple two-configuration model, we find qualitative agreement with the Fe 2p3/2 core-level spectrum, which allows for a qualitative explanation of the experimental spectral shapes.
- ItemTerrestrial vegetation redistribution and carbon balance under climate change(London : BioMed Central, 2006) Lucht, Wolfgang; Schaphoff, Sibyll; Erbrecht, Tim; Heyder, Ursula; Cramer, WolfgangBackground Dynamic Global Vegetation Models (DGVMs) compute the terrestrial carbon balance as well as the transient spatial distribution of vegetation. We study two scenarios of moderate and strong climate change (2.9 K and 5.3 K temperature increase over present) to investigate the spatial redistribution of major vegetation types and their carbon balance in the year 2100. Results The world's land vegetation will be more deciduous than at present, and contain about 125 billion tons of additional carbon. While a recession of the boreal forest is simulated in some areas, along with a general expansion to the north, we do not observe a reported collapse of the central Amazonian rain forest. Rather, a decrease of biomass and a change of vegetation type occurs in its northeastern part. The ability of the terrestrial biosphere to sequester carbon from the atmosphere declines strongly in the second half of the 21st century. Conclusion Climate change will cause widespread shifts in the distribution of major vegetation functional types on all continents by the year 2100.
- ItemSmall scale density variations of electrons and charged particles in the vicinity of polar mesosphere summer echoes(München : European Geopyhsical Union, 2003) Rapp, M.; Lübken, F.-J.; Blix, T.A.We present small scale variations of electron number densities and particle charge number densities measured in situ in the presence of polar mesosphere summer echoes. It turns out that the small scale fluctuations of electrons and negatively charged particles show a strong anticorrelation down to the smallest scales observed. Comparing these small scale structures with the simultaneously measured radar signal to noise profile, we find that the radar profile is well described by the power spectral density of both electrons and charged particles at the radar half wavelength (=the Bragg scale). Finally, we consider the shape of the power spectra of the observed plasma fluctuations and find that both charged particles and electrons show spectra that can be explained in terms of either neutral air turbulence acting on the distribution of a low diffusivity tracer or the fossil remnants of a formerly active turbulent region. All these results are consistent with the theoretical ideas by Rapp and Lübken (2003) suggesting that PMSE can be explained by a combination of active and fossil neutral air turbulence acting on the large and heavy charged aerosol particles which are subsequently mirrored in the electron number density distribution that becomes visible to a VHF radar when small scale fluctuations are present.