Observations of meteoric material and implications for aerosol nucleation in the winter Arctic lower stratosphere derived from in situ particle measurements

Number concentrations of total and non-volatile aerosol particles with size diameters >0.01 μm as well as particle size distributions (0.4–23 μm diameter) were measured in situ in the Arctic lower stratosphere (10–20.5 km altitude). The measurements were obtained during the campaigns European Polar Stratospheric Cloud and Lee Wave Experiment (EUPLEX) and Envisat-Arctic-Validation (EAV). The campaigns were based in Kiruna, Sweden, and took place from January to March 2003. Measurements were conducted onboard the Russian high-altitude research aircraft Geophysica using the low-pressure Condensation Nucleus Counter COPAS (COndensation PArticle Counter System) and a modified FSSP 300 (Forward Scattering Spectrometer Probe). Around 18–20 km altitude typical total particle number concentrations nt range at 10–20 cm−3 (ambient conditions). Correlations with the trace gases nitrous oxide (N2O) and trichlorofluoromethane (CFC-11) are discussed. Inside the polar vortex the total number of particles >0.01 μm increases with potential temperature while N2O is decreasing which indicates a source of particles in the above polar stratosphere or mesosphere. A separate channel of the COPAS instrument measures the fraction of aerosol particles non-volatile at 250°C. Inside the polar vortex a much higher fraction of particles contained non-volatile residues than outside the vortex (~67% inside vortex, ~24% outside vortex). This is most likely due to a strongly increased fraction of meteoric material in the particles which is transported downward from the mesosphere inside the polar vortex. The high fraction of non-volatile residual particles gives therefore experimental evidence for downward transport of mesospheric air inside the polar vortex. It is also shown that the fraction of non-volatile residual particles serves directly as a suitable experimental vortex tracer. Nanometer-sized meteoric smoke particles may also serve as nuclei for the condensation of gaseous sulfuric acid and water in the polar vortex and these additional particles may be responsible for the increase in the observed particle concentration at low N2O. The number concentrations of particles >0.4 μm measured with the FSSP decrease markedly inside the polar vortex with increasing potential temperature, also a consequence of subsidence of air from higher altitudes inside the vortex. Another focus of the analysis was put on the particle measurements in the lowermost stratosphere. For the total particle density relatively high number concentrations of several hundred particles per cm3 at altitudes below ~14 km were observed in several flights. To investigate the origin of these high number concentrations we conducted air mass trajectory calculations and compared the particle measurements with other trace gas observations. The high number concentrations of total particles in the lowermost stratosphere are probably caused by transport of originally tropospheric air from lower latitudes and are potentially influenced by recent particle nucleation

Classification of phase transitions in small systems

We present a classification scheme for phase transitions in finite systems like atomic and molecular clusters based on the Lee-Yang zeros in the complex temperature plane. In the limit of infinite particle numbers the scheme reduces to the Ehrenfest definition of phase transitions and gives the right critical indices. We apply this classification scheme to Bose-Einstein condensates in a harmonic trap as an example of a higher order phase transitions in a finite system and to small Ar clusters.Comment: 12 pages, 4 figures, accepted for publication in Phys. Rev. Let

Magnetic impurity resonance states and symmetry of the superconducting order parameter in iron-based superconductors

We investigate the effect of magnetic impurities on the local quasiparticle density of states (LDOS) in iron-based superconductors. Employing the two-orbital model where 3$d$ electron and hole conduction bands are hybridizing with the localized $f$-orbital of the impurity spin, we investigate how various symmetries of the superconducting gap and its nodal structure influence the quasiparticle excitations and impurity bound states. We show that the bound states behave qualitatively different for each symmetry. Most importantly we find that the impurity-induced bound states can be used to identify the nodal structure of the extended s-wave symmetry ($S^{\pm}$) that is actively discussed in ferropnictides.Comment: 7 pages, 5 figures, theory part is extended, figures are replace

Thermodynamic fermion-boson symmetry in harmonic oscillator potentials

A remarkable thermodynamic fermion-boson symmetry is found for the canonical ensemble of ideal quantum gases in harmonic oscillator potentials of odd dimensions. The bosonic partition function is related to the fermionic one extended to negative temperatures, and vice versa.Comment: 7 pages, no figures, submitted to PHYSICA A. More information available at http://www.physik.uni-osnabrueck.de/makrosysteme

Zur Polymorphie von TbCl3

3 different modifications of TbCl3 were synthesized. TbCl3 (UCl3type). probably in a metastable state, crystallizes in space group P63/m with a = 737.63(2) pm, c = 405.71(2) pm and Z = 2. TbCl3(PuBr3-type) crystallizes in space group Cmcm with a = 384.71(6) pm, b = 1177.37(7) pm, c = 851.77(4) pm and Z = 4. h-TbCl3, the high temperature phase being stable above 790 K, crystallizes in space group P42/mnm with a = 642.51(4) pm, c = 1177.14(18) pm and Z = 4. © 1988, Walter de Gruyter. All rights reserved

Nutzerverhalten in elektronischen Medien : theoretische Grundlagen und eine Analyse am Beispiel des Lufthansa InfoFlyway

Der Einsatz elektronischer Medien im Marketing hat in den letzten Jahren stark an Bedeutung gewonnen. Neuere technische Anwendungen wie das Internet, kommerzielle Online-Dienste oder das interaktive Fernsehen bieten Unternehmen die Möglichkeit, sich gegenüber ihren Wettbewerbern zu differenzieren. So können bspw. Kunden direkt und individuell angesprochen, neue Märkte erschlossen sowie effizientere Organisationsformen realisiert werden. Unternehmen fast aller Branchen setzen neuere elektronische Medien zunehmend als Kommunikationsmittel und/oder Vertriebskanal ein. Gemeinsames Merkmal der Nutzung dieser Medien ist die Interaktivität, die Dialogfähigkeit der Anwendungen, welche die Rolle des Konsumenten im Kommunikations- und Informationsprozeß in entscheidender Weise verändert. Im Gegensatz zu der eher passiven Rolle des Rezipienten bei traditionellen Massenmedien verfügen Konsumenten bei interaktiven Medien über die Möglichkeit, den Kommunikationsprozeß zu steuern und aktiv mitzugestalten. Relevante Informationen können gezielt ausgewählt, individuell kombiniert und nicht erwünschte Informationsangebote umgangen werden. Grundlage einer erfolgreichen Integration interaktiver Medien in den Marketing-Mix von Unternehmen ist daher ein umfassendes Verständnis der Entscheidungsprozesse und -mechanismen des Konsumenten bei der Auswahl des Mediums und der Selektion von Informationsinhalten. Die Konsumentenverhaltensforschung leistet hierfür einen wichtigen Beitrag. Für die Erklärung des Konsumentenverhaltens spielt die Analyse von Motiven, die der Mediennutzung zugrunde liegen bzw. ihre Befriedigung durch Medien- und Informationsangebote eine wichtige Rolle. In Anlehnung an die von Csikszentmihalyi entwickelte Flow-Theorie können in diesem Zusammenhang intrinsische Motive, d.h. der für Flow charakteristische Aspekt der Freude bzw. des Vergnügens an der Ausübung einer Aktivität als wesentliche Determinante der Nutzung elektronischer Medien betrachtet werden

Deceptive signals of phase transitions in small magnetic clusters

We present an analysis of the thermodynamic properties of small transition metal clusters and show how the commonly used indicators of phase transitions like peaks in the specific heat or magnetic susceptibility can lead to deceptive interpretations of the underlying physics. The analysis of the distribution of zeros of the canonical partition function in the whole complex temperature plane reveals the nature of the transition. We show that signals in the magnetic susceptibility at positive temperatures have their origin at zeros lying at negative temperatures.Comment: 4 pages, 5 figures, revtex4, for further information see http://www.smallsystems.d

Charge-Doping driven Evolution of Magnetism and non-Fermi-Liquid Behavior in the Filled Skutterudite CePt4Ge12-xSbx

The filled-skutterudite compound CePt4Ge12 is situated close to the border between intermediate-valence of Ce and heavy-fermion behavior. Substitution of Ge by Sb drives the system into a strongly correlated and ultimately upon further increasing the Sb concentration into an antiferromagnetically ordered state. Our experiments evidence a delicate interplay of emerging Kondo physics and the formation of a local 4f moment. An extended non-Fermi-liquid region, which can be understood in the framework of a Kondo-disorder model, is observed. Band-structure calculations support the conclusion that the physical properties are governed by the interplay of electron supply via Sb substitution and the concomitant volume effects.Comment: 5 pages, 3 Figur