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Search Results: 1 - 10 of 490007 matches for " S. C. St hler "
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Triplicated P-wave measurements for waveform tomography of the mantle transition zone
S. C. St hler, K. Sigloch,T. Nissen-Meyer
Solid Earth (SE) & Discussions (SED) , 2012, DOI: 10.5194/se-3-339-2012
Abstract: Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attempted, due to a mismatch between the complex and band-limited data and the (ray-theoretical) modelling methods. Here we present a data processing and modelling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30°) across their entire broadband frequency range, for both deep and shallow sources. We show that is it possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modelled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric Earth.
Triplicated P-wave measurements for waveform tomography of the mantle transition zone
S. C. Sthler,K. Sigloch,T. Nissen-Meyer
Solid Earth Discussions , 2012, DOI: 10.5194/sed-4-783-2012
Abstract: Triplicated body waves sample the mantle transition zone more extensively than any other wave type, and interact strongly with the discontinuities at 410 km and 660 km. Since the seismograms bear a strong imprint of these geodynamically interesting features, it is highly desirable to invert them for structure of the transition zone. This has rarely been attemped, due to the mismatch between the complex and bandlimited data and the (ray-theoretical) modeling methods. Here we present a data processing and modeling strategy to harness such broadband seismograms for finite-frequency tomography. We include triplicated P-waves (epicentral distance range between 14 and 30°) across their entire broadband frequency range, for both deep and shallow sources. We show that it is possible to predict the complex sequence of arrivals in these seismograms, but only after a careful effort to estimate source time functions and other source parameters from data, variables that strongly influence the waveforms. Modeled and observed waveforms then yield decent cross-correlation fits, from which we measure finite-frequency traveltime anomalies. We discuss two such data sets, for North America and Europe, and conclude that their signal quality and azimuthal coverage should be adequate for tomographic inversion. In order to compute sensitivity kernels at the pertinent high body-wave frequencies, we use fully numerical forward modelling of the seismic wavefield through a spherically symmetric earth.
Ultrafast exciton formation at the ZnO(10${\overline{\textbf{1}}}$0) surface
J. -C. Deinert,D. Wegkamp,M. Meyer,C. Richter,M. Wolf,J. Sthler
Physics , 2014, DOI: 10.1103/PhysRevLett.113.057602
Abstract: We study the ultrafast quasiparticle dynamics in and below the ZnO conduction band using femtosecond time-resolved two-photon photoelectron spectroscopy. Above band gap excitation causes hot electron relaxation by electron-phonon scattering down to the Fermi level $E_\text{F}$ followed by ultrafast (200 fs) formation of a surface exciton (SX). Transient screening of the Coulomb interaction reduces the SX formation probability at high excitation densities near the Mott limit. Located just below the surface, the SX are stable with regard to hydrogen-induced work function modifications and thus the ideal prerequisite for resonant energy transfer applications.
Local Aspects of Hydrogen-Induced Metallization of the ZnO(10$\mathbf{\overline{1}}$0) Surface
J. -C. Deinert,O. T. Hofmann,M. Meyer,P. Rinke,J. Sthler
Physics , 2015, DOI: 10.1103/PhysRevB.91.235313
Abstract: This study combines surface-sensitive photoemission experiments with density functional theory (DFT) to give a microscopic description of H adsorption-induced modifications of the ZnO(10${\overline{1}}$0) surface electronic structure. We find a complex adsorption behavior caused by a strong coverage dependence of the H adsorption energies: Initially, O--H bond formation is energetically favorable and H acting as an electron donor leads to the formation of a charge accumulation layer and to surface metallization. The increase of the number of O--H bonds leads to a reversal in adsorption energies such that Zn--H bonds become favored at sites close to existing O--H bonds, which results in a gradual extenuation of the metallization. The corresponding surface potential changes are localized within a few nanometers both laterally and normal to the surface. This localized character is experimentally corroborated by using sub-surface bound excitons at the ZnO(10${\overline{1}}$0) surface as a local probe. The pronounced and comparably localized effect of small amounts of hydrogen at this surface strongly suggests metallic character of ZnO surfaces under technologically relevant conditions and may, thus, be of high importance for energy level alignment at ZnO-based junctions in general.
Experimental investigation of homogeneous freezing of sulphuric acid particles in the aerosol chamber AIDA
O. M?hler,O. Stetzer,S. Schaefers,C. Linke
Atmospheric Chemistry and Physics Discussions , 2002,
Abstract: The homogeneous freezing of supercooled H2SO4/H2O solution droplets was investigated in the aerosol chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) of Forschungszentrum Karlsruhe. 24 freezing experiments were performed at temperatures between 194 and 235 K with aerosol particles in the diameter range 0.05 to 1 μm. Individual experiments started at homogeneous temperatures and ice saturation ratios between 0.85 and 0.95. Cloud cooling rates up to -2.8 K/min were simulated dynamically in the chamber by expansion cooling using a mechanical pump. Depending on the cooling rate and starting temperature, freezing threshold relative humidities were exceeded after expansion time periods between about 1 and 10 min. The onset of ice formation was measured with three independent methods showing good agreement among each other. Ice saturation ratios measured at the onset of ice formation increased from about 1.4 at 231 K to about 1.75 at 189 K. The experimental data set including thermodynamic parameters as well as physical and chemical aerosol analysis provides a good basis for microphysical model applications.
Spin lifetimes and strain-controlled spin precession of drifting electrons in zinc blende type semiconductors
M. Beck,C. Metzner,S. Malzer,G. H. D?hler
Physics , 2005, DOI: 10.1209/epl/i2006-10151-4
Abstract: We study the transport of spin polarized electrons in n-GaAs using spatially resolved continuous wave Faraday rotation. From the measured steady state distribution, we determine spin relaxation times under drift conditions and, in the presence of strain, the induced spin splitting from the observed spin precession. Controlled variation of strain along [110] allows us to deduce the deformation potential causing this effect, while strain along [100] has no effect. The electric field dependence of the spin lifetime is explained quantitatively in terms of an increase of the electron temperature.
Standard values and relationship-specific validity of the Bielefeld Relationship Expectations Questionnaire (BFPE)
Katja Petrowski, Hendrik Berth, S?ren Paul, Gesine Grande, Yve St?bel-Richter, Elmar Br?hler
BMC Medical Research Methodology , 2010, DOI: 10.1186/1471-2288-10-92
Abstract: The present sample (n = 1509) is representative for the German population aged 18 to 50. The mean age was 34.6 years. Most of the participants lived in a relationship (77.3 %). Discriminant validity was analyzed using a marital quality questionnaire (PFB), a social support questionnaire (F-Soz-U K-14), and a life satisfaction questionnaire (FLZ).All the BFPE scales have a satisfying internal consistency between r = .79 and .86. Those individuals who showed a secure pattern, i.e. increased "Readiness for Self-Disclosure" and "Conscious Need for Care" as well as reduced "Fear of Rejection" experienced their partner as socially supportive, reported higher marital quality in all of its facets, and were more satisfied within the life-domains "family/children" and "relationship/sexuality". Standard values for each scale are presented.The BFPE has repeatedly been verified as a short, reliable, and valid instrument applicable to research practice with healthy individuals as well as within clinical contexts.The attachment theory focuses on early interpersonal experience, affective patterns, and psychological development. In the attachment theory, John Bowlby [1] proposes that the early attachment experience with the primary caregiver is stored in an internal working model relied upon in attachment-relevant situations. This early attachment experience explains the development of normative relationship-specific behavior in later life. Hence, the attachment theory is widely used in research to explain normative as well as non-normative relationship-specific behavior.Since the 1980's, more and more questionnaires have been developed to assess attachment in adults. The Bielefeld Relationship Expectations Questionnaire ('Bielefelder Fragebogen zur Partnerschaftserwartung', BFPE) [2,3], an additional German instrument for capturing attachment in romantic relationships, was developed for two reasons. First, with the BFPE, attachment can be operationalized dimensionally as well as ca
Effects of dietary Na+ deprivation on epithelial Na+ channel (ENaC), BDNF, and TrkB mRNA expression in the rat tongue
Tao Huang, Frauke Sthler
BMC Neuroscience , 2009, DOI: 10.1186/1471-2202-10-19
Abstract: In situ hybridization analysis showed that all three ENaC subunit mRNAs were found in the rat fungiform taste buds and lingual epithelia, but in the vallate and foliate taste buds, only α ENaC mRNA was easily detected, while β and γ ENaC mRNAs were much less than those in the fungiform taste buds. Between control and low Na+ fed animals, the numbers of taste bud cells expressing α, β and γ ENaC subunits were not significantly different in the fungiform, vallate and foliate taste buds, respectively. Similarly, qRT-PCR also indicated that Na+ deprivation had no effect on any ENaC subunit expression in the three types of taste buds. However, Na+ deprivation reduced BDNF mRNA expression by 50% in the fungiform taste buds, but not in the vallate and foliate taste buds. The expression of TrkB was not different between control and Na+ deprived rats, irrespective of the taste papillae type.The findings demonstrate that dietary Na+ deprivation does not change ENaC mRNA expression in rat taste buds, but reduces BDNF mRNA expression in the fungiform taste buds. Given the roles of BDNF in survival of cells and target innervation, our results suggest that dietary Na+ deprivation might lead to a loss of gustatory innervation in the mouse fungiform taste buds.In rodents, salt taste is mainly processed by the taste buds in the fungiform papillae spread across the anterior tongue, where the taste bud cells are innervated by chorda tympani (CT) nerves [1-3]. Previous studies have shown that sodium deprivation leads to a reduction in taste neuron responses of the CT nerves to lingual NaCl stimulation, while the responses to other taste stimuli remain unchanged [4,5]. In the nucleus of the solitary tract (NST) and the parabrachial nucleus (PBN), the first and the second relays of central taste system, dietary Na+ deprivation also reduces nerve responses to lingual NaCl stimulation [6-8]. Taken together, this indicates that the taste responses to NaCl from CT nerves, and NST and PBN tas
Arrayed Continuous-wave THz Photomixers
S. T. Bauerschmidt,S. Malzer,G. H. D?hler,H. Lu,A. C. Gossard,S. Preu
Physics , 2013,
Abstract: We present both chip-scale and free space coherent arrays of continuous-wave THz photomixers. By altering the relative phases of the exciting laser signals, the relative THz phase between the array elements can be tuned, allowing for beam steering. The constructive interference of the emission of N elements leads to an increase of the focal intensity by a factor of NxN while reducing the beam width by ~1/N, below the diffraction limit of a single source. Such array architectures strongly improve the THz power distribution for stand-off spectroscopy and imaging systems while providing a huge bandwidth at the same time. We demonstrate this by beam profiles generated by a free space 2x2 and a 4x1 array for a transmission distance of 4.2 meters. Spectra between 70 GHz and 1.1 THz have been recorded with these arrays.
Are Small Grazers and/or Viruses a Structuring Factor of the Free-Living Bacterial Community in Lake Geneva?  [PDF]
Stéphan Jacquet, Isabelle Domaizon, Cécile Chardon, Sébastien Personnic
Advances in Microbiology (AiM) , 2013, DOI: 10.4236/aim.2013.33035
Abstract:

Two experiments were conducted to test whether viruses, small auto- and heterotrophic nanoflagellates were key factors regulating at relatively short-term (4 days) and nearby periods (April vs. May) the bacterial community in surface waters of Lake Geneva. 2.5 L containing polycarbonate bottles were incubated in situ with either <2 μm or <10 μm filtered water with additions of either virus-free water or a viral concentrate. Abundances of viruses, prokaryotes and small autotrophs were obtained each day using flow cytometry, while bacterial richness was assessed using 16S rDNA PCR-DGGE and auto- and heterotrophic flagellates counted with epifluorescence microscopy at t0 and t96. Transmission electron microscopy was also used to assess virus-induced bacterial mortality at the start and the end of the experiments. Cloning-sequencing was applied on PCR products obtained after excision of selected DGGE bands to highlight more specifically the identity of bacteria of interest in the context of the experiment. The autotrophs and grazer presence and/or the virus enrichment resulted in different effects on the structure of the bacterial community and the impact was also different with the period. In May, bacterial structure changes seemed to be related to the impact or influence of the eukaryotes (including nanoflagellate grazers), while viruses might have a higher impact on the bacterial community structure the month before. This study provides new persuasive evidence that the presence of viruses and small eukaryotes are likely to drive bacterial community composition and shifts on the short-term in lacustrine ecosystems. More interestingly, such effects seem to be different between viruses and grazers, the ones sustaining, the others reducing bacterial community composition.

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