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Search Results: 1 - 10 of 315918 matches for " P. B. Otte "
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Long slit spectroscopy of diffuse ionized gas in NGC 55
B. Otte,R. -J. Dettmar
Physics , 1999,
Abstract: Spectroscopic measurements of emission line ratios and velocities are presented for ionized gas across the central plane of NGC 55, a late-type galaxy in the Sculptor group. The low metallicity in NGC 55 leads to relatively low line ratios of [S II]/H$\alpha$ and [N II]/H$\alpha$ for H II regions as well as the diffuse ionized gas. These are the first spectroscopical measurements of line ratios in ionized gas exterior to the stellar disc of NGC 55. Analysis of the line ratios and the relative velocities of different features suggests that photoionization is a plausible explanation for the ionization of this diffuse gas. The observed shell structures and the corresponding velocities support the idea of diffuse gas being pushed into the halo by supernova explosions and stellar winds.
Tests of Lorentz Invariance Violation with Gamma Rays to probe Quantum Gravity
N. Otte,M. Errando,S. Griffiths,P. Kaaret,H. Krawczynski,A. McCann,G. Sinnis,F. Stecker,I. Taboada,V. Vasileiou,B. Zitzer
Physics , 2013,
Abstract: We discuss the prospects of doing tests of Lorentz invariance with gamma-rays observed with present and future ground based gamma-ray observatories.
Unexpected trend of exchange interactions in Fe clusters on Rh(111) and Ru(0001)
F. Otte,P. Ferriani,S. Heinze
Physics , 2013,
Abstract: We use first-principles calculations based on density functional theory to investigate the magnetic exchange interaction of Fe clusters on Rh(111) and Ru(0001). We consider dimers, trimers, tetramers, and pentamers of different shape in fcc and hcp stacking as well as infinite atomic and biatomic chains. From the dimer calculations we extract the exchange interaction as a function of adatom distance by mapping total energies to a Heisenberg model. The nearest-neighbor (NN) exchange constant is about one order of magnitude smaller than reported for other substrates due to the strong hybridization between the Fe atoms and the partly filled $4d$-band of the surface. We also find a transition from a ferromagnetic NN exchange interaction for Fe dimers on Rh(111) to an antiferromagnetic one on Ru(0001). The distance-dependent exchange coupling displays a RKKY-like oscillatory behavior which is nearly inverted for Fe dimers on the Rh(111) surface compared to those on Ru(0001). Unexpectedly, for Fe clusters beyond dimers, a complex trend of the magnetic ground state is observed which alternates between ferro- and antiferromagnetic configurations depending on cluster size and shape. In view of the exchange constants obtained for dimers, it is surprising that on both surfaces small compact clusters are ferromagnetic while open structures such as linear trimers or tetramers become antiferromagnetic. We demonstrate that both vertical and lateral structural relaxations of the clusters are crucial in order to understand this unexpected trend of magnetic order and connected to the competition of direct ferromagnetic exchange among Fe atoms in the cluster and the hybridization with the substrate.
Incremental testing of the Community Multiscale Air Quality (CMAQ) modeling system version 4.7
K. M. Foley, S. J. Roselle, K. W. Appel, P. V. Bhave, J. E. Pleim, T. L. Otte, R. Mathur, G. Sarwar, J. O. Young, R. C. Gilliam, C. G. Nolte, J. T. Kelly, A. B. Gilliland,J. O. Bash
Geoscientific Model Development (GMD) & Discussions (GMDD) , 2010, DOI: 10.5194/gmd-3-205-2010
Abstract: This paper describes the scientific and structural updates to the latest release of the Community Multiscale Air Quality (CMAQ) modeling system version 4.7 (v4.7) and points the reader to additional resources for further details. The model updates were evaluated relative to observations and results from previous model versions in a series of simulations conducted to incrementally assess the effect of each change. The focus of this paper is on five major scientific upgrades: (a) updates to the heterogeneous N2O5 parameterization, (b) improvement in the treatment of secondary organic aerosol (SOA), (c) inclusion of dynamic mass transfer for coarse-mode aerosol, (d) revisions to the cloud model, and (e) new options for the calculation of photolysis rates. Incremental test simulations over the eastern United States during January and August 2006 are evaluated to assess the model response to each scientific improvement, providing explanations of differences in results between v4.7 and previously released CMAQ model versions. Particulate sulfate predictions are improved across all monitoring networks during both seasons due to cloud module updates. Numerous updates to the SOA module improve the simulation of seasonal variability and decrease the bias in organic carbon predictions at urban sites in the winter. Bias in the total mass of fine particulate matter (PM2.5) is dominated by overpredictions of unspeciated PM2.5 (PMother) in the winter and by underpredictions of carbon in the summer. The CMAQv4.7 model results show slightly worse performance for ozone predictions. However, changes to the meteorological inputs are found to have a much greater impact on ozone predictions compared to changes to the CMAQ modules described here. Model updates had little effect on existing biases in wet deposition predictions.
Contribution of Priority PAHs and POPs to Ah Receptor-Mediated Activities in Sediment Samples from the River Elbe Estuary, Germany
Jens C. Otte, Steffen Keiter, Christopher Fa?bender, Eric B. Higley, Paula Suares Rocha, Markus Brinkmann, Dierk-Steffen Wahrendorf, Werner Manz, Markus A. Wetzel, Thomas Braunbeck, John P. Giesy, Markus Hecker, Henner Hollert
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0075596
Abstract: The estuary of the River Elbe between Hamburg and the North Sea (Germany) is a sink for contaminated sediment and suspended particulate matter (SPM). One major concern is the effect of human activities on the hydrodynamics, particularly the intensive dredging activities in this area that may result in remobilization of sediment-bound pollutants. The aim of this study was to identify pollutants contributing to the toxicological risk associated with re-suspension of sediments in the Elbe Estuary by use of an effect-directed analysis that combines chemical and biological analyses in with specific fractionation techniques. Sediments were collected from sites along the Elbe Estuary and a site from a small harbor basin of the Elbe Estuary that is known to be polluted. The sixteen priority EPA-PAHs were quantified in organic extracts of sediments. In addition, dioxin equivalents of sediments were investigated by use of the 7-ethoxyresorufin O-deethylase assay with RTL-W1 cells and the Ah receptor-mediated luciferase transactivation assay with H4IIE-luc cells. Quantification of the 16 priority PAHs revealed that sediments were moderately contaminated at all of the sites in the Elbe River Estuary (<0.02–0.906 μg/g dw). Sediments contained relatively small concentrations of dioxin equivalents (Bio-TEQ) with concentrations ranging from 15.5 to 322 pg/g dw, which were significantly correlated with dioxin equivalents calculated based on toxicity reference values and concentrations of PAH. The concentration of Bio-TEQ at the reference site exceeded 200,000 pg/g dw. In a potency balance the 16 PAHs explained between 47 and 118% of the Bio-TEQ in the luciferase assay, which can be explained by the constant input of PAHs bound to SPM from the upper course of the Elbe River into its estuary. Successful identification of a significant portion of dioxin-like activity to priority PAHs in complex environmental samples such as sediments has rarely been reported.
Emission Line Ratios and Variations in Temperature and Ionization State in the Diffuse Ionized Gas of Five Edge-on Galaxies
B. Otte,J. S. Gallagher III,R. J. Reynolds
Physics , 2002, DOI: 10.1086/340381
Abstract: We present spectroscopic observations of ionized gas in the disk-halo regions of five edge-on galaxies, covering a wavelength range from [OII] 3727A to [SII] 6716.4A. The inclusion of the [OII] emission provides additional constraints on the properties of the diffuse ionized gas (DIG), in particular, the origin of the observed spatial variations in the line intensity ratios. We have derived electron temperatures, ionization fractions and abundances along the slit. Our data include both slit positions parallel and perpendicular to the galactic disks. This allowed us to examine variations in the line intensity ratios with height above the midplane as well as distance from the galactic centers. The observed increase in the [OII]/Halpha line ratio towards the halo seems to require an increase in electron temperature caused by a non-ionizing heating mechanism. We conclude that gradients in the electron temperature can play a significant role in the observed variations in the optical emission line ratios from extraplanar DIG.
Atomically crafted spin lattices as model systems for quantum magnetism
A Spinelli,M P Rebergen,A F Otte
Physics , 2015,
Abstract: Low-dimensional quantum magnetism presents a seemingly unlimited source of rich, intriguing physics. Yet, as realistic experimental representations are hard to come by, the field remains predominantly theoretical. In recent years, artificial spin structures built through manipulation of magnetic atoms in a scanning tunnelling microscope have developed into a promising testing ground for experimental verification of theoretical models. Here we present an overview of available tools and discuss recent achievements as well as future avenues. Moreover, we show new observations on magnetic switching in a bistable bit that can be used to extrapolate information on the magnetisation of the microscope tip.
地理科学进展 , 1989, DOI: 10.11820/dlkxjz.1989.03.007
Abstract: 引言在地下水通道中的隧道和输水建筑物对地下水流来说是一堵很长的挡水墙。它把地下水流拦截或分开,设施潜入有水流的土体中的部分越多,拦水作用就越大。设施与地下水流动方向越垂直,所造成的拦水作用就越大,而且在多数情况下对工程技术都有重大影响。由于堵塞,地下水会在入流侧出现侧向流,或围绕设施形成侧环流。这样一来,在设施两侧水流的方向就发生变化。在水流下方侧地下水位会明显下降。
"Dizem-me que sou louco": as epistemologias poéticas de Baudelaire e Benjamin
Otte, Georg;
Alea : Estudos Neolatinos , 2007, DOI: 10.1590/S1517-106X2007000200008
Abstract: adorno?s refusal to publish the first version of benjamin?s text on baudelaire puts in evidence a deep divergence in the thinking and writing of both authors: whereas adorno demands the linearly mediated development of the theoretical themes, benjamin resists mediation replacing it by a poetic principle dear to baudelaire: the correspondence.
Der Charakter der Mathematik zwischen Philosophie und Wissenschaft
Michael Otte
Philosophica , 1989,
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