oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 4 )

2019 ( 220 )

2018 ( 279 )

2017 ( 280 )

Custom range...

Search Results: 1 - 10 of 219732 matches for " C. Stock "
All listed articles are free for downloading (OA Articles)
Page 1 /219732
Display every page Item
Reply to comment by Mayers et al. on "High energy neutron scattering from hydrogen using a direct geometry spectrometer"
C. Stock,R. A. Cowley
Physics , 2011, DOI: 10.1103/PhysRevB.84.056302
Abstract: In this reply, we point out several criticisms of the analysis in arXiv:0909.2633 and show that the comment does not change the underlying conclusion presented by ourselves that there is no measurable deficit in the scattering cross section of hydrogen. We therefore consider that our original conclusions are correct namely that the previous anomalies in the cross section are due to experimental effects related to the use of indirect geometry spectrometers.
Orbital ordering promotes weakly-interacting S=1/2 dimers in the triangular lattice compound Sr3Cr2O8
L. C. Chapon,C. Stock,P. G. Radaelli,C. Martin
Physics , 2008,
Abstract: The weakly interacting S=1/2 dimers system Sr3Cr2O8 has been investigated by powder neutron diffraction and inelastic neutron scattering. Our data reveal a structural phase transition below room temperature corresponding to an antiferro-orbital ordering with nearly 90 degrees arrangement of the occupied 3z^2-r^2 d-orbital. This configuration leads to a drastic reduction of the inter-dimer exchange energies with respect to the high temperature orbital-disorder state, as shown by a spin-dimer analysis of the super-superexchange interactions performed using the Extended Huckel Tight Binding method. Inelastic neutron scattering reveals the presence of a quasi non-dispersive magnetic excitation at 5.4 meV, in agreement with the picture of weakly-interacting dimers.
Ground-based lidar measurements from Ny- lesund during ASTAR 2007: a statistical overview
A. Hoffmann,C. Ritter,M. Stock,M. Shiobara
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) in March and April 2007, measurements obtained at the AWIPEV Research station in Ny- lesund, Spitsbergen (operated by the Alfred-Wegener-Institute for Polar and Marine Research and the Institut polaire fran ais Paul-Emile Victor), supported the airborne campaign. This included Lidar data from the Koldewey Aerosol Raman Lidar (KARL) and the Micro Pulse Lidar (MPL), located in the atmospheric observatory as well as photometer data and the daily launched radiosonde. The MPL features nearly continuous measurements; the KARL was switched on whenever weather conditions allowed observations (145 h in 61 days). From 1 March to 30 April, 71 meteorological balloon soundings were performed and compared with the corresponding MPL measurements; photometer measurements are available from 18 March. For the KARL data, a statistical overview based on the optical properties backscatter ratio and volume depolarization can be given. The altitudes of the occurrence of the named features (subvisible and visible ice and water as well as mixed-phase clouds, aerosol layers) as well as their dependence on different air mass origins are analyzed. Although the spring 2007 was characterized by rather clean conditions, diverse case studies of cloud and aerosol occurrence during March and April 2007 are presented in more detail, including temporal development and main optical properties as backscatter, depolarization and extinction coefficients. Links between air mass origins and optical properties can be presumed but need further evidence.
Airborne measurements of the nitric acid partitioning in persistent contrails
D. Sch?uble,C. Voigt,B. K?rcher,P. Stock
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: This study reports the first systematic measurements of nitric acid (HNO3) uptake in contrail ice particles at typical aircraft cruise altitudes. During the CIRRUS-III campaign cirrus clouds and almost 40 persistent contrails were probed with in situ instruments over Germany and Northern Europe in November 2006. Besides reactive nitrogen, water vapor, cloud ice water content, ice particle size distributions, and condensation nuclei were measured during 6 flights. Contrails with ages up to 8 hours were detected at altitudes 10–11.5 km and temperatures 211–220 K. These contrails had a larger ice phase fraction of total nitric acid (HNO3ice/HNO3tot = 6%) than the ambient cirrus layers (3%). On average, the contrails contained twice as much HNO3ice as the cirrus clouds, 14 pmol/mol and 6 pmol/mol, respectively. Young contrails with ages below 1 h had a mean HNO3ice of 21 pmol/mol. The contrails had higher nitric acid to water molar ratios in ice and slightly higher ice water contents than the cirrus clouds under similar meteorological conditions. The differences in ice phase fractions and molar ratios between developing contrails and cirrus are likely caused by high plume concentrations of HNO3 prior to contrail formation. The location of the measurements in the top region of frontal cirrus layers might account for slight differences in the ice water content between contrails and adjacent cirrus clouds. The observed dependence of molar ratios as a function of the mean ice particle diameter suggests that ice-bound HNO3 concentrations are controlled by uptake of exhaust HNO3 in the freezing plume aerosols in young contrails and subsequent trapping of ambient HNO3 in growing ice particles in older (age > 1 h) contrails.
Ground-based lidar measurements from Ny- lesund during ASTAR 2007
A. Hoffmann,C. Ritter,M. Stock,M. Shiobara
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: During the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) in March and April 2007, measurements obtained at the AWIPEV Arctic Research Base in Ny- lesund, Spitsbergen at 78.9° N, 11.9° E (operated by the Alfred Wegener Institute for Polar and Marine Research – AWI and the Institut polaire fran ais Paul-Emile Victor – IPEV), supported the airborne campaign. This included lidar data from the Koldewey Aerosol Raman Lidar (KARL) and the Micro Pulse Lidar (MPL), located in the atmospheric observatory as well as photometer data and the daily launched radiosonde. The MPL features nearly continuous measurements; the KARL was switched on whenever weather conditions allowed observations (145 h in 61 days). From 1 March to 30 April, 71 meteorological balloon soundings were performed and compared with the concurrent MPL measurements; photometer measurements are available from 18 March. For the KARL data, a statistical overview of particle detection based on their optical properties backscatter ratio and volume depolarization can be given. The altitudes of the occurrence of the named features (subvisible and visible ice and water as well as mixed-phase clouds, aerosol layers) as well as their dependence on different air mass origins are analyzed. Although the spring 2007 was characterized by rather clean conditions, diverse case studies of cloud and aerosol occurrence during March and April 2007 are presented in more detail, including temporal development and main optical properties as depolarization, backscatter and extinction coefficients. Links between air mass origins and optical properties can be presumed but need further evidence.
Rapid identification of Burkholderia mallei and Burkholderia pseudomallei by intact cell Matrix-assisted Laser Desorption/Ionisation mass spectrometric typing
Karger Axel,Stock Rüdiger,Ziller Mario,Elschner Mandy C
BMC Microbiology , 2012, DOI: 10.1186/1471-2180-12-229
Abstract: Background Burkholderia (B.) pseudomallei and B. mallei are genetically closely related species. B. pseudomallei causes melioidosis in humans and animals, whereas B. mallei is the causative agent of glanders in equines and rarely also in humans. Both agents have been classified by the CDC as priority category B biological agents. Rapid identification is crucial, because both agents are intrinsically resistant to many antibiotics. Matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-TOF MS) has the potential of rapid and reliable identification of pathogens, but is limited by the availability of a database containing validated reference spectra. The aim of this study was to evaluate the use of MALDI-TOF MS for the rapid and reliable identification and differentiation of B. pseudomallei and B. mallei and to build up a reliable reference database for both organisms. Results A collection of ten B. pseudomallei and seventeen B. mallei strains was used to generate a library of reference spectra. Samples of both species could be identified by MALDI-TOF MS, if a dedicated subset of the reference spectra library was used. In comparison with samples representing B. mallei, higher genetic diversity among B. pseudomallei was reflected in the higher average Eucledian distances between the mass spectra and a broader range of identification score values obtained with commercial software for the identification of microorganisms. The type strain of B. pseudomallei (ATCC 23343) was isolated decades ago and is outstanding in the spectrum-based dendrograms probably due to massive methylations as indicated by two intensive series of mass increments of 14 Da specifically and reproducibly found in the spectra of this strain. Conclusions Handling of pathogens under BSL 3 conditions is dangerous and cumbersome but can be minimized by inactivation of bacteria with ethanol, subsequent protein extraction under BSL 1 conditions and MALDI-TOF MS analysis being faster than nucleic amplification methods. Our spectra demonstrated a higher homogeneity in B. mallei than in B. pseudomallei isolates. As expected for closely related species, the identification process with MALDI Biotyper software (Bruker Daltonik GmbH, Bremen, Germany) requires the careful selection of spectra from reference strains. When a dedicated reference set is used and spectra of high quality are acquired, it is possible to distinguish both species unambiguously. The need for a careful curation of reference spectra databases is stressed.
Phase instability induced by polar nanoregions in a relaxor ferroelectric system
Guangyong Xu,Jinsheng Wen,C. Stock,P. M. Gehring
Physics , 2008, DOI: 10.1038/nmat2196
Abstract: Local inhomogeneities known as polar nanoregions (PNR) play a key role in governing the dielectric properties of relaxor ferroelectrics - a special class of material that exhibits an enormous electromechanical response and is easily polarized with an external field. Using neutron inelastic scattering methods, we show that the PNR can also significantly affect the structural properties of the relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-4.5%PbTiO3 (PZN-4.5%PT). A strong interaction is found between the PNR and the propagation of sound waves, i.e. acoustic phonons, the visibility of which can be enhanced with an external electric field. A comparison between acoustic phonons propagating along different directions reveals a large asymmetry in the lattice dynamics that is induced by the PNR. We suggest that a phase instability induced by this PNR-phonon interaction may contribute to the ultrahigh piezoelectric response of this and related relaxor ferroelectric materials. Our results also naturally explain the emergence of the various observed monoclinic phases in these systems.
Response of polar nanoregions in 68%Pb(Mg1/3Nb2/3)O3-32%PbTiO3 to a [001] electric field
Jinsheng Wen,Guangyong Xu,C. Stock,P. M. Gehring
Physics , 2008, DOI: 10.1063/1.2959077
Abstract: We report neutron diffuse scattering measurements on a single crystal of 68%Pb(Mg1/3Nb2/3)O3-32%PbTiO3. Strong diffuse scattering is observed at low temperatures. An external field applied along the [001] direction affects the diffuse scattering in the (HK0) plane significantly, suggesting a redistribution occurs between polar nanoregions of different polarizations perpendicular to the field. By contrast, the [001] field has no effect on the diffuse scattering in the (HOL) and (0KL) zones.
The Physics of ALICE HLT Trigger Modes
R. Bramm,T. Kollegger,C. Loizides,R. Stock
Physics , 2002,
Abstract: We discuss different physics cases, mainly of the ALICE TPC, such as pile-up, jets in pp and PbPb, Bottonium and Charmonium spectroscopy, and there corresponding demands on the ALICE High Level Trigger (HLT) System. We show that compression and filter strategies can reduce the data volume by factors of 5 to 10. By reconstructing (sub)events with the HLT, background events can be rejected with a factor of up to 100 while keeping the signal (low cross-section probes). Altogether the HLT improves the discussed physics capabilities of ALICE by a factor of 5-100 in terms of statistics.
Magnetic neutron scattering in hole doped cuprate superconductors
R. J. Birgeneau,C. Stock,J. M. Tranquada,K. Yamada
Physics , 2006, DOI: 10.1143/JPSJ.75.111003
Abstract: A review is presented of the static and dynamic magnetic properties of hole-doped cuprate superconductors measured with neutron scattering. A wide variety of experiments are described with emphasis on the monolayer La_{2-x}(Sr,Ba)_{x}CuO_{4} and bilayer YBa_{2}Cu_{3}O_{6+x} cuprates. At zero hole doping, both classes of materials are antiferromagnetic insulators with large superexchange constants of J > 100 meV. For increasing hole doping, the cuprates become superconducting at a critical hole concentration of x_{c}=0.055. The development of new instrumentation at neutron beam sources coupled with the improvement in materials has lead to a better understanding of these materials and the underlying spin dynamics over a broad range of hole dopings. We will describe how the spin dispersion changes across the insulating to superconducting boundary as well as the static magnetic properties which are directly coupled with the superconductivity. Experiments directly probing the competing magnetic and superconducting order parameters involving magnetic fields, impurity doping, and structural order will be examined. Correlations between superconductivity and magnetism will also be discussed.
Page 1 /219732
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.