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Search Results: 1 - 10 of 449871 matches for " C. J. Kampf "
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Identification and characterization of aging products in the glyoxal/ammonium sulfate system – implications for light-absorbing material in atmospheric aerosols
C. J. Kampf, R. Jakob,T. Hoffmann
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: In this study we report the identification of bicyclic imidazoles in aqueous aerosol mimics using HPLC-ESI-MS/MS. 2,2'-Biimidazole was identified to be a major contributor to the 280 nm absorbance band observed in mixtures of glyoxal and ammonium sulfate, despite the fact that its production rate is two orders of magnitude lower than the previously reported production rates of imidazole or imidazole-2-carboxaldehyde. The molar absorptivity of 2,2'-biimidazole was determined to be (36 690 ± 998) M 1 cm 1. This demonstrates the necessity of molecular product identification at trace levels to enable a better understanding of relevant absorbing species. Additionally, the formation of lower polarity products including formamides of imidazoles is proposed. The role of imidazoles and other light-absorbing species in the formation of SOA and optical properties of SOA is discussed and potentially interesting fields for future investigations are outlined.
Crystalline electric fields and the ground state of Ce$_{3}$Rh$_{4}$Pb$_{13}$
D. A. Sokolov,M. C. Aronson,C. Henderson,J. W. Kampf
Physics , 2006, DOI: 10.1103/PhysRevB.76.075109
Abstract: We have succeeded in synthesizing of single crystals of a new intermetallic compound, Ce$_{3}$Rh$_{4}$Pb$_{13}$. Magnetic susceptibility measurements indicate that the Ce moments are highly localized, despite the metallic character of the electrical resistivity. Heat capacity measurements reveal that the cubic crystal electric field lifts the six-fold degeneracy of the Ce$^{3+}$ ground state, with the quartet state separated by approximately 60 K from the doublet ground state. The magnetic field dependence of the heat capacity at low temperature indicates a further splitting of the doublet, but no sign of magnetic order was found above 0.35 K.
h/e-Periodicity in Superconducting Loops
F. Loder,A. P. Kampf,T. Kopp,J. Mannhart,C. W. Schneider,Yu. S. Barash
Physics , 2007, DOI: 10.1038/nphys813
Abstract: The magnetic flux periodicity of superconducting loops as well as flux quantization itself are a manifestation of macroscopic quantum phenomena with far reaching implications. They provide the key to the understanding of many fundamental properties of superconductors and are the basis for most bulk and device applications of these materials. In superconducting rings the electrical current has been known to periodically respond to a magnetic flux with a periodicity of $\bm{h/2e}$. Here, the ratio of Planck's constant and the elementary charge defines the magnetic flux quantum $\bm{h/e}$. The well-known $\bm{h/2e}$ periodicity is viewed to be a hallmark for electronic pairing in superconductors and is considered evidence for the existence of Cooper pairs. Here we show that in contrast to this long-term belief, rings of many superconductor bear an $\bm{h/e}$ periodicity. These superconductors include the high-$\bm{T_c}$ cuprates, Sr$_2$RuO$_4$, the heavy-fermion superconductors, as well as all other unconventional superconductors with nodes in the energy gap functions, and s-wave superconductors with small gaps or states in the gap. As we show, the 50-year-old Bardeen--Cooper--Schrieffer theory of superconductivity implies that for multiply connected paths of such superconductors the ground-state energies and consequently also the supercurrents are generically $\bm{h/e}$ periodic. The origin of this periodicity is a magnetic-field driven reconstruction of the condensate and a concomitant Doppler-shifted energy spectrum. The robust, flux induced reconstruction of the condensate will be an important aspect to understand the magnetic properties of mesoscopic unconventional superconductors.
Doping Evolution of Oxygen K-edge X-ray Absorption Spectra in Cuprate Superconductors
C. -C. Chen,M. Sentef,Y. F. Kung,C. J. Jia,R. Thomale,B. Moritz,A. P. Kampf,T. P. Devereaux
Physics , 2012, DOI: 10.1103/PhysRevB.87.165144
Abstract: We study oxygen K-edge x-ray absorption spectroscopy (XAS) and investigate the validity of the Zhang-Rice singlet (ZRS) picture in overdoped cuprate superconductors. Using large-scale exact diagonalization of the three-orbital Hubbard model, we observe the effect of strong correlations manifesting in a dynamical spectral weight transfer from the upper Hubbard band to the ZRS band. The quantitative agreement between theory and experiment highlights an additional spectral weight reshuffling due to core-hole interaction. Our results confirm the important correlated nature of the cuprates and elucidate the changing orbital character of the low-energy quasi-particles, but also demonstrate the continued relevance of the ZRS even in the overdoped region.
First measurements of reactive α-dicarbonyl concentrations on PM2.5 aerosol over the Boreal forest in Finland during HUMPPA-COPEC 2010 – source apportionment and links to aerosol aging
C. J. Kampf, A. L. Corrigan, A. M. Johnson, W. Song, P. Keronen, R. K nigstedt, J. Williams, L. M. Russell, T. Pet j , H. Fischer,T. Hoffmann
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: The first dataset for summertime boreal forest concentrations of two atmospherically relevant α-dicarbonyl compounds, glyoxal (Gly) and methylglyoxal (Mgly) on PM2.5 aerosol was obtained during the HUMPPA-COPEC-2010 field measurement intensive in Hyyti l , Finland. Anthropogenic influences over the course of the campaign were identified using trace gas signatures and aerosol particle chemical composition analysis. The data evaluation allowed the identification of different events such as urban pollution plumes, biomass burning and sawmill emissions as sources of high Gly and Mgly concentrations. Mean aerosol concentrations during periods of biogenic influence were 0.81 ng m 3 for Gly and 0.31 ng m 3 for Mgly. Mgly was generally less abundant in PM2.5, probably due to its shorter photolysis lifetime and less effective partitioning into the particle phase due to its smaller effective Henry's Law constant compared to Gly. This is in contrast with previous urban studies which show significantly more Mgly than Gly. Peak concentrations for Gly coincided with nearby sources, e.g. high VOC emissions from nearby sawmills, urban pollution plumes from the city of Tampere located 50 km southwest of the sampling site and biomass burning emissions from wildfires. Calculated ratios of Gly in PM2.5 and total organic matter in PM1 aerosols indicate higher values in less aged aerosols. Irreversible processing of Gly in the particle phase, e.g. via oxidation by OH radicals, organo sulfate or imidazole formation are processes currently discussed in the literature which could likely explain these findings.
A functional central limit theorem for integrals of stationary mixing random fields
Jürgen Kampf,Evgeny Spodarev
Mathematics , 2015,
Abstract: We prove a functional central limit theorem for integrals $\int_W f(X(t))\, dt$, where $(X(t))_{t\in\mathbb{R}^d}$ is a stationary mixing random field and the stochastic process is indexed by the function $f$, as the integration domain $W$ grows in Van Hove-sense. We discuss properties of the covariance function of the asymptotic Gaussian process.
The role of hydrogen in tellurites: crystal structure refinements of juabite, poughite and rodalquilarite
Kampf A R,Mills S J
Journal of Geosciences , 2011, DOI: 10.3190/jgeosci.093
Abstract: The crystal structures of the tellurite minerals juabite, CaCu10(Te4+O3)4(AsO4)4(OH)2(H2O)4, poughite, Fe3+2(Te4+O3)2(SO4)(H2O)2·H2O and rodalquilarite, Fe3+2(Te4+O2OH)3(Te4+O3)Cl, have been refined to R1 (Fo > 4sF) = 2.36%, 2.38% and 1.84%, respectively. The determination of H atom positions in all three structures has allowed the elucidation of the hydrogen bonding schemes and detailed bond-valence analyses. These are the only tellurite mineral structures for which H atom positions have been determined. The structures of all contain one-sided Te4+ coordinations as Te4+O3 pyramids with additional anions at greater distances. The one-sided coordinations are attributable to the stereochemically active 6s2 lone-electron-pair of the Te4+. The overall linkage schemes in these structures are quite different, yet all can be considered layer structures in which relatively weak long Te-O and/or Te-Cl bonds are involved in the linkages between layers. In juabite, a long apical Cu-O bond participates in the linkage between layers and, in poughite and rodalquilarite, hydrogen bonding also links the layers.
Minor Cause—Major Effect: A Novel Mode of Control of Bistable Gene Expression
Jan Kampf,J?rg Stülke
PLOS Genetics , 2015, DOI: 10.1371/journal.pgen.1005229
On the convex hull of symmetric stable processes
Jürgen Kampf,Günter Last
Mathematics , 2010,
Abstract: Let alpha \in (1, 2] and X be an R^d-valued alpha-stable process with independent and symmetric components starting in 0. We consider the closure S_t of the path described by X on the interval [0, t] and its convex hull Z_t. The first result of this paper provides a formula for certain mean mixed volumes of Z_t and in particular for the expected first intrinsic volume of Z_t. The second result deals with the asymptotics of the expected volume of the stable sausage Z_t+B (where B is an arbitrary convex body with interior points) as t \to 0.
Joachim Ohser,Konrad Sandau,Jürgen Kampf,Irene Vecchio
Image Analysis and Stereology , 2013, DOI: 10.5566/ias.v32.p45-55
Abstract: A new method is presented for estimating the specific fiber length from 3D images of macroscopically homogeneous fiber systems. The method is based on a discrete version of the Crofton formula, where local knowledge from 3x3x3-pixel configurations of the image data is exploited. It is shown that the relative error resulting from the discretization of the outer integral of the Crofton formula amonts at most 1.2%. An algorithmic implementation of the method is simple and the runtime as well as the amount of memory space are low. The estimation is significantly improved by considering 3x3x3-pixel configurations instead of 2x2x2, as already studied in literature.
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