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Search Results: 1 - 10 of 144423 matches for " B. Fluckiger "
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The rate of water vapor evaporation from ice substrates in the presence of HCl and HBr: implications for the lifetime of atmospheric ice particles
C. Delval, B. Fluckiger,M. J. Rossi
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2003,
Abstract: Using a multidiagnostic approach the rate Rev [ molec cm-3 s-1] or flux Jev [ molec cm-2 s-1] of evaporation of H2O and its corresponding rate constant for condensation, kcond [s-1 ], on a 1 μm thick ice film have been studied in the temperature range 190 to 240 K as well as in the presence of small amounts of HCl and HBr that left the vapor pressure of H2O on ice unchanged. The resulting Arrhenius expressions for pure ice are Jev = 1.6 · 10 28 ± 1 · exp (- 10.3 ± 1.2/ RT) [ molec cm-2 s-1] , kcond = 1.7 · 10 - 2 ± 1 · exp (+ 1.6 ± 1.5/ RT ) [s -1], in the presence of a HCl mole fraction in the range 3.2 · 10 - 5 - 6.4 · 10 - 3 : Jev = 6.4 · 10 26 ± 1 · exp (- 9.7 ± 1.2/ RT) [ molec cm-2 s-1] , kcond = 2.8 · 10 - 2 ± 1 · exp ( + 1.5 ± 1.6 /RT) [s -1], and a HBr mole fraction smaller than 6.4 · 10 - 3 : Jev = 7.4 · 10 25 ± 1 · exp ( - 9.1 ± 1.2 /RT) [ molec cm-2 s-1] , kcond = 7.1 · 10 - 5 ± 1 · exp (+ 2.6 ± 1.5/ RT) [s -1]. The small negative activation energy for H2O condensation on ice points to a precursor mechanism. The corresponding enthalpy of sublimation is DHsubl = Eev - Econd = 11.9 ± 2.7 kcal mol-1 , DHsubl = 11.2 ± 2.8 kcal mol-1, and DHsubl = 11.7 ± 2.8 kcal mol-1 whose values are identical within experimental uncertainty to the accepted literature value of 12.3 kcal mol-1 . Interferometric data at 633 nm and FTIR absorption spectra in transmission support the kinetic results. The data are consistent with a significant lifetime enhancement for HCl- and HBr-contaminated ice particles by a factor of 3–6 and 10–20, respectively, for submonolayer coverages of HX once the fraction of the ice not contaminated by HX has evaporated.
The rate of water vapor evaporation from ice substrates in the presence of HCl and HBr: Implications for the lifetime of atmospheric ice particles
C. Delval,B. Fluckiger,M. J. Rossi
Atmospheric Chemistry and Physics Discussions , 2003,
Abstract: Using a multidiagnostic approach the rate Rev or flux Jevof evaporation of H2O and its condensation, kcond, on a 1mm thick ice film have been studied in the temperature range 190 to 240 K as well as in the presence of small amounts of HCl and HBr that left the vapor pressure of H2O on ice unchanged. The resulting Arrhenius expressions with RT in kcal mol-1 for pure ice are Jev=1.6×1028+/ 1·exp({ 10.3+ 1.2}/{RT}) [molec cm 2 s 1], kcond=1.7×10 2+-1×exp({+1.6+ 1.5}/{RT}) [s 1], in the presence of an HCl mole fraction in the range 3.2×10 5-6.4×10 3: Jev=6.4×1026+/ 1×exp({ 9.7+/ 1.2}/{RT}) [molec cm 2 s 1], kcond=2.8×10 2+/-1×exp({+1.5+/ 1.6}/{RT}) [s 1], and an HBr mole fraction smaller than 6.4×10 3:Jev=7.4×1025+/ 1×exp({ 9.1+/ 1.2}/{RT}) [molec cm 2 s 1], kcond=7.1×10 5+ 1×exp({+2.6+/ 1.5}/{RT}) [s 1]}. The small negative activation energy for H2O condensation on ice points to a precursor mechanism. The corresponding enthalpy of sublimation is DHsubl=Eev-Econd=11.9+/ 2.7 kcal mol 1, DHsubl=11.2+/ 2.8 kcal mol 1, and DHsubl=11.7+/ 2.8 kcal mol 1 whose values are identical within experimental uncertainty to the accepted literature value of 12.3 kcal mol 1. Interferometric data at 633 nm and FTIR absorption spectra in transmission support the kinetic results. The data are consistent with a significant lifetime enhancement for HCl- and HBr-contaminated ice particles by a factor of 3–6 and 10–20, respectively, for submonolayer coverages of HX.
Embeddings of maximal tori in orthogonal groups
Eva Bayer-Fluckiger
Mathematics , 2013,
Abstract: We give necessary and sufficient conditions for an orthogonal group defined over a field of characteristic not 2 to contain a maximal torus of a given type.
Isometries of quadratic spaces
Eva Bayer-Fluckiger
Mathematics , 2013,
Abstract: Let k be a field of characteristic not 2, let q be a quadratic space over k and let f be an irreducible polynomial with coefficients in k. In 1969, Milnor raised the following question : how can we decide whether q has an isometry with minimal polynomial f ? We give an answer to this question in the case of global fields. A more general version of the question is also considered.
Sesquilinear forms over rings with involution
Eva Bayer-Fluckiger,Daniel Moldovan
Mathematics , 2012,
Abstract: Many classical results concerning quadratic forms have been extended to forms over algebras with involution. However, not much is known in the case of forms without any symmetry property. The present paper will establish Witt cancellation and base change results, as well as some local-global and finiteness results in this context.
Hermitian Categories, extension of scalars and systems of hermitian forms
Eva Bayer-Fluckiger,Daniel Moldovan
Mathematics , 2012,
Abstract: In this paper we define a notion of Witt group for sesquilinear forms in hermitian categories, which in turn provides a notion of Witt group for sesquilinear forms over rings with involution. We also study the extension of scalars for K-linear hermitian categories, where K is a field of characteristic not 2. We finally extend several results concerning sesquilinear forms to the setting of systems of such forms.
Upper bounds for the Euclidean minima of abelian number fields
Eva Bayer-Fluckiger,Piotr Maciak
Mathematics , 2013,
Abstract: The aim of this paper is to survey and extend results concerning bounds of the Euclidean minima of abelian number fields. In particular, we give upper bounds for the Euclidean minima of abelian number fields of prime power conductor.
Upper bounds for the Euclidean minima of abelian fields of odd prime power conductor
Eva Bayer-Fluckiger,Piotr Maciak
Mathematics , 2013,
Abstract: The aim of this paper is to give upper bounds for the Euclidean minima of abelian fields of odd prime conductor. In particular, these bounds imply Minkowski's conjecture for totally real number fields of conductor p^r, where p is an odd prime and r is at least 2.
Patching and Weak Approximation in Isometry Groups
Eva Bayer-Fluckiger,Uriya A. First
Mathematics , 2015,
Abstract: Let $R$ be a semilocal principal ideal domain. Two algebraic objects over $R$ in which scalar extension makes sense (e.g. quadratic spaces) are said to be of the same genus if they become isomorphic after extending scalars to all completions of $R$ and its fraction field. We prove that the number of isomorphism classes in the genus of unimodular quadratic spaces over (non necessarily commutative) $R$-orders is always a finite power of $2$, and under further assumptions, this number is $1$. The same result is also shown for related objects, e.g. systems of sesquilinear forms. A key ingredient in the proof is a weak approximation theorem for groups of isometries, which is valid over any (topological) base field, and even over semilocal base rings.
Rationally Isomorphic Hermitian Forms and Torsors of Some Non-Reductive Groups
Eva Bayer-Fluckiger,Uriya A. First
Mathematics , 2015,
Abstract: Let $R$ be a semilocal Dedekind domain. Under certain assumptions, we show that two (not necessarily unimodular) hermitian forms over an involutary $R$-algebra, which are rationally isometric and have isomorphic semisimple coradicals, are in fact isometric. The same result is also obtained for quadratic forms invariant under a group action. The results can be regarded as a version of the Grothendieck-Serre conjecture for certain non-reductive group schemes over $\mathrm{Spec}\,R$.
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