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1.
We study the quark mass expansion of the magnetic moments of the nucleon in a chiral effective field theory including nucleons,
pions and delta-resonances as explicit degrees of freedom. We point out that the usual power counting applied so far to this
problem misses important quark mass structures generated via an intermediate isovector M1 nucleon-delta transition. We propose a modified power counting and compare the resulting chiral extrapolation function to
available (quenched) lattice data. The extrapolation is found to work surprisingly well, given that the lattice data result
from rather large quark masses. Our calculation raises the hope that extrapolations of lattice data utilizing chiral effective
field theory might be applicable over a wider range in quark masses than previously thought, and we discuss some open questions
in this context. Furthermore, we observe that within the current lattice data uncertainties the extrapolations presented here
are consistent with the Padé fit ansatz introduced by the Adelaide group a few years ago.
Received: 23 April 2002 / Accepted: 18 July 2002 / Published online: 17 December 2002
RID="c"
ID="c"e-mail: themmert@physik.tu-muenchen.de
RID="d"
ID="d"e-mail: weise@ect.it
Communicated by A. Sch?fer 相似文献
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The passage of cosmic rays has been observed to excite mechanical vibrations in the resonant gravitational wave detector NAUTILUS operating at temperature of 100 mK. A very significant correlation (more than 10 standard deviations) is found. 相似文献
4.
Magnetic field-controlled microfluidic transport. 总被引:1,自引:0,他引:1
Kyle M Grant Jared W Hemmert Henry S White 《Journal of the American Chemical Society》2002,124(3):462-467
Several new forms of magnetohydrodynamic (MHD) flow occurring in the solution gap between two 250-microm-diameter Pt microdisk electrodes, oriented in a face-to-face geometry and immersed in a uniform magnetic field (1 T), are described. The MHD flow results from the Lorentz force generated by diffusion of electrochemically generated molecular ions through the magnetic field. Individual microscopic flow tubes ( approximately 50-microm radius) spanning the gap between the face-to-face electrodes are observed during the 1-e(-) reduction of nitrobenzene in acetonitrile solutions. The flow tubes extend up to approximately 2 cm in length and are stable for indefinite periods. Directional transport of the electrogenerated nitrobenzene radical anion over macroscopic distances within the flow tubes, with minimal diffusional broadening, is demonstrated using an ultramicroelectrode probe to map the convective flux of redox species. Pulsed MHD transport of small packets of molecules and the formation of large area (approximately 3 cm(2)), microscopically thin (25 microm) rotating sheets of solution are also demonstrated. The results suggest that electrochemical methods, in combination with magnetohydrodynamic principles, may be useful for external field-controlled microfluidic systems. 相似文献
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Martinez A Hemmert C Loup C Barré G Meunier B 《The Journal of organic chemistry》2006,71(4):1449-1457
We describe a general synthetic strategy for the preparation of a series of macrocyclic chiral manganese(III) salen complexes. The developed reaction pathway allows the modulation of the different key groups, namely, the chiral diimine, the bulky substituents in positions 3 and 3', and the linker used in the macrocyclization of the Schiff base. The different complexes presented here illustrate these readily available structural variations. The catalytic properties of the catalysts (5 mol %) were improved for the asymmetric epoxidation of 2,2'-dimethylchromene with NaOCl or H2O2 as oxygen atom donor. A large range of enantiomeric excesses was obtained (ee values from 30% to 96%), depending on the features and the stability of the complexes. The most efficient catalyst, in terms of stereoinduction (ee value = 96%), contains a diiminocyclohexyl moiety, ethyl groups in positions 3 and 3', and a short polyether junction arm. 相似文献
7.
Hemmert D. Neuber A.A. Dickens J. Krompholz H. Hatfield L.L. Kristiansen M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(3):472-477
Microwave window breakdown in vacuum is investigated for an idealized geometry, where a dielectric slab is located in the center of a rectangular waveguide with its normal parallel to the microwave direction of propagation. An S-band resonant ring with a frequency of 2.85 GHz and a power of 60 MW is used. With field enhancement tips at the edges of the dielectric slab, the threshold power for breakdown is observed to be dependent on the direction of the microwaves; i.e., it is approximately 20% higher for the downstream side of the slab than it is for the upstream side. Simple trajectory calculations of secondary electrons in an RF field show a significant forward motion of electrons parallel to the direction of microwave propagation. Electrons participating in a saturated secondary avalanche on the upstream side are driven into the surface, and electrons on the downstream side are driven off the surface, because of the influence of the microwave magnetic field. In agreement with the standard model of dielectric surface flashover for dc conditions (saturated avalanche and electron-induced outgassing), the corresponding change in the surface charge density is expected to be proportional to the applied breakdown threshold electric field parallel to the surface 相似文献
8.
François Jean-Baptiste dit Dominique Catherine Hemmert 《Journal of organometallic chemistry》2008,693(3):579-583
A range of new diimidazolium salts, held together by an alkyl unit and bearing alcohol pendant arms on their nitrogen, was synthesized. A short modular reaction pathway leads to the N-heterocyclic carbene (NHC) precursors, differing by the flexibility of the bridge, the steric bulk of substituents in α-position of the OH groups and the anions. Treatment of diimidazolium salts with Ag2O yields AgI(carbene)2 complexes. The related trimethylene-bridged bis-NHC silver complexes 6 and 7 were crystallised with di-tosylate and di-hexafluorophosphate anions, respectively. Their X-ray structures revealed dimeric species, involving two ligands with different arrangements around the Ag cations, leading to crossed and parallel conformations. 相似文献
9.
We summarize developments concerning the quark mass dependence of nucleon magnetic moments and the axial-vector coupling constant gA. The aim is to explore the feasibility of chiral effective field theory methods for the extrapolation of lattice QCD results, from the relatively large quark masses that can be handled in such computations down to the physically relevant range. 相似文献
10.
Dr. Chen Zhang Dr. Pierre-Yves Fortin Guillaume Barnoin Xue Qin Xing Wang Dr. Alvaro Fernandez Alvarez Dr. Christian Bijani Dr. Marie-Lise Maddelein Dr. Catherine Hemmert Dr. Olivier Cuvillier Prof. Dr. Heinz Gornitzka 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(29):12160-12166