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151.
Fleming DG Arseneau DJ Sukhorukov O Brewer JH Mielke SL Truhlar DG Schatz GC Garrett BC Peterson KA 《The Journal of chemical physics》2011,135(18):184310
The neutral muonic helium atom (4)Heμ, in which one of the electrons of He is replaced by a negative muon, may be effectively regarded as the heaviest isotope of the hydrogen atom, with a mass of 4.115 amu. We report details of the first muon spin rotation (μSR) measurements of the chemical reaction rate constant of (4)Heμ with molecular hydrogen, (4)Heμ + H(2) → (4)HeμH + H, at temperatures of 295.5, 405, and 500 K, as well as a μSR measurement of the hyperfine coupling constant of muonic He at high pressures. The experimental rate constants, k(Heμ), are compared with the predictions of accurate quantum mechanical (QM) dynamics calculations carried out on a well converged Born-Huang (BH) potential energy surface, based on complete configuration interaction calculations and including a Born-Oppenheimer diagonal correction. At the two highest measured temperatures the agreement between the quantum theory and experiment is good to excellent, well within experimental uncertainties that include an estimate of possible systematic error, but at 295.5 K the quantum calculations for k(Heμ) are below the experimental value by 2.1 times the experimental uncertainty estimates. Possible reasons for this discrepancy are discussed. Variational transition state theory calculations with multidimensional tunneling have also been carried out for k(Heμ) on the BH surface, and they agree with the accurate QM rate constants to within 30% over a wider temperature range of 200-1000 K. Comparisons between theory and experiment are also presented for the rate constants for both the D + H(2) and Mu + H(2) reactions in a novel study of kinetic isotope effects for the H + H(2) reactions over a factor of 36.1 in isotopic mass of the atomic reactant. 相似文献
152.
Manuela Ulberth-Buchgraber Monica Potalivo Andrea Held Annarita Baldan Adriaan M. H. van der Veen Hugo Ent Valnei S. Cunha Romeu J. Daroda Brian Lang Michele Schantz Ruth Hearn Richard J. C. Brown Paul J. Brewer 《Accreditation and quality assurance》2013,18(1):29-39
The results of an interlaboratory comparison, using various measurement methods to carry out biodiesel testing, are presented and the findings are discussed. The interlaboratory comparison was organised within the framework of an EU-funded project called BIOREMA. A general overview of the project and results of an interlaboratory comparison on bioethanol are published as Part 1 and 2 of this series of papers. In the study presented here, reference values, provided by national metrology institutes and expert laboratories, were used for evaluating the results. Consensus values, derived from the results of all participants, were used to assess any bias between the results from the national metrology institutes and testing laboratories. The emphasis in this interlaboratory comparison was not the performance rating of the individual laboratories, but recognising and interpreting differences caused by the measurement methods applied. For most biodiesel parameters, a good agreement of measurement results was found among different methods, and between the consensus and reference values. The study material was a rapeseed oil fatty acid methyl ester, for which it was demonstrated that it is feasible to prepare and characterise reference materials for biodiesel with well-established reference values for many parameters. 相似文献
153.
Ru,Rh,Ru supramolecules are known to undergo multielectron photoreduction and reduce H(2)O to H(2). Ru,Rh bimetallics were recently shown to photoreduce but not catalyze H(2)O reduction. Careful tuning of sterics and electronics for [(TL)(2)Ru(dpp)RhCl(2)(TL')](3+) produce active bimetallic photocatalysts (TL = terminal ligand). The system with TL,TL' = Ph(2)phen photocatalytically reduces H(2)O to H(2) while TL,TL' = phen,bpy or bpy,(t)Bu(2)bpy do not. 相似文献
154.
M. Meron J. Gebhardt H. Brewer J. P. Viccaro B. Lin 《The European physical journal. Special topics》2009,167(1):137-142
A fast pixel array detector, the Pilatus 100 K, has been
used in studies of organic monolayers at the air-water interface. The area
sensitivity and large dynamic range of the detector, in combination with a
“one dimensional pinhole” geometry, make it possible to observe surface
processes which were inaccessible to the previous generation of experimental
techniques. Especially, time dependent phenomena acting on time scales
ranging from seconds to minutes can be observed and analyzed. 相似文献
155.
Luke G. M. Kiefl R. F. Kreitzman S. R. Brewer J. H. Noakes D. R. Celio M. Keitel R. Uemura Y. J. Harshman D. R. Jaccarino V. 《Hyperfine Interactions》1986,31(1-4):29-34
We report the observation of μ+ Level-Crossing Resonances (LCR's) in the ordered phase of an antiferromagnetic material. Two LCR's were observed in MnF2 as a function of longitudinal magnetic field in the temperature range between 10K and 65K. Both are attributed to a muon
in an interstitial octahedral-like site. The low field resonance is attributed to a muon-nuclear spin flip-flop transition
involving the two nearest neighbour19F nuclei. The high field resonance occurs when the applied field cancels the local hyperfine field on the muon. The positions
and widths of the LCR's were seen to scale with the sublattice magnetization. 相似文献
156.
T. M. Riseman J. H. Brewer E. J. Ansaldo P. M. Grant M. E. Lopez-Morales B. M. Sternlieb 《Hyperfine Interactions》1991,63(1-4):249-252
Zero and weak transverse fieldμ
+ SR measurements on PrBa2Cu3O
x
samples withx≈6 andx≈7 show ordered magnetism in both oxygen concentration limits. As expected for equivalent doping (nominally PrBa2Cu3O
x
∼YBa2Cu3O
x
−0.5), neither sample is superconducting. Two muon signals are observed in thex≈6 sample, as in YBa2Cu3O6, but only one (the weaker) has the same local magnetic field as in YBa2Cu3O6. In thex≈7 sample, only one site is observed; its local field is reduced with respect to that of the primary site in YBa2Cu3O6 by a factor roughly consistent with the carrier-density dependence of the Cu ion moment in antiferromagnetic YBa2Cu3O
x
. 相似文献
157.
Re-examination of flexible fiberoptic videotaped laryngeal images of 39 patients with unilateral recurrent laryngeal nerve paralysis (URLNP) by four observer-judges revealed consistent findings of a unilaterally appearing shorter vocal fold with asymmetry of the arytenoid complex on the involved side. No previous similar experience in otolaryngological training or practice has been encountered. Multiple discrepancies between and among observer-judges regarding vocal fold positions during phonation were encountered. Possible explanations are discussed. The need for further investigation to determine the mechanics causing these differences is stressed. It is suggested that for the present, such terms as median, paramedian, and intermediate be used in teaching and in practice as generalities only. 相似文献
158.
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