排序方式: 共有14条查询结果,搜索用时 15 毫秒
1.
L. Fleischmann J. Bonn B. Bornschein P. Leiderer E.W. Otten M. Przyrembel Ch. Weinheimer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):521-529
The dewetting dynamics of solid films of hydrogen isotopes, quench-condensed on a graphite substrate, was measured at various
temperatures below desorption by observing the stray light from the film. A schematic model describing the dewetting process
by surface diffusion is presented, which agrees qualitatively with our data. The activation energies of different hydrogen
isotopes for surface diffusion were determined. The time constant for dewetting of a quench-condensed film at the working temperature of 1.86 K of the mainz neutrino mass experiment was extrapolated.
Received 30 December 1999 相似文献
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J. Bonn B. Bornschein L. Bornschein L. Fickinger O. Kazachenko A. Kovalik Ch. Kraus E. W. Otten H. Ulrich Ch. Weinheimer 《Physics of Atomic Nuclei》2000,63(6):969-974
The Mainz neutrino-mass experiment investigates the endpoint region of the tritium β-decay spectrum with a MAC-E spectrometer to determine the mass of the electron antineutrino. By the recent upgrade, the former problem of dewetting T2 films has been solved, and the signal-to-background ratio was improved by a factor of 10. The latest measurement leads to $m_\nu ^2 = - 3.7 \pm 5.3(stat.) \pm 2.1(syst.){{eV^2 } \mathord{\left/ {\vphantom {{eV^2 } {c^4 }}} \right. \kern-0em} {c^4 }}$ , from which an upper limit of $m_\nu < 2.8{{eV^2 } \mathord{\left/ {\vphantom {{eV^2 } {c^2 }}} \right. \kern-0em} {c^2 }}(95\% C.L.)$ is derived. Some indication for the anomaly, reported by the Troitsk group, was found, but its postulated half-year period is contradicted by our data. To push the sensitivity on the neutrino mass below 1 eV/c 2, a new larger MAC-E spectrometer is proposed. Besides its integrating mode, it could run in a new nonintegration operation MAC-E-TOF mode. 相似文献
3.
T. M. James M. Schlsser S. Fischer M. Sturm B. Bornschein R. J. Lewis H. H. Telle 《Journal of Raman spectroscopy : JRS》2013,44(6):857-865
The Raman depolarization ratios for individual Q1(J”) branch lines of all diatomic hydrogen isotopologues – H2, HD, D2, HT, DT, and T2 – were measured, for all rotational levels with population larger than 1/100 relative to the Boltzmann maximum at room temperature. For these measurements, the experimental setup normally used for the monitoring of the tritiated hydrogen molecules at KArlsruhe TRItium Neutrino experiment was adapted to optimally control the excitation laser power and polarization, and to precisely define the Raman light collection geometry. The measured Raman depolarization values were compared to theoretical values, which are linked to polarizability tensor quantities. For this, the ‘raw data’ were corrected taking into account distinct aspects affecting Raman depolarization data, including (1) excitation polarization impurities; (2) extended Raman excitation volumes; and (3) Raman light collection over finite solid angles. Our corrected depolarization ratios of the hydrogen isotopologues agree with the theoretical values (based on ab initio quantum calculations by R.J. LeRoy, University of Waterloo, Canada) to better than 5% for nearly all of the measured Q1(J”) lines, with 1σ confidence level. The results demonstrate that reliable, accurate Raman depolarization ratios can be extracted from experimental measurements, which may be substantially distorted by excitation polarization impurities and by geometrical effects. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
4.
M. Schlsser T. M. James S. Fischer R. J. Lewis B. Bornschein H. H. Telle 《Journal of Raman spectroscopy : JRS》2013,44(3):453-462
In this article, we address the notoriously difficult problem to quantitatively link measured Raman depolarization values to theoretical polarizability tensor quantities, since quantum calculations do not incorporate experimental parameters. For this, we introduce a numerical model to calculate, for realistic experimental configurations, effective Raman line strength functions, Φ, which find their way into depolarization ratios, ρ. The model is based on interlinked integrations over the angles in the light collection path and a finite Raman source volume along the excitation laser beam. The model deals also with the conditional aperture parameters, associated with more than one optical component in the light collection path. Finally, we also can take into account polarization aberrations introduced by the sample cell windows. The procedure was fully tested for Raman depolarization spectra of selected hydrogen isotopologues. Distinct aspects affecting Raman depolarization data were validated, namely: (1) excitation polarization impurities; (2) extended Raman excitation volumes; (3) Raman light collection over finite solid angles; and (4) polarization aberrations introduced by optics in the light collection path. The correction of the experimental measurement data for the aforementioned effects resulted in depolarization ratios for the Q1(J " ) Raman lines of H2 and T2, which mostly differed by less than 5% from those obtained by quantum‐calculations. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Ruthenium/Imidazolylphosphine Catalysis: Hydrogenation of Aliphatic and Aromatic Nitriles to Form Amines 下载免费PDF全文
Svenja Werkmeister Dr. Kathrin Junge Bianca Wendt Dr. Anke Spannenberg Dr. Haijun Jiao Christoph Bornschein Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(15):4227-4231
A convenient and efficient catalyst system for the hydrogenation of aliphatic nitriles towards the corresponding primary amines in high to excellent yields is presented. In addition, aromatic nitriles are reduced smoothly, too. The use of low catalyst loadings and molecular hydrogen make this protocol an attractive methodology. 相似文献
8.
Bornschein RE Hyung SJ Ruotolo BT 《Journal of the American Society for Mass Spectrometry》2011,22(10):1690-1698
Characterizing intact multiprotein complexes in terms of both their mass and size by ion mobility-mass spectrometry is becoming
an increasingly important tool for structural biology. Furthermore, the charge states of intact protein complexes can dramatically
influence the information content of gas-phase measurements performed. Specifically, protein complex charge state has a demonstrated
influence upon the conformation, mass resolution, ion mobility resolution, and dissociation properties of protein assemblies
upon collisional activation. Here we present the first comparison of charge-reduced multiprotein complexes generated by solution
additives and gas-phase ion-neutral reaction chemistry. While the charge reduction mechanism for both methods is undoubtedly
similar, significant gas-phase activation of the complex is required to reduce the charge of the assemblies generated using
the solution additive strategy employed here. This activation step can act to unfold intact protein complexes, making the
data difficult to correlate with solution-phase structures and topologies. We use ion mobility-mass spectrometry to chart
such conformational effects for a range of multi-protein complexes, and demonstrate that approaches to reduce charge based
on ion-neutral reaction chemistry in the gas-phase consistently produce protein assemblies having compact, ‘native-like’ geometries
while the same molecules added in solution generate significantly unfolded gas-phase complexes having identical charge states. 相似文献
9.
Ch Kraus B. Bornschein L. Bornschein J. Bonn B. Flatt A. Kovalik B. Ostrick E. W. Otten J. P. Schall Th Thümmler Ch Weinheimer 《The European Physical Journal C - Particles and Fields》2005,40(4):447-468
This paper reports on the improved Mainz experiment on tritium
spectroscopy which yields a 10 times higher signal to background ratio than before. The main experimental effects and systematic uncertainties have been investigated in side experiments, and possible error sources have been eliminated. Extensive data taking took place in the years 1997 to 2001. A residual analysis of the data sets yields for the square of the electron antineutrino mass the final result of
eV2/c4. We derive an upper limit of
eV/c2 at 95% confidence level for the mass itself.Received: 21 December 2004, Published online: 9 March 2005PACS:
1460.Pq, 23.40.-s, 2930.Dn, 2930.AjCh. Kraus: Present address: Department of physics, Queens university, K7L3N6 Kingston, CanadaB. Bornschein: Present address: Forschungszentrum Karlsruhe, Tritiumlabor, 76344 Eggenstein-Leopoldshafen, GermanyL. Bornschein: Present address: Universität Karlsruhe (TH), Institut für exp. Kernphysik, Postfach 6980, 76128 Karlsruhe, GermanyA. Kovalik: On leave from the Nuclear Physics Institute of the Acad. Sci. Czech Republic, 25068 Rez near PragueB. Ostrick: Present address: Helmholtz-Institut für Strahlen und Kernphysik, Universität Bonn, 53115 Bonn, Germany
Corresponding author: E.W. OttenCh. Weinheimer: Present address: Institut für Kernphysik, Universität Münster, 48149 Münster, GermanyThis paper comprises principal parts of the PhD theses of Christine Kraus, Beate Bornschein and Lutz Bornschein. 相似文献
10.
Sturm M. Schl?sser M. Lewis R. J. Bornschein B. Drexlin G. Telle H. H. 《Laser Physics》2010,20(2):493-507
We have recorded Raman spectra for all hydrogen isotopologues, using a CW Nd:YVO4 laser (5 W output power at 532 nm) and a high-throughput (f/1.8) spectrograph coupled to a Peltier-cooled (200 K) CCD-array detector (512 × 2048 pixels). A (static) gas cell was used
in all measurements. We investigated (i) “pure” fillings of the homonuclear isotopologues H2, D2, and T2; (ii) equilibrated binary fillings of H2 + D2, H2 + T2, and D2 + T2, thus providing the heteronuclear isotopologues HD, HT, and DT in a controlled manner; and (iii) general mixtures containing
all isotopologues at varying concentration levels. Cell fillings within the total pressure range 13–985 mbar were studied,
in order to determine the dynamic range of the Raman system and the detection limits for all isotopologues. Spectra were recorded
for an accumulation period of 1000 s. The preliminary data evaluation was based on simple peak-height analysis of the ro-vibrational
Q1-branches, yielding 3σ measurement sensitivities of 5 × 10−3, 7 × 10−3, and 25 × 10−3 mbar for the tritium-containing isotopologues T2, DT, and HT, respectively. These three isotopologues are the relevant ones for the KATRIN experiment and in the ITER fusion
fuel cycle. While the measurement reported here were carried out with static-gas fillings, the cells are also ready for use
with flowing-gas samples. 相似文献