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31.
Jäger F Wagner G Meijer HA Kerstel ER 《Isotopes in environmental and health studies》2005,41(4):373-378
The potential use of non-dispersive infrared spectroscopy for measuring delta(13)C in air is demonstrated. This technique has already been successfully established for breath test analyses in medical diagnostics, where the CO(2) concentration ranges from 1 to 5 vol.% in the exhaled breath of vertebrates. For breath tests, the sensitivity and accuracy has been improved to reach a standard deviation of 0.2 per thousand (delta-value). Further adjustments were necessary to improve the sensitivity of the instrument at concentration levels typical of atmospheric air. The long-term stability is given by a standard deviation of 0.35 per thousand for CO(2) concentrations of about 400 ppm with signal averaging over 60 s. 相似文献
32.
33.
Harro G. Andresen 《Zeitschrift für Physik A Hadrons and Nuclei》1969,223(1):71-102
The conventional atomic beam preparation technique for hydrogen maser operation consists of a six pole magnetic field focussing in combination with adiabatically changing magnetic fields in the transition region between focusser and maser cavity, which results in a state selected, polarized ensemble of hydrogen atoms. Hydrogen maser operation with state selected, but unpolarized atoms has the advantage to reduce considerably the sensitivity of hydrogen maser frequency on coherently excited, low frequency,Δm F =±1 Zeeman transitions. The influence of the magnetic field pattern in the transition region on the energy level population probabilities for the focussed hydrogen beam has been analysed. Atomic beam preparation techniques using non-adiabatically changing magnetic field configurations in the transition region are described. The dependence of hydrogen maser oscillation on the energy level population within the atomic beam is theoretically investigated and the results are used for the analysis of the experimentally achieved atomic beam populations. It has been shown that a pulsed magnetic spin guidance field in the transition region, which switches between adiabatically changing magnetic field configurations and a sudden magnetic field reversal, results in an ensemble of hydrogen atoms with vanishing time averaged polarization, which does not deteriorate the conventionally achieved maser oscillation amplitude. 相似文献
34.
The effect of vibrational anharmonicity on the thermal scattering of X-rays from crystals is calculated for temperatures above the Debye temperature. A revised method of interpreting the experimental data is suggested. The (temperature dependent) dispersion curves (frequency vs. wave-vector) for small wave-vectors are determined by the isothermal rather than the adiabatic elastic constants. A procedure is outlined to extrapolate from the (temperature dependent) scattering data the (temperature independent) dispersion curves which correspond to the harmonic approximation. 相似文献
35.
36.
Harro Walk 《Journal of multivariate analysis》2008,99(6):1035-1050
For kn-nearest neighbor estimates of a regression Y on X (d-dimensional random vector X, integrable real random variable Y) based on observed independent copies of (X,Y), strong universal pointwise consistency is shown, i.e., strong consistency PX-almost everywhere for general distribution of (X,Y). With tie-breaking by indices, this means validity of a universal strong law of large numbers for conditional expectations E(Y|X=x). 相似文献
37.
Philipp Walk Peter Jung Götz E. Pfander 《Applied and Computational Harmonic Analysis》2017,42(1):117-134
We give a stability result for sparse convolutions on for torsion-free discrete Abelian groups G such as . It turns out, that the torsion-free property prevents full cancellation in the convolution of sparse sequences and hence allows to establish stability, that is, injectivity with an universal lower norm bound, which only depends on the support cardinalities of the sequences. This can be seen as a reverse statement of the Young inequality for sparse convolutions. Our result hinges on a compression argument in additive set theory. 相似文献
38.
Erik R. T. Kerstel L. Gerko van der Wel Harro A. J. Meijer 《Isotopes in environmental and health studies》2013,49(3):207-216
We have studied the temporal behaviour of the deuterium isotope ratio of water vapour emerging from a freshly cut plant leaf placed in a dry nitrogen atmosphere. The leaf material was placed directly inside the sample gas cell of the stable isotope ratio infrared spectrometer. At the reduced pressure (~40 mbar) inside the cell, the appearance of water evaporating from the leaf is easily probed by the spectrometer, as well as the evolving isotope ratios, with a precision of about 1 ‰. The demonstration experiment we describe measures the 2H/1H isotope ratio only, but the experiment can be easily extended to include the 18O/16O and 17O/16O isotope ratios. Plant leaf water isotope ratios provide important information towards quantification of the different components in the ecosystem water and carbon dioxide exchange. 相似文献
39.
Frank Jäger Günter Wagner Harro A. J. Meijer Erik R. T. Kerstel 《Isotopes in environmental and health studies》2013,49(4):373-378
The potential use of non-dispersive infrared spectroscopy for measuring δ13C in air is demonstrated. This technique has already been successfully established for breath test analyses in medical diagnostics, where the CO2 concentration ranges from 1 to 5 vol.% in the exhaled breath of vertebrates. For breath tests, the sensitivity and accuracy has been improved to reach a standard deviation of 0.2 ‰ (delta-value). Further adjustments were necessary to improve the sensitivity of the instrument at concentration levels typical of atmospheric air. The long-term stability is given by a standard deviation of 0.35 ‰ for CO2 concentrations of about 400 ppm with signal averaging over 60 s. 相似文献
40.