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101.
Betz M Göger G Laubereau A Gartner P Bányai L Haug H Ortner K Becker CR Leitenstorfer A 《Physical review letters》2001,86(20):4684-4687
Femtosecond transmission spectra of highly polar CdTe are compared to more covalent GaAs contrasting semiclassical kinetics with two-time quantum kinetics based on the Dyson equation. Nonequilibrium heavy holes in CdTe show ultrafast energy redistribution via the Fr?hlich mechanism even if photoexcited below the LO phonon energy. This subthreshold relaxation is a genuine quantum kinetic effect. It gains importance if the polaron self-energy is comparable to the phonon energy. Conservation of the free-particle energies is not required under these conditions. 相似文献
102.
S. Hegstad E. Lundanes R. Reistad L. S. Haug G. Becher J. Alexander 《Chromatographia》2000,52(7-8):499-504
Summary A method for the determination of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human hair has been developed and validated. Hair samples (200 mg) were dissolved in NaOH (1 M) and PhIP
was isolated by successive solid-phase extraction on a polystyrene-divinylbenzene column and on a silica-based mixed-mode
column with C8 and-SO3
− functional groups. Quantification was performed by gas chromatography-electron-impact ionization high-resolution mass spectrometry
in selected-ion-monitoring mode. The method was validated for determination of PhIP in the concentration range 0.5–25 ng g−1 hair with [2H3]PhIP as internal standard. The limit of quantification was 0.26 ng g−1 hair. Within-day and between-day precision were in the ranges 1–27% and 2–15% relative standard deviation, respectively.
The hair sample used for method validation was found to contain 0.26 ng PhIP g−1 hair. 相似文献
103.
Oscillatory shear measurements on a series of branched graft polystyrenes (PS) synthesized by the macromonomer technique are presented. The graft PS have similar molar masses (M
w
between 1.3×105 g/mol and 2.4×105 g/mol) and a polydispersity M
w
/M
n
around 2. The molar masses of the grafted side chains M
w,br range from 6.8×103 g/mol to 5.8×104 g/mol, which are well below and above the critical entanglement molar mass M
c of linear polystyrene. The average number
of side chains per molecule ranges from 0.6 to 6.7. The oscillatory measurements follow the time–temperature superposition principle. The shift factors do not depend on the number of branches. The zero-shear viscosities of all graft PS are lower than those of linear PS with the same molar mass, which can be attributed to the smaller coil size of the branched molecules. It is shown that the influence of branching on the frequency dependence of the dynamic moduli is weak for all graft PS that were investigated, which can be explained by the low entanglement density.Electronic Supplementary Material Supplementary material is available for this article at
This article has already been published online first (DOI: ). Due to an oversight at the publisher's, this version contained several mistakes. The article is herewith republished in its entirety as a "publisher's erratum". 相似文献
104.
Transient laminar free convection to water in a rectangular container was investigated using a Mach-Zehnder interferometer. The experimental y observed temperature profiles are compared with analytically predicted profiles based on a computer program developed byBarakat. Good agreement between analysis and experiment was obtained. In addition qualitative observations of the conditions in the container during sudden discharge of the liquid are reported.
Zusammenfassung Untersucht wurde der nichtstationäre, laminare Wärmeübergang durch freie Konvektion in Wasser in einem rechteckigen Behälter mittels eines Zehnder-Mach-Interferometers. Die im Experiment beobachteten Temperaturprofile wurden mit den analytisch vorausgesagten Profilen verglichen, die mit einem Komputerprogramm, das vonBarakat entwickelt wurde, erzielt wurden. Gute Übereinstimmung zwischen Analyse und Experiment wurde erreicht. Außerdem werden qualitative Beobachtungen der Vorgänge im Behälter während des plötzlichen Leerens der geschichteten Behälterflüssigkeit berichtet.相似文献
105.
Vu T. Nguyen Viet D. Nguyen Graham C. Haug Ngan T. H. Vuong Hang T. Dang Hadi D. Arman Oleg V. Larionov 《Angewandte Chemie (International ed. in English)》2020,59(20):7921-7927
The development of efficient and selective C?N bond‐forming reactions from abundant feedstock chemicals remains a central theme in organic chemistry owing to the key roles of amines in synthesis, drug discovery, and materials science. Herein, we present a dual catalytic system for the N‐alkylation of diverse aromatic carbocyclic and heterocyclic amines directly with carboxylic acids, by‐passing their preactivation as redox‐active esters. The reaction, which is enabled by visible‐light‐driven, acridine‐catalyzed decarboxylation, provides access to N‐alkylated secondary and tertiary anilines and N‐heterocycles. Additional examples, including double alkylation, the installation of metabolically robust deuterated methyl groups, and tandem ring formation, further demonstrate the potential of the direct decarboxylative alkylation (DDA) reaction. 相似文献
106.
107.
S. I. Dorozhkin M. O. Dorokhova R. J. Haug K. Ploog 《Physica E: Low-dimensional Systems and Nanostructures》1998,1(1-4)
By the method of capacitance spectroscopy and of magnetotransport we have investigated the
and
fractional-quantum-Hall-effect (FQHE) states in gated GaAs
AlGaAs heterojunctions with tuned electron areal density. Our experimental results confirm the theoretical prediction of the fractional quasiparticle charge
in the
FQHE state and of the existence of spin-aligned quasiholes and spin-reversed quasielectrons in the fully spin-polarized
FQHE state. 相似文献
108.
Summary We show that an infinite field is interpretable in a stable torsion-free nilpotent groupG of classk, k>1. Furthermore we prove thatG/Z
k-1
(G) must be divisible. By generalising methods of Belegradek we classify some stable torsion-free nilpotent groups modulo isomorphism and elementary equivalence.Supported by the Deutsche Forschungsgemeinschaft 相似文献
109.
Exceedances over high thresholds are often modeled by fitting a generalized Pareto distribution (GPD) on R+. It is difficult to select the threshold, above which the GPD assumption is enough solid and enough data is available for inference. We suggest a new dynamically weighted mixture model, where one term of the mixture is the GPD, and the other is a light-tailed density distribution. The weight function varies on R+ in such a way that for large values the GPD component is predominant and thus takes the role of threshold selection. The full data set is used for inference on the parameters present in the two component distributions and in the weight function. Maximum likelihood provides estimates with approximate standard deviations. Our approach has been successfully applied to simulated data and to the (previously studied) Danish fire loss data set. We compare the new dynamic mixture method to Dupuis' robust thresholding approach in peaks-over-threshold inference. We discuss robustness with respect to the choice of the light-tailed component and the form of the weight function. We present encouraging simulation results that indicate that the new approach can be useful in unsupervised tail estimation, especially in heavy tailed situations and for small percentiles. 相似文献
110.
Hartmut Haug 《Zeitschrift für Physik A Hadrons and Nuclei》1966,195(1):74-97
The influence of electron intraband scattering processes on the semiconductor laser behaviour is investigated. These processes thermalize the electrons in each band in a very short time. For the example of optical band to band transitions withk-selection rule it is shown, that no holeburning is possible, if the scattering relaxation time is much shorter than the radiative lifetime. We show for this limit that in a linear approximation only one running laser mode is stable. In order to include both band and localisation effects the model of optical transitions between an impurity level and a band is treated. Diffusion processes between the impurities and scattering processes in the band are taken into account. The treatment shows that usually the local inhomogenity of the inversion produced by standing modes is more important than the energetic one for the stabilisation of different laser modes. The model of full energetic homogenisation in the presence of diffusion processes was introduced byStatz andTang. We discuss in a qualitative manner which deviations should be expected if this limit is not fully realized. 相似文献