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1.
V. T. Dolgopolov E. V. Deviatov A. A. Shashkin U. Wieser U. Kunze G. Abstreiter K. Brunner 《Superlattices and Microstructures》2003,33(5-6):271
The small, about 30% magnetoresistance at the onset of full spin polarization in the 2D electron system in a modulation-doped Si/SiGe quantum well gives evidence that it is the remote doping that determines the transport scattering time. Measurements of the mobility in this strongly-interacting electron system with remote-doping scattering allow us to arrive at a conclusion that the Hubbard form underestimates the local field corrections by about a factor of 2. 相似文献
2.
M. R. Yaftian M. Burgard D. Matt C. Wieser C. Dieleman 《Journal of inclusion phenomena and macrocyclic chemistry》1997,27(2):127-140
The complexing, extracting and mobile carrier properties of the tetra(phosphine oxide)-calix[4]arene 1 and the hybrid diamide-di(phosphine oxide)-calix[4]arene 2 were studied. Both ligands give 1 : 1 complexes with alkali cations in THF as shown by the picrate method. 1H NMR experiments were run to follow encapsulation of sodium and potassium cations. The corresponding spectra indicate C2-symmetrical structure. The observed extraction orders of the alkali picrates were as follows K+>Rb+>Li+>Cs+>Na+ for 1 and Li+>Na+>K+>Rb++ for 2. Transport kinetics was analysed by means of a model which assumes pure diffusion and which allows the evaluation of mass transfer coefficients in all systems. These coefficients and their influences on the transport rate are discussed in terms of size of the transporting species in the liquid membrane. 相似文献
3.
The rg structure of cyclopentene oxide has been determined by the simultaneous least squares analysis of electron diffraction and microwave spectroscopic data. The investigation has reaffirmed previous studies indicating that the molecule prefers a boat conformation. The methylene and epoxide flap angles obtained are 152.3±2.1° and 104.7±1.0° respectively. Other structural parameters determined are: rg (C-H avg.) = 1.120±0.004 Å; rg (C-C avg.) = 1.538±0.002 Å; rg (C-O) = 1.443±0.003 Å, and rg (C-C) = 1.482±0.004 Å for the carbon-carbon bond in the three membered epoxide ring. These results compare favorably with the reported structures of ethylene oxide and cyclohexene oxide. A tentative rationalization of the unusual boat conformation is also offered. 相似文献
4.
E. Y. Vedmedenko N. Mikuszeit T. Stapelfeldt R. Wieser M. Potthoff A. I. Lichtenstein R. Wiesendanger 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(3):331-336
Using exact diagonalization, Monte-Carlo, and mean-field techniques, characteristic temperature scales for ferromagnetic order
are discussed for the Ising and the classical anisotropic Heisenberg model on finite lattices in one and two dimensions.
The interplay between nearest-neighbor exchange, anisotropy and the presence of surfaces leads, as a function of temperature,
to a complex behavior of the distance-dependent spin-spin correlation function, which is very different from what is commonly
expected.
A finite experimental observation time is considered in addition, which is simulated within the Monte-Carlo approach by an
incomplete statistical average.
We find strong surface effects for small nanoparticles, which cannot be explained within a simple Landau or mean-field concept
and which give rise to characteristic trends of the spin-correlation function in different temperature regimes.
Unambiguous definitions of crossover temperatures for finite systems and an effective method to estimate the critical temperature
of corresponding infinite systems are given. 相似文献
5.
Nicoleta E. Mircescu Haibo Zhou Nicolae Leopold Vasile Chiş Natalia P. Ivleva Reinhard Niessner Andreas Wieser Christoph Haisch 《Analytical and bioanalytical chemistry》2014,406(13):3051-3058
Based on molecular-specific surface-enhanced Raman scattering (SERS) spectroscopy we were able to discriminate between rough and smooth strains of Escherichia coli and Proteus mirabilis bacteria. For this purpose, bacteria have been immobilized through electrostatic forces by inducing a positive charge on the glass slide. This way, SERS spectra on bacterial biomass and also on single bacteria could be recorded in less than 2 h, by using concentrated silver nanoparticles as SERS-active substrate. Single-bacterium SERS spectral fingerprints showed to be sensitive to the presence of the O-antigen at strain level and to the microorganisms growth phase. By using principal component analysis (PCA) on the SERS spectra recorded from E. coli and P. mirabilis, these two uropathogens could be fairly discriminated. 相似文献
6.
Stephen Lane Bernadette C. Proemse Alexander Tennant Michael E. Wieser 《Analytical and bioanalytical chemistry》2013,405(9):2957-2963
Here, we report the first measurements of the molybdenum (Mo) isotopic composition of aerosols collected on Teflon air filters. Mo concentrations and isotopic compositions were measured at selected locations in the city of Calgary, Canada, including a residence, the isotope laboratory at the University of Calgary, the University of Calgary weather station, and the City of Calgary Transit bus garage. Concentrations ranged from 0.07 ng/m3 in the laboratory to 19.0 ng/m3 in the bus garage. The concentrations of Mo in the air samples collected in the bus garage were the highest measured in this study. To date, there are no reported data for the Mo isotopic composition of airborne Mo. In this study, the δ98/95Mo values measured for the different urban sampling sites and reported relative to SRM 3134, ranged from ?0.18 to +0.94 ‰. The results of this investigation suggest that measurements of Mo concentrations and isotopic compositions have the potential to trace anthropogenic emissions in an urban environment. 相似文献
7.
A. Morozov T. Heindl J. Wieser R. Krücken A. Ulrich 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):51-57
Continuous and pulsed 12 keV electron beams were used to excite nitrogen
within a gas cell at pressures ranging from 10 to 1400 hPa. The pressure
dependence of the ratio of photon fluxes for emission from vibrational
levels v'=0 and 1 of the C 3Π u state has been studied. The
results confirm the presence of a collisional excitation mechanism
populating v'=0, 1 in addition to electron impact excitation. Rate constants
of (1.27 ±0.04)×10-11 cm3s-1 [ v'=0] and
(2.68 ±0.08)×10-11 cm3s-1 [ v'=1] were measured for
C 3Π u quenching by ground state nitrogen. For electron beam
conditions relative excitation efficiencies of 1:0.59:0.22 for
vibrational levels 0, 1 and 2 were calculated. The recorded flux ratios are
compared with the predictions given by a vibrational relaxation model. 相似文献
8.
The far-infrared spectrum of tetrahydrothiophene is reinvestigated with a resolution of 0.12 cm?1 in the region of 50–350 cm?1. In addition to the bend transitions (νb) below 120 cm?1 reported previously, a number of sequences revealed by the improved resolution are observed for the first time and assigned to transitions of 2νb, of the twist (νt), and of difference combinations (νt - νb). Simple one-dimensional modeling of the twist sequence, which is derived from a self-consistent bend-twist energy level diagram, with a quadratic-quartic Hamiltonian suggests a barrier to planarity on the order of 4250 cm?1. A two-dimensional potential function in the dimensionless coordinates is found to be V(qb, qt) = ?249.6qb2 + 4.48qb4 ? 215.5qt2 + 2.73qt4 + 7.00qb2qt2. 相似文献
9.
Ferromanganese nodules from Flysh deposits of West Carpathian Mountains were studied by Mössbauer spectroscopy method. The presence of small-grain goethite and hematite was established and grain sizes roughly estimated. 相似文献
10.
Bulk superconducting samples of type Tl0.5Pb0.5Sr1.6Ba0.4CaCu2−x
Ru
x
O7−δ, (Tl, Pb)/Sr-1212, with 0.0 ≤ x ≤ 0.525 were prepared by the conventional one-step solid-state reaction technique. The prepared samples were investigated
using X-ray powder diffraction, electrical resistivity and electron paramagnetic resonance (EPR) measurements. Enhancement
of the phase formation, superconducting transition temperature T
c and hole carriers concentration P was observed up to x = 0.075. For x > 0.075, a reverse trend was observed. EPR spectra were measured at different temperatures (120–290 K) for all prepared samples.
The number of spins N participating in the resonance and the paramagnetic susceptibility χ were calculated as a function of both Ru-content and
temperature. N and χ increased as the Ru-content increased. A linear relationship between logN and 1/T was established, from which the activation energy E
a was calculated as a function of the Ru-content. The temperature dependence of χ was fitted according to Curie–Weiss type
of magnetic behavior. Curie constant C, Curie temperature θ, the effective magnetic moment μ and the electronic specific heat γ were estimated as a function of the Ru-content. 相似文献