104 research outputs found
Internationale Kapitalgeber und Bildungsinvestition in der sogenannten Dritten Welt: Die Beispiele Namibia und Senegal
Anhang : Finanzierung des Bildungswesens in der Helvetischen Republik : Darstellung verschiedener Akteure sowie deren Einfluss und Wirkung in unterschiedlichen Regionen der Schweiz um 1800
Die Finanzierung von Schulen in der Schweiz um 1800 präsentiert sich äusserst vielfältig: von verschiedenen lokalen Finanzierungsquellen über diverse Währungen, Masseinheiten und Naturalien. Soziokulturelle Bedingungen prägten diese regionalen Eigenheiten und verhalfen ihnen – vor dem Hintergrund der politischen Instabilität – zu überraschender Persistenz, die allerdings durch dynamische Prozesse sowohl zwischen Individuen als auch Organisationen immer wieder durchbrochen wurde. [Die Autorin] analysiert mittels eines Standardisierungsverfahrens verschiedene Regionen, vergleicht Schultypen, Laufbahnen der Lehrpersonen, Organisationsstrukturen, wirtschaftliche Hintergründe und konfessionelle Aspekte. Gleichsam diskutiert die Autorin das Verhältnis zwischen finanziellen Ressourcen sowie den schulischen Angeboten und beleuchtet die soziale Stellung der Lehrpersonen in der Gesellschaft. (DIPF/Orig.
Intramolecular vibronic dynamics in molecular solids: C60
Vibronic coupling in solid C60 has been investigated with a combination of resonant photoemission spectroscopy (RPES) and resonant inelastic x-ray scattering (RIXS). Excitation as a function of energy within the lowest unoccupied molecular orbital resonance yielded strong oscillations in intensity and dispersion in RPES, and a strong inelastic component in RIXS. Reconciling these two observations establishes that vibronic coupling in this core hole excitation leads to predominantly inelastic scattering and localization of the excited vibrations on the molecule on a femtosecond time scale. The coupling extends throughout the widths of the frontier valence bands.
A Possible Phase Transition in beta-pyrochlore Compounds
We investigate a lattice of interacting anharmonic oscillators by using a
mean field theory and exact diagonalization. We construct an effective
five-state hopping model with intersite repulsions as a model for
beta-pyrochlore AOs_2O_6(A=K, Rb or Cs). We obtain the first order phase
transition line from large to small oscillation amplitude phases as temperature
decreases. We also discuss the possibility of a phase with local electric
polarizations. Our theory can explain the origin of the mysterious first order
transition in KOs_2O_6.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Phonon Dynamics and Multipolar Isomorphic Transition in beta-pyrochlore KOs2O6
We investigate with a microscopic model anharmonic K-cation oscillation
observed by neutron experiments in beta-pyrochlore superconductor KOs2O6, which
also shows a mysterious first-order structural transition at Tp=7.5 K. We have
identified a set of microscopic model parameters that successfully reproduce
the observed temperature dependence and the superconducting transition
temperature. Considering changes in the parameters at Tp, we can explain
puzzling experimental results about electron-phonon coupling and neutron data.
Our analysis demonstrates that the first-order transition is multipolar
transition driven by the octupolar component of K-cation oscillations. The
octupole moment does not change the symmetry and is characteristic to
noncentrosymmetric K-cation potential.Comment: 5 pages, 4 figures, submitted to J. Phys. Soc. Jp
Screening, Coulomb pseudopotential, and superconductivity in alkali-doped Fullerenes
We study the static screening in a Hubbard-like model using quantum Monte
Carlo. We find that the random phase approximation is surprisingly accurate
almost up to the Mott transition. We argue that in alkali-doped Fullerenes the
Coulomb pseudopotential is not very much reduced by retardation
effects. Therefore efficient screening is important in reducing
sufficiently to allow for an electron-phonon driven superconductivity. In this
way the Fullerides differ from the conventional picture, where retardation
effects play a major role in reducing the electron-electron repulsion.Comment: 4 pages RevTeX with 2 eps figures, additional material available at
http://www.mpi-stuttgart.mpg.de/docs/ANDERSEN/fullerene
Resonant Lifetime of Core-Excited Organic Adsorbates from First Principles
We investigate by first-principles simulations the resonant electron-transfer
lifetime from the excited state of an organic adsorbate to a semiconductor
surface, namely isonicotinic acid on rutile TiO(110). The
molecule-substrate interaction is described using density functional theory,
while the effect of a truly semi-infinite substrate is taken into account by
Green's function techniques. Excitonic effects due to the presence of
core-excited atoms in the molecule are shown to be instrumental to understand
the electron-transfer times measured using the so-called core-hole-clock
technique. In particular, for the isonicotinic acid on TiO(110), we find
that the charge injection from the LUMO is quenched since this state lies
within the substrate band gap. We compute the resonant charge-transfer times
from LUMO+1 and LUMO+2, and systematically investigate the dependence of the
elastic lifetimes of these states on the alignment among adsorbate and
substrate states.Comment: 24 pages, 6 figures, to appear in Journal of Physical Chemistry
Investigation of the Spin Density Wave in NaxCoO2
Magnetic susceptibility, transport and heat capacity measurements of single
crystal NaxCoO2 (x=0.71) are reported. A transition to a spin density wave
(SDW) state at Tmag = 22 K is observable in all measurements, except chi(ac)
data in which a cusp is observed at 4 K and attributed to a low temperature
glassy phase. M(H) loops are hysteretic below 15 K. Both the SDW transition and
low temperature hysteresis are only visible along the c-axis. The system also
exhibits a substantial (~40%) positive magnetoresistance below this
temperature. Calculations of the electronic heat capacity gamma above and below
Tmag and the size of the jump in C indicate that the onset of the SDW brings
about the opening of gap and the removal of part of the Fermi surface. Reduced
in-plane electron-electron scattering counteracts the loss of carriers below
the transition and as a result we see a net reduction in resistivity below
Tmag. Sodium ordering transitions at higher temperatures are observable as
peaks in the heat capacity with a corresponding increase in resistivity.Comment: 14 pages, 6 figure
Design S-N curves for old Portuguese and French riveted bridges connection based on statistical analyses
Maintenance of ancient road and railway metallic bridges has become a major concern for governmental agencies in the past few decades. Indeed, since the construction of these structures, between the end of the 19th century and the beginning of the 20th century, traffic conditions have evolved, both in weight and frequency. In the purpose to assess the remaining life of old metallic bridges, some critical structural details have been identified and associated to S-N curves in order to be used in damage estimation (using Palmgren-Miner’s rule for cumulative damage, for example). These constructional details are described by design rules of several European and North American standards, such as the Eurocode 3, BS 5400 and AASHTO standards. The particularity of ancient bridges is that hot riveted assemblies, commonly used for their construction, are not represented in most construction standards. Further experiences on the matter by numerous research teams have suggested detail category C71 from the Eurocode 3 as appropriate. In this paper, experimental data from double shear assemblies manufactures from three different metallic ancient bridges is used to identify, through a statistical analysis, the S-N curves that best fit this constructional detail.
Portuguese and French puddled iron bridges were considered.The authors of this paper thank the National Society of French Railways and the SciTech - Science and
Technology for Competitive and Sustainable Industries, R&D project NORTE-01-0145-FEDER-000022 cofinanced by Programa Operacional Regional do Norte ("NORTE2020"), through Fundo Europeu de Desenvolvimento Regional (FEDER) for their collaboration and support during this research works. The authors also acknowledge the Portuguese Science Foundation (FCT) for the financial support through the post-doctoral grant SFRH/BPD/107825/2015
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