300 research outputs found
Density and Stability in Ultracold Dilute Boson-Fermion Mixtures
We analyze in detail recent experiments on ultracold dilute 87Rb-40K mixtures
in Hamburg and in Florence within a mean-field theory. To this end we determine
how the stationary bosonic and fermionic density profiles in this mixture
depend in the Thomas-Fermi limit on the respective particle numbers.
Furthermore, we investigate how the observed stability of the Bose-Fermi
mixture with respect to collapse is crucially related to the value of the
interspecies s-wave scattering length.Comment: Author Information under
http://www.theo-phys.uni-essen.de/tp/ags/pelster_dir
Charge transfer crystallites as molecular electrical dopants
Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their FermiâDirac occupation that yields mobile charge carriers and, therefore, the co-crystallitesârather than individual acceptor moleculesâshould be regarded as the dopants in such systems
Measurement of the quasi-elastic axial vector mass in neutrino-oxygen interactions
The weak nucleon axial-vector form factor for quasi-elastic interactions is
determined using neutrino interaction data from the K2K Scintillating Fiber
detector in the neutrino beam at KEK. More than 12,000 events are analyzed, of
which half are charged-current quasi-elastic interactions nu-mu n to mu- p
occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for
oxygen and assume the form factor is approximately a dipole with one parameter,
the axial vector mass M_A, and fit to the shape of the distribution of the
square of the momentum transfer from the nucleon to the nucleus. Our best fit
result for M_A = 1.20 \pm 0.12 GeV. Furthermore, this analysis includes updated
vector form factors from recent electron scattering experiments and a
discussion of the effects of the nucleon momentum on the shape of the fitted
distributions.Comment: 14 pages, 10 figures, 6 table
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