453 research outputs found
Haben Öko-Käufer eine Präferenz für funktionelle Lebensmittel? - Ein Discrete-Choice-Experiment für Joghurt -
Health motives are an important driver of food choice. Triggering health motives in food choice is exactly the reason why health claims have been developed for the communication of functional food. Thus, it is of major interest how organic food consumers react to health claims on conventional products. For this purpose a German-wide Discrete-Choice-Experiment war carried out. The results show that occasional organic buyers were significantly more likely to choose products with a claim. It can be concluded that health claims can be beneficial in marketing when addressing this consumer segment
Triangular Mott-Hubbard Insulator Phases of Sn/Si(111) and Sn/Ge(111) Surfaces
The ground state of Sn/Si(111) and Sn/Ge(111) surface -phases is
reexamined theoretically, based on calculations where correlations
are approximately included through the orbital dependence of the Coulomb
interaction (in the local density + Hubbard U approximation). The effect of
correlations is to destabilize the vertical buckling in Sn/Ge(111) and to make
the surface magnetic, with a metal-insulator transition for both systems. This
signals the onset of a stable narrow gap Mott-Hubbard insulating state, in
agreement with very recent experiments. Antiferromagnetic exchange is proposed
to be responsible for the observed -point photoemission intensity, as
well asfor the partial metallization observed above above 60 K in Sn/Si(111).
Extrinsic metallization of Sn/Si(111) by, alkali doping, could lead to
a novel 2D triangular superconducting state of this and similar surfaces.Comment: 4 pages, 4 figure
Direct evaluation of the isotope effect within the framework of density functional theory for superconductors
Within recent developments of density functional theory, its numerical implementation and of the superconducting density functional theory is nowadays possible to predict the superconducting critical temperature, Tc, with sufficient accuracy to anticipate the experimental verification. In this paper we present an analytical derivation of the isotope coefficient within the superconducting density functional theory. We calculate the partial derivative of Tc with respect to atomic masses. We verified the final expression by means of numerical calculations of isotope coefficient in monatomic superconductors (Pb) as well as polyatomic superconductors (CaC6). The results confirm the validity of the analytical derivation with respect to the finite difference methods, with considerable improvement in terms of computational time and calculation accuracy. Once the critical temperature is calculated (at the reference mass(es)), various isotope exponents can be simply obtained in the same run. In addition, we provide the expression of interesting quantities like partial derivatives of the deformation potential, phonon frequencies and eigenvectors with respect to atomic masses, which can be useful for other derivations and applications
Electronic, dynamical and superconducting properties of CaBeSi
We report first-principles calculations on the normal and superconducting
state of CaBe(x)Si(2-x) (x=1), in the framework of density functional theory
for superconductors (SCDFT). CaBeSi is isostructural and isoelectronic to MgB2
and this makes possible a direct comparison of the electronic and vibrational
properties and the electron-phonon interaction of the two materials. Despite
the many similarities with MgB2 (e.g. sigma bands at the Fermi level and a
larger Fermi surface nesting), according to our calculations CaBeSi has a very
low critical temperature (Tc ~ 0.4 K, consistent with the experiment). CaBeSi
exhibits a complex gap structure, with three gaps at Fermi level: besides the
two sigma and pi gaps, present also in MgB2, the appearance of a third gap is
related to the anisotropy of the Coulomb repulsion, acting in different way on
the bonding and antibonding electronic pi states.Comment: 6 pages, 5 figure
Elemental Phosphorus: structural and superconducting phase diagram under pressure
Pressure-induced superconductivity and structural phase transitions in
phosphorous (P) are studied by resistivity measurements under pressures up to
170 GPa and fully crystal structure and superconductivity
calculations up to 350 GPa. Two distinct superconducting transition temperature
(T) vs. pressure () trends at low pressure have been reported more
than 30 years ago, and for the first time we are able to reproduce them and
devise a consistent explanation founded on thermodynamically metastable phases
of black-phosphorous. Our experimental and theoretical results form a single,
consistent picture which not only provides a clear understanding of elemental P
under pressure but also sheds light on the long-standing and unsolved
superconductivity trend. Moreover, at higher pressures we predict a
similar scenario of multiple metastable structures which coexist beyond their
thermodynamical stability range. Metastable phases of P experimentally
accessible at pressures above 240 GPa should exhibit T's as high as 15 K,
i.e. three times larger than the predicted value for the ground-state crystal
structure. We observe that all the metastable structures systematically exhibit
larger transition temperatures than the ground-state ones, indicating that the
exploration of metastable phases represents a promising route to design
materials with improved superconducting properties.Comment: 14 pages, 4 figure
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