7,582 research outputs found
Kondo effect in transport through molecules adsorbed on metal surfaces: from Fano dips to Kondo peaks
The Kondo effect observed in recent STM experiments on transport through CoPc
and TBrPP-Co molecules adsorbed on Au(111) and Cu(111) surfaces, respectively,
is discussed within the framework of a simple model (Phys. Rev. Lett. {\bf 97},
076806 (2006)). It is shown that, in the Kondo regime and by varying the
adequate model parameters, it is possible to produce a crossover from a
conductance Kondo peak (CoPc) to a conductance Fano dip (TBrPP-Co). In the case
of TBrPP-Co/Cu(111) we show that the model reproduces the changes in the shape
of the Fano dip, the raising of the Kondo temperature and shifting to higher
energies of the dip minimum when the number of nearest neighbors molecules is
lowered. These features are in line with experimental observations indicating
that our simple model contains the essential physics underlying the transport
properties of such complex molecules.Comment: 4 pages, 3 figures, submitted to PR
Critical behavior at Mott-Anderson transition: a TMT-DMFT perspective
We present a detailed analysis of the critical behavior close to the
Mott-Anderson transition. Our findings are based on a combination of numerical
and analytical results obtained within the framework of Typical-Medium Theory
(TMT-DMFT) - the simplest extension of dynamical mean field theory (DMFT)
capable of incorporating Anderson localization effects. By making use of
previous scaling studies of Anderson impurity models close to the
metal-insulator transition, we solve this problem analytically and reveal the
dependence of the critical behavior on the particle-hole symmetry. Our main
result is that, for sufficiently strong disorder, the Mott-Anderson transition
is characterized by a precisely defined two-fluid behavior, in which only a
fraction of the electrons undergo a "site selective" Mott localization; the
rest become Anderson-localized quasiparticles.Comment: 4+ pages, 4 figures, v2: minor changes, accepted for publication in
Phys. Rev. Let
Quantum Analogy of Poisson Geometry, Related Dendriform Algebras and Rota-Baxter Operators
We will introduce an associative (or quantum) version of Poisson structure
tensors. This object is defined as an operator satisfying a "generalized"
Rota-Baxter identity of weight zero. Such operators are called generalized
Rota-Baxter operators. We will show that generalized Rota-Baxter operators are
characterized by a cocycle condition so that Poisson structures are so. By
analogy with twisted Poisson structures, we propose a new operator "twisted
Rota-Baxter operators" which is a natural generalization of generalized
Rota-Baxter operators. It is known that classical Rota-Baxter operators are
closely related with dendriform algebras. We will show that twisted Rota-Baxter
operators induce NS-algebras which is a twisted version of dendriform algebra.
The twisted Poisson condition is considered as a Maurer-Cartan equation up to
homotopy. We will show the twisted Rota-Baxter condition also is so. And we
will study a Poisson-geometric reason, how the twisted Rota-Baxter condition
arises.Comment: 18 pages. Final versio
Ecología de los “Lameiros” en una aldea del planalto de Miranda, Trás-os-Montes, Portugal
Los pastizales semi-naturales se encuentran en franca regresión en todo el territorio de la UE,
tanto por su abandono, como por las alteraciones en el uso del suelo. La desaparición de este tipo de
hábitats implica el declive de la flora y fauna asociadas, dependientes del mantenimiento de las labores
de manejo tradicionales de carácter extensivo. En el presente trabajo se estudió el efecto del cese de
algunas de estas prácticas sobre la estructura florística de estos pastizales semi-naturales. En una serie
de estos pastizales semi-naturales del altiplano mirandés, en el nordeste de Portugal, se observó que la
eliminación de las labores de siega a finales de primavera modifica la estructura florística de las parcelas,
acompañada de una disminución de la diversidad vegetal.
Palabras clave: diversidad florística, siega, pastoreo, pastos abandonados
- …