834 research outputs found
Single Impurity Anderson Model with Coulomb Repulsion between Conduction Electrons on the Nearest-Neighbour Ligand Orbital
We study how the Kondo effect is affected by the Coulomb interaction between
conduction electrons on the basis of a simplified model. The single impurity
Anderson model is extended to include the Coulomb interaction on the
nearest-neighbour ligand orbital. The excitation spectra are calculated using
the numerical renormalization group method. The effective bandwidth on the
ligand orbital, , is defined to classify the state. This quantity
decreases as the Coulomb interaction increases. In the
region, the low energy properties are described by the Kondo state, where
is the hybridization width. As decreases in this region, the
Kondo temperature is enhanced, and its magnitude becomes comparable to
for . In the region, the local
singlet state between the electrons on the and ligand orbitals is formed.Comment: 5 pages, 3 figures, LaTeX, to be published in J. Phys. Soc. Jpn Vol.
67 No.
Wick's theorem for q-deformed boson operators
In this paper combinatorial aspects of normal ordering arbitrary words in the
creation and annihilation operators of the q-deformed boson are discussed. In
particular, it is shown how by introducing appropriate q-weights for the
associated ``Feynman diagrams'' the normally ordered form of a general
expression in the creation and annihilation operators can be written as a sum
over all q-weighted Feynman diagrams, representing Wick's theorem in the
present context.Comment: 9 page
The Kondo lattice model with correlated conduction electrons
We investigate a Kondo lattice model with correlated conduction electrons.
Within dynamical mean-field theory the model maps onto an impurity model where
the host has to be determined self-consistently. This impurity model can be
derived from an Anderson-Hubbard model both by equating the low-energy
excitations of the impurity and by a canonical transformation. On the level of
dynamical mean-field theory this establishes the connection of the two lattice
models. The impurity model is studied numerically by an extension of the
non-crossing approximation to a two-orbital impurity. We find that with
decreasing temperature the conduction electrons first form quasiparticles
unaffected by the presence of the lattice of localized spins. Then, reducing
the temperature further, the particle-hole symmetric model turns into an
insulator. The quasiparticle peak in the one-particle spectral density splits
and a gap opens. The size of the gap increases when the correlations of the
conduction electrons become stronger. These findings are similar to the
behavior of the Anderson-Hubbard model within dynamical mean-field theory and
are obtained with much less numerical effort.Comment: 7 pages RevTeX with 3 ps figures, accepted by PR
Magnetic impurity coupled to interacting conduction electrons
We consider a magnetic impurity which interacts by hybridization with a
system of weakly correlated electrons and determine the energy of the ground
state by means of an 1/N_f expansion. The correlations among the conduction
electrons are described by a Hubbard Hamiltonian and are treated to lowest
order in the interaction strength. We find that their effect on the Kondo
temperature, T_K, in the Kondo limit is twofold: First, the position of the
impurity level is shifted due to the reduction of charge fluctuations, which
reduces T_K. Secondly, the bare Kondo exchange coupling is enhanced as spin
fluctuations are enlarged. In total, T_K increases. Both corrections require
intermediate states beyond the standard Varma-Yafet ansatz. This shows that the
Hubbard interaction does not just provide quasiparticles, which hybridize with
the impurity, but also renormalizes the Kondo coupling.Comment: ReVTeX 19 pages, 3 uuenconded postscript figure
Ribbed tiled vaulting: Innovation through two design-build workshops
Traditional tile vaults are typically constructed springing off from walls or straight arches built from support element to support element on falsework. From these, the vault's surface can be built in space with minimal or no guidework. Built on previous research and focusing on continuous surface expression and fully representing three-dimensional equilibrium surfaces in compression, this research explores the design potential of three-dimensional networks of structural ribs, made possible by new funicular form-finding approaches. This new structural typology for tile vaults was investigated and tested through two intensive, design-build workshops in Australia, the first at the University of Technology, Sydney (UTS) in October 2012, and the second at Monash Art Design & Architecture (MADA), in May 2013
On Linear Differential Equations Involving a Para-Grassmann Variable
As a first step towards a theory of differential equations involving para-Grassmann variables the linear equations with constant coefficients are discussed and solutions for equations of low order are given explicitly. A connection to n-generalized Fibonacci numbers is established. Several other classes of differential equations (systems of first order, equations with variable coefficients, nonlinear equations) are also considered and the analogies or differences to the usual (''bosonic'') differential equations discussed
Classification and examples of next generation machine elements = Klassifizierung und Beispiele der nächsten Generation von Maschinenelementen
Periodic Anderson model with correlated conduction electrons
We investigate a periodic Anderson model with interacting conduction
electrons which are described by a Hubbard-type interaction of strength U_c.
Within dynamical mean-field theory the total Hamiltonian is mapped onto an
impurity model, which is solved by an extended non-crossing approximation. We
consider the particle-hole symmetric case at half-filling. Similar to the case
U_c=0, the low-energy behavior of the conduction electrons at high temperatures
is essentially unaffected by the f-electrons and for small U_c a quasiparticle
peak corresponding to the Hubbard model evolves first. These quasiparticles
screen the f-moments when the temperature is reduced further, and the system
turns into an insulator with a tiny gap and flat bands. The formation of the
quasiparticle peak is impeded by increasing either U_c or the c-f
hybridization. Nevertheless almost dispersionless bands emerge at low
temperature with an increased gap, even in the case of initially insulating
host electrons. The size of the gap in the one-particle spectral density at low
temperatures provides an estimate for the low-energy scale and increases as U_c
increases.Comment: 11 pages RevTeX with 13 ps figures, accepted by PR
In‐situ characterization of deposits in ceramic hollow fiber membranes by compressed sensing RARE‐MRI
Ultrafiltration with ceramic hollow fiber membranes was investigated by compressed sensing rapid acquisition relaxation enhancement (CS-RARE) magnetic resonance imaging (MRI) to characterize filtration mechanisms. Sodium alginate was used as a model substance for extracellular polymeric substances. Dependent on the concentration of divalent ions like Ca21 in an aqueous alginate solution, the characteristics of the filtration change from concentration polarization to a gel layer. The fouling inside the membrane lumen could be measured by MRI with a CS-RARE pulse sequence. Contrast agents have been used to get an appropriate contrast between deposit and feed. The lumen was analyzed quantitatively by exploring the membrane’s radial symmetry, and the resulting intensity could be modeled. Thus, different fouling mechanisms could be distinguished. CS-RARE-MRI was proven to be an appropriate in situ tool to quantitatively characterize the deposit formation during in-out filtration processes. The results were underlined by flux interruption experiments and length dependent studies, which make it possible to differentiate between gel layer or cake filtration and concentration polarization filtration processes
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