4,479 research outputs found
Strongly nonlinear thermovoltage and heat dissipation in interacting quantum dots
We investigate the nonlinear regime of charge and energy transport through
Coulomb-blockaded quantum dots. We discuss crossed effects that arise when
electrons move in response to thermal gradients (Seebeck effect) or energy
flows in reaction to voltage differences (Peltier effect). We find that the
differential thermoelectric conductance shows a characteristic Coulomb
butterfly structure due to charging effects. Importantly, we show that
experimentally observed thermovoltage zeros are caused by the activation of
Coulomb resonances at large thermal shifts. Furthermore, the power dissipation
asymmetry between the two attached electrodes can be manipulated with the
applied voltage, which has implications for the efficient design of nanoscale
coolers.Comment: 6 pages, 4 figure
Heat current through an artificial Kondo impurity beyond linear response
We investigate the heat current of a strongly interacting quantum dot in the
presence of a voltage bias in the Kondo regime. Using the slave- boson
mean-field theory, we discuss the behavior of the energy flow and the Joule
heating. We find that both contributions to the heat current dis- play
interesting symmetry properties under reversal of the applied dc bias. We show
that the symmetries arise from the behavior of the dot trans- mission function.
Importantly, the transmission probability is a function of both energy and
voltage. This allows us to analyze the heat current in the nonlinear regime of
transport. We observe that nonlinearities ap- pear already for voltages smaller
than the Kondo temperature. Finally, we suggest to use the contact and electric
symmetry coefficients as a way to measure pure energy currents.Comment: 9 pages, 2 figures, proceeding of the Low Temperature Physics
Conferenc
The Renormalization Group Method and Quantum Groups: the postman always rings twice
We review some of our recent results concerning the relationship between the
Real-Space Renormalization Group method and Quantum Groups. We show this
relation by applying real-space RG methods to study two quantum group invariant
Hamiltonians, that of the XXZ model and the Ising model in a transverse field
(ITF) defined in an open chain with appropriate boundary terms. The quantum
group symmetry is preserved under the RG transformation except for the
appearence of a quantum group anomalous term which vanishes in the classical
case. This is called {\em the quantum group anomaly}. We derive the new qRG
equations for the XXZ model and show that the RG-flow diagram obtained in this
fashion exhibits the correct line of critical points that the exact model has.
In the ITF model the qRG-flow equations coincide with the tensor product
decomposition of cyclic irreps of with .Comment: LATEX file, 21 pages, no figures. To appear in "From Field Theory to
Quantum Groups", World Scientific. Proceedings to honor J.Lukierski in his
60th birthda
Analytic Formulations of the Density Matrix Renormalization Group
We present two new analytic formulations of the Density Matrix
Renormalization Group Method. In these formulations we combine the block
renormalization group (BRG) procedure with Variational and Fokker-Planck
methods. The BRG method is used to reduce the lattice size while the latter are
used to construct approximate target states to compute the block density
matrix. We apply our DMRG methods to the Ising Model in a transverse field (ITF
model) and compute several of its critical properties which are then compared
with the old BRG results.Comment: LATEX file, 25 pages, 8 figures available upon reques
Fate of the spin-\frac{1}{2} Kondo effect in the presence of temperature gradients
We consider a strongly interacting quantum dot connected to two leads held at
quite different temperatures. Our aim is to study the behavior of the Kondo
effect in the presence of large thermal biases. We use three different
approaches, namely, a perturbation formalism based on the Kondo Hamiltonian, a
slave-boson mean-field theory for the Anderson model at large charging energies
and a truncated equation-of-motion approach beyond the Hartree-Fock
approximation. The two former formalisms yield a suppression of the Kondo peak
for thermal gradients above the Kondo temperature, showing a remarkably good
agreement despite their different ranges of validity. The third technique
allows us to analyze the full density of states within a wide range of
energies. Additionally, we have investigated the quantum transport properties
(electric current and thermocurrent) beyond linear response. In the
voltage-driven case, we reproduce the split differential conductance due to the
presence of different electrochemical potentials. In the temperature-driven
case, we observe a strongly nonlinear thermocurrent as a function of the
applied thermal gradient. Depending on the parameters, we can find nontrivial
zeros in the electric current for finite values of the temperature bias.
Importantly, these thermocurrent zeros yield direct access to the system's
characteristic energy scales (Kondo temperature and charging energy).Comment: 14 pages, 11 figures, revised versio
La adaptabilidad de la educación fÃsica en el medio natural en entornos urbanos
Realizamos un análisis de los antecedentes relacionados con la educación fÃsica en el medio natural. Considerando la importancia de esta, realizaremos una revisión legislativa y haremos una propuesta educativa para llevar la educación fÃsica en el medio natural a un centro situado en el centro de Madrid, en el que a priori, la puesta en práctica de la actividad fÃsica en el medio natural es más difÃcil.Grado en Educación Primari
Case study the poultry industry in Colombia
"As developing countries open their economies further to trade, their food industries are striving to raise safety and quality standards in order to compete in new markets. Such is the case with the Colombian poultry industry... Critical questions face the Colombian poultry industry: Is it ready to compete with foreign poultry producers on price, quality, and safety? Can industry efforts to produce better quality products assure an increased share of domestic and regional markets? This brief reviews the private initiatives undertaken by the Colombian poultry industry to assure food safety in light of these questions." from TextFood safety ,food security ,Public health ,
- …