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 $SU_q(2)$ with $q^4=1$.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 física en el medio natural en entornos urbanos

Realizamos un análisis de los antecedentes relacionados con la educación física en el medio natural. Considerando la importancia de esta, realizaremos una revisión legislativa y haremos una propuesta educativa para llevar la educación física 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 física en el medio natural es más difícil.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 ,