Heat Transport in Quantum Spin Chains: Stochastic Baths vs Quantum Trajectories

We discuss the problem of heat conduction in quantum spin chain models. To investigate this problem it is necessary to consider the finite open system connected to heat baths. We describe two different procedures to couple the system with the reservoirs: a model of stochastic heat baths and the quantum trajectories solution of the quantum master equation. The stochastic heat bath procedure operates on the pure wave function of the isolated system, so that it is locally and periodically collapsed to a quantum state consistent with a boundary nonequilibrium state. In contrast, the quantum trajectories procedure evaluates ensemble averages in terms of the reduced density matrix operator of the system. We apply these procedures to different models of quantum spin chains and numerically show their applicability to study the heat flow.Comment: 13 pages, 5 figures, submitted to European Physics Journal Special Topic

Magnetically Induced Thermal Rectification

We consider far from equilibrium heat transport in chaotic billiard chains with non-interacting charged particles in the presence of non-uniform transverse magnetic field. If half of the chain is placed in a strong magnetic field, or if the strength of the magnetic field has a large gradient along the chain, heat current is shown to be asymmetric with respect to exchange of the temperatures of the heat baths. Thermal rectification factor can be arbitrarily large for sufficiently small temperature of one of the baths.Comment: 4 pages, 5 figure

Dynamical mechanisms leading to equilibration in two-component gases

Demonstrating how microscopic dynamics cause large systems to approach thermal equilibrium remains an elusive, longstanding, and actively-pursued goal of statistical mechanics. We identify here a dynamical mechanism for thermalization in a general class of two-component dynamical Lorentz gases, and prove that each component, even when maintained in a non-equilibrium state itself, can drive the other to a thermal state with a well-defined effective temperature.Comment: 5 pages, 5 figure

El objetivo del trabajo es el proporcionar un marco de análisis general para entender el proceso de descentralización del Sector Público en España. Partiendo de un enfoque integrado, se estudiará tanto el modelo de financiación de las CC.AA. de régimen común como el caso foral, exponiendo sus similitudes y diferencias y viendo cómo ambos modelos han evolucionado en el tiempo. Además, se presenta como un sistema separado el del conjunto de recursos que financian las inversiones autonómicas, aspecto éste en que no existen diferencias entre CC.AA. comunes y forales. Tras la reforma del sistema de finales de 2001 se concluye que la incidencia de la Ley General de Estabilidad Presupuestaria, que se hará sentir de modo notable en el subsistema de financiación de las inversiones, tendrá consecuencias importantes en la forma en que las Haciendas autonómicas vayan a utilizar sus competencias fiscales, en una búsqueda previsible de recursos corrientes que compensen el hueco dejado por el endeudamiento.

Descentralización del Sector Público, asignación impositiva entre gobiernos

Federalismo fiscal y sistema foral. ¿Un concierto desafinado?

As a way of decentralizing Public Sector, the Foral System is a clear example of Asymmetrical Federalism, since Foral Finance can apply tax measures which the rest of Spanish Autonomous Communities cannot use. From the perspective of Fiscal Federalism, the Foral System gives great tax autonomy to Subcentral Finance, but as a result the Central Government has almost no tax devices. Nowadays, this system presents serious problems regarding to the contribution to national public goods financing and the cooperation to economic stabilization. In quantitative terms, analyzing financial relations between the Foral System of Basque Country and Central Government as a whole, the paid amount underestimates more than 2500 million of euros a year the contribution of Foral Finance for period 2002-2006Decentralization of Public Sector, Asymmetrical Federalism, Foral System of Basque Country.

La Seguridad Social y la Sanidad Pública

Este artículo pretende ofrecer una panorámica sintética y breve de la situación y principales transformaciones experimentadas en los últimos años por la Seguridad Social y la Sanidad Pública en España. Se describen sus características más notables y sus datos fundamentales y se enuncian los problemas más importantes desde las perspectivas de la financiación y del gasto

Entanglement Across a Transition to Quantum Chaos

We study the relation between entanglement and quantum chaos in one- and two-dimensional spin-1/2 lattice models, which exhibit mixing of the noninteracting eigenfunctions and transition from integrability to quantum chaos. Contrary to what occurs in a quantum phase transition, the onset of quantum chaos is not a property of the ground state but take place for any typical many-spin quantum state. We study bipartite and pairwise entanglement measures, namely the reduced Von Neumann entropy and the concurrence, and discuss quantum entanglement sharing. Our results suggest that the behavior of the entanglement is related to the mixing of the eigenfunctions rather than to the transition to chaos.Comment: 14 pages, 14 figure

Distribution of the least-squares estimators of a single Brownian trajectory diffusion coefficient

In this paper we study the distribution function $P(u_{\alpha})$ of the estimators $u_{\alpha} \sim T^{-1} \int^T_0 \, \omega(t) \, {\bf B}^2_{t} \, dt$, which optimise the least-squares fitting of the diffusion coefficient $D_f$ of a single $d$-dimensional Brownian trajectory ${\bf B}_{t}$. We pursue here the optimisation further by considering a family of weight functions of the form $\omega(t) = (t_0 + t)^{-\alpha}$, where $t_0$ is a time lag and $\alpha$ is an arbitrary real number, and seeking such values of $\alpha$ for which the estimators most efficiently filter out the fluctuations. We calculate $P(u_{\alpha})$ exactly for arbitrary $\alpha$ and arbitrary spatial dimension $d$, and show that only for $\alpha = 2$ the distribution $P(u_{\alpha})$ converges, as $\epsilon = t_0/T \to 0$, to the Dirac delta-function centered at the ensemble average value of the estimator. This allows us to conclude that only the estimators with $\alpha = 2$ possess an ergodic property, so that the ensemble averaged diffusion coefficient can be obtained with any necessary precision from a single trajectory data, but at the expense of a progressively higher experimental resolution. For any $\alpha \neq 2$ the distribution attains, as $\epsilon \to 0$, a certain limiting form with a finite variance, which signifies that such estimators are not ergodic.Comment: 27 pages, 5 figure