Aproximación lineal por tramos a comportamientos no lineales: estimación de señales de nivel de crecimiento

En este trabajo se propone una señal del nivel y del crecimiento tendencial de una variable económica, cuando ésta ha pasado por un período temporal específico en que determinados aconteeimientos especiales han truncado su tendencia. Para ello se analizan las consecuencias de emplear modelos univariantes no lineales, así como análisis de intervención. En el supuesto de ruptura estocástica, una alternativa a modelos no lineales se obtiene con modelos lineales para cada tramo, modificando así las condiciones iniciales del esquema en diferencias finitas estocásticas que regula la generación del proceso a partir del punto de ruptura. EI procedimiento propuesto, que precisa dispaner de un cierto número de observaciones tras el momento de ruptura, permite obtener la evolución subyacente de una serie en el entorno del período temporal específico evitando los inconveníentes de los procedimientos anteriores. Con el objeto de desarrollar esta idea, el trabajo analiza la seríe de importaciones no energóticas.Publicad

Ring exchange, the Bose metal, and bosonization in two dimensions

Motivated by the high-T_c cuprates, we consider a model of bosonic Cooper pairs moving on a square lattice via ring exchange. We show that this model offers a natural middle ground between a conventional antiferromagnetic Mott insulator and the fully deconfined fractionalized phase which underlies the spin-charge separation scenario for high-T_c superconductivity. We show that such ring models sustain a stable critical phase in two dimensions, the *Bose metal*. The Bose metal is a compressible state, with gapless but uncondensed boson and ``vortex'' excitations, power-law superconducting and charge-ordering correlations, and broad spectral functions. We characterize the Bose metal with the aid of an exact plaquette duality transformation, which motivates a universal low energy description of the Bose metal. This description is in terms of a pair of dual bosonic phase fields, and is a direct analog of the well-known one-dimensional bosonization approach. We verify the validity of the low energy description by numerical simulations of the ring model in its exact dual form. The relevance to the high-T_c superconductors and a variety of extensions to other systems are discussed, including the bosonization of a two dimensional fermionic ring model

A Two-dimensional Superconductor in a Tilted Magnetic Field - new states with finite Cooper-pair momentum

Varying the angle Theta between applied field and the conducting planes of a layered superconductor in a small interval close to the plane-parallel field direction, a large number of superconducting states with unusual properties may be produced. For these states, the pair breaking effect of the magnetic field affects both the orbital and the spin degree of freedom. This leads to pair wave functions with finite momentum, which are labeled by Landau quantum numbers 0<n<\infty. The stable order parameter structure and magnetic field distribution for these states is found by minimizing the quasiclassical free energy near H_{c2} including nonlinear terms. One finds states with coexisting line-like and point-like order parameter zeros and states with coexisting vortices and antivortices. The magnetic response may be diamagnetic or paramagnetic depending on the position within the unit cell. The structure of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states at Theta=0 is reconsidered. The transition n->\infty of the paramagnetic vortex states to the FFLO-limit is analyzed and the physical reason for the occupation of higher Landau levels is pointed out.Comment: 24 pages, 11 figure

Consideraciones sobre las fuentes estadísticas macroeconómicas en España: innovaciones recientes y procedimientos para el análisis de los datos

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Métodos cuantitativos para el análisis de la balanza comercial española

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Construction of a composite indicator for predicting inflation in Spain

Centro de Informacion y Documentacion Cientifica (CINDOC). C/Joaquin Costa, 22. 28002 Madrid. SPAIN / CINDOC - Centro de Informaciòn y Documentaciòn CientìficaSIGLEESSpai

Elaboracion de un indice sintetico para predecir la inflacion en EspaNa

Centro de Informacion y Documentacion Cientifica (CINDOC). C/Joaquin Costa, 22. 28002 Madrid. SPAIN / CINDOC - Centro de Informaciòn y Documentaciòn CientìficaSIGLEESSpai