1,404 research outputs found
Nonequilibrium dynamics of spin-boson models from phase space methods
An accurate description of the nonequilibrium dynamics of systems with
coupled spin and bosonic degrees of freedom remains theoretically challenging,
especially for large system sizes and in higher than one dimension. Phase space
methods such as the Truncated Wigner Approximation (TWA) have the advantage of
being easily scalable and applicable to arbitrary dimensions. In this work we
adapt the TWA to generic spin-boson models by making use of recently developed
algorithms for discrete phase spaces [Schachenmayer, PRX 5, 011022 (2015)].
Furthermore we go beyond the standard TWA approximation by applying a scheme
based on the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy of equations
[Pucci, PRB 93, 174302 (2016)] to our coupled spin-boson model. This allows in
principle to study how systematically adding higher order corrections improves
the convergence of the method. To test various levels of approximation we study
an exactly solvable spin-boson model which is particularly relevant for
trapped-ion arrays. Using TWA and its BBGKY extension we accurately reproduce
the time evolution of a number of one- and two-point correlation functions in
several dimensions and for arbitrary number of bosonic modes.Comment: 10+5 pages, 5 figure
Non-equilibrium Quantum Spin Dynamics from 2PI Functional Integral Techniques in the Schwinger Boson Representation
We present a non-equilibrium quantum field theory approach to the
initial-state dynamics of spin models based on two-particle irreducible (2PI)
functional integral techniques. It employs a mapping of spins to Schwinger
bosons for arbitrary spin interactions and spin lengths. At next-to-leading
order (NLO) in an expansion in the number of field components, a wide range of
non-perturbative dynamical phenomena are shown to be captured, including
relaxation of magnetizations in a 3D long-range interacting system with
quenched disorder, different relaxation behaviour on both sides of a quantum
phase transition and the crossover from relaxation to arrest of dynamics in a
disordered spin chain previously shown to exhibit many-body-localization. Where
applicable, we employ alternative state-of-the-art techniques and find rather
good agreement with our 2PI NLO results. As our method can handle large system
sizes and converges relatively quickly to its thermodynamic limit, it opens the
possibility to study those phenomena in higher dimensions in regimes in which
no other efficient methods exist. Furthermore, the approach to classical
dynamics can be investigated as the spin length is increased
Aplicaciones y limitaciones del coeficiente K de eficacia de la adición de escoria de horno alto en el hormigón
Recently, a k-value for ground granulated blast-furnace slag or k-value has been added to the revision of the European standard EN 206-1:2000. The proposed values during the disscusion in the working groups were very different because in most of cases the compressive strength was the only characteristic considered; while only in few cases the concrete durability was taken into account when ground granulated blast-furnace slag is added directly to the mix.
Advantages and disadvantages of the k-values found in the literature are discussed in this paper. The final conclusion may be summarised suggesting a logical proposal of addressing to each country the choice of the k-value in function of the concrete application, environment and placing conditions selected according to their own experience.Recientemente se ha incorporado un valor del coeficiente de eficacia K para la escoria de horno alto en la norma europea EN 206-1:2000. Los valores propuestos en los grupos de trabajo eran muy diversos ya que en algunos casos sólo consideraban la resistencia mecánica para su determinación mientras que en otros se remarcaba la importancia de tener en cuenta, además, aspectos relativos a la durabilidad del hormigón con dicha adición.
En el presente artÃculo se discuten las ventajas y desventajas de proponer unos valores del coeficiente de eficacia K más o menos conservadores. La conclusión final se resume con la propuesta de una recomendación lógica que consiste en trasladar a cada paÃs la elección del coeficiente K para que pueda aplicarse a los hormigones empleados en su territorio; tales valores de K deberán ser seleccionados de acuerdo con la experiencia de cada uno de los paÃses
Short-term effects on soil properties and wheat production from secondary paper sludge application on two Mediterranean agricultural soils
This study was conducted under greenhouse conditions to evaluate the potential use of SPS as a fertilizer, amendment and/or liming
agent for wheat (Triticum aestivum L.). Two representative Mediterranean agricultural soils, a Cambic Arenosol (cmAR) and a Cromic
Cambisol (crCM) were used. Treatments included four sludge rates ranging from 0 to 40 g kg 1 (equivalent of 0, 38, 88 and
120 Mg ha 1). A significant increment in soil pH, organic carbon, N total, available P and exchangeable K were observed in both soils.
Sludge application significantly increased N and decreased Zn, Mn and Cu concentrations in wheat. Wheat grain yields were reduced by
33% and 37% when 120 Mg SPS ha 1 was applied to cmAR and crCM soils, respectively, due apparently to unavailability of Mg. However,
straw yields, with much lower Mg requirements, increased significantly with SPS rates. Secondary pulp mill sludge seems to be a
potential source of organic matter, N, P, K and a potential soil amendment liming agent for acid soils, when appropriate supplemental
fertilizer was provided. For grain crops grown in these soils, addition of Mg is required for proper nutrient balance
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