Complementarity and coordination of macroeconomic and financial policies to tackle internal and external imbalances.

Policy responses to the global crisis have helped stabilise the economies and contained the threat of financial instability. But growing sovereign indebtedness, a weakened financial system and uneven economic growth prospects at the global level pose risks of new imbalances and vulnerabilities. To limit those risks it is essential to address both macroeconomic and fi nancial market failures. Important changes in financial market regulation and banking supervision are already being introduced. In the macroeconomic area, an effort is being made to strengthen the coordination of economic policies in the context of the G20. New institutions, such as macroprudential authorities, are being set up in many countries to monitor and contrast the emergence of systemic risk. There are, however, several areas where policy frameworks need to be further strengthened. At the international level we need surplus and deficit countries to rebalance global demand and ensure a return to sustained global growth, without conflicting policy actions leading to potential instability. Effective acroprudential policies require a clear definition of responsibilities, and need to be consistent with the conduct of monetary policies. In Europe, more effective economic governance is needed to proceed on the route towards greater economic integration and to fortify the euro, including tighter rules on fiscal policies, a broader surveillance over macroeconomic imbalances and an effective mechanism for crisis management.

Hedge funds and financial stability.

Much has been achieved to date in containing the financial stability risks that hedge funds could pose, while avoiding unnecessary restrictions that would distort market forces and prevent hedge funds from continuing to play their role in today’s markets. But in a continuously changing financial market environment, sustained attention is required by market participants and supervisory authorities to assess ongoing market developments and address any weaknesses in counterparty risk management practices and market discipline at an early stage. Dealers in the aggregate appear to be fairly well protected at present against the direct counterparty credit risks from hedge fund defaults, but the robustness of margining practices to a major deterioration in market conditions and liquidity needs to be examined further. The broader financial effects, via a deterioration in market liquidity and prices, from a market shock affecting hedge funds and other leveraged institutions remain difficult to gauge. This highlights the importance of improved stress testing and scenario analysis practices. A critical challenge in this regard will be to ensure improved assessment and mitigation of tail risks by all key participants in the system, so that unrealistic expectations that risks can be transferred to others do not lead to moral hazard and wider risks to the financial system.

Diffusion under confinement: hydrodynamic finite-size effects in simulation

We investigate finite-size effects on diffusion in confined fluids using molecular dynamics simulations and hydrodynamic calculations. Specifically, we consider a Lennard-Jones fluid in slit pores without slip at the interface and show that the use of periodic boundary conditions in the directions along the surfaces results in dramatic finite-size effects, in addition to that of the physically relevant confining length. As in the simulation of bulk fluids, these effects arise from spurious hydrodynamic interactions between periodic images and from the constraint of total momentum conservation. We derive analytical expressions for the correction to the diffusion coefficient in the limits of both elongated and flat systems, which are in excellent agreement with the molecular simulation results except for the narrowest pores, where the discreteness of the fluid particles starts to play a role. The present work implies that the diffusion coefficients for wide nanopores computed using elongated boxes suffer from finite-size artifacts which had not been previously appreciated. In addition, our analytical expression provides the correction to be applied to the simulation results for finite (possibly small) systems. It applies not only to molecular but also to all mesoscopic hydrodynamic simulations, including Lattice-Boltzmann, Multi-Particle Collision Dynamics or Dissipative Particle Dynamics, which are often used to investigate confined soft matter involving colloidal particles and polymers.Comment: 3 figures and 1 in the supplemental sectio

Transport anb Structural Properties of Aqueous Solutions of Organic Solvents.

Molecular Dynamics simulation technique has been used in this work to obtain equilibrium as well as transport properties of different aqueoussolutions. The peculiar behavior observed in pure water and its mixtures with other substances at different thermodynamic conditions, and the knowledge and understanding of the properties of these systems are the motivations of this work. We have made a direct connection between the local tetrahedral structure of water, created by the presence of hydrogen bonds, and the selfdiffusion coefficient at liquid-like densities. We have found some indications ofan order transition in the three dimensional structure of water at certain conditions of temperature (above 345 K) and densities (between 0.9 to 1.3 g/cm3).The strong hydrogen bond interaction observed in pure water plays a central role in aqueous solutions. We have studied several properties of aqueous mixtures of associating fluids, such as methanol, ethanol, acetone and dimethyl sulfoxide (DMSO). We observe that the presence of each type of solute perturb the local structure of water in a different manner, and this perturbation gives rise to the formation of chain-like structures with long-range correlation of hydrogen-bonded water molecules that is responsible for thehigh viscosity of the mixture. We have also computed the thermal conductivity of the different mixtures, obtaining very good agreement between our simulation results and the available experimental data.One of the properties that we have analyzed for these binary mixtures is the Ludwing-Soret effect, which is a macroscopic cross effect where a diffusion process is caused by the presence of a temperature gradient in a multicomponent system. This effect can be quantified through the thermal diffusion factor, which is usually positive for most solutions. However, in thecase associating fluids, the value of this coefficient may have a change in its sign at some particular composition. Our simulations reproduce even quantitatively the change in the sign of the Soret coefficient experimentally observed, and to the best of our knowledge, this is the first time that such achievement is reached for a mixture of molecular fluid employing molecular dynamic simulations. Additionally, we have devised a simple lattice model to support the hypothesis that the change in the sign of the Soret coefficient will appear in all cases in which the energy of the crossed interaction betweendifferent species is more negative than the interaction energies between pure components.The final part of this work is devoted to the computation of structural, transport and dielectric properties of benzene in water at supercritical conditions. We have employed a new Anisotropic United Atom (AUA) model of benzene that reproduces the quadrupolar moment of this molecule. We have computed different properties like self-diffusion coefficient and Maxwell-Stefancoefficients, and shear viscosity for the mixture at supercritical conditions. A strong density and composition dependence of the properties is observed.Experimental data shows the presence of aggregates between water and benzene molecules. This fact suggests the presence of some degree ofhydrogen bonding between these two molecules. Our simulations reproduce this behavior and we observed the formation of hydrogen bonds between the two species. In addition, we observe that these bonds are longer lived than the corresponding hydrogen bonds between water molecules. Similarly, we obtain an important reduction of the dielectric constant of the mixture with the increment of the amount of benzene molecules, at least at medium and highdensities.DE LA TESISLa simulación Dinámica Molecular ha sido la técnica empleada en este trabajo para la obtención de propiedades de transporte y de equilibrio de sistemas reales. El comportamiento peculiar observado por el agua a diferentes condiciones termodinámicas y en presencia de otras substancias, el conocimiento y entendimiento de las propiedades de este tipo de sistemas son una de las principales motivaciones de este trabajo. Adicionalmente, se ha realizado un extenso estudio de las relaciones intrínsecas existentes entre la estructura local del sistema, desde un punto de vista microscópico, y laspropiedades dinámicas de transporte, tanto en el caso del agua pura como en el caso de mezclas acuosas de solventes orgánicos.En primer lugar, se ha realizado un análisis de la relación existente entre la estructura local de puentes de hidrógeno presente en el agua pura en condiciones sub y supercríticas, para ello se realizó una comparación entre cuatro diferentes modelos comúnmente utilizados en la literatura. Los resultados obtenidos nos han permitido relacionar de una manera directa la estructura tetraédrica local de las moléculas de agua, creada por la presencia de los puentes de hidrógeno, y el valor que alcanza el coeficiente de autodifusión en condiciones de densidad de líquido.La fuerte interacción debida a los puentes de hidrógeno presente en las moléculas de agua juega un papel central en el comportamiento de soluciones acuosas. En este trabajo se han estudiado mezclas acuosas de fluidos asociantes, como metanol, etanol, acetona y sulfóxido de dimetilo. El análisis de los resultados de simulación muestra que la presencia dediferentes tipos de soluto perturban de una manera diferente la estructura tetraédrica local del agua. Esta pérdida en la estructura tetraédrica del agua origina un incremento en la rigidez de las moléculas de agua, con respecto aotras, más simétricas y menos rígidas, presentes en el agua pura. Como consecuencia, se ha observado un incremento del tiempo de vida de lospuentes de hidrógeno presentes en la mezcla, hecho que justifica el aumento observado en la viscosidad de la mezcla. Por otro lado, se han realizado simulaciones para calcular la conductividad térmica de la mezcla obteniendoresultados que presentan un acuerdo excelente con los datos experimentales.El efecto Ludwig-Soret es otra de las propiedades calculadas para las mezclas estudiadas. Este efecto cruzado macroscópico consiste en unproceso difusivo causado por la presencia de un gradiente de temperatura en sistemas multicomponentes. Este efecto es cuantificado por medio del factor de difusión térmica, el cual suele ser siempre positivo en la mayor parte delas soluciones. Sin embargo, para el caso de fluidos asociantes, el valor de este coeficiente puede cambiar de signo a una concentración particular. Se ha calculado el coeficiente de Soret para soluciones acuosas de loscompuestos orgánicos antes mencionados. Nuestras simulaciones reproducen el cambio de signo observado en estos sistemas obteniendo unacuerdo cuantitativo excelente con los datos experimentales. Adicionalmente, se ha podido observar que el cambio de signo en de coeficiente aparece siempre que la energía de interacción cruzada, entre las moléculas de diferentes especies, es mas negativa que las energías de interacción entre los componentes puros.Finalmente, se han estudiado las propiedades estructurales, dieléctricas y de transporte de mezclas acuosas de benceno en condiciones supercríticas. En nuestras simulaciones se ha utilizado un nuevo modelo anisotrópico deátomo unificado. Entre las propiedades de la mezcla calculadas se encuentran los coeficientes de auto difusión, difusión de Maxwell-Stefan ycoeficiente de viscosidad en condiciones supercríticas. Adicionalmente, datos experimentales recientes han mostrado la presencia de ciertos grupos de moléculas de benceno y agua formando grupos de agregados. Nuestras simulaciones reproducen la formación de puentes de hidrógeno entre las dos especies con tiempos de vida media superiores a los encontrados entre las moléculas de agua

Thermodynamically consistent force field for coarse-grained modeling of aqueous electrolyte solution

International audienceWe propose a thermodynamically consistent methodology to parameterizeinteractions between charged particles inside the dissipative particle dynamics (DPD) formalism.We have used experimental data of osmotic pressure as a function of the salinity in order tooptimize the required interaction parameters. Our results for NaCl aqueous solution show that theuse of mean osmotic coefficient, as well as the activity coefficient of individual ions, allow tounambiguously determine the Na+-water, cr-water and Na+-cr DPD repulsion parameters. Wepropose a simple linear relationship between the hydration free energies· of ions and the ionwaterrepulsion parameters that allows the parameterization of the complete series of halide andalkaline ions. Two different strategies have been used to derive the anion-cation interactionparameters for halide and alkaline but NaCl. In the first one, parameters are obtained for ail pairsof ions based on the numericàl optimization of the anion-cation repulsion parameter with respectto experimental osmotic pressure data. The mean absolute relative deviation between simuJatedand experimental data is then smaller than 4%. Second, we propose a simple, purely predictiveapproach to obtain the anion-cation interaction parameters based on the free energy difference ofhydration energies of anions and cations in the spirit of the law of matching water affinities(LMW A). This approach predict sait properties with a mean absolute relative deviation of theorder of 13 %, and with an accuracy better than 6% if small ions (Lt and F) are removed

2D Coordination Polymers Based on Isoquinoline-5-Carboxylate and Cu(II)

By combining isoquinoline-5-carboxilic acid with Cu(II) ions under several different conditions, we were able to obtain novel metallorganic materials, among which two 2D coordination polymers, CP 1 and CP 2 which were also characterized by SC-XRD. Ratio of solvents (EtOH : DMF) in the mixture employed during their synthesis has a marked effect in selecting the formation of one species or the other, which basically differ in the coordination at the Cu(II) center due to k1/k2 denticity of the carboxylate ligands.Two 2D coordination polymers which exclusively form depending on DMF : EtOH solvent mixture, fully characterized by SC-XRD, are among the novel materials formed by the combination of Cu(II) with isoquinoline-5-carboxylate ligand described here.imag