Atomic motions in the αβ\alpha\beta-region of glass-forming polymers: Molecular versus Mode Coupling Theory approach

We present fully atomistic Molecular Dynamics simulation results on a main-chain polymer, 1,4-Polybutadiene, in the merging region of the $\alpha$- and $beta$-relaxations. A real space analysis reveals the occurrence of localized motions (``$\beta$-like'') in addition to the diffusive structural relaxation. A molecular approach provides a direct connection between the local conformational changes reflected in the atomic motions and the secondary relaxations in this polymer. Such local processes occur just in the time window where the $\beta$-process of the Mode Coupling Theory is expected. We show that the application of this theory is still possible, and yields an unusually large value of the exponent parameter. This result might originate from the competition between two mechanisms for dynamic arrest: intermolecular packing and intramolecular barriers for local conformational changes (``$\beta$-like'').Comment: 10 pages, 6 figure

The soft X-ray excess AGN RE J2248-511

We model the spectral energy distribution of the ultrasoft broad-line AGN RE J2248-511 with Comptonised accretion disc models. These are able to reproduce the steep optical and ultrasoft X-ray slopes, and the derived black hole mass is consistent with independent mass estimates. This AGN displays properties of both broad and narrow line Seyfert 1 galaxies, but we conclude that it is intrinsically a `normal' Seyfert 1 viewed at high inclination angle.Comment: 4 pages, 1 figure. MG10 Proceeding

Methyl group dynamics in a confined glass

We present a neutron scattering investigation on methyl group dynamics in glassy toluene confined in mesoporous silicates of different pore sizes. The experimental results have been analysed in terms of a barrier distribution model, such a distribution following from the structural disorder in the glassy state. Confinement results in a strong decreasing of the average rotational barrier in comparison to the bulk state. We have roughly separated the distribution for the confined state in a bulk-like and a surface-like contribution, corresponding to rotors at a distance from the pore wall respectively larger and smaller than the spatial range of the interactions which contribute to the rotational potential for the methyl groups. We have estimated a distance of 7 Amstrong as a lower limit of the interaction range, beyond the typical nearest-neighbour distance between centers-of-mass (4.7 Amstrong).Comment: 5 pages, 3 figures. To be published in European Physical Journal E Direct. Proceedings of the 2nd International Workshop on Dynamics in Confinemen

SIZE-WEIGHT RELATIONSHIPS OF THE BIGEYE TUNA (THUNNUS OBESUS) FROM NORTH ATLANTIC AREAS USING LINEAR AND NON-LINEAR FITS

Linear and non-linear fits of 1501 observations of size (FL cm) and live-weight (RW kg) of bigeye (Thunnus obesus) obtained in the NE Atlantic over recent years were tested. Results were compared among themselves and with those considered as a reference for this species-stock. The equations obtained from linear and non-linear fits (RW=5.29919E-05 * FL 2.8211264 and RW=6.0568-05 * FL 2.79379, respectively) showed a minor difference in predicting individual weight by size class. The non-linear fit parameters slightly increase the predicted mean weight of the whole sample in around +0.2% compared to the linear fit parameters suggesting that the type of fit would have a negligible impact on both the predictive individual mean weight and the whole sample mean weights. The comparison of results obtained with both types of fits versus the equation considered as a reference also showed minor differences in the estimated average individual weight from size. However, the average weight of the whole sample analysed would increase by over 4% in relation to that obtained when using the reference equation. A review of the literature on size-weight relationships for this species is also included suggesting a considerable diversity of results probably due to diverse factors that are discussed.En prens

Tests of mode coupling theory in a simple model for two-component miscible polymer blends

We present molecular dynamics simulations on the structural relaxation of a simple bead-spring model for polymer blends. The introduction of a different monomer size induces a large time scale separation for the dynamics of the two components. Simulation results for a large set of observables probing density correlations, Rouse modes, and orientations of bond and chain end-to-end vectors, are analyzed within the framework of the Mode Coupling Theory (MCT). An unusually large value of the exponent parameter is obtained. This feature suggests the possibility of an underlying higher-order MCT scenario for dynamic arrest.Comment: Revised version. Additional figures and citation

Risks perceptions and risk management instruments in the European Union: Do farmers have a clear idea of what they need?

This paper explores and analyzes farmers’ risk perceptions, risk management instruments’ demand and usage in five Member States (Hungary, Spain, the Netherlands, Germany and Poland). A survey completed by 1047 representative farmers of these EU Member Status collected information that allowed us to set apart two focus areas: the first looks at the declared importance of several sources of farms’ risk and income instability, and at the actual means that farmers pursue to manage and face them. The second area focuses on the demand for risk management instruments. The paper’s objective is to determine the factors that explain farmers’ responses in the first area, and based on those factors, analyse the demands for two instruments (insurance, and future & option markets). After carrying out basic descriptive statistic analyses, we perform factor analysis in order to establish the linkages between the perceptions and ranking of risks with the declared strategies to manage them. Logit models were fit to determine potential demand of insurance, and futures & options based on the three factors, and other variables like activity types and other controls, like nationality. Results from the factor analysis show that the perception of risk and actual use of risk management are very diverse. Logit models show that insurance is clearly an alternative instrument to diversification, but its demand is poorly explained by the other factors. Furthermore the demand for the use of futures and options is explained by the three factors, with the volatility factor, positively linked; market access /contractual risks; and diversification, negatively linked. In conclusion, policy makers should proceed with caution selecting the most adequate risk management instruments for farmers. It appears that the expected demand of risk management tools does not fit perfectly with the stated perception of risks

Nanodielectric mapping of a model polystyrene-poly(vinyl acetate) blend by electrostatic force microscopy

4 páginas, 4 figuras.-- PACS number(s): 61.41.+e, 62.23.-c.-- et al.We present a simple method to quantitatively image the dielectric permittivity of soft materials at nanoscale using electrostatic force microscopy (EFM) by means of the double pass method. The EFM experiments are based on the measurement of the frequency shifts of the oscillating tip biased at two different voltages. A numerical treatment based on the equivalent charge method allows extracting the values of the dielectric permittivity at each image point. This method can be applied with no restrictions of film thickness and tip radius. This method has been applied to image the morphology and the nanodielectric properties of a model polymer blend of polystyrene and poly(vinyl acetate).The financial support of Donostia International Physics Center (DIPC) is acknowledged. The authors would like to acknowledge the financial support provided by the Basque Country Government (Reference No. IT-436-07, Depto. Educación, Universidades e Investigación), the Spanish Ministry of Science and Innovation (Grant No. MAT 2007-63681), the European Community (SOFTCOMP program), and the PPF Rhéologie et plasticité des matériaux mous hétérogènes 2007–2010 Contract No. 20071656.Peer reviewe