Short-Time Elasticity of Polymer Melts: Tobolsky Conjecture and Heterogeneous Local Stiffness

An extended Molecular-Dynamics study of the short-time "glassy" elasticity exhibited by a polymer melt of linear fully-flexible chains above the glass transition is presented. The focus is on the infinite-frequency shear modulus $G_\infty$ manifested in the picosecond time scale and the relaxed plateau $G_p$ reached at later times and terminated by the structural relaxation. The local stiffness of the interactions with the first neighbours of each monomer exhibits marked distribution with average value given by $G_\infty$. In particular, the neighbourhood of the end monomers of each chain are softer than the inner monomers, so that $G_\infty$ increases with the chain length. $G_p$ is not affected by the chain length and is largely set by the non-bonding interactions, thus confirming for polymer melts the conjecture formulated by Tobolsky for glassy polymers.Comment: 18 pages, 6 figure

Cage rattling does not correlate with the local geometry in molecular liquids

Molecular-dynamics simulations of a liquid of short linear molecules have been performed to investigate the correlation between the particle dynamics in the cage of the neighbors and the local geometry. The latter is characterized in terms of the size and the asphericity of the Voronoi polyhedra. The correlation is found to be poor. In particular, in spite of the different Voronoi volume around the end and the inner monomers of a molecule, all the monomers exhibit coinciding displacement distribution when they are caged (as well as at longer times during the structural relaxation). It is concluded that the fast dynamics during the cage trapping is a non-local collective process involving monomers beyond the nearest neighbours.Comment: 15 pages, 6 figure

Understanding Effective Supervision and the Relationship between Supervision Effectiveness and Education

Supervision is a function at the core of the social work profession. The goal of social work supervision is to provide practitioners with the needed support, oversight, and education so that practitioners can ultimately render efficient and effective services. Despite positive outcomes, little is empirically known about effective supervision and its relationship with educational background. Recognizing the lack of empirical evidence regarding effective supervision practices within the social work profession, this study examined the delivery of supervision within a large Pennsylvania human service organization delivering fee for service case management. Using the MCSS-26©, supervisees rated their experiences of supervision; then with SPSS statistical analysis, an overall supervision score was derived. While additional study is warranted, results from this study have wide ranging implications for supervisory practices within the social work curriculum and practice standards, as well as considerations for agency leaders responsible for the implementation of supervision

Does urbanization matter in the expenditure-happiness nexus?

This study aims to improve the regional well-being literature on the so-called “reversal issue” of the expenditure-happiness nexus, accounting for two main sources of heterogeneity: degree of urbanization and individual spending habits. Moreover, we investigate the role of happiness across the entire expenditure distribution using a quantile modelling approach. The results show that satisfaction has a positive, significant and non-linear effect on total expenditure across different urbanization categories. To better investigate the multidimensional nature of happiness, analysis of the nexus is expounded to different satisfaction domains and related spending aggregates offering a comprehensive and complex behavioural profile of individuals

Poverty-happiness nexus: Does the use of regional poverty lines matter?

This analysis aims to provide a comprehensive representation of the role of regional disparities in the nexus between poverty and subjective well-being, by adding the territorial dimension to the definition of poverty conditions. We investigate the nexus using regional poverty lines, including different poverty measures and considering different life domains. The analysis focuses on Italy because of its strong regional socio-economic disparities. Results show that the relevance of being poor on the well-being of citizens is in general higher and significant; the intensity and severity of poverty also change for different life domains. Findings are fundamental in designing local policies against poverty

Cage effect in supercooled molecular liquids: Local anisotropies and collective solid-like response

Both local geometry and collective extended excitations drive the moves of a particle in the cage of its neighbours in dense liquids. The strength of their influence is investigated by the molecular dynamics simulations of a supercooled liquid of fully flexible trimers with semirigid or rigid bonds. The rattling in the cage is investigated on different length scales. First, the rattling anisotropy due to local order is characterized by two order parameters sensing the monomers succeeding or failing to escape from the cage. Then the collective response of the surroundings excited by the monomer-monomer collisions is considered. The collective response is initially restricted to the nearest neighbours of the colliding particle by a Voronoi analysis revealing elastic contributions. Then the long-range excitation of the farthest neighbours is scrutinised by searching spatially extended correlations between the simultaneously fast displacements of the caged particle and the surroundings. It is found that the longitudinal component has stronger spatial modulation than the transverse one with a wavelength of about one particle diameter, in close resemblance with experimental findings on colloids. It is concluded that the cage rattling is largely affected by solid-like extended modes

Competition of the connectivity with the local and the global order in polymer melts and crystals

The competition between the connectivity and the local or global order in model fully-flexible chain molecules is investigated by molecular-dynamics simulations. States with both missing (melts) and high (crystal) global order are considered. Local order is characterized within the first coordination shell (FCS) of a tagged monomer and found to be lower than in atomic systems in both melt and crystal. The role played by the bonds linking the tagged monomer to FCS monomers (radial bonds), and the bonds linking two FCS monomers (shell bonds) is investigated. The detailed analysis in terms of Steinhardt's orientation order parameters Q_l (l = 2 - 10) reveals that increasing the number of shell bonds decreases the FCS order in both melt and crystal. Differently, the FCS arrangements organize the radial bonds. Even if the molecular chains are fully flexible, the distribution of the angle formed by adjacent radial bonds exhibits sharp contributions at the characteristic angles {\theta} = 70{\deg}, 122{\deg}, 180{\deg}. The fractions of adjacent radial bonds with {\theta} = 122{\deg}, 180{\deg} are enhanced by the global order of the crystal, whereas the fraction with 70{\deg} < {\theta} < 110{\deg} is nearly unaffected by the crystallization. Kink defects, i.e. large lateral displacements of the chains, are evidenced in the crystalline state.Comment: J. Chem. Phys. in pres

Aumento da resistência mecanica a penetração em função da perda natural de umidade no solo.

Nosso objetivo foi verificar a variação de umidade e sua interferência sobre a resistência mecânica a penetração em um latossolo amarelo disrófico (Lad) sobre relevo plano em área de pastagem, sob condições de clima Amazônico, através de modelo estatísticos de regressão polinomial de 2º grau