On the correlation between fragility and stretching in glassforming liquids

We study the pressure and temperature dependences of the dielectric relaxation of two molecular glassforming liquids, dibutyl phtalate and m-toluidine. We focus on two characteristics of the slowing down of relaxation, the fragility associated with the temperature dependence and the stretching characterizing the relaxation function. We combine our data with data from the literature to revisit the proposed correlation between these two quantities. We do this in light of constraints that we suggest to put on the search for empirical correlations among properties of glassformers. In particular, argue that a meaningful correlation is to be looked for between stretching and isochoric fragility, as both seem to be constant under isochronic conditions and thereby reflect the intrinsic effect of temperature

Microscopic measurement of the linear compressibilities of two-dimensional fatty acid mesophases

The linear compressibility of two-dimensional fatty acid mesophases has determined by grazing incidence x-ray diffraction. Surface pressure vs molecular area isotherms were reconstructed from these measurements, and the linear compressibility (relative distortion along a given direction for isotropic applied stress) was determined both in the sample plane and in a plane normal to the aliphatic chain director (transverse plane). The linear compressibilities range over two orders of magnitude from 0.1 to 10 m/N and are distributed depending on their magnitude in 4 different sets which we are able to associate with different molecular mechanisms. The largest compressibilities (10m/N) are observed in the tilted phases. They are apparently independent of the chain length and could be related to the reorganization of the headgroup hydrogen-bounded network, whose role should be revalued. Intermediate compressibilities are observed in phases with quasi long-range order (directions normal to the molecular tilt in L_2 or L_2' phases, S phase), and could be related to the ordering of these phases. The lowest compressibilities are observed in the solid untilted CS phase and for 1 direction of the S and L_2'' phases. They are similar to the compressibility of crystalline polymers and correspond to the interactions between methyl groups in the crystal. Finally, negative compressibilities are observed in the transverse plane for L_2' and L_2'' phases and can be traced to subtle reorganizations upon untilting.Comment: 24 pages, 17 figure

The Chrono-geometrical Structure of Special and General Relativity: a Re-Visitation of Canonical Geometrodynamics

A modern re-visitation of the consequences of the lack of an intrinsic notion of instantaneous 3-space in relativistic theories leads to a reformulation of their kinematical basis emphasizing the role of non-inertial frames centered on an arbitrary accelerated observer. In special relativity the exigence of predictability implies the adoption of the 3+1 point of view, which leads to a well posed initial value problem for field equations in a framework where the change of the convention of synchronization of distant clocks is realized by means of a gauge transformation. This point of view is also at the heart of the canonical approach to metric and tetrad gravity in globally hyperbolic asymptotically flat space-times, where the use of Shanmugadhasan canonical transformations allows the separation of the physical degrees of freedom of the gravitational field (the tidal effects) from the arbitrary gauge variables. Since a global vision of the equivalence principle implies that only global non-inertial frames can exist in general relativity, the gauge variables are naturally interpreted as generalized relativistic inertial effects, which have to be fixed to get a deterministic evolution in a given non-inertial frame. As a consequence, in each Einstein's space-time in this class the whole chrono-geometrical structure, including also the clock synchronization convention, is dynamically determined and a new approach to the Hole Argument leads to the conclusion that "gravitational field" and "space-time" are two faces of the same entity. This view allows to get a classical scenario for the unification of the four interactions in a scheme suited to the description of the solar system or our galaxy with a deperametrization to special relativity and the subsequent possibility to take the non-relativistic limit.Comment: 33 pages, Lectures given at the 42nd Karpacz Winter School of Theoretical Physics, "Current Mathematical Topics in Gravitation and Cosmology", Ladek, Poland, 6-11 February 200

Measuring gravitational lens time delays using low-resolution radio monitoring observations

Obtaining lensing time delay measurements requires long-term monitoring campaigns with a high enough resolution (< 1 arcsec) to separate the multiple images. In the radio, a limited number of high-resolution interferometer arrays make these observations difficult to schedule. To overcome this problem, we propose a technique for measuring gravitational time delays which relies on monitoring the total flux density with low-resolution but high-sensitivity radio telescopes to follow the variation of the brighter image. This is then used to trigger high-resolution observations in optimal numbers which then reveal the variation in the fainter image. We present simulations to assess the efficiency of this method together with a pilot project observing radio lens systems with the Westerbork Synthesis Radio Telescope (WSRT) to trigger Very Large Array (VLA) observations. This new method is promising for measuring time delays because it uses relatively small amounts of time on high-resolution telescopes. This will be important because instruments that have high sensitivity but limited resolution, together with an optimum usage of followup high-resolution observations from appropriate radio telescopes may in the future be useful for gravitational lensing time delay measurements by means of this new method.Comment: 10 pages, 7 figures, accepted by MNRA

Effect of soil characteristics on phenolic compounds and antioxidant activity of merlot wine.

The objective of this work was to establish the effect of three taxonomic classes of soil, i. e., Argissolo (Ultisol), Cambissolo (Inceptisol) and Neossolo (Entisol), on the phenolic compounds of wines made from grapes grown on these soils in the DO Vale dos Vinhedos, Bento Gonçalves, RS

Efeito do tipo de solo nos componentes de produção da videira e na composição da uva merlot no vale dos vinhedos - safra 2014.

Este trabalho teve o objetivo de avaliar o efeito de cinco tipos de solo nos componentes de produção da videira Merlot e na composição do mosto da uva durante a safra de 2014.Resumo expandido

Aptidão dos solos pra o cultivo do arroz irrigado no estado do Rio Grande do Sul.

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Efeito da variabilidade espacial de solos do Vale dos Vinhedos na composição do vinho Merlot - Safra 2012.

A importação de vinhos tem dificultado a comercialização de produtos nacionais. Para mitigar este efeito, é necessário aumentar a competitividade do vinho brasileiro, o que pode ser obtido pela redução de custos e melhoria da qualidade. A competitividade pode ser atingida, em parte, com a aplicação de tecnologias de agricultura de precisão. Com este objetivo, estudou-se o efeito de cinco unidades de mapeamento de solos do Vale dos Vinhedos, RS, na composição do vinho Merlot de 2012, avaliando-se 39 variáveis, cujos parâmetros foram submetidos à análise de componentes principais. Três componentes representaram 91,49% da variação total e discriminaram, principalmente, os vinhos elaborados com uvas de videiras cultivadas em Argissolo e Neossolo. Os principais resultados mostram que o vinho do Argissolo Bruno Acinzentado Alítico abrúptico caracterizou-se especialmente por valores elevados de variáveis relacionadas à cor, taninos e extrato seco. O vinho do Neossolo Regolítico Húmico típico caracterizou-se por valores mais elevados da alcalinidade das cinzas, alcoóis amílicos e soma de alcoóis superiores. Esses resultados evidenciam o efeito de diferentes unidades de mapeamento de solos na composição e qualidade do vinho, o que remete à importância de estudos pedológicos que visem ao uso racional de insumos nos vinhedos e à produção de vinhos com qualidade e tipicidade diferenciadas