Ionization of Acetylacetone in Me2SO—Water Mixtures. Reactivity—Selectivity Principle or Principle of Imperfect Synchronization?

Rate constants for the reversible deprotonation of acetylacetone were measured in carboxylate and amine buffers in water and in 50%, 90% and 95% Me₂SO at 20°C. The Brønsted plot for the carboxylate ions is curved in the Me₂SO—water mixtures, but straight in water. The curvature is in the direction predicted by the Reactivity—Selectivity Principle (RSP). However, the Brønsted plot for the reaction with primary amines is straight in all solvents. This suggests that the curvature observerd with the carboxylate ions is caused by loss of solvation of the base; this loss of solvation is ahead of bond formation in the transition state rather than being a manifestation of the RSP. (Note that all Brønsted plots are based on pK_a values measured in the respective solvents.) The intrinsic rate constant (k₀) for proton transfer increases with the addition of Me₂SO, and more so with the carboxylate buffers than with the amines. This increase in k₀ is attributed to delayed solvation of the developing enolate ion in the transition state; with the carboxylate buffers, an additional factor is the early loss of solvation of the base. The various solvation effects observed in this study can all be understood in the context of the Principle of Imperfect Synchronization (PIS).     

Influence of the counter-ion on the effective charge of polyacrylic acid in dilute condition

Osmotic pressure measurements were satisfactorily used to compute the effective charge of poly(acrylic) acid (PAA) at different pHs and with different monovalent and divalent counterions. This experimental method is sensitive to the osmotically active species (polymer and counterions). After correction for the polymer contribution to the total osmotic pressure (solvency and excluded volume), the remaining pressure can be attributed to the polyelectrolyte counterions and processed with Donnan and equation of state in order to compute the effective charge number per polymeric chain (Z^eff). The behavior of Z^eff against the chain concentration and pH was investigated after neutralization of PAA with LiOH, NaOH, and TMAOH. The results clearly indicate that the nature of the monovalent counterion has no effect on Z^eff leading to the conclusion that the interaction between monovalent counterions and the acrylate functionality is purely electrostatic in agreement with conductimetric and potentiometric results reported in the literature. The behavior of Z^eff against the degree of ionization of the polymer and its concentration is also in good agreement with the theoretical expectations of the theory of ionic condensation. Osmotic measurements were also used in order to understand the influence of divalent cations (Mg²⁺, Ca²⁺, Ba²⁺) on Z^eff of the sodium salt of PAA at pH 9 and at different divalent/acrylate molar ratio. All the divalent cations depress Z^eff each of one at different degrees, confirming a specific divalent/polymer interaction. The energy of hydration of cations can explain most of the observed results with divalents.     

Standards and industrial property

This article is primarily concerned with standards seen as a means for collective appropriation of technological information. It begins with an attempt to throw light on the relationships between standards, patents and licenses. Then we develop a two-stage duopolistic model whereby each firm must decide on a programme of standardization before choosing its level of production. The risks of multiple or inefficient equilibria are strong enough to justify the intervention of standardization organizations to inform and coordinate individual firms. But the paper also explains why some organizations likeetsi try to play a new role by promoting open access to master patents when used in the definition of a standard.     

Glass fiber-filled thermoplastics. I. Wall and processing effects on rheological properties

A systematic study of wall effects on the shear viscosity of short glass fiber-filled polypropylene and polystyrene is presented. The dependence of these effects on capillary radius, shear rate, temperature, and polymer matrix is examined. The “true” viscosity curves of these materials (free from wall effects) can be obtained by an extrapolation procedure. Breakage of glass fibers in the high shear-rate processes of extrusion and injection molding lead to an appreciable reduction of the viscosity of these materials and is probably the more important effect to take into account in these processes.     

Compatibility equations for large deformations

Compatibility equations for large deformations are developed on the sole basis of the div and curl concepts.     

Natural isotope fractionation in the discrimination of sugar origins

More than 500 carbohydrate samples have been characterised by hydrogen, carbon and oxygen isotopic parameters measured on ethanol and water resulting from controlled fermentation. Different chemical states of the carbohydrate pool have been considered: polysaccharides from cereals, tubers and leguminosae (maize, sorghum, rice, wheat, barley, potato, bean), glucose, fructose and sucrose from fruits (pineapple, citrus, apple, soft fruits), sucrose from sugar plants (beet, cane). The overall carbon-13 content of ethanol and the deuterium and oxygen-18 contents of water before fermentation were determined by mass spectrometry of isotope ratios whereas the investigation of site-specific natural isotope fractionation by deuterium NMR has provided access to the deuterium contents in the methyl (I) and methylene (II) sites of ethanol. The results have been analysed in the multidimensional space of these isotopic variables. Hierarchical clustering, principal component and discriminant analyses have been performed. Among fruits, for example, the pineapple group exhibits a 100% discrimination with respect to the apple and citrus groups which are themselves well distinguished. A still higher discrimination is reached between the three groups, citrus, cane and beet, and the addition of 10% exogenous cane or beet sucrose to citrus juice is unambiguously detected.     

Ignition of exterior building details in bushfires: An experimental study

A laboratory study of the ignition of building details incorporating timber, under bushfire conditions, using ‘mock-ups’ of these details and both realistic (leaves and twigs) and, mainly, artificial (cribs) ignition sources has been carried out. Parameters such as mock-up type, moisture content of the timber comprising the mock-ups, and temperature and relative humidity of the experimental atmosphere were examined. It was found that all these parameters affected the ignition and flame propagation induced and that under conditions typical of a severe bushfire, only very small amounts of fuel were required to cause ignition. These results support the belief, based on field studies, that ignition of exterior building details composed of timber plays an important role in the destruction of buildings in bushfires.     

Self-image resilience and dissonance: The role of affirmational resources.

Predicted that high self-esteem Ss (HSEs) would rationalize an esteem-threatening decision less than low self-esteem Ss (LSEs), because HSEs presumably had more favorable self-concepts with which to affirm, and thus repair, their overall sense of self-integrity. This prediction was supported in 2 experiments within the "free-choice" dissonance paradigm: one that manipulated self-esteem through personality feedback and the other that varied it through selection of HSEs and LSEs, but only when Ss were made to focus on their self-concepts. A 3rd experiment countered an alternative explanation of the results in terms of mood effects that may have accompanied the experimental manipulations. Results were discussed in terms of the following: (1) their support for a resources theory of individual differences in resilience to self-image threats—an extension of self-affirmation theory, (2) their implications for self-esteem functioning, and (3) their implications for the continuing debate over self-enhancement vs self-consistency motivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pyramid collaborative filtering technique for an intelligent autonomous guide agent

This article presents an autonomous guide agent that can observe a community of learners on the web, interpret the learners' inputs, and then assess their sharing. The goal of this agent is to find a reliable helper (tutor or other learner) to assist a learner in solving his task. Despite the growing number of Internet users, the ability to find helpers is still a challenging and important problem. Although helpers could have much useful information about courses to be taught, many learners fail to understand their presentations. For that, the agent must be able to deal autonomously with the following challenges: Do helpers have information that the learners need? Will helpers present information that learners can understand? And can we guarantee that these helpers will collaborate effectively with learners? We have developed a new filtering framework, called a pyramid collaborative filtering model, to whittle the number of helpers down to just one. We have proposed four levels for the pyramid. Moving from one level to another depends on three filtering techniques: domain model filtering, user model filtering, and credibility model filtering. A new technique is filtering according to helpers' credibilities. Our experiments show that this method greatly improves filtering effectiveness. © 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 1065–1082, 2007.