On Burgers fluids

We investigate several qualitative aspects concerning the solutions to the flow of a Burgers fluid, a model that has been used to describe a variety of materials: polymeric liquids, asphalt and asphalt mixtures, and the earth's mantle. Continuous dependence of the solutions with respect to initial data and supply terms, uniqueness of solutions and the impossibility of localization of the solutions are proved. Exponential stability and structural stability are analysed. We also consider uniaxial shear flows. We prove instability of solutions whenever the constitutive parameters do not satisfy certain relations. Also we study the spatial behaviour of the solutions. Copyright © 2006 John Wiley & Sons, Ltd.     

Chromatography in pore networks II — The role of structure and adsorption in the band broadening

Summary The complex intraparticle structure typical of chromatographic column packings has been analyzed by use of an equivalent network model which emphasizes pore size distribution and connectivity. Special attention is given as to the way in which diffusion and adsorption interact and display modified peak spreading characteristics according to the morphology of the pore space. This study reveals a very significant increase in the column band broadening over that expected from physical adsorption which can arise from particular distributions of pore sizes. This has implications for designing packings which take advantage of the separating power due to adsorption but do not compromise the resolution of the chromatographic system.     

Untersuchungen über die Halogenierung von Benzalacetophenon, 1. Mitt.: Bromierung (Kurze,vorläufige Mitteilung)

Zusammenfassung Die Bromierung von (teilweise mit Alkylgruppen verätherten) Polyhydroxychalkonen, die reaktive Hydroxylgruppen im Benzoylteil des Moleküls besitzen, wird unter kontrollierten Bedingungen untersucht. Die Ergebnisse stimmen mit früheren Beobachtungen überein, daß die Bromsubstitution am Kern (u. zw. an der 5-Position, falls diese frei ist) gegenüber einer Addition an der Doppelbindung bevorzugt wird, wenn die Reagentien in äquimolaren Verhältnissen zur Reaktion kommen. Mit überschüssigem Brom in Lösung oder mit flüssigem Brom finden sowohl Substitution als auch Addition statt. Eine elektronentheoretische Interpretation dieser Bevorzugung der Substitution am Kern vor der Addition an der Doppelbindung wird nun zur Diskussion gestellt.     

On the thermomechanics of materials that have multiple natural configurations Part I: Viscoelasticity and classical plasticity

Many bodies, both solid and fluid, are capable of being stress-free in numerous configurations that are not related to each other through a rigid body motion. Moreover, it is possible that these bodies could have different material symmetries in these different stress-free natural configurations. In order to describe the response of such bodies, it is necessary to know the manner in which these natural configurations evolve as well as a class of response functions for the stress that are determined by kinematical quantities that are measured from these evolving natural configurations. In this review article, we provide a framework to describe the mechanics of such bodies whose natural configurations evolve during a thermodynamic process. The framework is capable of describing a variety of responses and has been used to describe traditional metal plasticity, twinning, traditional viscoelasticity of both solids and fluids, solid-to-solid phase transitions, polymer crystallization, response of multi-network polymers, and anisotropic liquids. The classical theories of elastic solids and viscous fluids are included as special cases of the framework. After a review of the salient features of the framework, we briefly discuss the status of viscoelasicity, traditional plasticity, twinning and solid to solid phase transitions within the context of the framework.     

Gapless color-flavor-locked quark matter

In neutral cold quark matter that is so dense that the strange quark mass Ms is unimportant, all three quark flavors pair in a color-flavor locked (CFL) pattern, and all nine fermionic quasiparticles have a gap Delta (or 2Delta). We argue that, as the density decreases (or Ms increases), there is a quantum phase transition (at M(2s/mu approximately 2Delta) to a new "gapless CFL phase" in which only seven quasiparticles have a gap. There is still an unbroken U(1)(Q) gluon/photon, but, unlike CFL, gapless CFL is a Q conductor with gapless (charged) quasiquarks and a nonzero electron density at zero temperature, so its low energy effective theory and astrophysical properties are qualitatively new. At the transition, the dispersion relations of both gapless quasiparticles are quadratic, but for larger M2s/mu, one becomes conventionally linear while the other remains quadratic, up to tiny corrections.     

Self-assembly of octarhenium-based neutral luminescent rectangular prisms

Self-assembly of rhenium-based nanoscale rectangular prismatic boxes has been achieved in quantitative conversion. The fac-rhenium corner provided three mutually perpendicular coordination sites and served as a good candidate for the construction of 3-D boxes. These are the first Re-based, neutral, luminescent prisms of M(8)L(2)L'(8) type that has been characterized crystallographically. Their luminescent properties and molecular recognition capabilities make these molecular prisms interesting supramolecules.