60,536 research outputs found
The reaction of slag in cement: theory and computer modelling
In this study, theoretical models available for the reaction of both pure slag\ud
(alkali-activated) and slag-blended cement are reviewed. They were developed by using stoichiometric computations
The influence of convective exchanges on coandã effect
Modeling Coandã effect has been a fundamental issue in fluid dynamic research in the XX century. It has lost some interest because of the improvement in CFD, even if it could be still important in the area of the preliminary design of aerodynamic devices that benefits of fluid deflection by convex surfaces. An effective model of Coandã effect has not been defined, and fundamental questions are still open. The influence of convective heat exchange on Coandã adhesion of a fluid stream on a convex surface in the presence of a temperature gradient between the fluid and the convex surface is a problem, which affects many practical cases, but it is still marginally approached by scientific literature. This paper aims to start an effective research direction on the effects of convective heat exchange on Coandã effect. It approaches the problem with a set of CFD simulations. It analyses the previous hypotheses, which are based on Prandtl number and evidences the need of a more effective model that accounts also for the Reynolds number
Casimir forces for inhomogeneous planar media
Casimir forces arise from vacuum uctuations. They are fully understood only for simple models, and are important in nano- and microtechnologies. We report our experience of computer algebra calculations towards the Casimir force for models involving inhomogeneous dielectrics. We describe a methodology that greatly increases condence in any results obtained, and use this methodology to demonstrate that the analytic derivation of scalar Green's functions is at the boundary of current computer algebra technology. We further demonstrate that Lifshitz theory of electromagnetic vacuum energy can not be directly applied to calculate the Casimir stress for models of this type, and produce results that have led to alternative regularisations. Using a combination of our new computational framework and the new theory based on our results, we provide specic calculations of Casimir forces for planar dielectrics having permittivity that declines exponentially. We discuss the relative strengths and weaknesses of computer algebra systems when applied to this type of problem, and describe a combined numerical and symbolic computational framework for calculating Casimir forces for arbitrary planar models.Publisher PD
Formalization of Universal Algebra in Agda
In this work we present a novel formalization of universal algebra in Agda. We show that heterogeneous signatures can be elegantly modelled in type-theory using sets indexed by arities to represent operations. We prove elementary results of heterogeneous algebras, including the proof that the term algebra is initial and the proofs of the three isomorphism theorems. We further formalize equational theory and prove soundness and completeness. At the end, we define (derived) signature morphisms, from which we get the contravariant functor between algebras; moreover, we also proved that, under some restrictions, the translation of a theory induces a contra-variant functor between models.Fil: Gunther, Emmanuel. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Gadea, Alejandro Emilio. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; ArgentinaFil: Pagano, Miguel Maria. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Universidad Nacional de Córdoba. Facultad de Matemática, AstronomÃa y FÃsica; Argentin
Polymer desorption under pulling: a novel dichotomic phase transition
We show that the structural properties and phase behavior of a self-avoiding
polymer chain on adhesive substrate, subject to pulling at the chain end, can
be obtained by means of a Grand Canonical Ensemble (GCE) approach. We derive
analytical expressions for the mean length of the basic structural units of
adsorbed polymer, such as loops and tails, in terms of the adhesive potential
and detachment force, and determine values of the universal exponents which
govern their probability distributions. Most notably, the hitherto
controversial value of the critical adsorption exponent is found to
depend essentially on the interaction between different loops. The chain
detachment transition turns out to be of the first order, albeit dichotomic,
i.e., no coexistence of different phase states exists. These novel theoretical
predictions and the suggested phase diagram of the adsorption-desorption
transformation under external pulling force are verified by means of extensive
Monte Carlo simulations.Comment: 10 pages, 4 figure
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