Search

This paper aims to develop asphalt binder fatigue models by time sweep tests under constant strain. By investigating the fatigue life in neat and modified asphalts under linear and nonlinear viscoelastic responses, results were analyzed in terms of strain levels, asphalt type, and additive content. The dissipated energy and dissipated energy ratio concepts were utilized to develop the phenomenological models for estimating fatigue lives of asphalt binders. Results showed that the dissipated energy ratio-based equations give relatively identical fatigue models irrespective of the strain level or asphalt binder type. Moreover, statistical analyses were performed to investigate the contribution of each parameter in the fatigue model prediction. A comparison was made between fatigue life predictions by means of traditional and energy-based methods. Results proved that the fatigue life prediction models based on the concept of dissipated energy ratio follow a similar trend. Key words: asphalt binder, fatigue, time sweep, dissipated energy, viscoelasticity. Le but vise de cet article est de developper des modeles de fatigue de liants d'asphalte au moyen d'essais de balayage temporel sous contrainte constante. En examinant la longevite a la fatigue des asphaltes purs et modifies selon les reponses viscoelastiques lineaires et non lineaires, les resultats ont ete analyses sur le plan des niveaux de deformation, du type d'asphalte et de la teneur en additif. Les concepts d'energie dissipee et de rapport d'energie dissipee ont servi a elaborer les modeles phenomenologiques permettant d'estimer la longevite a la fatigue des liants d'asphalte. Les resultats ont montre que les equations fondees sur le rapport d'energie dissipee donnent des modeles de fatigue relativement identiques quel que soit le niveau de deformation ou le type de liant d'asphalte. De plus, des analyses statistiques ont ete effectuees afin d'etudier la contribution de chaque parametre dans la prevision du modele de fatigue. Une comparaison a ete faite entre les predictions de la longevite a la fatigue au moyen de methodes traditionnelles et fondees sur l'energie. Les resultats ont demontre que les modeles de prediction de la longevite a la fatigue fondes sur le concept de rapport d'energie dissipee suivent une tendance similaire. [Traduit par la Redaction] Mots-cles : liant asphaltique, fatigue, balayage temporel, energie dissipee, viscoelasticite., Introduction Fatigue is the dominant mode of distress in flexible pavements at intermediate temperatures. It has been reported that the crack initiation and(or) propagation in asphalt pavements often originate from [...]

Atheoretical treatment for the orbital response of an infinite, periodic system to a static, homogeneous, magnetic field is presented. It is assumed that the system of interest has an energy gap separating occupied and unoccupied orbitals and a zero Chern number. In contrast to earlier studies, we do not utilize a perturbation expansion, although we do assume the field is sufficiently weak that the occurrence of Landau levels can be ignored. The theory is developed by analyzing results for large, finite systems and also by comparing with the analogous treatment of an electrostatic field. The resulting many-electron Hamilton operator is forced to be hermitian, but hermiticity is not preserved, in general, for the subsequently derived single-particle operators that determine the electronic orbitals. However, we demonstrate that when focusing on the canonical solutions to the single-particle equations, hermiticity is preserved. The issue of gauge-origin dependence of approximate solutions is addressed. Our approach is compared with several previously proposed treatments, whereby limitations in some of the latter are identified. [ABSTRACT FROM AUTHOR]

The interactions of amino acids Glycine and Alanine with gold clusters, Aun (n=3, 8, 16) have been studied in both gas and aqueous phase within the formalism of density functional theory (DFT). The amino acid binds to the cluster with its amine/carboxyl end securely anchored to the cluster. Selective peptide synthesis has been explored for Glycylglycine (GlyGly) and Glycylalanine (GlyAla) dipeptides in aqueous medium via two different reaction pathways. Path‐ [ABSTRACT FROM AUTHOR]

Global geometry optimization of metal clusters is an important problem in nanophysics. The starting geometries of the clusters generated with empirical or other model potentials are generally optimized further by density functional theory (DFT)-based energy minimization. For this purpose, several algorithms such as simulated annealing, genetic algorithms, basin hopping, etc. are used. Our building-up procedure generates putative lower-energy structures of metal (M) clusters, M n +1 , M n +2 , etc., by anchoring one or more metal atoms in the vicinity of the minima of the molecular electrostatic potential (MESP) of M n . Here, we report an application of this method to Ag n clusters, for 5 ≤ n ≤ 20, followed up by DFT-based geometry optimization, generating several lower-energy structures than those reported in the literature. New low-energy isomers are obtained by applying the same procedure to the test case of mixed-metal clusters, Ni n Ag m , for n + m = 4 and 5. In conclusion, our MESP-based building-up procedure offers a new general methodology for generating lower-energy geometries of metal clusters.