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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 [...]

The structural and energetic properties of small silver clusters Ag n with n = 2–100 atoms are reported. For n = 2–100 the embedded atom model for the calculation of the total energy of a given structure in combination with the basin-hopping search strategy for an unbiased structure optimization has been used to identify the energies and structures of the three energetically lowest-lying isomers. These optimized structures for n = 2–11 were subsequently studied further through density-functional-theory calculations. These calculations provide additional information on the electronic properties of the clusters that is lacking in the embedded-atom calculations. Thereby, also quantities related to the catalytic performance of the clusters are studied. The calculated properties in comparison to other available theoretical and experimental data show a good agreement. Previously unidentified magic (i.e., particularly stable) clusters have been found for n > 80 . In order to obtain a more detailed understanding of the structural properties of the clusters, various descriptors are used. Thereby, the silver clusters are compared to other noble metals and show some similarities to both copper and nickel systems, and also growth patterns have been identified. All vibrational frequencies of all the clusters have been calculated for the first time, and here we focus on the highest and lowest frequencies. Structural effects on the calculated frequencies were considered. [ABSTRACT FROM AUTHOR]

This study deals with the trends of fatigue life between asphalt binders and mixtures using the rate of dissipated energy change (RDEC) approach. To this end, the time sweep and four-point beam fatigue tests were utilized to assess the fatigue life of bituminous materials under different strain amplitudes. The results indicated that the RDEC approach can be utilized as asphalt mix fatigue estimation in terms of asphalt binder fatigue life. A separate unique relationship exists between the fatigue life of asphalt materials and their plateau value (PV) covering different types of materials and strain levels. Furthermore, a fatigue model was developed based solely on the PV values of asphalt binders and mixtures including all the materials and the strain levels used in this study. Results revealed conformity between time sweep and four-point beam fatigue tests in terms of RDEC methodology, and a strong correlation exists between these two fatigue tests. [ABSTRACT FROM AUTHOR]

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]

The contribution of surface units to bulk properties are often neglected in theoretical and computational studies of crystalline systems. We demonstrate that this assumption has to be made with caution in the case of (electric field) polarization. As a generalization of an earlier work on quasi-one-dimensional systems [Springborg, et al., Phys. Rev. B: Condens. Matter Mater. Phys., 2010, 82, 165442], it is shown that the polarization for 2D and 3D systems contains a surface contribution that can, in principle, take any value (within physical limits) and has consequences for converse piezoelectric responses. Subsequently, we determine the surface effects quantitatively for a group of ferroelectric perovskite structures. Our results indicate that such contributions can be substantial. [ABSTRACT FROM AUTHOR]

Molecular level insights into the mechanism and thermodynamics of CO oxidation by a (TiO 2 ) 6 cluster have been obtained through density functional calculations. Thereby, in this study, as an example, two different structural isomers of (TiO 2 ) 6 are considered with the purpose of understanding the interplay between local structure and activity for the CO oxidation reaction. Active sites in the two isomeric forms were identified on the basis of global and local reactivity descriptors. For the oxidation of CO to CO 2 , the study considered both sequential and simultaneous adsorption of CO and O 2 on (TiO 2 ) 6 cluster through the ER and LH mechanisms, respectively. Three different pathways were obtained for CO oxidation by (TiO 2 ) 6 cluster, and the mechanistic route of each pathway were identified by locating the transition-state and intermediate structures. The effect of temperature on the rate of the reaction was investigated within the harmonic approximation. The structure-dependent activity of the cluster was rationalized through reactivity descriptors and analysis of the frontier orbitals. [ABSTRACT FROM AUTHOR]

We present an improved inverse-design approach for automatically identifying molecular (or other) systems with optimal values for prechosen properties. The new approach uses SMILES (simplified molecular input line entry system) to describe molecular structures efficiently, a genetic algorithm to optimize the molecules automatically, and the DFTB+ (self-consistent charge density functional tight-binding) method to calculate electronic properties. Thereby, almost every class of materials─even macromolecules or monomers─can be studied easily. Without crossover operators but with only mutation operators, the genetic algorithm is more adaptive to SMILES while keeping its efficiency. DFTB+ is more accurate than the DFTB method used in our previous inverse-design approach for the study of excited states and charge transfer processes. The improved approach is applied to optimize benzene, pyridine, pyridazine, pyrimidine, and pyrazine derivatives for seven electronic properties, which all are highly relevant and important for the performance of molecules in solar cells. We found that for some electronic properties, the precise composition and structure of the backbone have remarkable impacts on the value of the electronic properties and/or on the set of functional groups that leads to the best performance. On the contrary, for other properties, these effects are less pronounced. The reasonable optimal functional groups and/or substitution patterns are reported.

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.