Aging in Structural Changes of Amorphous Solids: A Study of First Passage Time and Persistence Time Distribution

The time distribution of relaxation events in an aging system is investigated via molecular dynamics simulations. The focus is on the distribution functions of the first passage time, $p_1(\Delta t)$, and the persistence time, $p(\tau)$. In contrast to previous reports, both $p_1$ and $p$ are found to evolve with time upon aging. The age dependence of the persistence time distribution is shown to be sensitive to the details of the algorithm used to extract it from particle trajectories. By updating the reference point in event detection algorithm and accounting for the event specific aging time, we uncover age dependence of $p(\tau)$, hidden to previous studies. Moreover, the apparent age-dependence of $p_1$ in continuous time random walk with an age independent $p(\tau)$ is shown to result from an implicit synchronization of all the random walkers at the starting time

Maintaining the equipartition theorem in small heterogeneous molecular dynamics ensembles

It has been reported recently that the equipartition theorem is violated in molecular dynamics simulations with periodic boundary condition [Shirts et al, J. Chem. Phys. 125, 164102 (2006)]. This effect is associated with the conservation of the center of mass momentum. Here, we propose a fluctuating center of mass molecular dynamics approach (FCMMD) to solve this problem. Using the analogy to a system exchanging momentum with its surroundings, we work out --and validate via simulations-- an expression for the rate at which fluctuations shall be added to the system. The restoration of equipartition within the FCMMD is then shown both at equilibrium as well as beyond equilibrium in the linear response regime

Diffusion on the torus for Hamiltonian maps

For a mapping of the torusT2 we propose a definition of the diffusion coefficientD suggested by the solution of the diffusion equation ofT2. The definition ofD, based on the limit of moments of the invariant measure, depends on the set Ω where an initial uniform distribution is assigned. For the algebraic automorphism of the torus the limit is proved to exist and to have the same value for almost all initial sets Ω in the subfamily of parallelograms. Numerical results show that it has the same value for arbitrary polygons Ω and for arbitrary moments

Dielectric Elastomer Composites: Macroscopic Behavior and Instabilities

Dielectric Elastomers (DEs) are an interesting class of active materials that can exhibit coupled electrical and mechanical behaviors, for example they can respond to an external electric field by changing their shape or size. This unique property is known as electrostriction, and makes such materials promising candidates for a wide range of practical applications, and therefore there is a need for the design of DEs with enhanced electromechanical couplings. In this work we investigate the possibility of enhancing the electrostriction by making composites consisting of one or more family of filler phases in a soft dielectric host. We use homogenization techniques to obtain estimates for the effective response of such DECs under general electrical and mechanical loading conditions. Next, we use the homogenization estimates developed in this work to investigate the effect of various microstructural parameters on the overall response of DECs. We also study failure of DECs as characterized by dielectric breakdown and/or the onset of material instabilities. Two types of material instabilities will be considered: Loss of Positive Definiteness (LPD) and Loss of Ellipticity (LE). Finally, we attempt an optimal design for the microstructure of DECs with enhanced electromechanical couplings, which are capable of achieving large electrostrictive strains before the failure. Our results show that composites consisting of a very small concentration of rigid circular fibers with vanishing contrast in the dielectric properties can achieve the largest electrostrictive strains before failure. Finally, we attempt to study DECs in the post-bifurcated deformation regime. This is important since after the composite loses strong ellipticity, the solution of the homogenization problem may bifurcate into a lower energy (with generally softer mechanical response) solution, which is different from the pre-bifurcated solutions. This raises the interesting possibility of operating DECs in their softer post-bifurcated deformation regimes to further increase the maximum achievable electrostrictive strains

Bègues – Voie communale no 2

Identifiant de l'opération archéologique : OA6816 Date de l'opération : 2011 (SD) En vue de la construction d’une salle polyvalente sur la commune de Bègues (Allier), une campagne de sondages archéologiques préventifs a été conduite du1er au 4 mars 2011 par les agents du service d’Archéologie Préventive de l’Allier sur la parcelle concernée par l’aménagement. Douze sondages ont ainsi été ouverts et huit se sont avérés positifs. Ils ont permis de découvrir des éléments mobiliers vraisemblablem..

AUTOMATIC TUBE CLEANING SYSTEM (ATCS) INSTALLATION IN SULFIDE RETRIEVAL MONOETHANOLAMINE TREATMENT PLANT: CASE STUDY AND FOULING GLOBAL PERSPECTIVES

Automatic cleaning of heat exchangers and condensers tubes by means of sponge balls is well known since the early fifties, with expanding application from steam power plants to process industry to industrial cooling and air conditioning systems. Main benefits bottom-lined in cost savings are generally considered as: elimination of maintenance down-time and need for chemical and more efficient operation of process and plant. This paper presents the performance and benefits of an Automatic Tube Cleaning System (ATCS) implementations, in a hydrogen sulfide retrieval Monoethanolamine treatment Plant in Paz Ashdod Refinery, one of the two refineries in Israel. Patented by CQM for the balls injection and trapping methods, their unique operation benefits are revealed and resulting O&M cost savings are evaluated in detail. The paper concludes by presenting the main costs of heat exchanger fouling and discusses how heat exchanger fouling mitigation meets the main goals of global energy efficiency