Granular Contact Lubrication: Theory and Experiment

This dissertation is devoted to a theoretical and experimental study of the granular contact lubrication, both. The theory is based on the kinetic of the granular material where the granules interact with each other and with the boundary surfaces through instantaneous, binary collisions, characterized by a constant coefficient of restitution. Specifically this study focuses on granular lubrication in Couette flows. A series of simulations is reported and the results show good agreement with several published papers. Also, a theory that ties the true temperature to the grain mobility is developed. The true temperature of a granular material depends on the balance between the source of energy and the dissipation of energy due to inelastic collisions. In treating rapid shearing regime the collision is generally considered to be instantaneous. However, in a dense regime and at relatively small sliding speeds, the contact time between the granules is larger than the time between collisions and thus the friction between the granules starts to play an important role. Therefore, the effect of enduring contact becomes dominant over that of the kinetic and collisional stresses. The enduring contact between granules is into consideration by making use of Coulomb friction model. The results reveal that the enduring contact is a strong function of the solid volume fraction and its effect tends to dominate the solution at relatively small sliding speeds. A series of experimental investigations is presented that demonstrate the lift phenomenon observed in an annular shear cell apparatus. The effects of the friction coefficient and the surface roughness are expressed as a function of the rotational speed and the applied load. The theoretical results and the experimental measurements are compared. The results of experiments provide a unique quantitative evidence for the measure of the phenomenon of the lift. Furthermore, a series of experimental investigation on the nature of stick-slip associated with granular materials sheared at low speeds is demonstrated. The results reveal the occurrence of stick-slip at low speed. The behavior of the stick-slip is similar to the results presented by several researchers interested in physics and geology fields

Surface Dynamics of Silicon Low-Index Surfaces Studied by Reflection High-Energy Electron Diffraction

Surface morphology during the growth of Si on Si(111)-(7x7) by femtosecond pulsed laser deposition (fsPLD) is studied using reflection high-energy electron diffraction (RHEED) at different temperatures. The growth of Si on Si(111) has received considerable attention as a model system of homoepitaxy. PLD is a deposition technique that uses much more energetic species (atoms and ions) compared to other physical vapor deposition (PVD), such as in molecular beam epitaxy. In this work, in situ reflection high energy electron diffraction (RHEED) was used to study the dynamics of PLD of Si on Si(111)-(7x7). Epitaxial growth of Si/Si(111)-(7x7) at temperatures as low as 210°C was observed. For this substrate temperature, no change in RHEED patterns after growth, and only reduction in intensity during deposition was observed. Surface Debye temperature of the topmost layer of the Si(111)-7x7 is measured by using RHEED. The diffraction intensity is distorted by the thermal vibration amplitude of atoms on the topmost layer of the surface. Influence of Si deposition on the temperature of Si(111) to (7x7) phase transition is also studied. The phase transition showed that Si deposition lowers the transition temperature. A Ti-sapphire laser (100 fs, 800 nm, 1 kHz) was used to ablate a Si target on Si(111)-(1x1) during quenching from high temperature. The RHEED intensity was observed as the substrate was exposed to the Si plume and the Si(111) substrate was quenched. The RHEED patterns showed a shift in the transition temperature from 840°C without the plume to 820°C with the plume. With laser fluence below the damage threshold, laser enhanced epitaxial growth shows a great improvement in deposit Si on Si(111)-7x7 at low temperature (room temperature)

Improved confinement of reinforced concrete columns

AbstractTraditional steel ties reinforcement cannot provide superior confinement for reinforced concrete (RC) columns due to the constraints on tie spacing and disturbance of concrete continuity. This paper presents a practical confinement configuration consisting of single Expanded Metal Mesh (EMM) layer in additional to regular tie reinforcement. The EMM layer is warped above ties. The proposed transverse reinforcement, with various volumetric ratios of ties, was investigated in sixteen square short RC column specimens categorized in two groups according to their slenderness ratios. The specimens were cast in vertical position simulating the construction field and they were tested under concentric compression till failure. The results indicated that the columns, confined with proposed lateral reinforcement, revealed significant improvement in the strength and ductility. Also, high reduction in ties volumetric ratio with no loss in ultimate load could be achieved by installing the EMM layer

On manimax theory in two Hilbert spaces

In this paper, we investigated the minimax of the bifunction J:H1(Ω)xV2→RmxRn, such that J(v1,v2)=((12a(v1,v1)−L(v1)),v2) where a(.,.) is a finite symmetric bilinear bicontinuous, coercive form on H1(Ω) and L belongs to the dual of H1(Ω)

Formal Specification and Automatic Verification of Multi-Agent Conditional Commitments and their Applications

Modeling agent communication using social commitments in the form of obligatory contracts among intelligent agents in a multi-agent system (MAS) provides a quintessential basis for capturing flexible and declarative interactions and helps in addressing the challenge of ensuring compliance with specifications. However, on the one hand, social commitments exclusively are not able to model agent communication actions, the cornerstone of the fundamental agent communication theory, namely speech act theory. These actions provide mechanisms for dynamic interactions and enable designers to track the evolution of active commitments. On the other hand, the designers of the system cannot guarantee the emergence of expected behaviors, such as self-contained intelligent agent complies with its protocols and honors its activated commitments. Moreover, the designers might still wish to develop effective and scalable algorithms to tackle the problem of model checking complex interactions modeled by conditional commitments and conditional commitment actions and regulated by commitment-based protocols at design time. Conditional commitments are a natural and universal frame of social commitments and cope with business conditional contracts. This dissertation is in principle about addressing two open challenging issues: 1) formally defining computationally grounded semantics for agent communication messages in terms of conditional commitments and associated actions (fulfill, cancel, release, assign and delegate), which is yet to be studied; and 2) developing a symbolic algorithm dedicated to tackle the raised model checking problem and to ensure the development of correct systems. In this dissertation, we start with distinguishing between two types of conditional commitments: weak and strong. Weak conditional commitments are those that can be activated even if the antecedents will never be satisfied, while strong conditional commitments are those that can be solely activated when there is at least one possibility to satisfy their assigned antecedents. We develop a branching-time temporal logic called CTL{cc,\alpha} that extends computation tree logic (CTL) with new modalities for representing and reasoning about the two types of conditional commitments and their actions using the formalism of interpreted systems. We present a set of valid properties, a set of reasoning rules, and a set of action postulates in order to explore the capabilities of CTL{cc,\alpha}. Furthermore, we propose a new life cycle of conditional commitments. Having a new logic (CTL{cc,\alpha}), we introduce a new symbolic algorithm to tackle the problem of its model checking. Instead of developing our algorithm from scratch, we extend the standard CTL model checking algorithm with symbolic algorithms needed for new modalities. We also investigate important theoretical results (soundness and termination) of the algorithm. Given that, we completely implement our algorithm and then assemble it on top of the symbolic model checker MCMAS, developed to automatically and directly test MAS specifications. The resulting symbolic model checker is so-called MCMAS+. We extend MCMAS's input modeling and encoding language called ISPL with shared and unshared variables needed for agent interactions and with the syntactic grammar of new modalities to produce a new one called ISPL+. We also extend the MCMAS's graphical user interface to display verified models to reduce inefficient and labor-intensive processes performed by the designers. To evaluate the performance of the developed algorithm, we analyze its time and space computational complexity. The computed time and space complexity are P-complete for explicit models and PSPACE-complete for concurrent programs. Such results are positive because model checking CTL{cc,\alpha} has the same time and space complexity of model checking CTL although CTL{cc,\alpha} extends CTL. Therefore, CTL{cc,\alpha} balances between expressive power and verification efficiency. Regarding the feasibility aspect, we apply our approach in three different application domains: business interaction protocols, health care processes, and web service compositions. The MAS paradigm is successfully employed in these domains wherein a component is represented, implemented and enacted by an agent. The proposed approach improved the employed MAS paradigm by formally modeling and automatically verifying interactions among participating agents so that the bad behaviors can be detected and then eliminated or repaired at design time and the confidence on the safety, efficiency and robustness is increased. We conduct extensive experiments to evaluate the computational performance and scalability of MCMAS+ using very large case studies. The obtained results strongly confirm the theoretical findings and make MCMAS+ practical. We finally compare our approach to other available approaches and show that it outperforms such approaches in terms of execution time, memory usage and number of considered intelligent agents