Physical/thermal activation process

The Monte Carlo method as described so far is useful to evaluate equilibrium properties but says nothing about the time evolution of the system. However, it is in some cases possible to construct a Monte Carlo algorithm that allows the simulated system to evolve like a physical system. This is the case when the dynamics can be described as thermally activated processes, such as adsorption, desorption, and diffusion. Since these processes are particularly well defined in the case of lattice models, these are particularly well suited for this approach. The foundations of dynamical Monte Carlo (DMC) or kinetic Monte Carlo (KMC) simulations have been discussed by Eichthom and Weinberg (1991) in terms of the theory of Poisson processes. The main idea is that the rate of each process that may eventually occur on the surface can be described by an equation of the Arrhenius type ... 

However, dislocations will still move by thermally activated processes below the Peierls force. 8For more about the dispersion relation, see a reference on solid-state physics, such as Kittel [6]. 

However, it is not only the spot size s that governs the final spatial resolution of the electrode reaction, but illumination of the sample is just the first step in a whole series of induced processes resulting in the final state of the system. For instance, in semiconductor interfaces the lateral hole drift causes an extension of the reaction zone. For the thermally activated processes, the heat conductivity of the sample determines the reaction zone. Therefore, both optical and physical effects determine the final spatial resolution of optical/electrical laser methods. 

This is physically the ratio of energy lost to energy stored per deformation cycle. A peak in tan 8 occurs when the impressed frequency matches the frequency of molecular relaxation through thermally activated processes. If X is the average molecular relaxation time at temperature T, then a loss peak will be observed at this temperature if the impressed vibration frequency (/max) satisfies the relation ... 

LAUNAY - I have a comment and a question. Your treatment of proton transfer is very analogous to the case of electron transfer when there is no temperature dependence (i.e. one does not take into account vibrations). To complete the analogy one would expect some thermally activated process, but it has not been introduced in your model. Instead of that you find that the rate constant could increase when the temperature decreases. What is the physical reason for that ... 

As noted above, amorphous carbon films can be produced from carbon-containing gas phases (physical vapour deposition, PVD). They can also be produced from hydrocarbon-containing gases (chemical vapour deposition, CVD), Both PVD and CVD processes can be thermally-activated or can be plasma- and/or electric field-assisted processes (e.g., microwave assisted CVD and ion beam deposition). As a consequence a wide range of processes have been developed to form amorphous carbon films and a correspondingly complex nomenclature has evolved [70, 71],... 

Creep-rupture represents, ultimately, the thermally activated breaking of bonds. Russian authors, in particular, have tried to describe it as a mechanically aided chemical process rather than a physical one. So far, however, there has been no widely used combined description of degradation by chemical and mechanical means. 

The complex three-dimensional structure of these materials is determined by their carbon-based polymers (such as cellulose and lignin), and it is this backbone that gives the final carbon structure after thermal degradation. These materials, therefore, produce a very porous high-surface-area carbon solid. In addition, the carbon has to be activated so that it will interact with and physisorb (i.e., adsorb physically, without forming a chemical bond) a wide range of compounds. This activation process involves controlled oxidation of the surface to produce polar sites. 

The unique mechanical and structural properties of crystals necessitate the application of special experimental methods for the investigation of thd chemical kinetics of solids. In principle, all the physical parameters of substances involved in a chemical process can be used to follow the kinetics. These processes normally occur at high temperatures since they need thermal activation. Conventionally, the outcome of a solid state reaction experiment is inspected only after quenching. However, the quenching process is prone to alter many properties of the system, which explains the ambiguous results often found in the studies of solid state kinetics. 

Small solute atoms in the interstices between the larger host atoms in a relaxed metallic glass diffuse by the direct interstitial mechanism (see Section 8.1.4). The host atoms can be regarded as immobile. A classic example is the diffusion of H solute atoms in glassy Pd8oSi2o- For this system, a simplified model that retains the essential physics of a thermally activated diffusion process in disordered systems is used to interpret experimental measurements [20-22]. 

DIN EN ISO 8044 defines wear as the progressive loss of material from the surface of a solid body due to mechanical causes, i. e., contact with solid, liquid, or gaseous bodies and relative motion. Wear is manifested in the presence of loosened particles (wear particles) and in the change in material and shape of the surface layer. Thermal, physical, and chemical processes are activated in the case of most wear processes (triboreactions). Wear is fundamentally caused by mechanically transferred energy. 

Extensive studies on different rubber compounds (see, for example, Table 1 in [105]) yield Ec 0.05 to 0.15 eV per filler-filler bond [105,106], i.e., typical values for physical (van der Waals like) bonds. Similar values were obtained within an approach which assumes a hypothetical analogy between the structure of a statistical carbon black network and that of a Gaussian elastomeric (unfilled) polymer network [107]. As in the Kraus approach, the carbon black network scission process is assumed to be thermally activated. 

Activation always involves some form of chemical attack. However, chemical activation is a term often used to indicate the prior impregnation of the precursor with a chemical agent such as phosphoric acid or zinc chloride before heat treatment. Physical activation, on the other hand, signifies the heat treatment of the char in a mildly reactive atmosphere such as steam or carbon dioxide. This type of process is preferably referred to as thermal activation (Baker, 1992). The apparent distinction between chemical and physical is somewhat unsatisfactory for two reasons first, it implies a fundamental difference in the mechanism of activation and second, it does not allow for the many procedures which involve both types of treatment. 

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