Elasticity elementary particle

A quite different approach to the van der Waals interaction which employs methods from theoretical elementary particle physics has appeared [5.79,80]. By considering the van der Waals interaction as an elastic two-photon exchange process, they derived a formula for the two-particle potential valid only in the fully retarded case which has been generalized by LUBKIN [5.81] to... 

All the known forces of interaction existing in nature can be reduced to a small number of main types. Belonging to the first type are the gravitational and electromagnetic forces belonging to the last type are the forces of interatomic and intermolecular interaction pertaining to which macroscopic manifestation are elasticity forces. (Outside the scope of this book are the short-range nuclear forces, bonded nucleons in nuclei, and weak interactions, revealed in the decay of elementary particles.)... 

Figure 9 Adsorption process of NO on Pd particles supported on MgO(l 00). (a) Global adsorption probability as a function of surface temperature and for various particle sizes (from Ref. [89]). (b) Schematic representation of die elementary processes in die molecular adsorption of NO on supported Pd particles (1) quasi-elastic redection on die bare support, (2) physisorption-diffusion-desorption from the bare support, (3) direct chemisorption on die Pd particles, (4) NO chemisorption on the Pd particles via a precursor physisorbed state on die bare support. Xs is die mean diffusion length of die NO molecules on the support and p is die width of die collection zone around die Pd particles.

From the above example, it should be clear that all the elementary excitations are the result of the collective interactions of the bare fields in the system, and therefore pertain to the system as a whoIe24). Elementary excitations, which will be identified with the physical particles we observe, correspond to superpositions of large numbers of exact stationary states of the field Hamiltonian it, Eq. (2.3), with a narrow spread in energy i.e. they are wave-packets. An equivalent way of saying this is that the elementary excitations interact with one another, and so have finite lifetimes their interactions may lead to reactive, inelastic or elastic scattering processes. 

Boerhaave also brought together different genres of experiments on air to devise a consistent picture of its nature and operations. He was familiar with Boyle s and Mariotte s experiments with the air-pump, which characterized the elasticity of air, as well as with Hales s experiments on the fixation of air. On the one hand, this elastic medium functioned as an instrument of many chemical operations. On the other hand, air particles exhibited a tendency towards a union. The air fixed in bodies seemed to take up a very small space when divided into smaller particles of its proper substance, but it expanded considerably when these particles were collected together. Boerhaave s discussion of air, like the one on fire, is remarkable for the facility with which he mixed different genres of instrumental practices to create a coherent ontology of these supposedly elementary bodies. He discussed various effects... 

Computer simulations for several models (Weber and Stillinger, 1985 Ohmine, 1995) have determined that the elementary transitions between neighboring basins entail shifts of only small local groups of particles. To be precise, the difference between the inherent structures of the two basins involved in a large V-particle system is concentrated on a neighboring set of (9(1) particles the remainder particles experience at most a minor elastic response to the localized repacking (Lacks, 1998). In view of the fact that the number of such localized repacking possibilities is proportional to system size, the number of transition states (saddle points) in the boundary of any basin will be O(V), i.e., an extensive property. So too, then, will be the net kinetic exit rate from any basin at positive temperature. 

Binary elastic collisions between the moving particle/atom and the stationary lattice atom represent the dominant mechanism for the formation of primary defects in metal crystals, and are natural elementary steps in all models and computer simulations of damage processes. 

---