Joining models

DNA polymerase and ligase base replication and strand joining 

Another phenomenon that still lacks an explanation is the ordered usage of JK 

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How parallelism is expressed implicitly, as in an automatically parallelized DO loop, or explicitly, as in a UNIX fork-and-join model.- 39... 

Fig. 1. Joining model of a D to J segment joint. For explanation, see the text. (Taken from [1] and [20])...

Another important class of materials which can be successfiilly described by mesoscopic and contimiiim models are amphiphilic systems. Amphiphilic molecules consist of two distinct entities that like different enviromnents. Lipid molecules, for instance, comprise a polar head that likes an aqueous enviromnent and one or two hydrocarbon tails that are strongly hydrophobic. Since the two entities are chemically joined together they cannot separate into macroscopically large phases. If these amphiphiles are added to a binary mixture (say, water and oil) they greatly promote the dispersion of one component into the other. At low amphiphile... 

Both the dissipative force and the random force act along the line joining the pair of beads and also conserve linear and angular momentum. The model thus has two unknown functions vP rij) and w Yij) and two unknown constants 7 and a. In fact, only one of the two weight functions can be chosen arbitrarily as they are related [Espanol and Warren 1995]. Moreover, the temperature of the system relates the two constants ... 

Most of the SpartanView models on the CD have been constructed using quantum mechanical calculations although some simplifications have been used to accelerate the calculations This means that the models although closely resembling real molecules never precisely duplicate the properties of real molecules Even so the models are suf ficiently similar to real molecules that they can usually be treated as equivalent This is important because models can contain more types of information and models can be constructed for molecules that cannot be studied m the laboratory Also models can be joined together to make animations that show how molecules move... 

Recently, Langer (1999) has joined the debate. He at first sounds a distinct note of scepticism ... the term numerical simulation makes many of us uncomfortable. It is easy to build models on computers and watch what they do, but it is often unjustified to claim that we learn anything from such exercises. He continues by examining a number of actual simulations and points out, first, the value of... 

As indicated, an implicit assumption of the JKR theory is that there are no interactions outside the contact radius. More specifically, the energy arguments used in the development of the JKR theory do not allow specific locations of the adhesion forces to be determined except that they must be associated with the contact line where the two surfaces of the particle and substrate become joined. Adhesion-induced stresses act at the surface and not a result of action-at-a-distance interatomic forces. This results in a stress singularity at the circumference of the contact radius [41]. The validity of this assumption was first questioned by Derjaguin et al. [42], who proposed an alternative model of adhesion (commonly referred to as the DMT theory ). Needless to say, the predictions of the JKR and DMT models are vastly different, as discussed by Tabor [41]. 

The micro-mechanical processes will be presented next, followed by the models used to describe them. The predictions of the models will then be compared with results obtained using well-defined coupling chains. Application of the models to the joining of dissimilar polymers will then be described. Finally welding of glassy polymers will be considered. 

Fig. 9. The upper panel shows the predietions of Brown s [15] model for the eoupling of an immiscible polymer interface. Clearly the predietions do not agree with his experimental results on PMMA joined to PS-r-PMMA shown in the lower panel.

The usual structure of off-lattice chain models is reminiscent of the Larson models the water and oil particles are represented by spheres (beads), and the amphiphiles by chains of spheres which are joined together by harmonic springs... 

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