Initial models alteration

The processes of scattering and absorption of radiation in the atmosphere so significantly alter the spectral distribution that any similarity to extra terrestrial radiation is almost coincidental. Experiments with radiation between surfaces have shown that blackbody radiation theory can be extended successfully to many radiation heat transfer situations. In these situations the strict equilibrium requirements of the initial model have so far not proved to be necessary for practical designs. Most importantly the concept of temperature has proved useful in non-equilibrium radiation flux situations(3). 

The initial model is transformed by altering the atom type and by removal or addition of atoms. With the addition of atoms, the corresponding change in bond length is considered. 

The peak positions are important information for an RDF descriptor. Two RDF descriptors that exhibit the same peak positions must have the same distance distribution in the molecule and, thus, a similar basic structure. The differences in the RDF descriptor can then be attributed to the atomic properties. When atomic properties are used that are independent of the chemical neighborhood, this kind of comparison is useful to find initial models, which contain similar skeletons and which can be optimized through alteration of atom types and shifting operations. The tolerance of the method can be chosen optionally. The initial model chosen and the criterion for similarity of the RDF descriptors determine the strategy for optimization. 

The initial model is altered in several ways to adapt the resulting RDF descriptor to that obtained from the CPG neural network. For this task a program was developed that contains empirical rules for the optimization of an RDF descriptor. The program searches for the molecule having an RDF descriptor most similar to the one retrieved from the CPG neural network using different similarity criteria. Although several similarity criteria may be chosen, some rules must be considered. 

After an initial model is retrieved, the molecule is manipulated by addition, removal, and changing of the atom type. The decision for the sequence of optimization steps is dynamically adapted to the properties of the RDF descriptor, the chosen atomic properties, and the similarity criterion. The following properties are altered ... 

MD has been appUed for the determination of changes of physical properties of lipid bilayers caused by the incorporated peptide as well as for the determination of possible peptide stractural alterations. MD were performed under periodie boundary conditions using the GROMACS software [68] and the GROMOS87 [69] forcefield with corrections for hpids [70, 71]. The initial models of transmembrane a-helix peptides have been generated by means of HyperChem [72]. Preequilibrated DMPC and DPPC bilayers with 128 lipid molecules and 3655 molecules of water in L hquid-ciystalline state pubhshed by Tieleman et al. [73] have been used in bilayer modehng. For the simulations with membrane in Lp gel state, we created... 

A di awback is that the evaluation scheme for modeling the course of chemical reactions, as set up by the initial developer, is difficult to change as any alteration might have unexpected consequences for other types of reactions. Thus, it is a beautiful edifice that has basically not been changed since the early Nineties. 

The examples outlined above are intended to show the utility of a generalized computer model for polymer processing problems. Such a model is able to adapt itself to a wide variety of situations simply by adjustments to the input dataset, rather than requiring alterations to the code itself. This flexibility makes the code somewhat more difficult to learn initially, but this might be minimized by embedding the finite-element code itself in a more "user-friendly" graphics-oriented shell. 

Several boundary conditions have been used to prescribe the outer limit of an individual rhizosphere, (/ = / /,). For low root densities, it has been assumed that each rhizosphere extends over an infinite volume of. soil in the model //, is. set sufficiently large that the soil concentration at r, is never altered by the activity in the rhizosphere. The majority of models assume that the outer limit is approximated by a fixed value that is calculated as a function of the maximum root density found in the simulation, under the assumption that the roots are uniformly distributed in the soil volume. Each root can then extract nutrients only from this finite. soil cylinder. Hoffland (31) recognized that the outer limit would vary as more roots were formed within the simulated soil volume and periodically recalculated / /, from the current root density. This recalculation thus resulted in existing roots having a reduced //,. New roots were assumed to be formed in soil with an initial solute concentration equal to the average concentration present in the cylindrical shells stripped away from the existing roots. The effective boundary equation for all such assumptions is the same ... 

The dynamic surface tension of a monolayer may be defined as the response of a film in an initial state of static quasi-equilibrium to a sudden change in surface area. If the area of the film-covered interface is altered at a rapid rate, the monolayer may not readjust to its original conformation quickly enough to maintain the quasi-equilibrium surface pressure. It is for this reason that properly reported II/A isotherms for most monolayers are repeated at several compression/expansion rates. The reasons for this lag in equilibration time are complex combinations of shear and dilational viscosities, elasticity, and isothermal compressibility (Manheimer and Schechter, 1970 Margoni, 1871 Lucassen-Reynders et al., 1974). Furthermore, consideration of dynamic surface tension in insoluble monolayers assumes that the monolayer is indeed insoluble and stable throughout the perturbation if not, a myriad of contributions from monolayer collapse to monomer dissolution may complicate the situation further. Although theoretical models of dynamic surface tension effects have been presented, there have been very few attempts at experimental investigation of these time-dependent phenomena in spread monolayer films. 

---