Simulation by computer

Today, particle accelerators and computers are as much apart of astronomy as telescopes intent on spying out the visible and the invisible. In their accelerators, high-energy physicists are able to reproduce conditions in the Big Bang and in the stellar core. Then, taking over from them, numerical simulation by computer can write the story of matter through its various cycles of concentration, nucleosynthesis and dispersion. 

Until now, the theoretical discussion has focused on monodisperse two-dimensional model systems. However, some studies have been performed on polydisperse systems, notably by Weaire et al. [68-72] The evolution of a soap froth of random cell sizes and shapes, known as a Voronoi network, was simulated by computer [68] (Fig. 7). The condition that three films must always meet at angles of 120° was again used. Cells with more than six sides were found... 

Figure 60. Comet-tail CO+(A1l —>X2 2+) spectra from (a, c) luminescent ion-molecule reaction C++02- C0+ + 0 at lab = 5 eV (b,d), charge-transfer reaction Ar+ +CO->CO+ + Ar at lab=1000 eV. Experimental spectra (a, b) were obtained with 2-nm spectral resolution. Tabulated band heads for CO+ (A— BX) system are indicated. Spectral lines designated as Ar(II) and C(I) do not belong to CO+ emission. Dashed portion of curves was not actually measured. Spectra simulated by computer calculations are given in diagrams (c and d). Rotational distributions assumed in simulation calculations were thermal with T= 45,000°K (c) and 1000°K (

Figure 10. Combustion efficiencies of fuels simulated by computer model.

As discussed in Sect. 2.1, Frank [2] suggested that a screw dislocation emerging at a crystal surface provided the necessary steps for growth, even at low supersaturation when two-dimensional nucleation is improbable. When the solution in contact with a crystal becomes supersaturated, steps are generated which wind into spirals about the centre of the dislocation. A number of such spirals have been found [26] and, indeed, the process of formation of a spiral step pattern has been simulated by computer [25]. The results, shown in Fig. 11, illustrate how two associated steps wind up into a double spiral that covers the entire crystal face. Two-dimensional nuclei are also observed, some of which are incorporated into the advancing spiral. 

The relative rates of hydrogen and carbon interchange have been measured by Saunders et al. (1973c) using a mixture of (1,1,1- H3)- and (2- C)-labelled isopropyl cations at —88°C. The changes in the relative areas of different peaks as well as C-satellites were observed, and the time dependence of the concentrations of different labelled isomers were simulated by computer [using mechanisms (34)-(36)]. A combination of mechanisms (34) and (35) or mechanisms (34) and (36) could match the measurements. The rate for (34)... 

The impedance behavior of electrode reactions is often complex but can be conveniently simulated by computer calculations, especially in the case of the method based on kinetic equations (108, 113). The forms of the frequency response represented in terms of the Z versus Z" complex-plane plots and by relations of Z or phase angle to frequency ai or log (o (Bode plots) are often characteristic of the reaction mechanism and involvement of one or more adsorbed intermediates, and they thus provide diagnostic bases for mechanism determination complementary to those based on dc, steady-state rate versus potential responses. The variations of Z versus Z" plots with dc -level potential, in controlled-potential experiments, also give rise to useful diagnostic information related to the dc Tafel behavior. 

Figure 3.09 (a) Time variation of , the potential energy per atom in a 150-atom niekel-phosphorous amorphous deposit, as simulated by computer, (b) Logarithm of the distribution of potential energy minima, plotted against potential energy per atom. (After Stillinger and Weber, 1984). 

Bioinformatics is an instrument for suggestions, no more and no less. For a long time to come, Nature will be too complex to be accurately modeled and simulated by computer. This means that we will have to cope with rough and inaccurate models that lead to predictions that are not fail-safe. 

The AAMI Bl Method The AAMI B1 method is based on inactivation of a hypothetical mixed culture of microorganisms. This hypothetical mixed culture contains microorganisms of various 0 q values present in different defined frequencies this is referred to as the standard but arbitrary" distribution of radiation responses. Inactivation of populations of various different initial numbers, but always conforming to the standard but arbitrary" distribution of radiation responses, was simulated by computer. From the simulation a series of tables was derived relating initial number of contaminants to dose and SAL. 

The first simulation by computer of a molecular system was carried out using this method. It consists of generating configurations of a system introducing random changes in the position of its constituents. 

Selection, data analysis and simulation by computer software... 

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