" Unlike the quarks, they do not possess a quality called "color", and their interactions are only weak and electromagnetic, and fall off with distance. On the other hand, the strong or "color" force between quarks gets stronger with distance, so that quarks are always found in colorless combinations called hadrons, a phenomenon known as quark confinement . These are either fermionic baryons composed of three quarks (the proton and neutron being the most familiar example) or bosonic mesons composed of a quark-antiquark pair (such as pions). The mass of such aggregates exceeds that of the components due to their binding energy. Tests and predictions The Standard Model predicted the existence of W and Z bosons, the gluon, the top quark and the charm quark before these particles had been observed. Their predicted properties were experimentally confirmed with good precision. The Large Electron-Positron collider at CERN tested various predictions about the decay of Z bosons, and found them confirmed. Model Airplane Gas Engine To get an idea of the success of the Standard Model a comparison between the measured and the predicted values of some quantities are shown in the following table: Quality Measured (GeV) SM prediction (GeV) Mass of W boson 80,4120±0,0420 80,3900±0,0180 Mass of Z boson 91,1874±0,0021 91,1874±0,0021 Challenges to the Standard Model Although the Standard Model has had great success in explaining experimental results, it has never been accepted as a complete theory of fundamental physics. This is because it has two important defects: The model contains 19 free parameters, such as particle masses, which must be determined experimentally (plus another 10 for neutrino masses). "

" For conceptual models to be the shared property of a research community the concepts they involve must be capable of being shared. That is the case when a consensual understanding of these concepts has been achieved or can be achieved by means of definition, examples, etc. With respect to what is shown by a conceptual model there are differences at least with respect to computer science, mathematics and logic. Mathematical models in one way or another establish a functional cohesion between entities such as input values and output values. Logical models establish an interpretation relationship between formulae and structures. Models in Computer Science are largely organizational in that they show how data, a cooperation between agents, the process of creating a response to an external stimulus, an algorithm, or similar is structured. The emphasis of organization that is apparent in many models of computer science appears to be a consequence of either of the following: (1) complexity issues need to be dealt with such that a functional cohesion actually can be evaluated. Antique Model Airplane (2) a domain of individuals or universe of discourse has to be established and the individuals within that domain are supposed to be capable of being distinguished from each other by means of their condition in that organization or particular handles available to a user of that model. III. "