") The other two species are a more complex mix of colors and anti-colors. The Higgs bosons, which induce spontaneous symmetry breaking of the gauge groups and are responsible for the existence of inertial mass . It turns out that the gauge transformations of the gauge bosons can be exactly described using a unitary group called a "gauge group". The gauge group of the strong interaction is SU(3), and the gauge group of the electroweak interaction is SU(2)×U(1). Therefore, the Standard Model is often referred to as SU(3)×SU(2)×U(1). The Higgs boson is the only boson in the theory which is not a gauge boson; it has a special status in the theory, and has been the subject of some controversy. Gravitons, the bosons believed to mediate the gravitational interaction, are not accounted for in the Standard Model. Model Railroad Track Layout There are twelve different types, or "flavours", of fermions in the Standard Model. Amongst the proton, neutron, and electron, those fermions which constitute the vast majority of matter, the Standard Model considers only the electron a fundamental particle. "

" a "fashion model") or other personal items of artistic or aesthetic value, and who is often physically attractive; a model who attains celebrity status or is otherwise widely known is said to be a "supermodel". promotion model— promotes a product or service role model — person who acts as a behavioural or moral example to others. Models as physical objects physical model — physical representation of an object; in engineering, similitude is used in the scientific testing of physical models. scale model — a replica or prototype of an object built as a hobby or for research. a particular version of a series of vehicles produced by an automobile manufacturer is known as a model. Model-View-Controller (MVC) is a software architecture that separates an application's data model, user interface, and control logic into three distinct components so that modifications to one component can be made with minimal impact to the others. MVC is often thought of as a software design pattern. Atlas Model Railroad Co However, MVC encompasses more of the architecture of an application than is typical for a design pattern. Hence the term architectural pattern may be useful (Buschmann, et al 1996), or perhaps an aggregate design pattern. "