Vibration frequency response function can be calculated, thereby characterizing the system. This technique is used in the field of experimental modal analysis to determine the vibration characteristics of a structure. The simple mass–spring–damper model is the foundation of vibration analysis, but what about more complex systems? The mass–spring–damper model described above is called a single degree of freedom (SDOF) model since the mass is assumed to only move up and down. In more complex systems, the system must be discretized into more masses that move in more than one direction, adding degrees of freedom. The major concepts of multiple degrees of
Catch per unit effort that decisions about stock management can also be made by the people doing the harvesting. The best practice is to standardise the effort employed ("e.g." number of traps or duration of searching), which controls for the reduction in catch size that often results from subsequent efforts. Although CPUE is a relative measure of abundance, it can be used to estimate absolute abundances. The main difficulty when using measures of CPUE is to define the unit of effort. Catch per unit effort In fisheries and conservation biology, the catch per unit effort (CPUE) is an indirect measure of the abundance of