.NTA2Mw.MjU4MTY0

Another method consists in measuring the length of the skeleton of the particle (2). This method is also ineffective in the case where the particle has round ends or a rough boundary (see fig. 2). Figure 2 : The définition of the length of a particle as the length of its skeleton is not always effective. It is our aim to define the length of a particle precisely. The two définitions given above were both rejected, because they were not sufficiently général. They are applicable only to a limited class of particles. We thus arrive at the question of how the class of long narrow particles can be defined. Unfortunately, it is impossible to answer such a question, because the description of a particle as long and narrow is quite subjective. At what length/width ratio- can a rectangle be considered as being elongated ? Without information on the shape of the particles under study, length must be defined regardless of shape, so as to remain applicable to particles of any shape. Consider an arbitrarily shaped particle X and let x and y be two points within X. There exist several paths in X linking x and y (see fig. 3-1). The shortest one is called "géodésie arc" (see fig. 3-2), and Figure 3-1 : Paths within the particle 3-2 : Géodésie arc 3-3 : The length of the particle is defined as the length of its longest géodésie arc