What is rarefaction?

What Does rarefaction Mean

The Latin word rarefactum came to our language as a rarefaction . It is about the process and the consequences of rarefying , an action that consists in making a matter in a gaseous state lose its density , according to what is explained by the Royal Spanish Academy ( RAE ) in its dictionary.

It is possible to oppose rarefaction to compression : whereas, in rarefaction, low pressure and a low number of molecules are recorded in each space, in compression there is high pressure and many molecules that move closer and closer to each other. It can be said, therefore, that the rarefaction process leads a body to dilate , expanding and occupying more space due to the decrease in density.

Rarefaction spreads through expansive and longitudinal waves that, over time, become longer. The sound , for example, is formed by the succession of numerous rarefaction and compression waves whose propagation takes place by air.
In the layers of the Earth's atmosphere we can see a clear example of rarefaction: due to gravity, almost all the atmospheric mass is very close to the ground, which generates that in the upper layers the air has less density (than is rare) compared to the one found in the lower ones. In this way, the concept of rarefaction can be used to describe a decrease in the density of space over a fraction of time, as much as that of a specific area in a given period.
In the field of ecology , the rarefaction method is known as a technique that allows the comparison of the existing diversity in two collections that were collected through sampling of different intensity. Rarefaction, in this case, consists of reducing the number of individuals in the largest sample but preserving the proportion observed between the species.
It is a method created in 1968 by the oceanographer Howard L. Sanders. When individuals are sampled from an area, their diversity inevitably increases with each step, since adding individuals results in more species; consequently, even if two samples come from populations with equal diversity, the larger one will show more species, and this is the problem that Sanders wanted to solve with the rarefaction technique.
Despite being a useful solution, it was not perfect. For this reason, within a few years other researchers proposed improvements to the equation to obtain more precise results and avoid, for example, overestimating the number of species.

For medicine , bone rarefaction means the loss of bone mass, which is usually linked to advancing age. One of the most common diseases involving bone rarefaction is osteoporosis .
Osteoporosis is a disorder that affects the skeleton and can be caused by the alteration of the metabolism of its tissue . Its course is chronic and is characterized by bone rarefaction; in addition, it especially attacks the elderly, mainly women. It is not possible to detect and diagnose osteoporosis by means of radiographs directly, which is why to achieve this, professionals rely on the concept of bone rarefaction to take as a parameter, among others.
From a clinical point of view, osteoporosis consists of the reduction of bone mass to the point of beginning to manifest itself through symptoms . For radiology, on the other hand, the perception is different: it is seen as a loss of bone mass that occurs progressively over time, and is known as "physiological involution of the bone" or "physiological aging of the bone. bone".

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