Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spring-damper equivalents of the fractional, poroelastic, and
  poroviscoelastic models for elastography   In MR elastography it is common to use an elastic model for the tissue's
response in order to properly interpret the results. More complex models such
as viscoelastic, fractional viscoelastic, poroelastic, or poroviscoelastic ones
are also used. These models appear at first sight to be very different, but
here it is shown that they all may be expressed in terms of elementary
viscoelastic models.
  For a medium expressed with fractional models, many elementary spring-damper
combinations are added, each of them weighted according to a long-tailed
distribution, hinting at a fractional distribution of time constants or
relaxation frequencies. This may open up for a more physical interpretation of
the fractional models.
  The shear wave component of the poroelastic model is shown to be modeled
exactly by a three-component Zener model. The extended poroviscoelastic model
is found to be equivalent to what is called a non-standard four-parameter
model. Accordingly, the large number of parameters in the porous models can be
reduced to the same number as in their viscoelastic equivalents. As long as the
individual displacements from the solid and fluid parts cannot be measured
individually the main use of the poro(visco)elastic models is therefore as a
physics based method for determining parameters in a viscoelastic model.

22
The categories of this paper are: chao-dyn
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
5
The categories of this paper are: gr-qc