Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Concentration Dependen Sedimentation of Collidal Rods   In the first part of this paper, an approximate theory is developed for the
leading order concentration dependence of the sedimentation coefficient for
rod-like colloids/polymers/macromolecules. To first order in volume fraction
$\phi$ of rods, the sedimentation coefficient is written as $1+\alpha \phi$.
For large aspect ratio L/D (L is the rod length, D it's thickness) $\alpha$ is
found to very like $\propto (\frac{L}{D})^2/\log (\frac{L}{D})$. This
theoretical prediction is compared to experimental results. In the second part,
experiments on {\it fd}-virus are described, both in the isotropic and nematic
phase. First order in concentration results for this very long and thin
(semi-flexible) rod are in agreement with the above theoretical prediction.
Sedimentation profiles for the nematic phase show two sedimentation fronts.
This result indicates that the nematic phase becomes unstable with the respect
to isotropic phase during sedimentation.

14
The categories of this paper are: math-ph
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom