Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Retractable Prosthesis for Transfemoral Amputees Using Series Elastic
  Actuators and Force Control   We present a highly functional and cost-effective prosthesis for transfemoral
amputees that uses series elastic actuators. These actuators allow for accurate
force control, low impedance and large dynamic range. The design involves one
active joint at the knee and a passive joint at the ankle. Additionally, the
socket was designed using mirroring of compliances to ensure maximum comfort.

28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ