Aerospace & Defense Technology - June 2021 - 34

Tech Briefs
positive and monotone systems, capture
strategies for 3D reach-avoid games, and
collective cell migration.
In designing efficient surveillance, information
gathering, and coordination
strategies for robotic networks in dynamic
environments and applying them
to DoD scenarios, it could be argued that
sensor scheduling, motion planning and
coordination algorithms for surveillance
and anomaly detection is a crucial objective.
The key technological challenge is
how to search an area in a persistent
manner, with minimal average time to
detection, with unpredictable trajectories
and with optimally partitioned
workload among multiple assets.
The key scientific subject is the study
of optimization criteria, convexity
properties, relaxations and coordination
strategies defined via the theory of
Markov chains and random walks. This
technical approach is based on a combination
of tools from the study of
Markov chains, convex optimization,
dynamical systems, distributed algorithms,
robotic coordination, and network
systems. The research effort on
stochastic surveillance can be articulated
via the following tasks:
1) Characterizing optimal stationary
distributions, i.e., deciding where to
focus the search efforts;
2) Computing optimal reversible Markov
chains via convex optimization;
3) Computing optimal non-reversible
Markov chains on lifted spaces;
4) Computing optimal Markov chains
with entropy-rate constrains, i.e., designing
unpredictable fast searchers;
5) Designing and characterizing search
strategies for randomly moving
evaders; and
6) Defining, analyzing and optimizing
an appropriate notion of group Kemeny
constant (i.e., a mean first passage
time for multiple walkers),
thereby designing multivehicle surveillance
policies.
This work was done by Francesco Bullo
of the University of California, Santa Barbara
for the Air Force Research Laboratory.
For more information, download the
Technical Support Package (free white
paper) at www.aerodefensetech.com/tsp
under the Unmannaed Vehicles & Robotics
category. AFRL-0304
Biobased Carbon Fibers and Thermosetting Resins for Use
in DOD Composites Applications
The use of biological resources to make advanced fibers and high-performance thermosetting resins
will help reduce the dependence of military composites on the volatile cost of petroleum, result in significant
technological gains, and reduce toxicity of composite materials.
Army Research Laboratory, Aberdeen Proving Ground, Maryland
T
he goal of this research is to explore
the use of renewable resources
derived from plants and other
sources to prepare high-performance
carbon fiber and thermosetting matrix
resins with high-strength and highthermal
resistance. The scientific objectives
of this work are to 1) develop
methods for breaking down, modifying,
and processing renewable resources
to make epoxy resins, vinyl
resins, and carbon fibers and 2) determine
structure-property relationships
for these novel materials.
Bacteria can successfully decompose
lignin into useable structures for the
formation of small filaments that might
be able to be converted into carbon
fibers. Approximately 300 strains of
bacteria that decompose lignin were
identified, and some have the potential
to make lignin into fiber-forming
oligomers, including newly identified
species of Serratia. However, scale-up of
this process proved problematic and unfeasible
for completion in this project.
34
Cov
Various weapons platforms that use composite materials including the Apache helicopter, the high-mobility
multipurpose wheeled vehicle, Stiletto, F-22, and USS Radford.
Lignin was chemically fractionated to
alter its molecular weight distribution
and alter its usefulness for separating
chemically modified lignin. Various
chemical modifications of lignin have
www.aerodefensetech.com
ToC
been used successfully in carbon fiber
development. These methods include
acetylation and methacrylation, and
separation strategies were developed to
produce carbon fiber precursors. Both
Aerospace & Defense Technology, June 2021
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Aerospace & Defense Technology - June 2021

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