291 research outputs found
A Hybrid Observer for a Distributed Linear System with a Changing Neighbor Graph
A hybrid observer is described for estimating the state of an channel,
-dimensional, continuous-time, distributed linear system of the form
. The system's state is
simultaneously estimated by agents assuming each agent senses and
receives appropriately defined data from each of its current neighbors.
Neighbor relations are characterized by a time-varying directed graph
whose vertices correspond to agents and whose arcs depict
neighbor relations. Agent updates its estimate of at "event
times" using a local observer and a local parameter
estimator. The local observer is a continuous time linear system whose input is
and whose output is an asymptotically correct estimate of
where a matrix with kernel equaling the unobservable space of .
The local parameter estimator is a recursive algorithm designed to estimate,
prior to each event time , a constant parameter which satisfies the
linear equations , where is a small
positive constant and is the state estimation error of local observer
. Agent accomplishes this by iterating its parameter estimator state
, times within the interval , and by making use of
the state of each of its neighbors' parameter estimators at each iteration. The
updated value of at event time is then . Subject to the assumptions that (i) the neighbor graph
is strongly connected for all time, (ii) the system whose state
is to be estimated is jointly observable, (iii) is sufficiently large, it
is shown that each estimate converges to exponentially fast as
at a rate which can be controlled.Comment: 7 pages, the 56th IEEE Conference on Decision and Contro
The Use of Force Feedback Control for Robotic Mating of Umbilical Fuel Lines
NASA has long desired the ability to remotely connect, disconnect, and reconnect the umbilical fuel lines to the Space Shuttle Vehicle (SSV). The Robotic Application and Development Laboratory (RADL) at Kennedy Space Center has been investigating the application of robotics to this problem. A generic remote umbilical system has been identified for a proof-of-concept demonstration, wherein a robot is used to mate an umbilical connector with a moving target representing the SSV. This task is a variation of the classic peg-inthe- hole problem, where the hole is undergoing random motions.
For umbilical docking, the ability to minimize and control contact forces between the umbilical lines and the SSV is vital. These forces occur both during the mating of the fuel line with the SSV and also as a result of the relative motion between the robot and the SSV after mating.
This paper describes work on the force feedback control problems encountered by the RADL for umbilical mating. An outline of a proposed docking protocol is first presented, indicating the role required offeree feedback. The use of active force feedback control is described, along with the performance requirements and experimental results. Proposed modifications to the existing force feedback controller, including passive compliance requirements are described. Finally description of future work is presented
Leisingera sp. JC1, a Bacterial Isolate from Hawaiian Bobtail Squid Eggs, Produces Indigoidine and Differentially Inhibits Vibrios
Female members of many cephalopod species house a bacterial consortium that is part of their reproductive system, the accessory nidamental gland (ANG). These bacteria are deposited into eggs that are then laid in the environment where they must develop unprotected from predation, pathogens and fouling. In this study, we characterized the genome and secondary metabolite production of Leisingera sp. JC1, a member of the roseobacter clade (Rhodobacteraceae) of Alphaproteobacteria isolated from the jelly coat of eggs from the Hawaiian bobtail squid, Euprymna scolopes. Whole genome sequencing and MLSA analysis revealed that Leisingera sp. JC1 falls within a group of roseobacters associated with squid ANGs. Genome and biochemical analyses revealed the potential for and production of a number of secondary metabolites, including siderophores and acyl-homoserine lactones involved with quorum sensing. The complete biosynthetic gene cluster for the pigment indigoidine was detected in the genome and mass spectrometry confirmed the production of this compound. Furthermore, we investigated the production of indigoidine under co-culture conditions with Vibrio fischeri, the light organ symbiont of E. scolopes, and with other vibrios. Finally, both Leisingera sp. JC1 and secondary metabolite extracts of this strain had differential antimicrobial activity against a number of marine vibrios, suggesting that Leisingera sp. JC1 may play a role in host defense against other marine bacteria either in the eggs and/or ANG. These data also suggest that indigoidine may be partially, but not wholly, responsible for the antimicrobial activity of this squid-associated bacterium.
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