2,394 research outputs found
Digital multichannel photometer
System was developed for use in astronomy and other research areas concerned with detection of faint-light images. Photometer system is comparable in performance to good photomultiplier tube array except that digital electronics are used instead of analog
Beyond Reynolds: A Constraint-Driven Approach to Cluster Flocking
In this paper, we present an original set of flocking rules using an
ecologically-inspired paradigm for control of multi-robot systems. We translate
these rules into a constraint-driven optimal control problem where the agents
minimize energy consumption subject to safety and task constraints. We prove
several properties about the feasible space of the optimal control problem and
show that velocity consensus is an optimal solution. We also motivate the
inclusion of slack variables in constraint-driven problems when the global
state is only partially observable by each agent. Finally, we analyze the case
where the communication topology is fixed and connected, and prove that our
proposed flocking rules achieve velocity consensus.Comment: 6 page
Experimental Validation of a Real-Time Optimal Controller for Coordination of CAVs in a Multi-Lane Roundabout
Roundabouts in conjunction with other traffic scenarios, e.g., intersections,
merging roadways, speed reduction zones, can induce congestion in a
transportation network due to driver responses to various disturbances.
Research efforts have shown that smoothing traffic flow and eliminating
stop-and-go driving can both improve fuel efficiency of the vehicles and the
throughput of a roundabout. In this paper, we validate an optimal control
framework developed earlier in a multi-lane roundabout scenario using the
University of Delaware's scaled smart city (UDSSC). We first provide conditions
where the solution is optimal. Then, we demonstrate the feasibility of the
solution using experiments at UDSSC, and show that the optimal solution
completely eliminates stop-and-go driving while preserving safety.Comment: 6 Pages, 4 Figures, 1 tabl
A Geometric Analysis to Protect Manned Assets from Newly Launched Objects - COLA Gap Analysis
A safety risk was identified for the International Space Station (ISS) by The Aerospace Corporation following the launch of GPS IIR-20 (March 24, 2009), when the spent upper stage of the launch vehicle unexpectedly crossed inside the ISS notification box shortly after launch. This event highlighted a 56-hour vulnerability period following the end of the launch Collision Avoidance (COLA) process where the ISS would be unable to react to a conjunction with a newly launched object. Current launch COLA processes screen each launched object across the launch window to determine if an object's nominal trajectory is predicted to pass within 200 km of the ISS (or any other manned/mannable object), resulting in a launch time closure. These launch COLA screens are performed from launch through separation plus I 00 minutes. Once the objects are in orbit, they are cataloged and evaluated as part of routine on-orbit conjunction assessment processes. However, as the GPS IIR-20 scenario illustrated, there is a vulnerability period in the time line between the end of launch COLA coverage and the beginning of standard on-orbit COLA assessment activities. The gap between existing launch and on-orbit COLA processes is driven by the time it takes to track and catalog a launched object, identify a conjunction, and plan and execute a collision avoidance maneuver. For the ISS, the total time required to accomplish an of these steps is 56 hours. To protect human lives, NASA/JSC has requested that an US launches take additional steps to protect the ISS during this "COLA gap" period. The uncertainty in the state of a spent upper stage can be quite large after all bums are complete and all remaining propellants are expelled to safe the stage. Simply extending the launch COLA process an additional 56 hours is not a viable option as the 3-sigma position uncertainty will far exceed the 200 km miss-distance criterion. Additionally, performing a probability of collision (Pc) analysis over this period is also not practical due to the limiting effects of these large orbit state uncertainties. An estimated upper bound for Pc for a typical spent upper stage if nominally aligned for a direct broadside collision with the ISS is only on the order of 10-6. For a smaller manned object such as a Soyuz capsule, the risk level decreases to an order of 10'8 . In comparison, the Air Force Range policy (AFI 91-217) for launch COLAs would only eliminate launch opportunities when conjunctions with objects exceed a Pc of 10'5 This paper demonstrates a conservative geometry-based methodology that may be used to determine if launch opportunities pose a threat to the ISS during the COLA gap period. The NASA Launch Services Program at Kennedy Space Center has developed this COLA gap analysis method and employed it fQr three NASA missions to identify potential ISS conjunctions and corresponding launch window closures during the 56-hour at-risk period. In the analysis, for each launch opportunity, the nominal trajectory of the spent upper stage and the orbit state of the ISS are propagated over the 56 hour period. Each time the upper stage crosses the orbit plane of the ISS, the relative radial and argument of latitude separations are calculated. A window cutout is identified if these separation differences fall within a mission-specific violation box, which is determined from the evaluation of a Monte Carlo dispersions analysis that quantifies the potential variation in the upper stage radial and argument of latitude differences. This paper details the results of these analyses and their impacts to each mission
An Optimal Control Approach to Flocking
Flocking behavior has attracted considerable attention in multi-agent
systems. The structure of flocking has been predominantly studied through the
application of artificial potential fields coupled with velocity consensus.
These approaches, however, do not consider the energy cost of the agents during
flocking, which is especially important in large-scale robot swarms. This paper
introduces an optimal control framework to induce flocking in a group of
agents. Guarantees of energy minimization and safety are provided, along with a
decentralized algorithm that satisfies the optimality conditions and can be
realized in real time. The efficacy of the proposed control algorithm is
evaluated through simulation in both MATLAB and Gazebo.Comment: 6 pages, 4 figures. To appear at the 2020 American Control Conferenc
Inheritance and QTL Analysis of Field Resistance to Ashy Stem Blight in Common Bean
Ashy stem blight [caused by Macrophomina phaseolina (Tassi) Goid.] can be a serious disease of common bean (Phaseolus vulgaris L.) under drought and high temperature conditions in some regions. The mode of inheritance of valuable sources of resistance is lacking. We studied inheritance of field resistance to ashy stem blight in a recombinant inbred population (’Dorado’ × XAN 176) consisting of 119 F5:7 recombinant inbred lines (RILs) tested in replicated experiments across 2 yr. A score from 1 to 9 (no disease to severe disease) was used to measure disease reaction. Moderate HNs (0.53 and 0.57) and near-normal frequency distribution of RILs for mean disease score each year indicated a lack of discrete segregation classes. The phenotypic variation across a subgroup composed of 79 RILs was further investigated with 165 randomly amplified polymorphic DNA (RAPD) markers by one-way analyses of variance and interval mapping. Five quantitative trait loci (QTL), explaining 19, 15, 15, 13, and 13% of the phenotypic variation for disease score, were detected in 1993. Three of these QTL, explaining 15,12, and 12% of the variation in disease reaction, were detected in 1994. Multiple QTL regression models (P \u3c 0.01) explained up to 47% (four loci) of the phenotypic variation for disease score in 1993 and 28% (three loci) in 1994. The five QTL, all derived from XAN 176, generally showed additive effects. These QTL-linked RAPD markers may prove useful for indirect selection of field resistance to ashy stem blight derived from XAN 176
- …