360 research outputs found
Methodology for Prototyping Increased Levels of Automation for Spacecraft Rendezvous Functions
The Crew Exploration Vehicle necessitates higher levels of automation than previous NASA vehicles, due to program requirements for automation, including Automated Rendezvous and Docking. Studies of spacecraft development often point to the locus of decision-making authority between humans and computers (i.e. automation) as a prime driver for cost, safety, and mission success. Therefore, a critical component in the Crew Exploration Vehicle development is the determination of the correct level of automation. To identify the appropriate levels of automation and autonomy to design into a human space flight vehicle, NASA has created the Function-specific Level of Autonomy and Automation Tool. This paper develops a methodology for prototyping increased levels of automation for spacecraft rendezvous functions. This methodology is used to evaluate the accuracy of the Function-specific Level of Autonomy and Automation Tool specified levels of automation, via prototyping. Spacecraft rendezvous planning tasks are selected and then prototyped in Matlab using Fuzzy Logic techniques and existing Space Shuttle rendezvous trajectory algorithms
Efficiently Combining Human Demonstrations and Interventions for Safe Training of Autonomous Systems in Real-Time
This paper investigates how to utilize different forms of human interaction
to safely train autonomous systems in real-time by learning from both human
demonstrations and interventions. We implement two components of the
Cycle-of-Learning for Autonomous Systems, which is our framework for combining
multiple modalities of human interaction. The current effort employs human
demonstrations to teach a desired behavior via imitation learning, then
leverages intervention data to correct for undesired behaviors produced by the
imitation learner to teach novel tasks to an autonomous agent safely, after
only minutes of training. We demonstrate this method in an autonomous perching
task using a quadrotor with continuous roll, pitch, yaw, and throttle commands
and imagery captured from a downward-facing camera in a high-fidelity simulated
environment. Our method improves task completion performance for the same
amount of human interaction when compared to learning from demonstrations
alone, while also requiring on average 32% less data to achieve that
performance. This provides evidence that combining multiple modes of human
interaction can increase both the training speed and overall performance of
policies for autonomous systems.Comment: 9 pages, 6 figure
Piezo-Electric Activity of Rochelle Salt Under Various Conditions
University of Minnesota Ph.D. dissertation. May 1922. Major: Physics. Advisor: Professor W. F. G. Swann. 1 computer file (PDF); 13 pages. [479-491]. Reprinted in Physical Review
Polar distortions in hydrogen bonded organic ferroelectrics
Although ferroelectric compounds containing hydrogen bonds were among the
first to be discovered, organic ferroelectrics are relatively rare. The
discovery of high polarization at room temperature in croconic acid [Nature
\textbf{463}, 789 (2010)] has led to a renewed interest in organic
ferroelectrics. We present an ab-initio study of two ferroelectric organic
molecular crystals, 1-cyclobutene-1,2-dicarboxylic acid (CBDC) and
2-phenylmalondialdehyde (PhMDA). By using a distortion-mode analysis we shed
light on the microscopic mechanisms contributing to the polarization, which we
find to be as large as 14.3 and 7.0\,C/cm for CBDC and PhMDA
respectively. These results suggest that it may be fruitful to search among
known but poorly characterized organic compounds for organic ferroelectrics
with enhanced polar properties suitable for device applications.Comment: Submitte
Integrated environmental risk assessment of major accidents in the transport of hazardous substances
At present, the environmental risk assessment of major accidents is mainly carried out for stationary risk sources. Only marginal attention is paid to mobile risk sources, while the currently available methodologies require a relevant expertise and time for their application, which is only partially possible in most scenarios. In the present study, an integrated approach to environmental risk assessment in the transport of hazardous substances (iTRANSRISK) was developed. The approach proposed is based on the principle of index-based assessment of leakage scenarios involving toxic and flammable substances during transport, in the context of indexing environmental vulnerability. The key point of the method is the conversion of local-specific data concerning the risk potential of the transported substance, the consequences and the probability of a major accident, and environmental vulnerability assessment into a single entity. The created integral approach is proposed for the needs of carriers of the hazardous substances and the state administration bodies. The proposed approach is determined for the screening risk assessment at the beginning of the process of the planning a suitable transport routes and the results are for information only. An example of the application of the iTRANSRISK integrated approach is demonstrated considering an explosion scenario following a propane tanker leak (18 t) in a forested area, with moderately susceptible soils and no surface water or groundwater affected
Theoretical current-voltage characteristics of ferroelectric tunnel junctions
We present the concept of ferroelectric tunnel junctions (FTJs). These
junctions consist of two metal electrodes separated by a nanometer-thick
ferroelectric barrier. The current-voltage characteristics of FTJs are analyzed
under the assumption that the direct electron tunneling represents the dominant
conduction mechanism. First, the influence of converse piezoelectric effect
inherent in ferroelectric materials on the tunnel current is described. The
calculations show that the lattice strains of piezoelectric origin modify the
current-voltage relationship owing to strain-induced changes of the barrier
thickness, electron effective mass, and position of the conduction-band edge.
Remarkably, the conductance minimum becomes shifted from zero voltage due to
the piezoelectric effect, and a strain-related resistive switching takes place
after the polarization reversal in a ferroelectric barrier. Second, we analyze
the influence of the internal electric field arising due to imperfect screening
of polarization charges by electrons in metal electrodes. It is shown that, for
asymmetric FTJs, this depolarizing-field effect also leads to a considerable
change of the barrier resistance after the polarization reversal. However, the
symmetry of the resulting current-voltage loop is different from that
characteristic of the strain-related resistive switching. The crossover from
one to another type of the hysteretic curve, which accompanies the increase of
FTJ asymmetry, is described taking into account both the strain and
depolarizing-field effects. It is noted that asymmetric FTJs with dissimilar
top and bottom electrodes are preferable for the non-volatile memory
applications because of a larger resistance on/off ratio.Comment: 14 pages, 8 figure
Mathematical and computer modeling of electro-optic systems using a generic modeling approach
The conventional approach to modelling electro-optic sensor systems is to develop separate models for individual systems or classes of system, depending on the detector technology employed in the sensor and the application. However, this ignores commonality in design and in components of these systems. A generic approach is presented for modelling a variety of sensor systems operating in the infrared waveband that also allows systems to be modelled with different levels of detail and at different stages of the product lifecycle. The provision of different model types (parametric and image-flow descriptions) within the generic framework can allow valuable insights to be gained
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