17,175 research outputs found
Systematic experimental exploration of bifurcations with non-invasive control
We present a general method for systematically investigating the dynamics and
bifurcations of a physical nonlinear experiment. In particular, we show how the
odd-number limitation inherent in popular non-invasive control schemes, such as
(Pyragas) time-delayed or washout-filtered feedback control, can be overcome
for tracking equilibria or forced periodic orbits in experiments. To
demonstrate the use of our non-invasive control, we trace out experimentally
the resonance surface of a periodically forced mechanical nonlinear oscillator
near the onset of instability, around two saddle-node bifurcations (folds) and
a cusp bifurcation.Comment: revised and extended version (8 pages, 7 figures
Location of geologic structures from interpretation of ERTS-1 imagery, Carbon County, Wyoming
The author has identified the following significant results. Possible geologic structures in the basin sediments of Carbon County and vicinity were located by interpretation of ERTS-1 imagery. These same structures are not evident on existing conventional geologic maps of the area. Subsequent field checks confirmed much of the geologic interpretation, but revealed that two apparent closed structures identified on the ERTS-1 imagery were actually topographic pseudostructures in flat or homoclinal sediments. Stereoscopic coverage (where available) allows the interpreter to avoid such misinterpretations
Apollo oxygen tank stratification analysis, volume 2
An analysis of flight performance of the Apollo 15 cryogenic oxygen tanks was conducted with the variable grid stratification math model developed earlier in the program. Flight conditions investigated were the CMP-EVA and one passive thermal control period which exhibited heater temperature characteristics not previously observed. Heater temperatures for these periods were simulated with the math model using flight acceleration data. Simulation results (heater temperature and tank pressure) compared favorably with the Apollo 15 flight data, and it was concluded that tank performance was nominal. Math model modifications were also made to improve the simulation accuracy. The modifications included the addition of the effects of the tank wall thermal mass and an improved system flow distribution model. The modifications improved the accuracy of simulated pressure response based on comparisons with flight data
Conceptual design of the 6 MW Mod-5A wind turbine generator
The General Electric Company, Advanced Energy Programs Department, is designing under DOE/NASA sponsorship the MOD-5A wind turbine system which must generate electricity for 3.75 cent/KWH (1980) or less. During the Conceptual Design Phase, completed in March, 1981, the MOD-5A WTG system size and features were established as a result of tradeoff and optimization studies driven by minimizing the system cost of energy (COE). This led to a 400' rotor diameter size. The MOD-5A system which resulted is defined in this paper along with the operational and environmental factors that drive various portions of the design. Development of weight and cost estimating relationships (WCER's) and their use in optimizing the MOD-5A are discussed. The results of major tradeoff studies are also presented. Subsystem COE contributions for the 100th unit are shown along with the method of computation. Detailed descriptions of the major subsystems are given, in order that the results of the various trade and optimization studies can be more readily visualized
The Fishes of Maryland
Fish, from both a commercial and a sporting standpoint.
Based on fishes collected in Maryland only. A general treatise on fishes, setting forth the species, describing them and telling of their distribution, habits and other pertinent facts such as adaptations and coloring. Includes marine, freshwater littoral fishes. (PDF contains 120 pages
Fluctuations of the Casimir-Polder force between an atom and a conducting wall
We consider the quantum fluctuations of the Casimir-Polder force between a
neutral atom and a perfectly conducting wall in the ground state of the system.
In order to obtain the atom-wall force fluctuation we first define an operator
directly associated to the force experienced by the atom considered as a
polarizable body in an electromagnetic field, and we use a time-averaged force
operator in order to avoid ultraviolet divergences appearing in the fluctuation
of the force. This time-averaged force operator takes into account that any
measurement involves a finite time. We also calculate the Casimir-Polder force
fluctuation for an atom between two conducting walls. Experimental
observability of these Casimir-Polder force fluctuations is also discussed, as
well as the dependence of the relative force fluctuation on the duration of the
measurement.Comment: 6 page
Shear-invariant Sliding Contact Perception with a Soft Tactile Sensor
Manipulation tasks often require robots to be continuously in contact with an
object. Therefore tactile perception systems need to handle continuous contact
data. Shear deformation causes the tactile sensor to output path-dependent
readings in contrast to discrete contact readings. As such, in some
continuous-contact tasks, sliding can be regarded as a disturbance over the
sensor signal. Here we present a shear-invariant perception method based on
principal component analysis (PCA) which outputs the required information about
the environment despite sliding motion. A compliant tactile sensor (the TacTip)
is used to investigate continuous tactile contact. First, we evaluate the
method offline using test data collected whilst the sensor slides over an edge.
Then, the method is used within a contour-following task applied to 6 objects
with varying curvatures; all contours are successfully traced. The method
demonstrates generalisation capabilities and could underlie a more
sophisticated controller for challenging manipulation or exploration tasks in
unstructured environments. A video showing the work described in the paper can
be found at https://youtu.be/wrTM61-pieUComment: Accepted in ICRA 201
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