20,245 research outputs found
Computation of output feedback gains for linear stochastic systems using the Zangnill-Powell Method
Because conventional optimal linear regulator theory results in a controller which requires the capability of measuring and/or estimating the entire state vector, it is of interest to consider procedures for computing controls which are restricted to be linear feedback functions of a lower dimensional output vector and which take into account the presence of measurement noise and process uncertainty. To this effect a stochastic linear model has been developed that accounts for process parameter and initial uncertainty, measurement noise, and a restricted number of measurable outputs. Optimization with respect to the corresponding output feedback gains was then performed for both finite and infinite time performance indices without gradient computation by using Zangwill's modification of a procedure originally proposed by Powell. Results using a seventh order process show the proposed procedures to be very effective
Charge-exchange plasma generated by an ion thruster
The charge exchange plasma generated by an ion thruster was investigated experimentally using both 5 cm and 15 cm thrusters. Results are shown for wide ranges of radial distance from the thruster and angle from the beam direction. Considerations of test environment, as well as distance from the thruster, indicate that a valid simulation of a thruster on a spacecraft was obtained. A calculation procedure and a sample calculation of charge exchange plasma density and saturation electron current density are included
Orientation of particle attachment and local isotropy in diffusion limited aggregation (DLA)
We simulate 50 off-lattice DLA clusters, one million particles each. The
probability distribution of the angle of attachment of arriving particles with
respect to the local radial direction is obtained numerically. For increasing
cluster size, , the distribution crosses over extremely accurately to a
cosine, whose amplitude decreases towards zero as a power-law in . From this
viewpoint, asymptotically large DLA clusters are locally . This
contradicts previous conclusions drawn from density-density correlation
measurements [P. Meakin, and T. Viscek, Phys. Rev. A {\bf 32}, 685 (1985)]. We
present an intuitive phenomenological model random process for our numerical
findings.Comment: 10 pages, RevTex 3.0, 11-9
Analysis and application of minimum variance discrete time system identification
An on-line minimum variance parameter identifier is developed which embodies both accuracy and computational efficiency. The formulation results in a linear estimation problem with both additive and multiplicative noise. The resulting filter which utilizes both the covariance of the parameter vector itself and the covariance of the error in identification is proven to be mean square convergent and mean square consistent. The MV parameter identification scheme is then used to construct a stable state and parameter estimation algorithm
Analysis and application of minimum variance discrete time system identification
An on-line minimum variance parameter identifier was developed which embodies both accuracy and computational efficiency. The new formulation resulted in a linear estimation problem with both additive and multiplicative noise. The resulting filter is shown to utilize both the covariance of the parameter vector itself and the covariance of the error in identification. It is proven that the identification filter is mean square covergent and mean square consistent. The MV parameter identification scheme is then used to construct a stable state and parameter estimation algorithm
Electrostatic ion rocket engine Patent
Electron bombardment ion rocket engine with improved propellant introduction syste
Electrostatic ion engine having a permanent magnetic circuit Patent
Ion engine with magnetic circuit for optimal discharg
Stable Direct Adaptive Control of Linear Infinite-dimensional Systems Using a Command Generator Tracker Approach
A command generator tracker approach to model following contol of linear distributed parameter systems (DPS) whose dynamics are described on infinite dimensional Hilbert spaces is presented. This method generates finite dimensional controllers capable of exponentially stable tracking of the reference trajectories when certain ideal trajectories are known to exist for the open loop DPS; we present conditions for the existence of these ideal trajectories. An adaptive version of this type of controller is also presented and shown to achieve (in some cases, asymptotically) stable finite dimensional control of the infinite dimensional DPS
Extended Defects in the Potts-Percolation Model of a Solid: Renormalization Group and Monte Carlo Analysis
We extend the model of a 2 solid to include a line of defects. Neighboring
atoms on the defect line are connected by ?springs? of different strength and
different cohesive energy with respect to the rest of the system. Using the
Migdal-Kadanoff renormalization group we show that the elastic energy is an
irrelevant field at the bulk critical point. For zero elastic energy this model
reduces to the Potts model. By using Monte Carlo simulations of the 3- and
4-state Potts model on a square lattice with a line of defects, we confirm the
renormalization-group prediction that for a defect interaction larger than the
bulk interaction the order parameter of the defect line changes discontinuously
while the defect energy varies continuously as a function of temperature at the
bulk critical temperature.Comment: 13 figures, 17 page
Experimental Simulation of the Interaction of Biased Solar Arrays with the Space Plasma
The phenomenon of unexpectedly large leakage currents collected by small exposed areas of high voltage solar arrays operating in a plasma environment was investigated. Polyimide (Kapton) was the insulating material used in all tests. Both positive bias (electron collection) and negative bias (ion collection) tests were performed. A mode change in the electron collection mechanism was associated with a glow discharge process and was found to be related to the neutral background density. Results indicate that the glow discharge collection mode does not occur in a space environment where the background density is considerably lower than that of the vacuum facility used
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