Linear Reference Research Articles

Direct Adaptive Control of Partially Known Nonlinear Systems

A direct adaptive control strategy for minimum-phase nonlinear systems is presented. The major advantage of the proposed method is that controller design is not based on a detailed nonlinear model. The only information required about the plant is the state vector, the relative degree, and the sign of a Lie derivative which appears in the associated input-output linearizing control law. Unknown controller functions are approximated via locally supported radial basis functions that are introduced only in regions of the state space where the closed-loop system actually evolves. Lyapunov stability analysis is used to derive parameter update laws which ensure (under certain assumptions) the state vector remains bounded and the plant output asymptotically tracks the output of a linear reference model. The technique is successfully applied to a nonlinear bioreactor model.

Design of two syllabic nonlinear multichannel signal processors and the results of speech tests in noise.

Multichannel syllabic compressors have not yet shown clear advantages for speech perception. New multichannel syllabic nonlinear processors are designed and evaluated in this study to test whether they enhance speech perception scores. Nonsense consonant-vowel-consonant words have been processed in real time with two syllabic nonlinear methods in nine different frequency channels: 1) 30 dB of speech information is mapped into the residual dynamic range (DR) of the subjects with hearing impairment using either compression or expansion; 2) speech levels above the rms level are compressed with a ratio of 3:1, and input levels below the rms level are mapped into the reduced DR of the subjects. The overall frequency spectrum of speech is tilted with more high-frequency output for this condition. The two syllabic nonlinear processors were compared with two linear reference systems (one of them with the same spectral tilt as the second nonlinear condition) for seven hearing-impaired subjects. On average, the syllabic nonlinear processors show scores similar to one of the linear systems. The linear reference with tilt has, on average, 3% higher scores, mainly due to improved vowel identification. No negative effects were shown on average for the syllabic nonlinear processors, but no positive effects were demonstrated either. Tilting of the overall speech spectrum was advantageous.

Identification of flow faults in continuous reactors by relating linear model parameters and physical magnitudes

A new procedure for predicting dead volume and bypassing in reactors was explored. The method is specific for processes already implemented with a linear reference model. It is based on using a neural network (NN) to obtain relationships between the parameters of the linear model and the dead volume and bypassing. Several experiments with bench scale reactors were carried out and the dead volume and bypassing were found by using classical flow models. By computer simulation we studied the combination of a NN and the linear model of a CSTR with dead volume and bypassing. The NN is a three-layered perception, with sigmoid processing element and back-propagation learning. The input layer receives the parameters of the linear model and the output layer provides the predicted dead volume and bypassing. The accuracy of the trained NN was verified by presenting unseen data to the NN. The prediction errors are less than 15%.

Location Translation Within a Geographic Information System

Location translation allows the use of multiple spatial referencing methods within a geographic information system (GIS). Most GIS users are familiar with planar or spherical coordinates expressed as (x, y) pairs of numbers whose values reflect the map projection used. Coordinates are characterized as unique physical locations on the earth’s surface. Transportation professionals have added many methods of referencing data that occur along lines. Linear referencing systems generally reflect a measure of distance from a known point. Common linear referencing methods are route–milepoint and route–reference post–offset. Street (postal) address systems also fall into the category of linear references. Linear referencing methods do not uniquely define locations on the earth’s surface without additional information about the location of the line (or road) on the earth’s surface. Although many of the off-the-shelf GIS systems allow conversion among a wide variety of planar or spherical referencing systems, few accommodate linear referencing systems, and none are capable of translating among linear referencing systems or between planar or spherical and linear systems. Some of the issues that arise in the development of location translation systems are discussed. A description of the data model and database requirements of the system designed for the Utah Department of Transportation is included. This location translation system was developed to facilitate crash reporting in urban areas, although there are numerous applications within transportation agencies.

Automated synthesis of branched oligodeoxynucleotide analogues using arabino-uridine as branching nucleotide

Fully automated synthesis of branched oligodeoxynucleotides (branched ODNs) has been accomplished using 2′-O-levulinyl- or 5′-O-levulinyl-protected arabino-uridine derivatives as branching monomers. Selective removal of the levulinyl groups is accomplished using 0.5 M hydrazine hydrate in a pyridine–acetic acid–water (4∶3∶0.35, v/v/v) buffer. The affinity of the branched ODNs towards complementary DNA has been evaluated at 260 nm and 284 nm during thermal denaturing experiments. Enhanced affinity of a branched ODN compared with the corresponding linear reference is attributed to bimolecular triple helix formation.

Nonlinear model predictive control of a simulated multivariable polymerization reactor using second-order Volterra models

Two formulations of a nonlinear model predictive control scheme based on the second-order Volterra series model are presented. The first formulation determines the control action using successive substitution, and the second method directly solves a fourth-order nonlinear programming problem on-line. One case study is presented for the SISO control of an isothermal reactor which utilizes the first controller formulation. A second case study is presented for the multivariable control of a large reactor, and uses the nonlinear programming formulation for the controller. The model coefficients for both examples are obtained by discretizing the bilinear Taylor series approximation of the fundamental model and calculating Markov parameters. The relationships between discrete and continuous-time bilinear model matrices using an explicit fourth-order Runge-Kutta method are also included. The responses to setpoint changes of both reactors controlled with a linear model predictive control scheme and the second-order Volterra model predictive control scheme are compared to desired, linear reference trajectories. In the majority of the cases examined, the responses obtained by the Volterra controller followed the reference trajectories more closely. Practical issues, including the reduction of the number of model parameters, are addressed in both case studies.

Tooth thickness at the furcation entrance of lower molars.

Better understanding of the furcation anatomy may serve to decrease the risk of pulpal injury during rotary odontoplasty, a procedure often used in conjunction with guided tissue regeneration. The purpose of this study was to determine (i) the tooth thickness about the furcation entrance of lower molars, and (ii) whether there is a relationship between tooth thickness and patient age. 40 mandibular 1st molars (M1) (mean age = 36.2; range 10-65 years) and 40 mandibular 2nd molars (M2) (mean age = 37.9; range 14-70 years) were collected. Age, gender and furcation involvement (if any) were noted for each tooth at the time of extraction. Teeth were sectioned in half, buccal-lingual, at the furcation entrance with a rotary diamond blade. A standardized linear reference scale was placed on each experimental section and an 8 x 10 in. photograph generated. The distance from the floor of the pulp chamber to 5 predetermined sites on the root surface was calculated. The data were expressed as (a) the mean of each site and (b) the mean of each tooth (the average of the 5 points of each tooth). Analysis of covariance failed to show a relationship between thickness measurements and gender or furcation involvement. Thus, the data was subjected to simple regression analysis to determine the relationship of age with tooth and cementum thickness. This study revealed that by site, the mean measurements ranged from 2.7-3.0 mm for both M1 and M2. The single least/greatest measurements of the 5 sites were for M1: 1.6/4.7 mm and for M2: 1.8/4.2 mm. By tooth, the average distance from the pulp to the root surface was 2.83 mm (+/- 0.49) for M1 and 2.88 mm (+/- 0.44) for M2. Regression analysis of tooth thickness with age was significant for M1 only. The maximum slope of the 5 sites was approximately 0.3 mm/10 years. No relationship was found between cementum thickness and age for either tooth group. The results of this study indicate that the majority of times the pulp is 1.6-4.2 mm from the root surface in the vicinity of the furcation entrance of lower 1st and 2nd molars. Although tooth thickness in this area may increase with age, the amount is not enough to forego judicious odontoplasty on older patients.

Nonlinear tracking and input disturbance rejection with application to pH control

This paper presents a nonlinear observer-based controller configuration for a class of nonlinear single-input single-output systems with certain observability and stability properties. Particular attention is paid to the effect of input disturbances typically present in chemical processes. It is pointed out that conventional feedback linearizing internal model controllers reject output disturbances linearly, but that they can experience significant performance degradation in the presence of input disturbances. This problem is shown to originate in the lack of the linear superposition property. It is proven that the proposed control architecture rejects constant input disturbances from the control signal and then recovers linear reference tracking. The convenient tuning and improved performance are illustrated for pH neutralization.

Pulse distortion in MR and GMR playback heads

Distortion of the playback pulse shape due to saturation is studied via a 3-D micromagnetic model for both MR/SAL and spin-valve heads. The deviation from linearity is examined as a function of both the Mr/spl delta/ of the recording medium and the off-track position of the device. Playback voltages for isolated transitions of both polarities are calculated and their shapes are compared to linear references. The differences in structure between MR and GMR sensors result in very dissimilar distortions of the playback pulse shape under large applied fields.

Reference functional and characteristic space for Lagrange and Bernstein operators

This paper deals with the description and the representation of polynomials defined, over n-simplices. The polynomials are computed by using two recurrent schemes, the Neville-Aitken one for the Lagrange interpolating operator and the De Casteljau one for the Bernstein-Bezier approximating operator. Both schemes fall into the framework of transformation of the form Open image in new window where the Fj are given numbers (for example, at the initial step they coincide with the values of the function on a given lattice), and the coefficients c i,j p (x) are linear polynomials valued in x and x is fixed. A general theory for such sequence of transformations can be found in [2] where it is also proved that these transformations are completely characterized in term of a linear functional reference functional. This functional is associated with a linear space; characteristic space.

Stable observer-based trajectory controller for asymptotic model matching of a rigid robot

This paper considers a control problem that requires the design of an observed-based compensator in order to guarantee the asymptotic convergence of the output (namely, the joint generalized coordinates of ann-degree of freedom robot) to a corresponding output produced by a linear reference model. It is shown that, for a model having a relative degree vector {r 1, ...,r n}, withr i ≥2, it is possible to determine a controller-observer yielding a robot output that converges exponentially to the desired model output. Moreover, the combined system comprising the plant and the controller is internally stable in the semiglobal sense. The solution to the standard trajectory-following problem in robotics is obtained as a simplified case of the underlying model matching problem. While the controller-observer is nonlinear, its dynamic part is linear time-varying; in addition, the construction does not assume a priori the knowledge or even the existence of an upper bound to the model state vector.

Novel linear and branched oligodeoxynucleotide analogues containing 4′- c-(hydroxymethyl)thymidine

4′-C-(Hydroxymethyl)thymidine has been incorporated into novel linear and branched oligodeoxynueleotide (ODN) analogues by use of the phosphoramidite synthons 4, 7 and 11. ODNs containing modification X (from amidite 4, unnatural 5′-hydroxy to 4′- C-hydroxymethyl backbone) displayed significantly decreased thermal stabilities towards complementary DNA compared to unmodified controls. On the contrary, ODNs containing modification Y (from amidite 7, natural 5′-hydroxyl to 3′-hydroxyl backbone) formed highly stable duplexes towards both complementary DNA and RNA. Phosphoramidite 11 containing two dimethoxytrityl protective groups was used for fully automated synthesis of a branched ODN analogue containing identical sequences in two out of the three branches originating from the branching point (modification Z). Branched ODN S exhibited only moderately decreased thermal stability (towards complementary linear DNA) compared to the linear reference (ODN R). This demonstrates the versatility of the additional 4′- C-hydroxymethyl functionality (in modification Y) as an attachment point for introduction of molecular entities pointing into the minor groove of a DNA:DNA duplex.

Control system design issues for unstable linear systems with saturated inputs

The paper studies stable setpoint tracking for linear open-loop unstable systems with saturated control input. A linear reference filter is introduced that allows the independent design of the prestabilising and setpoint tracking controllers in an internal model control configuration. A nonlinear reference conditioning filter is also proposed that avoids saturation in the main control loop, which remains stable thereafter. Rules of thumb giving bounds on amplitude and frequency for sinusoidal references are given that ensure stable saturated operation of the nonlinear reference filter.

Planar and linear fiber optic acoustic sensors embedded in an elastomer material

A interferometric planar and linear fiber optic sensor system comprised of a sensor element and a reference element. In the planar fiber optic sensor system the sensor and reference fibers are shaped in loops circularly and uniformly, heat treated or bonded together and embedded in a spiral pattern within a low Bulk Modulus and Young's Modulus elastomer encapsulant. The invention results in high and frequency independent sensitivity which minimizes acceleration effects. For the linear sensor, the sensing fiber is shaped in loops forming a linear chain which is embedded in an appropriate low bulk modulus elastomeric encapsulant. The reference fiber is shaped in loops around a cylindrical aluminum mandrel within which the input and output fiber cables and couplers are encapsulated in a high bulk modulus material epoxy resin. In both the planar and linear forms, the sensing and reference fiber may be of equal length, however, the reference fiber may be of a shorter length when a coherent light source is utilized.

Observer based Throttle valve control for drive by wire and idle control

Drive by wire systems require a precise and fast electronic driven positioning of the throttle control unit. Magneti Marelli has chosen to control the positioning of the throttle valve with a direct coupled torque motor. Even if the problem of the positioning of an electrical motor is certainly one of the most common problems and a lot of literature is available on this subject, a practical design approach is here presented, with the most important evolutions of this control, from an easy, non satisfactory PID to a multiple order observer based controller with non linear compensations, reference filter and feed foreword nets. The design of this control is especially conceived for its implementation on a cheap microcontroller. Practical and theoretical aspects are considered, as well as an approach to the determination of a reasonable compromise between complexity of the control algorithm, hardware costs and performance.

Matched Spatial Filtering by Primitive Reference Patterns and Correlation Diagrams for Shape Invariant Pattern Recognition

In this paper, twelve linear primitive reference patterns are proposed for synthesizing a matched spatial filter, known as a shape invariant filter, which can recognize all patterns with various shapes. Furthermore, reprocessed data, given by correlation between the input object of the system and the reference patterns “correlation diagrams” are introduced for processing peak signals in a digital system. By correlating the diagram from the input object with the standard diagrams, the 26 of the alphabet letters were recognized in the experiment. Moreover, feasibility of the rotational invariance of the filter was suggested by the computer simulation.

Selective recognition of cyclic RGD peptides of NMR defined conformation by alpha IIb beta 3, alpha V beta 3, and alpha 5 beta 1 integrins.

The binding of purified fibrinogen receptor alpha IIb beta 3, vitronectin receptor alpha V beta 3, and fibronectin receptor alpha 5 beta 1 to their corresponding ligands in solid-phase binding assays was used to examine the inhibitory activity of various linear and cyclic penta- and hexapeptides of different conformation containing RGD or RAD sequences. Cyclic peptides with different defined backbone conformations were designed by introducing a single D-amino acid or a proline at different positions in the ring. The data were calibrated for alpha IIb beta 3 integrin incorporated into a planar lipid bilayer by a physical method (total internal reflection fluorescence microscopy) which yielded KD = 1.7 microM for a linear RGD peptide and KD = 0.03 microM for fibrinogen. With this integrin, three cyclic hexapeptides ([GRGDFL], [ARGDFV], [GRGDFV]) were 2-4-fold more inhibitory than the linear GRGDS peptide in solid-phase assays and showed similar inhibition as the fibrinogen ligand. Six peptides had the same or a 2-fold lower activity as the linear reference peptide, and three peptides were up to 7-fold less active. Replacement of Arg or Asp by their stereoisomers or Gly by Ala resulted in a 100-1000-fold reduction in activity. With the two other integrins, a single cyclic pentapeptide [RGDFV] was 10-fold more active (alpha V beta 3) or equal in activity (alpha 5 beta 1) to linear GRGDS, while all of the other cyclic peptides were moderately or distinctly less active. Changes in the RGD sequence caused a less dramatic reduction in binding strength for alpha V beta 3 and alpha 5 beta 1 than for alpha II beta 3. Inhibitory activity was compared with the distance between the C beta atoms of Arg and Asp residues as determined by NMR and indicated that the optimum distance is in the range of 0.75-0.85 nm for alpha IIb beta 3 and at or below 0.67 nm for alpha V beta 3 and alpha 5 beta 1. This indicates that alpha IIb beta 3 less sensitive to variations in the RGD backbone structure and can accommodate a larger distance than the integrins alpha V beta 3 and alpha 5 beta 1.

Adaptive Model Matching for Finite Volterra Series System

In this paper, the model matching problem is investigated and its application to the model reference adaptive control (MRAC) for a class of finite Volterra series system is also considered. At first, a class of finite Volterra series system which has a bilinear realization is treated, and a scheme for matching the input-output relation to a given linear reference model is presented by using a bilinear observer. Secondly, a model reference adaptive control scheme is proposed. Furthermore, the exact model matching problem for an extended class of the finite Volterra series system is also discussed.

Adaptive model-following controller for robotic manipulators

A nonlinear state-space model representing the robot dynamics and containing a disturbance term due to gravitational loading is presented. An adaptive model-following control problem satisfying the matching conditions is formulated using a suitable linear time-invariant reference model. The control input is designed to have two components: a non-adaptive linear component to do the task of model-following and a nonlinear unit-vector component based on hyperstability theory to do the adaptive task. An additional integral feedback term is further added and then the overall asymptotic hyperstability is established. Simulation experiments on the first three joints of a PUMA 560 robot manipulator have indicated the potential of our design approach.

A design approach to adaptive model-following control of robotic manipulators

In this paper, the robot dynamics are represented by a nonlinear state-space model containing a disturbance term due to gravitational loading. Using a suitable linear time-invariant reference model, an adaptive model-following control problem is formulated which satisfies the matching conditions. The control input is designed to have two components: a nonadaptive linear component to do the task of model-following and a nonlinear unit-vector component based on hyperstability theory to do the adaptive task. An additional integral feedback term is further superimposed and then the overall asymptotic hyperstability is established. The simulation results on the first three joints of PUMA 560 robot manipulator indicate the potential of our design approach.