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At least 397 records · Page 22Linked to original sources
PubMed2006

Robust and nominal stability conditions for a simplified model predictive controller.

A new condition is derived that guarantees robust stability for a set of stable, linear time-invariant plants controlled by using a simplified model predictive control algorithm (SMPC). Discrete single-input-single-output control systems are considered in this paper. Uncertainty is treated in the time domain by considering the stabilization of a set of pulse response functions. The method presented is suitable for stabilizing a set of plants that are not necessarily related. Central to this method is a bounding function, which is a function of the model and controller parameters. The bounding function is designed to have a larger magnitude than all of the pulse response functions in the set of plants to be stabilized. Using this method, it was found that the bounding function is monotonically decreasing when a first-order plus dead-time model is used to design the controller. This allows the coincidence point used in SMPC to be employed directly as a tuning "knob" for robustness, and also simplifies the analysis for dead-time uncertainty. In addition, a comparison of two nominal stability conditions is provided.

Journal Article↗
PubMed2002

Robustness of discrete-time state feedback control systems.

This paper presents stability robustness results for linear multivariable discrete-time systems with uncertainties. Robust stability of the full-state feedback linear quadratic regulator in the presence of perturbations of the system parameters is investigated. These results are based on recently developed bounds on structured perturbations of a stable linear discrete-time system. The paper applies these results to a paper-machine head box system example.

Feedback↗
PubMed2003

Design and experimental evaluation of a simple and robust control setup for measurement optimization in industrial applications.

Theoretical and experimental aspects are discussed concerning design and experimental setup of a simple and robust controller for optimization of on-line measurement of coating thickness, using a PC-based approach. Solutions assumed for a feedback control system are described in order to satisfy the main requirements set by this application: accuracy of operation, dynamic bandwidth, modularity of settings depending on the specific coating, handiness of using and modifying when necessary, robustness of control, and global operating reliability. Experimental results confirm that an acceptable measurement uncertainty can be achieved in tin plate coating thickness measurements by this simple displacement control system of the fiber optic measuring head.

Journal Article↗
PubMed2004

Robust and efficient vision system for group of cooperating mobile robots with application to soccer robots.

In this paper a global vision scheme for estimation of positions and orientations of mobile robots is presented. It is applied to robot soccer application which is a fast dynamic game and therefore needs an efficient and robust vision system implemented. General applicability of the vision system can be found in other robot applications such as mobile transport robots in production, warehouses, attendant robots, fast vision tracking of targets of interest and entertainment robotics. Basic operation of the vision system is divided into two steps. In the first, the incoming image is scanned and pixels are classified into a finite number of classes. At the same time, a segmentation algorithm is used to find corresponding regions belonging to one of the classes. In the second step, all the regions are examined. Selection of the ones that are a part of the observed object is made by means of simple logic procedures. The novelty is focused on optimization of the processing time needed to finish the estimation of possible object positions. Better results of the vision system are achieved by implementing camera calibration and shading correction algorithm. The former corrects camera lens distortion, while the latter increases robustness to irregular illumination conditions.

Algorithms↗
PubMed2006

SISO extended predictive control: implementation and robust stability analysis.

The proposed algorithm of extended predictive control (EPC) represents an exact method for removing the ill-conditioning in the system matrix by developing a unique weighting structure for any control horizon. The main feature of the EPC algorithm is that it uses the condition number of the system matrix to evaluate a single tuning parameter that provides a specified closed-loop response. Robust analysis demonstrated that EPC is more robust in comparison with move-suppressed and m-shifted predictive controllers in all aspects of process variation in gain, delay, and time-constant ratios. Tuning of EPC is effective and simple since there is a direct relationship between closed-loop performance and its tuning parameter.

Algorithms↗
PubMed2000

Robustness testing of a reversed-phase high-performance liquid chromatographic assay: comparison of fractional and asymmetrical factorial designs.

Robustness tests were performed on a reversed-phase HPLC assay for triadimenol. Different experimental designs were compared. Two-level fractional factorial designs with different resolutions were used to study the influence of procedure-related factors. The factors chromatographic column manufacturer at four levels and instrument at three levels were stepwise included in the study using asymmetrical factorial designs. The significance of the factor effects was determined statistically, using two types of error estimates in the calculation of critical effects, and graphically, by means of half-normal plots. The asymmetrical designs turned out to be an efficient and economic method to examine the influence of factors at different numbers of levels in the robustness testing of analytical methods.

Chromatography, High Pressure Liquid↗
PubMed2000

Robustness testing for a capillary electrophoresis method using the "short-end injection" technique.

A multivariate approach for testing the robustness of a capillary electrophoresis method using the "short-end injection" technique is presented. Firstly, a Plackett and Burman (PB) design with 11 factors (eight real factors and three dummies) was used to identify the critical factors on resolution, plate number, plate count, asymmetry and assay. Then, the factors which were found to be significant were studied in a central composite design to predict the variation of resolution inside the area investigated in the PB design. PB and central composite designs yielded conclusions that were in good agreement with one another. They showed that the separation could be considered as robust, notwithstanding the fact that some factors where found to be statistically significant and should be controlled (injected volume and electrolyte concentration). Using the factor values which gave the worst-case situation for Rs still led to acceptable values for this parameter.

Electrophoresis, Capillary↗
PubMed2000

Full and fractionated experimental designs for robustness testing in the high-performance liquid chromatographic analysis of codeine phosphate, pseudoephedrine hydrochloride and chlorpheniramine maleate in a pharmaceutical preparation.

This paper describes the testing of a saturated factorial design using a full factorial design. Saturated factorial designs are often used to test the robustness of high-performance liquid chromatography (HPLC) methods, however they are based on several assumptions. A full factorial design relies on fewer assumptions and hence could be used to evaluate the effectiveness of the saturated design. Both designs were used to test a gradient HPLC method for the assay of codeine phosphate, pseudoephedrine hydrochloride and chlorpheniramine maleate. Six HPLC conditions, including wavelength, mobile phase pH and ion pairing reagent concentration were tested using the saturated design. Three of these factors were selected for full evaluation using a full factorial design. The results showed that the main effects calculated by each design were comparable. However, the saturated design showed higher standard errors, probably due to the effects of changing several more factors. One interaction effect was indicated as a confounding effect by the saturated design and this was confirmed by the calculation of the same interaction effect using the full design. Overall the method was shown to be robust under the variety of HPLC conditions tested.

Chlorpheniramine↗
PubMed2003

Robust development as a consequence of generated positional information.

The origin and robustness of morphogenesis are studied by dynamical system modeling of a cell society, in which cells possessing internal chemical reaction dynamics interact with each other through their mutual interaction with diffusive chemicals in a two-dimensional medium. It is found that stem-type cells differentiate into various cell types (where a cell 'type' is defined by a type of intra-cellular dynamics) due to a dynamic instability caused by cell-cell interactions in a manner described by the isologous diversification theory. The differentiations are spatially regulated by the concentration of chemicals in the medium, while the chemical concentrations are locally influenced by the intra-cell dynamics. Through this reciprocal relationship, chemical concentrations come to exhibit spatial variation as differentiated cell types begin to emerge, and as a result the regulation exercised by the chemical concentrations become spatially inhomogeneous. This reinforces the process of differentiation, through which spatial patterns of differentiated cells appear. Within this reciprocal relationship, the concentration gradients are read and interpreted by the cell as positional information. A spatial order of cells realized in this process represents a stable state of the system governed by this reciprocal relationship, and that the developmental process through which this state is realized is robust with respect to perturbations. The dependence of the morphogenesis on history and the community effect in cell differentiation are also discussed.

Animals↗
PubMed2003

Evolution of mutational robustness.

We review recent advances in the understanding of the mutation-selection balance of asexual replicators. For over 30 years, population geneticists thought that an expression derived by Kimura and Maruyama in 1966 fully solved this problem. However, Kimura and Maruyama's result is only correct in the absence of neutral mutations. The inclusion of neutral mutations leads to a wealth of interesting new effects, and, in particular, to a selective pressure to evolve robustness against mutations. We cover recent literature on the population dynamics of asexual replicators on networks of neutral genotypes, on the outcompetition of fast replicators by slower ones with better mutational support, and on the probability of fixation at high mutation rates. We discuss empirical evidence for the evolution of mutational robustness, and speculate on its relevance for higher organisms.

Biological Evolution↗
PubMed1997

Specific inhibition of cyclic AMP-dependent protein kinase by warangalone and robustic acid.

The prenylated isoflavone warangalone from the insecticidal plant Derris scandens is a selective and potent inhibitor of rat liver cyclic AMP-dependent protein kinase catalytic subunit (cAK) (IC50 3.5 microM). The inhibition of rat liver cAK by warangalone is non-competitive with respect to both ATP and the synthetic peptide substrate (LRRASLG) employed in this study. Warangalone is a poor inhibitor of avian calmodulin-dependent myosin light chain kinase (MLCK), rat brain Ca(2+)- and phospholipid-dependent protein kinase C (PKC) and wheat embryo Ca(2+)-dependent protein kinase (CDPK). The related plant derived prenylisoflavones are also potent cAK inhibitors. Thus, 8-gamma-gamma-dimethylallylwighteone, 3' -gamma-gamma-dimethlallylwighteone and nallanin are inhibitors of cAK with IC50 values in the range 20-33 microM. The prenyl-substituted isoflavones tested in this study are ineffective or poor as inhibitors of PKC. Thus nallanin is a poor PKC inhibitor (IC50 value of 120 microM). The related isoflavones biochanin A and genistein are poor inhibitors of cAK (IC50 values 100 microM and 126 microM, respectively). Genistein inhibits MLCK (IC50 value 14 microM) but biochanin A is a poor MLCK inhibitor (IC50 value 300 microM). The D. scandens prenyl-isoflavones and related isoflavones are ineffective inhibitors of wheat embryo Ca(2+)-dependent protein kinase (CDPK). The 4-methoxy-3-phenyl-coumarin robustic acid is a potent inhibitor of rat liver cAK (IC50 value 10 microM) but is a poor inhibitor of rat brain PKC, avian MLCK and wheat embryo CDPK. The coumarins 5-methoxypsoralen and 4,4'-di-O-methyl scandenin are poor cAK inhibitors (IC50 values 240 and 248 microM, respectively). All of the non-prenylated coumarins examined are ineffective as inhibitors of the eukaryote signal-regulated protein kinases cAK, MLCK, PKC and CDPK. The selective, high affinity interaction of warangalone and robustic acid with cAK may contribute to their biological effects in vivo and to the insecticidal activity of the plant D. scandens.

Animals↗
PubMed2003

Last Glacial Maximum ages for robust humans at Kow Swamp, southern Australia.

The Kow Swamp people are a fossil population of robust modern humans. We report optically stimulated luminescence (OSL) ages on sediments from Kow Swamp that are at odds with radiocarbon ages obtained previously for the site. The calibrated 14C ages place the Kow Swamp people in the period 15-9 ka. Our single aliquot OSL ages suggest that they lived around the time of the Last Glacial Maximum (LGM) between 22 and 19 ka. An LGM age for the Kow Swamp people is supported by palaeoenvironmental reconstruction. The shoreline silt, in which most of them were interred, was deposited by high lake levels between 26 and 19 ka. Few robust people were left after 19 ka when a sand lunette formed. Climate change may explain the demise of this unusual genetic population.

Anthropology, Physical↗
PubMed2003

Stoichiometric design of metabolic networks: multifunctionality, clusters, optimization, weak and strong robustness.

Starting from a limited set of reactions describing changes in the carbon skeleton of biochemical compounds complete sets of metabolic networks are constructed. The networks are characterized by the number and types of participating reactions. Elementary networks are defined by the condition that a specific chemical conversion can be performed by a set of given reactions and that this ability will be lost by elimination of any of these reactions. Groups of networks are identified with respect to their ability to perform a certain number of metabolic conversions in an elementary way which are called the network's functions. The number of the network functions defines the degree of multifunctionality. Transitions between networks and mutations of networks are defined by exchanges of single reactions. Different mutations exist such as gain or loss of function mutations and neutral mutations. Based on these mutations neighbourhood relations between networks are established which are described in a graph theoretical way. Basic properties of these graphs are determined such as diameter, connectedness, distance distribution of pairs of vertices. A concept is developed to quantify the robustness of networks against changes in their stoichiometry where we distinguish between strong and weak robustness. Evolutionary algorithms are applied to study the development of network populations under constant and time dependent environmental conditions. It is shown that the populations evolve toward clusters of networks performing a common function and which are closely neighboured. Under changing environmental conditions multifunctional networks prove to be optimal and will be selected.

Algorithms↗
PubMed2003

A robust statistics-based global energy function for the alignment of serially acquired autoradiographic sections.

Autoradiographic analysis of the functional changes occurring in the rat brain are most often performed on coronal sections that allow a good insight into the events occurring at the structural level but lacks the 3D context which is necessary to fully understand the involvement of the brain structures in specific situations like focal seizures with or without generalization. Therefore a robust, fully-automated algorithm for the registration of serially acquired autoradiographic sections is presented. The method accounts for the main difficulties of autoradiographic alignment: corrupted data (cuts and tears), dissimilarities or discontinuities between slices, non parallel or missing slices. The approach relies on the minimization of a global energy function based on robust statistics. The energy function measures the similarity between a slice and its neighborhood in the 3D volume. No particular direction is privileged in the method, so that global offsets, biases in the estimation or error propagations are avoided. The method is evaluated qualitatively and quantitatively on real autoradiographic data. Rat brain autoradiographic volumes are reconstructed with registration errors less than 1 degree in rotation and less than 1 pixel in translation.

Algorithms↗
PubMed1998

A sensitive and robust method for measles RNA detection.

The aim of this study was to compare measles RNA amplification methods and to develop and select the most rapid, sensitive and robust procedure. The use of hybrid capture for measles RNA isolation was evaluated, and three RNA amplification detection techniques were compared. These were: (a) reverse transcription followed by nested polymerase chain reaction (RT-PCR) with MMLV reverse transcriptase and Taq polymerase; (b) a combined RT-PCR reaction using rTth polymerase; and (c) NASBA. An internal positive control was also developed. The sensitivities of the detection methods were quantified by using a dilution series of a known amount of total RNA from measles-infected Vero cells or by calculation of the number of transcript molecules (produced from a recombinant plasmid containing an insert measles nucleoprotein DNA) present in each amplification reaction, respectively. The results indicated that hybrid capture followed by combined RT-PCR with rTth polymerase was the most reproducibly robust and sensitive protocol and could detect as few as 10(4) synthetic measles RNA transcripts added to tissue homogenates. However, NASBA proved to be the most sensitive method for measles RNA detection in water.

Animals↗
PubMed1997

Rats with partial striatal dopamine depletions exhibit robust and long-lasting behavioral deficits in a simple fixed-ratio bar-pressing task.

It is widely accepted that enduring parkinsonian symptoms are only evident if there are few remaining dopaminergic neurons in the substantia nigra and dopamine levels in the basal ganglia are very low [26,41]. In the present study, partial dopamine depletions were produced by infusing 6-OHDA bilaterally into the ventrolateral striatum as previously described [11,12,44]. Consistent with previous studies, behavioral deficits were detectable in rats with partial lesions with a simple fixed-ratio bar-pressing task. The present study demonstrated that these behavioral deficits were long-lasting, and that the sensitivity of this bar-pressing task could be increased by manipulating the level of difficulty of the task-higher fixed ratios were more sensitive to partial dopamine depletions. Deficits in rats with partial dopamine depletions could also be detected using non-automated neurological tests of parkinsonian symptoms developed for rats with severe unilateral dopamine depletions, but these deficits were transient and not as robust as those detected with the bar-pressing task. Oral Sinemet (L-DOPA:carbidopa) did not attenuate behavioral deficits related to partial dopamine depletions in this simple fixed-ratio bar-pressing task, but the present results suggest that Parkinson's patients might be identifiable earlier in the disease process, at a time when they could benefit from treatment with neuroprotective/neurotrophic agents. In addition, the results of the present study demonstrate that robust behavioral deficits may emerge with age. Mild dopamine depletions that were not detectable behaviorally at the time of the insult became clearly evident 10 months after the lesion with this bar-pressing task, and this may represent a more clinically relevant rodent model of Parkinson's disease.

Animals↗
PubMed1999

Robust pupil center detection using a curvature algorithm.

Determining the pupil center is fundamental for calculating eye orientation in video-based systems. Existing techniques are error prone and not robust because eyelids, eyelashes, corneal reflections or shadows in many instances occlude the pupil. We have developed a new algorithm which utilizes curvature characteristics of the pupil boundary to eliminate these artifacts. Pupil center is computed based solely on points related to the pupil boundary. For each boundary point, a curvature value is computed. Occlusion of the boundary induces characteristic peaks in the curvature function. Curvature values for normal pupil sizes were determined and a threshold was found which together with heuristics discriminated normal from abnormal curvature. Remaining boundary points were fit with an ellipse using a least squares error criterion. The center of the ellipse is an estimate of the pupil center. This technique is robust and accurately estimates pupil center with less than 40% of the pupil boundary points visible.

Algorithms↗
PubMed2003

A robust and automatic method for evaluating accuracy in 3-D ultrasound-based navigation.

We present a robust and automatic method for evaluating the 3-D navigation accuracy in ultrasound (US) based image-guided systems. The method is based on a precisely built and accurately measured phantom with several wire crosses and an automatic 3-D template matching by correlation algorithm. We investigated the accuracy and robustness of the algorithm and also addressed optimization of algorithm parameters. Finally, we applied the method to an extensive data set from an in-house US-based navigation system. To evaluate the algorithm, eight skilled observers identified the same wire crosses manually and the average over all observers constitutes our reference data set. We found no significant differences between the automatic and the manual procedures; the average distance between the point sets for one particular volume (27 point pairs) was 0.27 +/- 0.17 mm. Furthermore, the spread of the automatically determined points compared with the reference set was lower than the spread for any individual operator. This indicates that the automatic algorithm is more accurate than manual determination of the wire-cross locations, in addition to being faster and nonsubjective. In the application example, we used a set of 35 3-D US scans of the phantom under various acquisition configurations. The US frequency was 6.7 MHz and the average target depth was 6 cm. The accuracy, represented by the mean distance between automatically-determined wire-cross locations and physically measured locations, was found to be 1.34 +/- 0.62 mm.

Algorithms↗