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At least 595 records · Page 33Linked to original sources
PubMed2004

Delay-dependent robust H infinity control for a class of uncertain switched systems with time delay.

For linear switched system with both parameter uncertainties and time delay, a delay-dependent sufficient condition for the existence of a new robust H infinity feedback controller was formulated in nonlinear matrix inequalities solvable by an LMI-based iterative algorithm. Compared with the conventional state-feedback controller, the proposed controller can achieve better robust control performance since the delayed state is utilized as additional feedback information and the parameters of the proposed controllers are changed synchronously with the dynamical characteristic of the system. This design method was also extended to the case where only delayed state is available for the controller. The example of balancing an inverted pendulum on a cart demonstrates the effectiveness and applicability of the proposed design methods.

Algorithms↗
PubMed2003

Robust dosage-PCR for detection of heterozygous chromosomal deletions.

Robust dosage-PCR (RD-PCR) was developed to detect heterozygous large deletions, an important class of mutations missed by conventional PCR strategies. PCR-based methods are available for distinguishing between the dosage of one or two template copies, but general application is limited by the laborious nature of the method and/or the optimization required for each new set of gene exons to be analyzed. RD-PCR depends on a combination of (i) co-amplification of an autosomal and an X-chromosomal segment so that internal dosage controls are available for any segment to be analyzed and (ii) a robust primer design that includes a 5'tail and a 3'sequence-specific region in the PCR protocol. The ratio of yields (ROY) of the target to the internal control segment is directly proportional to the ratio of the two input templates over a wide range (at least 1:1 to 1:258 with a correlation coefficient of 0.99). The ROY is not dependent on the amount of genomic DNA or the number of cycles of amplification under typical conditions. RD-PCR eliminates errors in the preparation and manipulation steps by using an internal dosage control. A blinded analysis of gene dosage was performed to detect deletions of the human factor IX gene with 100% accuracy. Prospective analyses demonstrate that exons and flanking splice junctions can be analyzed for gene dosage with minimal optimization.

Chromosome Deletion↗
PubMed2006

Robust Selection of Predictive Genes via a Simple Classifier.

Identifying genes that direct the mechanism of a disease from expression data is extremely useful in understanding how that mechanism works. This in turn may lead to better diagnoses and potentially could lead to a cure for that disease. This task becomes extremely challenging when the data are characterised by only a small number of samples and a high number of dimensions, as is often the case with gene expression data. Motivated by this challenge, we present a general framework that focuses on simplicity and data perturbation. These are the keys for robust identification of the most predictive features in such data. Within this framework, we propose a simple selective naive Bayes classifier discovered using a global search technique, and combine it with data perturbation to increase its robustness for small sample sizes. An extensive validation of the method was carried out using two applied datasets from the field of microarrays and a simulated dataset, all confounded by small sample sizes and high dimensionality. The method has been shown to be capable of selecting genes known to be associated with prostate cancer and viral infections.

Artificial Intelligence↗
PubMed2006

The effects of hydraulic and organic shock loads on the robustness of upflow anaerobic sludge blanket reactors treating sewage.

In this investigation, the robustness and stability of UASB reactors was evaluated on the basis of four indicators: (i) COD removal efficiency; (ii) effluent variability; (iii) pH stability; and (iv) recovery time. The experiments were carried out using six pilot-scale UASB reactors fed with domestic sewage and operated under different operational conditions. After establishment of a "steady-state", organic and hydraulic shock loads (six times the loading rate during six hours) were imposed. The results show that the UASB reactors are robust systems with regards to COD removal efficiency and pH stability when exposed to shock loads. However, this reactor cannot attenuate the imposed fluctuation in the influent COD. A secondary treatment unit is needed to retain the expelled sludge occurring as a result of a hydraulic shock load, or prior to the shock, a sufficient amount of sludge needs to be discharged from the reactor.

Anaerobiosis↗
PubMed1996

Robustness of taxometric analysis with skewed indicators: I. A Monte Carlo study of the MAMBAC procedure.

A small Monte Carlo study was conducted to determine whether Meehl and Yonce's (1994) MAMBAC procedure--a taxometric method for testing between discrete and continuous models of latent variables--is robust when the latent variable and its manifest indicators are skewed. Analysis of constructed data sets containing three levels of skew indicated that the MAMBAC procedure is highly unlikely to yield spurious findings of discreteness ("taxonicity") even when skewness is considerable. MAMBAC appears to be a robust and promising addition to the family of taxometric procedures.

Humans↗
PubMed1997

Developing mortality patterns: robust modified generalized likelihood ratio algorithm for infant mortality rate change detection.

A new robust modified generalized likelihood ratio algorithm, which enables the changes of mortality rates to be detected automatically, is applied. The procedure is based on the calculation of discrimination function using robust least squares estimates of AR mortality rates residuals. The feasibility of the approach is demonstrated with experimental data concerning infant mortality rate in Serbia.

Algorithms↗
PubMed1999

Leap-frog is a robust algorithm for training neural networks.

Optimization of perceptron neural network classifiers requires an optimization algorithm that is robust. In general, the best network is selected after a number of optimization trials. An effective optimization algorithm generates good weight-vector solutions in a few optimization trial runs owing to its inherent ability to escape local minima, where a less effective algorithm requires a larger number of trial runs. Repetitive training and testing is a tedious process, so that an effective algorithm is desirable to reduce training time and increase the quality of the set of available weight-vector solutions. We present leap-frog as a robust optimization algorithm for training neural networks. In this paper the dynamic principles of leap-frog are described together with experiments to show the ability of leap-frog to generate reliable weight-vector solutions. Performance histograms are used to compare leap-frog with a variable-metric method, a conjugate-gradient method with modified restarts, and a constrained-momentum-based algorithm. Results indicate that leap-frog performs better in terms of classification error than the remaining three algorithms on two distinctly different test problems.

Algorithms↗
PubMed2000

Robust autofocusing in microscopy.

BACKGROUND: A critical step in automatic microscopy is focusing. This report describes a robust and fast autofocus approach useful for a wide range of microscopic modalities and preparations. METHODS: The focus curve is measured over the complete focal range, reducing the chance that the best focus position is determined by dust or optical artifacts. Convolution with the derivative of a Gaussian smoothing function reduces the effect of noise on the focus curve. The influence of mechanical tolerance is accounted for. RESULTS: The method is shown to be robust in fluorescence, bright-field and phase contrast microscopy, in fixed and living cells, as well as in fixed tissue. The algorithm was able to focus accurately within 2 or 3 s, even under extremely noisy and low contrast imaging conditions. CONCLUSIONS: The proposed method is generally applicable in light microscopy, whenever the image information content is sufficient. The reliability of the autofocus method allows for unattended operation on a large scale.

Animals↗
PubMed2000

A novel robust blood pressure control system.

A adaptive robust control of postoperative hypertension is presented to reduce the mean arterial blood pressure using vasoactive drugs. It is shown that the control algorithm provides stability-guaranteed regulation subject to infusion rate saturation. Simulation results under clinical conditions show that the control system exhibits strong robustness and is capable of reducing blood pressure.

Algorithms↗
PubMed2000

Robust parametric and semi-parametric spot fitting for spot array images.

In this paper we address the problem of reliably fitting parametric and semi-parametric models to spots in high density spot array images obtained in gene expression experiments. The goal is to measure the amount of label bound to an array element. A lot of spots can be modelled accurately by a Gaussian shape. In order to deal with highly overlapping spots we use robust M-estimators. When the parametric method fails (which can be detected automatically) we use a novel, robust semi-parametric method which can handle spots of different shapes accurately. The introduced techniques are evaluated experimentally.

Animals↗
PubMed2001

Deriving robust operating rules for the interim control of the Kirazdere reservoir.

A methodology is developed for deriving robust operating rules for the interim control of a multipurpose reservoir. The methodology includes the generation of policies using optimisation models, the derivation of robust operating rules using artificial neural networks and the evaluation of the identified policies through simulation. The approach developed is demonstrated through an application to the Kirazdere Reservoir located on the Kiraz River in Turkey.

Conservation of Natural Resources↗
PubMed2001

Global structure, robustness, and modulation of neuronal models.

The electrical characteristics of many neurons are remarkably robust in the face of changing internal and external conditions. At the same time, neurons can be highly sensitive to neuromodulators. We find correlates of this dual robustness and sensitivity in a global analysis of the structure of a conductance-based model neuron. We vary the maximal conductance parameters of the model neuron and, for each set of parameters tested, characterize the activity pattern generated by the cell as silent, tonically firing, or bursting. Within the parameter space of the five maximal conductances of the model, we find directions, representing concerted changes in multiple conductances, along which the basic pattern of neural activity does not change. In other directions, relatively small concurrent changes in a few conductances can induce transitions between these activity patterns. The global structure of the conductance-space maps implies that neuromodulators that alter a sensitive set of conductances will have powerful, and possibly state-dependent, effects. Other modulators that may have no direct impact on the activity of the neuron may nevertheless change the effects of such direct modulators via this state dependence. Some of the results and predictions arising from the model studies are replicated and verified in recordings of stomatogastric ganglion neurons using the dynamic clamp.

Action Potentials↗
PubMed2002

Normalized residual activity: usual values and robustness of the method.

UNLABELLED: The objectives of this study were 2-fold: first, to investigate the robustness of the normalized residual activity (NORA), a parameter that has recently been proposed for the estimation of renal emptying during renography; and second, to define the usual values of NORA in 2 categories of kidneys-those with a normal renogram and those that are dilated but definitely unobstructed. METHODS: NORA was defined as the renal activity at a given moment (end of renogram, end of furosemide acquisition, image after micturition) divided by the renal activity between 1 and 2 min. Two variables that might influence the results of NORA were evaluated: the choice of background correction, and an error in the estimation of the 1- to 2-min renal activity. To estimate the values of NORA in usual clinical conditions, 2 sets of data were analyzed: normal kidneys with a normal renogram pattern, and dilated but definitely unobstructed kidneys. RESULTS: Using a perirenal or a subrenal background correction, NORA was, on average, 67% or 83%, respectively, of the value obtained without background correction. The use of a renal activity of 1 min 20 s to 2 min 20 s instead of a 1- to 2-min activity resulted in a systematic 10%-15% underestimation of NORA. The 90th percentile values of NORA were, in the normal group, 0.70 at 20 min, 0.23 at the end of the furosemide test, and 0.10 after micturition. In the kidneys that had undergone surgery, the 90th percentile values were 3.92 at 20 min, 2.91 at the end of the furosemide test, and 1.99 after micturition. A good correlation was observed between NORA and output efficiency. CONCLUSION: If adequately standardized, NORA is a robust and simple parameter that allows evaluation of renal emptying at any time of the acquisition. One should be aware of the fact that high NORA values, corresponding to poor renal emptying, may be observed in the operated unobstructed kidneys, even after micturition.

Adult↗
PubMed2002

Oxazolinone derivative of leucine for GC-MS: a sensitive and robust method for stable isotope kinetic studies of lipoproteins.

Stable isotope labeled amino acids are commonly used as endogenous tracers to study the metabolism of lipoproteins. The determination of isotopic enrichment of particular amino acids in apolipoproteins is carried out by gas chromatography mass spectrometry (GC-MS). This report describes a robust and sensitive derivative for analysis of d3-leucine by GC-MS and its utility in studying the metabolism of human lipoproteins. The trifluoromethyloxazolinone (oxazolinone) derivative of leucine was formed in a rapid single step procedure using a mixture of trifluoroacetic anhydride (TFAA) and trifluoroacetic acid (TFA). Analysis of the oxazolinone by negative ion chemical ionization GC-MS gave excellent sensitivity and precision, which enabled accurate determination of low levels of isotopic enrichment from small amounts of protein. For example, enrichments between 0.05% and 100% in 100 pg leucine can be measured with a coefficient of variation of <3%. To demonstrate the utility of this procedure, we measured d3-leucine enrichment in apolipoprotein B (apoB) isolated from VLDL and LDL as well as apoA-I isolated from HDL by gel electrophoresis and western blotting. The derivatization procedure gave excellent enrichment data from a single intravenous bolus dose of 5 mg/kg, from which the fractional catabolic rate and production rate of the lipoproteins were calculated. In conclusion, the oxazolinone derivative provides a robust and simple procedure for the sensitive analysis of isotopic enrichment for metabolic studies of human lipoproteins.

Apolipoprotein A-I↗
PubMed2002

Body size and postcranial robusticity of European Upper Paleolithic hominins.

The robust diaphyses of Pleistocene hominins are said to indicate higher activity levels in these prehistoric humans than among people today. Thus, it could be argued that the prediction of body mass from fossil lower limb diaphyseal cortical area (CA) using recent human regressions might lead to erroneously high body mass estimates. This study uses three body mass prediction formulae based on the following features: reconstructed femoral 80% (subtrochanteric) CA, femoral head diameter (FH), and bi-iliac breadth and stature (BIB-St) among European Early and Late Upper Paleolithic (EUP and LUP) and recent humans from Africa and Europe. All three methods produce similar body mass estimates for all groups studied, including recent humans. Gleaning behavioral differences from these data is more difficult, as no significant differences in CA were found among the fossil and recent Europeans. It has been suggested that the EUP had less robust diaphyses than their LUP counterparts. However, here this result is only obtained when CA is size-standardized to femoral length(3) (Ruff et al., 1993, Am. J. phys. Anthrop.91, 21-53 Trinkaus et al., 1998, in Neandertals and Modern Humans in Western Asia, pp.391-404, New York: Plenum). This should not be interpreted as evidence for lower activity levels in the EUP, but rather as an artefact of standardization, for as Wolpoff (1999), Am. J. phys. Anthrop.109, 416-423 points out, these standardized variables are extremely sensitive to limb length differences, and the EUP have longer limbs than their LUP counterparts. With this in mind, these data do not support a pattern of behavioral differences between EUP and LUP humans, and therefore more sensitive measures than CA may be required to detect such differences.

Animals↗
PubMed2002

Robustness of empirical search strategies for clinical content in MEDLINE.

BACKGROUND: It is important for clinical end users of MEDLINE to be able to retrieve articles that are both scientifically sound and directly relevant to clinical practice. The use of methodologic search filters (such as "random allocation" for sound studies of medical interventions) has been advocated to improve the accuracy of searching for such studies. Methodologic search filters have been tested in previous MEDLINE files but indexing continues to evolve and the operating characteristics of these search filters in current MEDLINE files are unknown. OBJECTIVE: To determine the robustness of empirical search strategies developed in 1991 for detecting clinical content in MEDLINE in the year 2000. DESIGN: A survey based on a hand search of 171 core health care journals using predetermined quality indicators for scientific merit and clinical relevance. METHODS: 6 trained, experienced research assistants read all issues of 171 journals for the publishing year 2000. Each article was rated using purpose and quality indicators and categorized into clinically relevant original studies, review articles, general papers, or case reports. The original and review articles were then categorized as 'pass' or 'fail' for methodologic rigor in the areas of therapy/quality improvement, diagnosis, prognosis, causation, economics, clinical prediction, and qualitative and review articles. Search strategies developed in 1991 were tested in the 2000 database. MAIN OUTCOME MEASURES: Sensitivity, specificity, precision, and accuracy of the search strategies. RESULTS: Search strategies developed in 1991 generally performed at least as well in 2000 for both best single terms and combinations of terms for high-sensitivity MEDLINE searches for studies of treatment, prognosis, etiology and diagnosis. For example, the accuracy of "clinical trial (pt)" rose from 91.6% to 94.4% (P<0.05) for retrieving high-quality studies of treatments. CONCLUSION: Most MEDLINE search strategies developed in 1991 are robust when searching in the publishing year 2000.

Information Storage and Retrieval↗
PubMed2002

Correction of partial-volume effect for PET striatal imaging: fast implementation and study of robustness.

UNLABELLED: PET imaging of D(2) receptors or (18)F-L-dopa metabolism are reference protocols to follow and study neurodegenerative diseases, but the accuracy of striatal PET imaging is limited by the partial-volume effect (PVE). For such studies, the geometric transfer matrix (GTM) method has been proposed to correct the regional mean values for PVE and is now widely used. METHODS: The GTM method models the geometric interactions induced by the PET system between the anatomic regions in which PVE correction is performed. This implies estimation of the corresponding regional spread function (RSF). The literature describes 2 implementations for the RSF calculation; they differ in the way the point spread function (PSF) of the imaging system is modeled, but no comparison or discussion has been given. The first and reference implementation uses an accurate intrinsic detector PSF that is applied in the sinogram space. The second uses a global PSF that is applied in the image space. In this work, we compared the 2 GTM implementations for 3-dimensional (3D) PET striatal imaging using Monte Carlo simulations and a phantom study. We studied the robustness of the GTM correction with respect to residual registration errors between PET and anatomy and with respect to residual segmentation errors. RESULTS: Despite the differences in RSF calculation and computation cost between the 2 implementations, similar recovery results were obtained (between 95% and 100%). The study of robustness of the GTM correction yielded 2 results. A realistic residual misregistration between the anatomic and PET images did not modify the algorithm accuracy but decreased its precision. Conversely, a realistic residual missegmentation of the anatomic regions submitted to GTM correction decreased the correction accuracy. CONCLUSION: A simple but efficient implementation in the image space of the GTM method yields accurate PVE correction in striatal regions in studies with 3D PET and enables clinical use. The method is less sensitive to residual misregistration errors between PET and anatomy than to residual missegmentation of the anatomy. Special care should be taken with segmentation of the regions to correct for PVE.

Corpus Striatum↗
PubMed1998

[A robust method for automated retinal vascular images mosaic based on phase correlation method and mathematical morphology].

Precise mosaic techniques are essential for quantitative evaluation of retinal images to make early detection of fundus anomalies feasible. Opening of a gray-scale image by a gray-scale structuring element(SE) can generate a background image. Image mosaic was achieved by subtraction this background image from the original image and then applying a phase correlation method to find translation difference. Because of the accuracy characteristics of the phase correlation method and the speed of the FFT hardware, this new algorithm can work very fast and accurately, compared to conventional techniques. The method was also characterized by an outstanding robustness against correlated noise and disturbances, such as those encountered with nonuniform illumination. The results confirm the robustness of the chosen approach.

Algorithms↗