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At least 721 records · Page 40Linked to original sources
PubMed1985

Evaluation of an index of peripheral vascular resistance in human subjects.

Based on evidence in animal studies, an index of resistance in man has been evaluated. In 10 human subjects, ranging in age from 31 to 60 years, direct brachial arterial pressure was measured, and a computer program using linear regression calculated the index of resistance from the slope of the logarithm of the pressure versus time during the second half of diastole. Resistance was independently calculated from 20-s averages of pressure and cardiac output obtained by thermodilution. Resistance was varied by infusion of phenylephrine and nitroprusside. The values of the index of resistance were compared with independently calculated resistance by linear regression and correlation. The index of resistance was variably correlated with independently calculated resistance. However, when the comparison was limited to points with a model correlation coefficient greater than or equal to 0.98 (i.e. a good fit of a straight line to the logarithm of pressure versus time), the correlation of the index of resistance with calculated resistance approached or exceeded 0.9 in eight of 10 subjects. In the two subjects showing poor correlation of the index with calculated resistance, estimated compliance from the same model was much lower than in the other subjects. In the same two subjects pressure dependence of estimated compliance was much higher than in the other subjects, suggesting the presence of significant atherosclerosis. We concluded that the diastolic decay of pressure may be used to calculate a useful index of resistance, provided that a single exponential decay fits the observed diastolic waveform well, and arterial compliance is not significantly reduced by atherosclerosis.

Adult↗
PubMed2006

Solving quadratic programming problems by delayed projection neural network.

In this letter, the delayed projection neural network for solving convex quadratic programming problems is proposed. The neural network is proved to be globally exponentially stable and can converge to an optimal solution of the optimization problem. Three examples show the effectiveness of the proposed network.

Algorithms↗
PubMed2006

Global convergence of decomposition learning methods for support vector machines.

Decomposition methods are well-known techniques for solving quadratic programming (QP) problems arising in support vector machines (SVMs). In each iteration of a decomposition method, a small number of variables are selected and a QP problem with only the selected variables is solved. Since large matrix computations are not required, decomposition methods are applicable to large QP problems. In this paper, we will make a rigorous analysis of the global convergence of general decomposition methods for SVMs. We first introduce a relaxed version of the optimality condition for the QP problems and then prove that a decomposition method reaches a solution satisfying this relaxed optimality condition within a finite number of iterations under a very mild condition on how to select variables.

Algorithms↗
PubMed2006

A simplified dual neural network for quadratic programming with its KWTA application.

The design, analysis, and application of a new recurrent neural network for quadratic programming, called simplified dual neural network, are discussed. The analysis mainly concentrates on the convergence property and the computational complexity of the neural network. The simplified dual neural network is shown to be globally convergent to the exact optimal solution. The complexity of the neural network architecture is reduced with the number of neurons equal to the number of inequality constraints. Its application to k-winners-take-all (KWTA) operation is discussed to demonstrate how to solve problems with this neural network.

Algorithms↗
PubMed2004

A controlled genetic programming approach for the deceptive domain.

Traditional genetic programming (GP) randomly combines subtrees by applying crossover. There is a growing interest in methods that can control such recombination operations in order to achieve faster convergence. In this paper, a new approach is presented for guiding the recombination process for genetic programming. The method is based on extracting the global information of the promising solutions that appear during the genetic search. The aim is to use this information to control the crossover operation afterwards. A separate control module is used to process the collected information. This module guides the search process by sending feedback to the genetic engine about the consequences of possible recombination alternatives.

Algorithms↗
PubMed2005

Visual learning by coevolutionary feature synthesis.

In this paper, a novel genetically inspired visual learning method is proposed. Given the training raster images, this general approach induces a sophisticated feature-based recognition system. It employs the paradigm of cooperative coevolution to handle the computational difficulty of this task. To represent the feature extraction agents, the linear genetic programming is used. The paper describes the learning algorithm and provides a firm rationale for its design. Different architectures of recognition systems are considered that employ the proposed feature synthesis method. An extensive experimental evaluation on the demanding real-world task of object recognition in synthetic aperture radar (SAR) imagery shows the ability of the proposed approach to attain high recognition performance in different operating conditions.

Algorithms↗
PubMed1978

Interaction between penicillin and the DD-carboxypeptidase of the unstable L-form of Proteus mirabilis strain 19.

Binding of penicillin to the DD-carboxypeptidase of the unstable spheroplast L-form of Proteus mirabilis results in the rapid formation of a modified enzyme-inhibitor complex which in turn undergoes rapid decay into reactivated enzyme and an antibiotically inactive penicillin degradation product. Major antibiotic metabolites recovered from such interactions were benzylpenicilloic acid and phenoxymethylpenicilloic acid from benzylpenicillin and phenoxymethylpenicillin, respectively, suggesting a second enzymic function of the DD-carboxypeptidase as a penicillinase of low efficiency. Statistical analyses made with the help of a linear regression program show that the enzyme interacts with the substrate UDP-N-acetylmuramoyl-L-alanyl-D-gamma-glutamyl-(L)-meso-2,6-diaminopimelyl-(L)-D-alanyl-D-alanine and either benzympenicillin or carbenicillin in a non-competitive manner.

Carboxypeptidases↗
PubMed1990

Estimate of the number and of the temporal sequence of measurements in a kinetic experiment.

The optimal choice of the number and the temporal sequence of measurements is that which minimizes the expected error on the parameters of the model later used to fit the observations. Practical constraints regarding the feasibility of a given temporal distribution of measurements, cost-benefit ratio as well as prior knowledge about the parameters and their variability in the selected population must be integrated in the decisional process. A non-linear integer programming procedure is used to find reasonable solutions to this problem.

Models, Biological↗
PubMed1995

Human-like dynamic programming neural networks for dynamic time warping speech recognition.

This paper presents a human-like dynamic programming neural network method for speech recognition using dynamic time warping. The networks are configured, much like human's, such that the minimum states of the network's energy function represent the near-best correlation between test and reference patterns. The dynamics and properties of the neural networks are analytically explained. Simulations for classifying speaker-dependent isolated words, consisting of 0 to 9 and A to Z, show that the method is better than conventional methods. The hardware implementation of this method is also presented.

Humans↗
PubMed2004

Evaluation of combination chemotherapy: integration of nonlinear regression, curve shift, isobologram, and combination index analyses.

Isobologram and combination index (CI) analyses are the two most popular methods for evaluating drug interactions in combination cancer chemotherapy. As the commonly used CI-based software program uses linear regression, our first objective was to evaluate the effects of logarithmic data transformation on data analysis and conclusions. Monte-Carlo simulations were conducted with experimentally relevant parameter values to generate error-containing effect or concentration-effect data of single agents and combinations. The simulated data were then analyzed with linear and nonlinear regression. The results showed that data transformation reduced the accuracy and precision of the regression-derived IC(50), curve shape parameter and CI values. Furthermore, as neither isobologram nor CI analyses provide output of concentration-effect curves for investigator evaluation, our second objective was to develop a method and the associated computer program/algorithm to (a) normalize drug concentrations in IC(50) equivalents and thereby enable simultaneous presentation of the curves for single agents and combinations in a single plot for visual inspection of potential curve shifts, (b) analyze concentration-effect data with nonlinear regression, and (c) use the curve shift analysis simultaneously with isobologram and CI analyses. The applicability of this method was shown with experimentally obtained data for single agent doxorubicin and suramin and their combinations in cultured tumor cells. In summary, this method, by incorporating nonlinear regression and curve shift analysis, although retaining the attractive features of isobologram and CI analyses, reduced the potential errors introduced by logarithmic data transformation, enabled visual inspection of data variability and goodness of fit of regression analysis, and simultaneously provided information on the extent of drug interaction at different combination ratios/concentrations and at different effect levels.

Animals↗
PubMed1989

Stereotactic radiosurgery for fractionated radiation: a proposal applicable to linear accelerator and proton beam programs.

A stereotactic radiosurgery technique is described which allows stereotactic radiation therapy to be easily fractionated on a daily or weekly basis. This permits adequate and safe radiation therapy to lesions larger than 2.5 cm, such as large arteriovenous malformations, and possibly safer radiation to smaller lesions near crucial intracranial structures. The technique utilizes external scalp landmarks and avoids the need for standard stereotactic head devices.

Equipment Design↗
PubMed2003

Managing risk and expected financial return from selective expansion of operating room capacity: mean-variance analysis of a hospital's portfolio of surgeons.

UNLABELLED: Surgeons using the same amount of operating room (OR) time differ in their achieved hospital contribution margins (revenue minus variable costs) by >1000%. Thus, to improve the financial return from perioperative facilities, OR strategic decisions should selectively focus additional OR capacity and capital purchasing on a few surgeons or subspecialties. These decisions use estimates of each surgeon's and/or subspecialty's contribution margin per OR hour. The estimates are subject to uncertainty (e.g., from outliers). We account for the uncertainties by using mean-variance portfolio analysis (i.e., quadratic programming). This method characterizes the problem of selectively expanding OR capacity based on the expected financial return and risk of different portfolios of surgeons. The assessment reveals whether the choices, of which surgeons have their OR capacity expanded, are sensitive to the uncertainties in the surgeons' contribution margins per OR hour. Thus, mean-variance analysis reduces the chance of making strategic decisions based on spurious information. We also assess the financial benefit of using mean-variance portfolio analysis when the planned expansion of OR capacity is well diversified over at least several surgeons or subspecialties. Our results show that, in such circumstances, there may be little benefit from further changing the portfolio to reduce its financial risk. IMPLICATIONS: Surgeon and subspecialty specific hospital financial data are uncertain, a fact that should be taken into account when making decisions about expanding operating room capacity. We show that mean-variance portfolio analysis can incorporate this uncertainty, thereby guiding operating room management decision-making and reducing the chance of a strategic decision being made based on spurious information.

Analysis of Variance↗
PubMed1989

Dynamics of Drosophila eye development and temporal requirements of sevenless expression.

The development of the compound eye of Drosophila consists of a linear, stereotyped program starting at the posterior end of the eye imaginal disc and progressing towards the anterior border. The determination of the R7 photoreceptor cells is part of this process and is dependent on the sevenless gene. In this study, we used a heat-shock-inducible sevenless gene as a conditional allele to determine the exact temporal requirements of sevenless gene expression and to reveal the stages of ommatidial development during which the presumptive R7 cell can respond to the presence of sevenless protein. Our results indicate that sevenless gene function is only required during a brief, defined period for the initiation of R7 development; subsequently sevenless is dispensable for both differentiation and function of the R7 photoreceptors. Furthermore, using rescue of R7 cells as an internal marker to monitor the progression of eye development we could examine when and at what rate ommatidial columns form.

Alleles↗
PubMed2002

Evaluation of skin barrier function using direct current I: effects of conductivity, voltage, distance between electrodes and electrode area.

The objective of this study was to evaluate the reduction in skin barrier function caused by direct current iontophoresis by measuring resistance in the short term. The experiments were carried out using rat abdominal skin in vivo. The resistance was measured every 125 ms and analyzed using a two-compartment model consisting of surface and skin resistance. Moreover, the initial value and the rate constant of each resistance were calculated with the non-linear approximation program. The proposed method could evaluate the reduction in barrier function from the initial value and the rate constant of surface resistance with high sensitivity and accuracy. Using this proposed method, the effects of the conductivity of an adhesive pad, voltage, the distance between electrodes and the area of electrode were examined. The increase in conductivity of the adhesive pad decreased the initial value since the rate constant increased. The reduction in barrier function depends on voltage. Although the barrier function decreased up until an electrode distance of 1 cm, it increased beyond 1 cm. These phenomena contributed to the current pass portion in the skin because the resistance was in the order of the stratum corneum, epidermis and dermis. The initial value decreased with increasing electrode area. However, the rate constant was little affected since the current density of a topical electrode adjacent to the other electrode was high.

Administration, Cutaneous↗
PubMed2002

Evaluation of skin barrier function using direct current II: effects of duty cycle, waveform, frequency and mode.

The aim of this study was to evaluate the reduction in skin barrier function caused by pulsed iontophoresis by measuring resistance in the short term. Experiments under direct current (DC) and pulsed direct current (PDC) conditions were carried out using rat abdominal skin in vivo. The resistance was measured every 62.5 micros and analyzed using a two-compartment model consisting of surface and skin resistance. Moreover, the initial value and the rate constant of surface resistance were calculated with the non-linear approximation program. Using this method, effects of duty cycle, waveform, frequency and mode on the skin barrier function were examined. The barrier function decreased with increasing duty cycle. With regard to waveforms, the influence on the skin barrier function was greatest in the order of sine, rectangular, saw and triangular waveforms. A frequency of less than 100 Hz reduced the barrier function. Considering the reduction in barrier function and skin polarization, the PDC of a rectangular waveform (around 75% as duty cycle and less than 100 Hz as frequency) or sine waveform was most suitable. In addition, the difference in the amount of drug delivered by DC and by PDC was discussed.

Administration, Cutaneous↗