SEARCH · PubMed Health

Results for “Algorithms”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,261 records · Page 70Linked to original sources

PubMed1986

Fluid resuscitation of hypotensive emergency patients with and without an algorithm.

Seventy-seven consecutive hypotensive (mean arterial pressure (MAP) less than 80 mmHg) surgical emergency patients were resuscitated according to either physicians' individual orders (38 patients) or an algorithm (39 patients). The shock was mainly caused by accidental injuries or acute gastrointestinal bleeding. The patients of the algorithm group were given more plasma expanders than the patients of the control group, while the total amount of fluids administered was similar in both groups. The primary goal of the resuscitation (MAP greater than 80 mmHg) was reached within 30 min in three cases in the control group and in seven cases in the algorithm group. The treatment times at the emergency department and the intensive care unit were similar for the groups. The number of severe and moderate pulmonary disturbances was the same, but mild disturbances were significantly more common in the control group. Renal failure was somewhat more common in the control group and the renal function disturbances were significantly more severe among the control patients. The results suggest that the physicians in some extent altered their practices in fluid resuscitation when the algorithm was put to use, and that this change, perhaps, produced the somewhat better outcome of the patients. The authors recommend the algorithm to be used as a basis of shock treatment and particularly in those emergency departments where the resuscitation of hypotensive patients is performed by junior or inexperienced physicians.

Adolescent↗

PubMed2005

A finite element based algorithm for determining interfacial tension (gamma) from pendant drop profiles.

This paper introduces a robust algorithm to determine the interfacial tension (gamma) from pendant drop profiles using the Galerkin finite element method (gamma-PD-FEM) to solve the axisymmetric form of the Young-Laplace (YL) equation. In this algorithm, the theoretical profiles are generated by solving the spherical coordinate form of the YL equation. gamma-PD-FEM also solves for the parameter estimates by minimizing the difference between the theoretical and experimental surface functions, f(theta). This technique is compared to the widely used method of converting the YL equation to the three arc length-based (ALB) first-order ODEs developed by Bashforth and Adams (BA) in 1883, or as denoted in this paper, the gamma-PD-BA method. The drop apex is the initial condition for the gamma-PD-BA algorithm and the integration is terminated at a specified location along the drop profile. In contrast to techniques based on the BA approach, computation of the theoretical drop profile in gamma-PD-FEM is obtained from a second-order ordinary differential equation and requires boundary conditions at the drop apex and at the contact line of the drop to the nozzle. By incorporating both boundary conditions into the problem formulation, the algorithm can also determine if the drop shape is at static equilibrium. Results to be presented include an outline of the computer algorithm, and comparison of gamma values obtained from the gamma-PD-FEM and the traditional gamma-PD-BA method using simulated and experimental drop profile data sets.

Journal Article↗

PubMed2006

Direct descent curvature optimal control with a modification algorithm and its application to nonlinear process.

This paper presents a direct descent second order or direct descent curvature algorithm with some modifications for the optimal control computations. This algorithm is compared with Hamiltonian methods in the literature. The proposed algorithm has generated numerically robust solutions with respect to conjugate points. The weighting matrix updating scheme was developed to improve the second-order optimal control algorithm, tested the performance of the algorithm, and shown on the benchmark and industrial process. The time-varying optimal feedback (TVOFB) gains are also generated along the trajectory as byproducts. If the trajectory deviates from the optimal trajectory for any reason (i.e., changing of system parameters, step disturbance into the plant, changing of initial conditions), it is held on the optimal trajectory by means of the optimal feedback. Simulations have been given for controlling the Van der Pol and bioreactor system, which are nonlinear benchmark systems.

Journal Article↗

PubMed2002

Algorithms for suppressing ultrasonic backscattering from material structure.

In pulse-echo ultrasonic inspection the backscattering from the material structure appears in the received ultrasonic images as clutter, often referred to as grain noise, which impairs the inspection results. A toolbox including algorithms for suppressing ultrasonic clutter is presented in the paper. Several processing algorithms capable of suppressing grain noise have been proposed, of which the split spectrum processing (SSP) probably is the most renowned. The classical SSP technique applies a filter bank to some frequency band that has to be precisely known in advance, to obtain a set of narrow-band signals that are tested for mutual correlation using some statistical operation. A number of SSP algorithms with different statistical operations are included in the toolbox. A completely different approach is to use explicit statistical models of grain noise and defects and to design an optimal filter based on those models. A simple such algorithm, based on noncoherent detection (NCD) known from communications, is also included in the toolbox. The toolbox, implemented in Matlab, is provided with a user-friendly graphical interface facilitating comparison of the algorithms.

Journal Article↗

PubMed2000

Non-linear algorithms based on SAFT ideas for reconstruction of flaws

The main idea and the assumptions of time domain synthetic aperture focusing technique (SAFT) are discussed. It is underlined that the major SAFT assumption is that the flaw can be represented by a number of single non-interacting scalar point scatterers, which act as point sources after illumination with the incident wavefield. As a result some important classes of flaws are incorrectly reconstructed by means of SAFT. Among them are cracks from which reflected signals are similar to those from mirror-shaped flaws. Different non-linear SAFT algorithms proposed earlier by the author are discussed and compared. Among them are SAFT with non-linear normalization (NSAFT), second order SAFT, and the radial tomography technique. The principles of these algorithms are discussed. Then their advantages and disadvantages are analysed. Unfortunately each algorithm cannot be considered universal as a classical SAFT, but for many important cases these algorithms are useful for solving inverse problems in ultrasonics. The ideas of non-linear SAFT algorithms are illustrated by physical experiments.

Journal Article↗

PubMed1997

An Efficient EM-based Training Algorithm for Feedforward Neural Networks.

A fast training algorithm is developed for two-layer feedforward neural networks based on a probabilistic model for hidden representations and the EM algorithm. The algorithm decomposes training the original two-layer networks into training a set of single neurons. The individual neurons are then trained via a linear weighted regression algorithm. Significant improvement on training speed has been made using this algorithm for several bench-mark problems. Copyright 1997 Elsevier Science Ltd. All Rights Reserved.

Journal Article↗

PubMed1997

Stability Analysis of Learning Algorithms for Blind Source Separation.

Recently a number of adaptive learning algorithms have been proposed for blind source separation. Although the underlying principles and approaches are different, most of them have very similar forms. Two important issues remained to be elucidated further: the statistical efficiency and the stability of learning algorithms. The present letter analyzes a general form of statistically efficient algorithms and gives a necessary and sufficient condition for the separating solution to be a stable equilibrium of a general learning algorithm. Moreover, when the separating solution is unstable, a simple method is given for stabilizing the separating solution by modifying the algorithm.

Journal Article↗

PubMedDate not supplied

Competence of alpha spectrometry analysis algorithms used to resolve the 241Am and 243Am alpha peak overlap.

Five alpha spectrometry analysis algorithms were evaluated for their ability to resolve the 241Am and 243Am peak overlap present under typical low-level counting conditions. The major factors affecting the performance of the algorithms were identified using design-of-experiment combined with statistical analysis of the results. The study showed that the accuracy of the 241Am/243Am ratios calculated by the algorithms depends greatly on the degree of peak deformation and tailing. Despite the improved data quality obtained using an algorithm that may include peak addition and tail estimation, the accurate determination of 241Am by alpha spectrometry relies primarily on reduction of peak overlap rather than on algorithm selection.

Journal Article↗

PubMed2005

A comprehensive two-dimensional retention time alignment algorithm to enhance chemometric analysis of comprehensive two-dimensional separation data.

A comprehensive two-dimensional (2D) retention time alignment algorithm was developed using a novel indexing scheme. The algorithm is termed comprehensive because it functions to correct the entire chromatogram in both dimensions and it preserves the separation information in both dimensions. Although the algorithm is demonstrated by correcting comprehensive two-dimensional gas chromatography (GC x GC) data, the algorithm is designed to correct shifting in all forms of 2D separations, such as LC x LC, LC x CE, CE x CE, and LC x GC. This 2D alignment algorithm was applied to three different data sets composed of replicate GC x GC separations of (1) three 22-component control mixtures, (2) three gasoline samples, and (3) three diesel samples. The three data sets were collected using slightly different temperature or pressure programs to engender significant retention time shifting in the raw data and then demonstrate subsequent corrections of that shifting upon comprehensive 2D alignment of the data sets. Thirty 12-min GC x GC separations from three 22-component control mixtures were used to evaluate the 2D alignment performance (10 runs/mixture). The average standard deviation of first column retention time improved 5-fold from 0.020 min (before alignment) to 0.004 min (after alignment). Concurrently, the average standard deviation of second column retention time improved 4-fold from 3.5 ms (before alignment) to 0.8 ms (after alignment). Alignment of the 30 control mixture chromatograms took 20 min. The quantitative integrity of the GC x GC data following 2D alignment was also investigated. The mean integrated signal was determined for all components in the three 22-component mixtures for all 30 replicates. The average percent difference in the integrated signal for each component before and after alignment was 2.6%. Singular value decomposition (SVD) was applied to the 22-component control mixture data before and after alignment to show the restoration of trilinearity to the data, since trilinearity benefits chemometric analysis. By applying comprehensive 2D retention time alignment to all three data sets (control mixtures, gasoline samples, and diesel samples), classification by principal component analysis (PCA) substantially improved, resulting in 100% accurate scores clustering.

Journal Article↗

PubMedDate not supplied

A probabilistic derivation of the partial least-squares algorithm.

Traditionally the partial least-squares (PLS) algorithm, commonly used in chemistry for ill-conditioned multivariate linear regression, has been derived (motivated) and presented in terms of data matrices. In this work the PLS algorithm is derived probabilistically in terms of stochastic variables where sample estimates calculated using data matrices are employed at the end. The derivation, which offers a probabilistic motivation to each step of the PLS algorithm, is performed for the general multiresponse case and without reference to any latent variable model of the response variable and also without any so-called "inner relation". On the basis of the derivation, some theoretical issues of the PLS algorithm are briefly considered: the complexity of the original motivation of PLS regression which involves an "inner relation"; the original motivation behind the prediction stage of the PLS algorithm; the relationship between uncorrelated and orthogonal latent variables; the limited possibilities to make natural interpretations of the latent variables extracted.

Journal Article↗

PubMedDate not supplied

Global optimization of Lennard-Jones clusters by a parallel fast annealing evolutionary algorithm.

A parallel fast annealing evolutionary algorithm (PFAEA) was presented and applied to optimize Lennard-Jones (LJ) clusters. All the lowest known minima up to LJ(116) with both icosahedral and nonicosahedral structure, including the truncated octahedron of LJ(38), central fcc tetrahedron of LJ(98), the Marks' decahedron of LJ(75)(-)(77), and LJ(102)(-)(104), were located successfully by the unbiased algorithm. PFAEA is a parallel version of fast annealing evolutionary algorithm (FAEA) that combines the aspect of population in genetic algorithm and annealing algorithm with a very fast annealing schedule. A master-slave paradigm is used to parallelize FAEA to improve the efficiency. The performance of PFAEA is studied, and the scaling of execution time with the cluster size is approximately cubic, which is important for larger scale energy minimization systems.

Journal Article↗

PubMedDate not supplied

Over 20 years of reaction access systems from MDL: a novel reaction substructure search algorithm.

From REACCS, to MDL ISIS/Host Reaction Gateway, and most recently to MDL Relational Chemistry Server, a new product based on Oracle data cartridge technology, MDL's reaction database management and retrieval systems have undergone great changes. The evolution of the system architecture is briefly discussed. The evolution of MDL reaction substructure search (RSS) algorithms is detailed. This article mainly describes a novel RSS algorithm. This algorithm is based on a depth-first search approach and is able to fully and prospectively use reaction specific information, such as reacting center and atom-atom mapping (AAM) information. The new algorithm has been used in the recently released MDL Relational Chemistry Server and allows the user to precisely find reaction instances in databases while minimizing unrelated hits. Finally, the existing and new RSS algorithms are compared with several examples.

Journal Article↗

PubMedDate not supplied

A genetic algorithm based on prepotency evolution using chaotic initiation used for network training.

The concept of "prepotency" is introduced in evolution algorithm. The logistic mapping as a simple and powerful device in the chaos theory is combined with the newly proposed prepotency evolution (PE) algorithm to formulate a new genetic algorithm. PE with a population initialized by chaotic numbers is applied to the multiple-layer feed-forward ANN training (PECNN). The logistic mapping ensures the PE starts each time from different initial population never used before. The newly designed PE operator partially includes the crossover and mutation operations implicitly. The proposed algorithm has a higher convergence speed comparing to the conventional GA. During the PE operation the distances between members would become smaller and smaller until all members turning to be almost identical with the potential best minimum being found. It does not waste searching time surrounding the testing minima like the conventional GA and not show symptoms of overfitting to the training set samples. The combination of logistic mapping and PE used in ANN training makes PECNN be able to test lots of minima rapidly and effectively. This greatly enlarges the opportunity to find the global minimum. The proposed algorithm has been testified by prediction of the frequency data of tetrahedral vibration modes (nu(1) and nu(2)) of tetrahalide MX(4)(n) ions. The results obtained by the proposed PECNN compared favorably with those of the conventional chemometric method PLS regression.

Journal Article↗

PubMed2000

Heterogeneous catalyst design using stochastic optimization algorithms

We describe the application of two stochastic optimization algorithms to heterogeneous catalyst design. In particular, we discuss the optimal design of a two-component catalyst for the diffusion limited A + B --> 0 and A + B2 --> 0 reactions in which each of the reactants are adsorbed specifically on one of the two distinct catalytic sites. The geometric arrangement of the catalytic sites that maximizes the catalyst activity is determined by the use of a genetic algorithm and a simulated annealing algorithm. In the case of the A + B --> 0 reaction, it is found that the catalyst surface with the optimal active site distribution, that of a checkerboard, is approximately 25% more active than a random site distribution. A similar increase in catalytic activity is obtained for the A + B2 --> 0 reaction. While both the genetic and simulated annealing algorithms obtain identical optimal solutions for a given reaction, the simulated annealing algorithm is shown to be more efficient.

Journal Article↗

PubMed2006

Larger water clusters with edges and corners on their way to ice: structural trends elucidated with an improved parallel evolutionary algorithm.

For the difficult task of finding global minimum energy structures for molecular clusters of nontrivial size, we present a highly efficient parallel implementation of an evolutionary algorithm. By completely abandoning the traditional concept of generations and by replacing it with a less rigid pool concept, we have managed to eliminate serial bottlenecks completely and can operate the algorithm efficiently on an arbitrary number of parallel processes. Nevertheless, our new algorithm still realizes all of the main features of our old, successful implementation. First tests of the new algorithm are shown for the highly demanding problem of water clusters modeled by a potential with flexible, polarizable monomers (TTM2-F). For this problem, our new algorithm not only reproduces all of the global minima proposed previously in considerably less CPU time but also leads to improved proposals in several cases. These, in turn, qualitatively change our earlier predictions concerning the transitions from all-surface structures to cages with a single interior molecule, and from one to two interior molecules. Furthermore, we compare preliminary results up to n = 105 with locally optimized cuts from several ice modifications. This comparison indicates that relaxed ice structures may start to be competitive already at cluster sizes above n = 90.

Journal Article↗

PubMed2005

Brownian dynamics algorithm for bead-rod semiflexible chain with anisotropic friction.

A model of semiflexible bead-rod chain with anisotropic friction can mimic closely the hydrodynamics of a slender filament. We present an efficient algorithm for Brownian dynamics simulations of this model with configuration dependent anisotropic bead friction coefficients. The algorithm is an extension of that given previously for the case of configuration independent isotropic friction coefficients by Grassia and Hinch [J. Fluid Mech. 308, 255 (1996)]. We confirm that the algorithm yields predicted values for various equilibrium properties. We also present a stochastic algorithm for evaluation of the stress tensor, and we show that in the limit of stiff chains the algorithm recovers the results of Kirkwood and Plock [J. Chem. Phys. 24, 665 (1956)] for rigid rods with hydrodynamic interactions.

Journal Article↗

PubMed2005

Operator splitting algorithm for isokinetic SLLOD molecular dynamics.

We apply an operator splitting method to develop a simulation algorithm that has complete analytical solutions for the Gaussian thermostated SLLOD equations of motion [D. J. Evans and G. P. Morriss, Phys. Rev. A 30, 1528 (1984)] for a system under shear. This leads to a homogeneous algorithm for performing both equilibrium and nonequilibrium isokinetic molecular dynamics simulation. The resulting algorithm is computationally efficient. In particular, larger integration time steps can be used compared to simulations with regular Gaussian thermostated SLLOD equations of motion. The utility and accuracy of the algorithm are demonstrated through application to the Weeks-Chandler-Anderson fluid. Although strict conservation of the kinetic energy suppresses thermal fluctuations in the system, this algorithm does not allow simulations at lower shear rates than those normally afforded by older nonequilibrium molecular dynamics simulations.

Journal Article↗

PubMed2005

A lattice Boltzmann algorithm for electro-osmotic flows in microfluidic devices.

In this paper, a finite-difference-based lattice Boltzmann (LB) algorithm is proposed to simulate electro-osmotic flows (EOF) with the effect of Joule heating. This new algorithm enables a nonuniform mesh to be adapted, which is desirable for handling the extremely thin electrical double layer in EOF. The LB algorithm has been validated by simulating a problem with an available analytical solution and it is found that the numerical results predicted by the algorithm are in good agreement with the analytical solution. The LB algorithm is also applied to modeling a mixed electro-osmotic/pressure driven flow in a channel. The numerical results show that Joule heating plays an important role in EOF.

Journal Article↗