PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Measuring algorithm”

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 775 records · Page 43Linked to original sources
PubMed2006

Measures for the assessment of fuzzy predictions of protein secondary structure.

Many of the recent secondary structure prediction methods incorporate the idea of fuzzy set theory, where instead of assigning a definite secondary structure to a query residue, probability for the residue being in each of the conformational states is estimated. Moreover, continuous assignment of conformational states to the experimentally observed protein structures can be performed in order to reflect inherent flexibility. Although various measures have been developed for evaluating performances of secondary structure prediction methods, they depend only on the most probable secondary structures. They do not assess the accuracy of the probabilities produced by fuzzy prediction methods, and they cannot incorporate information contained in continuous assignments of conformational states to observed structures. Three important measures for evaluating performance of a secondary structure prediction algorithm, Q score, Segment OVerlap (SOV) measure, and the k-state correlation coefficient (Corr), are deformed into fuzzy measures F score, Fuzzy OVerlap (FOV) measure, and the fuzzy correlation coefficient (Forr), so that the new measures not only assess probabilistic outputs of fuzzy prediction methods, but also incorporate information from continuous assignments of secondary structure. As an example of application, prediction results of four fuzzy secondary structure prediction methods, PSIPRED, PROFking, SABLE, and PREDICT, are assessed using the new fuzzy measures.

Computer Simulation↗
PubMed2003

Monocular chromatic contrast threshold and achromatic contrast sensitivity in children born prematurely.

PURPOSE: To study the effect of prematurity on monocular chromatic contrast thresholds (CCT) and achromatic contrast sensitivity (ACS). DESIGN: Case-control study. METHODS: A prospective study of 59 children born at less than 33 weeks' gestation was undertaken. Subjects were identified during routine neonatal screening for retinopathy of prematurity and recalled for testing at age 7 to 13 years. Five had stage 1 retinopathy of prematurity, seven had stage 2, and three had stage 3. Sixty-eight full-term children were recruited as controls. Those with major cerebral or eye disease were excluded. The CCT and ACS were measured monocularly in the eye with better visual acuity using static, computer-generated, sinusoidal gratings, displayed on a high-resolution monitor. The CCT and ACS were determined using a randomized double-staircase reversal algorithm. The ACS was measured at five spatial frequencies (0.22, 0.44, 0.88, 1.75, and 3.50 cycles/degree), and the CCT was measured along red-green and tritan confusion axes. RESULTS: Red-green (P =.326) and tritan (P =.910) contrast thresholds and ACS (P >.394 for all spatial frequencies) were similar to the control group. CONCLUSIONS: Previous research suggests that prematurity adversely affects color vision and ACS. This study used a computerized psychophysical test that minimized the test errors inherent in many previous studies. Unexpectedly, CCT and ACS were found to be similar to full-term children.

Adolescent↗
PubMed2003

Tri-dimensional automatic segmentation of PET volumes based on measured source-to-background ratios: influence of reconstruction algorithms.

A method for automatic volume segmentation of functional imaging based on a relationship between source-to-background ratio and the iso-activity level to be used is described. Such method, which has been established with radioactive spheres in a phantom, is independent of the a priori knowledge of the lesion of interest and is valid for small (>2 ml) and/or poorly contrasted (S/B>1.5) lesions. Accuracy varies slightly with the image reconstruction algorithm used.

Algorithms↗
PubMed2006

Ischemic cerebral tissue response to subventricular zone cell transplantation measured by iterative self-organizing data analysis technique algorithm.

To investigate the changes of the ischemic lesion in rat brain after subventricular zone (SVZ) cell transplantation and the influence of the grafted cells on the appearance of angiogenesis, SVZ cells, superparamagnetically labeled, were intracisternally transplanted into the rat brain 48 h after onset of embolic stroke. A complete set of magnetic resonance (MR) images was acquired for all animals with (n=8) and without (n=3) cell grafting at approximately 24 h, 72 h, and weekly for 6 weeks after stroke. Transplanted cells were tracked by high-resolution three-dimensional gradient-echo images and the interaction between the cells and ischemic lesion was detected by ISODATA (Iterative Self-Organizing Data Analysis Technique Algorithm) calculated from T(1), T(2) and T(1sat) maps. Tissue status from ISODATA was characterized by a specific signature, which represents the deviation from normal tissue in the feature space. Transplanted SVZ cells selectively migrated towards the ischemic side of the rat brain and approached the lesion boundary within 1-week after grafting. Cell treated rats exhibited a significant reduction of average lesion size compared with control rats (P<0.05). A significant reduction of tissue signature (P<0.001) induced by cell transplantation was localized to the position of grafted cells, and these sites exhibited stably restored cerebral blood flow (CBF) (approximately 85% of normal CBF). Angiogenesis was present in sites either immediately adjacent to or surrounded by the grafted cells. Our data indicate that map-ISODATA accurately and dynamically characterizes the ischemic lesion and its response to cell therapy.

Algorithms↗
PubMed2003

Measuring the fit between human judgments and automated alerting algorithms: a study of collision detection.

Methodologies for assessing human judgment in complex domains are important for the design of both displays that inform judgment and automated systems that suggest judgments. This paper uses the n-system lens model to evaluate the impact of displays on human judgment and to explicitly assess the similarity between human judgments and a set of potential judgment algorithms for use in automated systems. First, the need for and concepts underlying judgment analysis are outlined. Then the n-system lens model and its parameters are formally described. This model is then used to examine a previously conducted study of aircraft collision detection that had been analyzed using standard analysis of variance methods. Our analysis found the same main effects as did the earlier analysis. However, n-system lens model analysis was able to provide greater insight into the information relied upon for judgments and the impact of displays on judgment. Additionally, the analysis was able to identify attributes of human judgments that were--and were not--similar to judgments produced by automated systems. Potential applications of this research include automated aid design and operator training.

Accident Prevention↗
PubMedDate not supplied

[Generalized ordering parameter S2 for N-H peptide bonding as measure of the conformational flexibility of proteins: comparison of algorithms of S2 calculation from molecular dynamics simulation data].

NMR spectroscopy in combination with molecular dynamics (MD) simulation technique is a powerful tool for investigation of biomolecule conformations. In the present study we compare the two algorithms of calculation of the generalized order parameter S2 for the peptide N-H bond from MD simulation data. The program based on this algorithm has been written and the effect of an adjustible parameter on results of calculation was studied. HIV-1 protease MD simulation was performed during 7.36 ns using GROMACS 3.1.4. software package. The calculated order parameter values are in good agreement with those obtained by other authors using NMR.

Algorithms↗
PubMed1995

Resting membrane potentials: a student test of alternate hypotheses.

The frog sartorius muscle is a model tissue for demonstrating to physiology students the principles underlying both membrane phenomena and hypothesis testing. Myocytes can be impaled with conventional glass microelectrodes to measure membrane voltage (Vm). Further, Vm is observed as extracellular K+ is altered and a K+ channel blocker is added. After the experiment, students examine the underlying assumptions of the Nernst equilibrium and the Goldman-Hodgkin-Katz equation. They ultimately determine which of the two algorithms best predicts the measured Vm. In addition, students learn micromanipulation and impalement techniques. This experiment facilitates the student's understanding of membrane permeability, ionic gradients, and membrane voltage.

Algorithms↗
PubMed1997

[A method for measuring QT and T duration and beat to beat variability].

The QT interval duration is an important non-invasive electrophysiological parameter that reflects ventricular depolarization and repolarization time. A knowledge of QT variability also provides specific information on the normal and pathological ventricular myocardium, and the influence of the autonomic nervous system. A numerical algorithm was developed for measuring QT interval and T-wave duration in the surface electrocardiogram. In comparison with numerous other approaches, this method calculates these durations without averaging of QRS complexes on a beat-to-beat basis. The main aim of this study was to assess the efficacy of this method for characterizing cardiac diseases. In 6 patients with hypertrophic cardiomyopathy and a control group of 5 healthy, age-matched subjects, different interval durations were calculated. In contrast to the mean QT interval duration, only the T-wave duration differed significantly between the two groups.

Algorithms↗
PubMed1993

Computational waveform analysis and classification of auditory brainstem evoked potentials.

The widely used quantitative descriptors of amplitude and latency of evoked potentials, for peaks and troughs along the waveform, relate to only a limited number of points along the waveform, ignoring the interposed data. Moreover, these descriptors are typically determined manually, rendering them susceptible to user bias. We propose and demonstrate a machine-scoring algorithm for the identification and measurement of Auditory Brainstem Evoked Potentials (ABEP) peaks I, III and V. We further introduce an algorithm for the quantitative analysis of ABEP by waveform, and for clustering records according to waveform characteristics. The results of computerized peak identification and measurement, without user intervention, were correlated with manual measurements of the same peaks in a large number of waveforms. The waveform analysis and classification procedure differentiated waveforms to monaural left, monaural right and binaural stimulation, as well as according to the recording montage. These results underscore the advantages of using information in the waveform of ABEP, which has so far been overlooked. The automated algorithms for evaluation of ABEP by waveform hold the promise of a more comprehensive and consistent evaluation, and hence improved sensitivity.

Adult↗
PubMed2005

Correcting movement errors in frequency-sweeping interferometry.

Absolute distance measurements can be performed with an interferometric method that uses only a single tunable laser. This method has one major drawback, because a small target movement of the order of one wavelength during a measurement will be interpreted as a movement of one synthetic wavelength. This effect is usually mitigated by adding a second (nonscanning) laser. We show that absolute distance measurements can be performed with only one laser if the movements encountered are smooth, on the time scale of one measurement. In this case the movement errors can be compensated with a simple algorithm that combines several subsequent measurements. First experimental results show good agreement with theory.

Journal Article↗
PubMed2003

The integration of similar clinical research data collection instruments.

We devised an algorithm for integrating similar clinical research data collection instruments to create a common measurement instrument. We tested this algorithm using questions from several similar surveys. We encountered differing levels of granularity among questions and responses across surveys resulting in either the loss of granularity or data. This algorithm may make survey integration more systematic and efficient.

Algorithms↗
PubMed2003

Determining finger segmental centers of rotation in flexion-extension based on surface marker measurement.

This paper describes the development of a novel algorithm for deriving finger segmental center of rotation (COR) locations during flexion-extension from measured surface marker motions in vivo. The algorithm employs an optimization routine minimizing the time-variance of the internal link lengths, and incorporates an empirically quantifiable relationship between the local movement of a surface marker around a joint (termed "surface marker excursion") and the joint flexion-extension. The latter relationship constrains and simplifies the optimization routine to make it computationally tractable. To empirically investigate this relationship and test the proposed algorithm, an experiment was conducted, in which hand cylinder-grasping movements were performed by 24 subjects (12 males and 12 females). Spherical retro-reflective markers were placed at various surface landmarks on the dorsal aspect of each subject's right (grasping) hand, and were measured during the movements by an opto-electronic system. Analysis of experimental data revealed a highly linear relationship between the "surface marker excursion" and the marker-defined flexion-extension angle: the average R(2) in linear regression ranged from 0.89 to 0.97. The algorithm successfully determined the CORs of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints of digits 2-5 during measured motions. The derived CORs appeared plausible as examined in terms of the physical locations relative to surface marker trajectories and the congruency across different joints and individuals.

Adult↗
PubMed2002

Double three-step phase-shifting algorithm.

We describe what we believe is a new phase-shifting algorithm called a double three-step algorithm developed to reduce the measurement error of a three-dimensional shape-measurement system, which is based on digital fringe-projection and phase-shifting techniques. After comparing the performance of different existing phase-shifting algorithms, we present the new double three-step algorithm based on the error analysis of the standard three-step algorithm. In this algorithm, three-step phase shifting is done twice with an initial phase offset of 60 degrees between them, and the two obtained phase maps are averaged to generate the final phase map. Both theoretical and experimental results showed that this new algorithm worked well in significantly reducing the measurement error.

Journal Article↗