Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Principal component”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 1,639 records · Page 91Linked to original sources
PubMed2006

Knowledge levels of Korean intensive care nurses towards brain death and organ transplantation.

AIMS AND OBJECTIVES: To develop and examine the reliability and validity of an instrument assessing knowledge levels of Korean intensive care unit nurses. To conduct a survey with Korean ICU nurses. BACKGROUND: Organ donation from brain dead patients is a contentious issue in Korea following recent legal recognition of brain death, given the context of a Confucian belief system. Implementation of the new Organ Transplant Act has highlighted the importance of identifying Korean intensive care unit nurses' knowledge regarding brain death and organ donation. DESIGN: Multi-stage multi-method development of an original instrument with a cross-sectional analysis survey of participants. METHOD: An 18-item instrument was developed based on previous literature and key informant interviews, and validated by an expert panel and a pilot study. A survey was conducted with Korean intensive care unit nurses (n=520). Principal component analysis with varimax rotation was used to determine construct validity. Item-to-total correlations and Cronbach's coefficient alpha were used to determine the scale's internal consistency. RESULTS: Principal component analysis yielded a two-component structure: Diagnostic testing and Co-morbid factors of brain death. The scale demonstrated acceptable internal consistency for the two components (alpha=0.74, 0.64, respectively). Most of the participants had a sound knowledge of diagnostic testing for brain death, but demonstrated a lack of knowledge regarding co-morbid factors of brain dead patients. CONCLUSIONS: The knowledge scale was reliable and valid for this cohort. Further research is warranted in related areas of nursing practice. RELEVANCE TO CLINICAL PRACTICE: Effective education for intensive care unit nurses is necessary to increase the organ donor pool in Korea.

Adult↗
PubMed2005

Nonlinear complex-valued extensions of Hebbian learning: an essay.

The Hebbian paradigm is perhaps the best-known unsupervised learning theory in connectionism. It has inspired wide research activity in the artificial neural network field because it embodies some interesting properties such as locality and the capability of being applicable to the basic weight-and-sum structure of neuron models. The plain Hebbian principle, however, also presents some inherent theoretical limitations that make it impractical in most cases. Therefore, modifications of the basic Hebbian learning paradigm have been proposed over the past 20 years in order to design profitable signal and data processing algorithms. Such modifications led to the principal component analysis type class of learning rules along with their nonlinear extensions. The aim of this review is primarily to present part of the existing fragmented material in the field of principal component learning within a unified view and contextually to motivate and present extensions of previous works on Hebbian learning to complex-weighted linear neural networks. This work benefits from previous studies on linear signal decomposition by artificial neural networks, nonquadratic component optimization and reconstruction error definition, neural parameters adaptation by constrained optimization of learning criteria of complex-valued arguments, and orthonormality expression via the insertion of topological elements in the networks or by modifying the network learning criterion. In particular, the learning principles considered here and their analysis concern complex-valued principal/minor component/subspace linear/nonlinear rules for complex-weighted neural structures, both feedforward and laterally connected.

Algorithms↗
PubMed2004

Influence of wavelength-shifted calibration spectra on multivariate calibration models.

Multivariate calibration models are sensitive to wavelength shifts in calibration spectra as such disturbances are linearly independent from unshifted spectra and increase the calibration model's dimension. However, if wavelength shifts included in the calibration model are random, the predictability of the model is not improved. On the contrary, overfitting is introduced, thereby increasing the prediction error. Because calibration spectra are defined to be error free and are the only available data at that point, there is no analytical way to find out that the calibration model is erroneous. This study gives a mathematical explanation of how the model's dimension is increased by wavelength shifts and that the additional basis vectors, principal components for instance, possess derivative-shaped features. It is also demonstrated by means of an example that the reverse is not necessarily true. Hence, derivative-shaped features found in principal components are no indication of wavelength-shifted calibration spectra. A method is presented for analyzing calibration spectra for such shifts. The algorithm takes advantage of the fact that artificial shift compensations of true shifts increase the similarity, i.e., correlation, of shifted spectra with respect to the remaining, unshifted spectra. Synthetic and experimental data are used to demonstrate and assess the performance of the algorithm. It is shown that wavelength shifts in calibration spectra can be detected and corrected if a small number of spectra are disturbed. Significant improvements of the prediction errors of chemometric calibration models can be achieved by means of this shift-correction algorithm.

Acetone↗
PubMed2001

Metabolic syndrome and ischemic heart disease in elderly men and women.

Associations between metabolic syndrome components and prevalent ischemic heart disease (IHD) were investigated in a cross-sectional, community-based study of elderly men (n = 1,015) and women (n = 1,259) in Rancho Bernardo, California, in 1984-1987. In both sexes, there were significant positive associations between IHD defined by resting electrocardiogram criteria and age, systolic blood pressure, fasting and postchallenge hyperglycemia, total cholesterol/high density lipoprotein cholesterol (HDL cholesterol) ratio, and triglycerides and an inverse significant association with HDL cholesterol. High collinearity and interactions between serum insulin and metabolic syndrome variables were accounted for by uncorrelated principal components identified by factor analysis. In both men and women, three uncorrelated principal components were identified, representing a central metabolic factor (body mass index, fasting and 2-hour serum insulin, high serum triglycerides, and low HDL cholesterol), a glucose factor, and a blood pressure factor. In a multivariate model with age and sex, all three factors were significantly associated with IHD by electrocardiogram criteria; central metabolic factor (odds ratio (OR) = 1.6, p = 0.001), glucose factor (OR = 1.4, p < 0.001), blood pressure factor (OR = 1.2, p = 0.005), age (10 years) (OR = 1.8, p < 0.001), and female sex (OR = 0.5, p < 0.02). Similar results were obtained in analyses using clinically manifest IHD as the outcome. These results support the thesis that the metabolic syndrome exerts effects through different risk factors by different mechanisms.

Aged↗
PubMed1983

Middle and long latency auditory evoked potentials in cat. II. Component distributions and dependence on stimulus factors.

The middle (10-50 ms) and long (50-600 ms) latency periods of the auditory evoked potential (AEP) were investigated in muscle-paralyzed, artificially respired cats with respect to two issues: (1) the distribution of components across the skull, and (2) the effects of changing stimulus intensity on component latencies and amplitudes. The distributional data were gathered during a behavioral study in which four behavioral tasks related to classical pupillary conditioning were used to vary attentional and arousal processes. The distributions across the skull surface (averaged across tasks) of 12 peaks and troughs (P10, N13, P17, N22, P31, N41, P55, N70, N100, N140, P260 and N520) and seven principal components derived from the set of waveforms collected during this experiment are reported. Both peak amplitudes and principal component scores were distributed differentially across the skull surface. In the second experiment, acoustic stimulus intensity was varied, and AEPs collected from a vertex and temporal electrode site. In general, increasing stimulus intensity had a stronger influence on the earlier portions of the AEP, where increased amplitude and decreased latency was the rule, than on later ones. The relationships between cat and human AEP components were discussed based on both the data presented in this paper and in previous papers.

Acoustic Stimulation↗
PubMed2003

Quantitative analysis of Neanderthal temporal bone morphology using three-dimensional geometric morphometrics.

The temporal bone is the location of several traits thought to differentiate Neanderthals from modern humans, including some proposed Neanderthal-derived traits. Most of these, however, are difficult to measure and are usually described qualitatively. This study applied the techniques of geometric morphometrics to the complex morphology of the temporal bone, in order to quantify the differences observed between Neanderthal and modern human anatomy. Two hundred and seventy modern human crania were measured, representing 9 populations of 30 individuals each, and spanning the extremes of the modern human geographical range. Twelve Neanderthal specimens, as well as Reilingen, Kabwe, Skhul 5, Qafzeh 9, and 4 Late Paleolithic European specimens, were included in the fossil sample. The data were collected in the form of three-dimensional (3-D) landmark coordinates, and specimen configurations were superimposed using generalized Procrustes analysis. The fitted coordinates were then analyzed by an array of multivariate statistical methods, including principal components analysis, canonical variates analysis, and Mahalanobis D(2). The temporal bone landmark analysis was very successful in separating Neanderthals from modern humans. Neanderthals were separated from modern humans in both the principal components and canonical variates analyses. They were much further in Mahalanobis distances from all modern human populations than any two modern human groups were from each other. Most of the previously described temporal bone traits contributed to this separation.

Animals↗
PubMed2005

Behavioral outcomes following below-knee amputation in the coordination between balance and leg movement.

Lateral leg movement is accompanied by opposite movements of the supporting leg and trunk segments. This kinematic synergy shifts the center of mass (CM) towards the supporting foot and stabilizes its final position, while the leg movement is being performed. The aim of the present study was to provide insight in the behavioral substitution process responsible for the performance of this kinematic synergy. The kinematic synergy was assessed by the principal component analysis (PCA) applied to both hip joints and supporting ankle joint. Patients after unilateral below-knee amputation and control subjects were asked to perform a lateral leg raising. The first principal component (PC(1)) accounted for more than 99% of the total angular variance for all subjects (amputees and controls). PC(1) thus well represents the possibility to describe this complex multi-joint movement as a one degree of freedom movement with fixed ratios between joint angular time course. In control subjects, the time covariation between joints changes holds during all phases of the leg movement (postural phase, ascending and braking phases). In amputees, PC(1) score decreased during the ascending phase of the movement (i.e. when the body weight transfer is completed, while the movement is initiated). We conclude that a feedback mechanism is involved and discuss the hypothesis that this inter-joint coordination in amputees results from a failure in the pre-setting of the inter-joint coupling.

Adult↗
PubMed1992

Vegetation structure influences the burden of immature Ixodes dammini on its main host, Peromyscus leucopus.

To determine whether the relative abundance of immature Ixodes dammini (the vector of Lyme disease and human babesiosis) is related to habitat structure, we examined tick burdens on their main host, the white-footed mouse (Peromyscus leucopus), in 4 structurally diverse sites on Great Island, Massachusetts, USA. Vegetation structure at each site was quantified with respect to 25 habitat variables. Principal components analysis was used to reduce this set of habitat variables to seven new and orthogonal variables. Immature tick abundance varied widely among grids. Regression analysis of tick burdens on the habitat principal components showed that larval burdens were related strongly to the density of woody vegetation and negatively to herbaceous vegetation. Nymphal burdens were related negatively to herbaceous vegetation, but the relationship was not as strong as in the case of larvae. An experimental reduction in the abundance of white-tailed deer (Odocoileus virginianus), the main host of adult ticks, substantially reduced tick burdens and altered their relationships to habitat structure. Nymphal burdens were unrelated to habitat structure following deer removal. Manipulating habitat structure may have utility as a control strategy against this important vector.

Animals↗
PubMed1999

Survey of environmental complex systems: pattern recognition of physicochemical data describing coastal water quality in the Gulf of Trieste.

A data set reporting temperature, salinity, dissolved oxygen, nitrogen as ammonia, nitrite and nitrate, silicate, chlorophyll a and phaeopigment values, determined in seawaters sampled during two years with a monthly frequency in 16 stations in the Gulf of Trieste, and at different depths of the water column, has been studied. In order to find synthetic descriptors useful for following the spatial and temporal variations of biogeochemical phenomena occurring in the considered ecosystem, the data set has been factorized using principal component analysis. A graphical display of scores, by means of boxplots and biplots, helped in the interpretation of the data set. The first factor conditioning the system is related to the input of freshwater from the estuary of the Isonzo River and to the stratification of the seawater (thermohaline discontinuity), while the second and third components describe interactions between biological activity, nutrients and physicochemical parameters; typical spring and autumn phytoplankton blooms were identified, in addition to an exceptional winter bloom conditioned by anomalous meteorological/climatic conditions. The fourth principal component explains the reducing activity of seawaters, which often increases when the decomposition of organic matter is relevant. The simple linear model proposed, and the related graphs, are shown to be useful tools for monitoring the main features of such a complex dynamic environmental system. The outlined approach to the considered complex data structure presents in a cognitive easy way (graphical outputs) the significant variations of the data, and allows for a detailed interpretation of the results of the monitoring campaign. Temporal and spatial effects are outlined, as well as those related to the depth in the water column.

Ammonia↗
PubMed1998

Using sensory and instrumental data to interpret the effect of storage at elevated temperatures on aroma of Chardonnay wines.

The effect of elevated temperatures during storage on the aroma of commercial Chardonnay wines was monitored by sensory and instrumental methods. Aromas of wines stored at 40 degrees C for 0, 15, 30 and 45 days were profiled by descriptive analysis by a trained panel. Heated storage decreased intensity of fruity and floral notes, while increasing attributes such as honey, butter/vanilla, oak, and rubber. Volatiles recovered by solvent extraction from the same wines were separated by gas chromatography (GC) and identified by GC-mass spectrometry (MS). Principal component analysis of instrumental variables (PCAIV) was used to reduce the initial set of 67 quantified GC peaks. Six compounds, selected by PCAIV to yield the configuration closest to that of the principal component analysis of the sensory data, provided a highly significant fit with the sensory configuration, as shown by a permutation test. This solution was the statistically optimal one, but was not unique, as demonstrated by significant fits between the sensory and instrumental spaces upon use of other GC peaks, which were highly correlated with the original six variables.

Female↗
PubMed1989

[The effects of morphological variation of the spheno-occipital complex to the formation of skeletal facial pattern].

The purpose of this study was first to classify the morphological type of spheno-occipital complex and second to verify the relationship between the type of spheno-occipital complex and skeletal facial pattern. Materials used in this study were latelal cephalograms of 341 Japanese female adults. None of the subjects underwent any orthodontic therapy. Data were evaluated by multivariate analysis. The following results were obtained. 1. By the cluster analysis, the spheno-occipital complex was classified into three types, namely Thick type, Average type, and Slender type. 2. By the principal component analysis, it was shown that the classification was made by the factor of the inclination of posterior cranial base as the first component and the factor of the projection of sphenoidal rostrum as the second component. The Thick type group had less inclined posterior cranial base and more projected sphenoidal rostrum. 3. There was little relationship between mandibular pattern and the spheno-occipital complex. 4. The principal component analysis of the skeletal facial pattern showed that the Thick type group showed skeletal Cl. III tendency and the Slender type group showed skeletal Cl. II tendency, but there was no significant relationship between the vertical skeletal facial pattern and the spheno-occipital complex. In conclusion, the spheno-occipital complex was divided into three type groups according to the inclination of posterior cranial base and the projection of sphenoidal rostrum. It was concluded that the spheno-occipital complex has a close relationship to the skeletal facial pattern and contributes to the facial formation.

Adult↗
PubMed1989

[Classification of crown forms. Morphological interrelationship between upper central incisors and facial forms].

The interrelationship between tooth forms and facial outlines is represented in multivariate linear combinations. Principal Component Analysis was used in this study as an expression of morphological features. Measured data on the tooth and the face could be classified into 4 types by the first and second principal components of multivariate analysis. Of the 117 subjects, the largest group of 33 (28.9%) had of oval faces and were Class III for the face and Class II for the teeth, respectively. Of the 117 subjects, 36 showed morphological similarity between teeth and face.

Face↗
PubMed1980

Geographic variation in helminth parasites from the digestive tract of Tennessee raccoons, Procyon lotor.

The stomachs and intestinal tracts of 253 raccoons, Procyon lotor, were examined for helminth parasites. Sixteen species of helminths were found including eight trematodes, two cestodes, five nematodes, and one acanthocephalan. Fourteen of these helminths are new geographic records for the state of Tennessee. Multivariate statistical techniques were used to analyze two-state and multistate character sets. Matrices of correlation among characters were computed and the first three principal components were extracted, accounting for 79.7% and 66.5% of the variation in the respective character sets. Three-dimensional projections of Tennessee's eight geographic localities onto two-state and multistate principal components demonstrated that raccoons in western localities were parasitized most heavily by Atriotaenia procyonis. Mesocestoides variabilis, Gnathostoma procyonis, and Pharyngostomoides procyonis. Parallelorchis diglossus, Euparyphium beaveri. Eurytrema procyonis, Euryhelmis squamala, Molineus barbatus, and Macracanthorhynchus ingens were most common to P. lotor from eastern areas.

Acanthocephala↗
PubMedDate not supplied

[Attention and executive function tests components in attention deficit/hyperactivity children].

INTRODUCTION: It has been suggested that children with attention deficit/hyperactivity disorder (ADHD) have problems in attention and executive functions. A factor analysis showed that ADHD children had a different factor structure of the executive functions when they were compared with controls. AIM. To determine the factor structure of attention and executive functions in a group of ADHD children compared with a group of controls. SUBJECTS AND METHODS: 249 ADHD children and 372 controls of both genders, aged 6 to 11 years old, and from the different socio economic strata of Medellín city, were selected. Attention --Mental Control and Auditory Continuous Performance Test (ACPT)-- and executive functions --Phonologic and Semantic Verbal Fluency (FAS)--, and a shortened version of the Wisconsin Card Sorting Test (WCST) were assessed in both groups. Factor analyses were developed with principal components procedure were developed for each group and the total sample, using principal component procedure with orthogonal rotation. RESULTS: Stable factor structures were found for each group and for the total sample. The general factor structure was constituted by three independent factors: 1- Categorization, 2- Verbal fluency and verbal sustained attention, and 3- Cognitive flexibility. This factor structure explained 74.9% of the variance. CONCLUSION: The factor structures suggested that the components of attention and executive functions are similar for ADHD and control groups. The differences between groups would be quantitative.

Attention Deficit Disorder with Hyperactivity↗
PubMed2001

The development of a decisional balance measure of physician smoking cessation interventions.

BACKGROUND: Decreasing the prevalence of smoking is an important health care goal, and there is evidence that physicians' advice to quit is an important motivator for patients. However, fewer than half of smokers report that they have ever been advised to quit. This study was conducted to develop a decisional balance measure for physician delivery of smoking cessation interventions. METHODS: This study included a convenience sample of 155 primary care physicians. A decisional balance measure was developed using item generation and development, pilot testing, and principal components analyses. Validity was established by relating the decisional balance measure to a previously validated item of counseling behavior and to physician stage of readiness to deliver smoking cessation counseling. RESULTS: Based on principal components analyses and item analyses, the final measure consisted of 10 Pro and 10 Con items with coefficient alpha of 0.83 and 0.86. The Pros and Cons scales were significantly associated with self-reported counseling to patients who smoke and to stage of readiness to deliver smoking cessation counseling. CONCLUSIONS: A decisional balance measure of physician smoking cessation interventions can be used to assist investigators in developing effective interventions to enhance the delivery of smoking cessation interventions in primary care settings.

Adult↗
PubMed1991

Deuterium quadrupole coupling in N-acetylglycine and librational dynamics in solid poly(gamma-benzyl-L-glutamate).

To study the dynamics of peptide groups in solid proteins, we have accurately determined the principal components and molecular orientation of the electric field gradient tensor for the exchangeable deuterons in monoclinic N-acetylglycine by single-crystal deuterium nuclear magnetic resonance. These results are compared with the principal components of the amide deuterons in solid poly(gamma-benzyl-L-glutamate) measured in powder samples over a wide temperature range (140-400 K). The comparison indicates that in the solid polypeptide the N-D bonds undergo a small-amplitude torsional reorientation (libration) perpendicular to the peptide plane. To estimate dynamic rates, longitudinal relaxation times (T1 values) are reported for N-acetylglycine and poly(gamma-benzyl-L-glutamate). T1 values for the carboxyl and amide deuterons in N-acetylglycine are approximately 100 s, whereas for the amide deuterons in the polypeptide T1 approximately 1 s, also indicating that the N-D bonds are not stationary in the polypeptide. We determine from the reduced quadrupole coupling tensor the mean-square amplitude for the libration and show that it increases linearly with temperature. A simple qualitative theory for the relaxation times is presented on the basis of the assumption that the N-D reorientation is described either as a diffusion process in a square well or as a damped Langevin oscillator with a harmonic restoring force. The conclusion is that the short relaxation times of the polypeptide amide deuterons result from substantial frictional effects on reorientation that increase with temperature.

Deuterium↗
PubMed2000

Volatile constituents in fresh and processed juices from grapefruit and new grapefruit hybrids.

Forty-five volatile constituents of juices from grapefruit and grapefruit hybrids were quantified by headspace gas chromatography. The three types of grapefruit juice analyzed include pasteurized juice not from concentrate, reconstituted single strength juice from concentrate, and fresh, unpasteurized juice. Principal component and discriminant analyses were carried out using 48 grapefruit juice samples, and the samples were classified into the three types of juice based on degree of processing. Discriminant analysis was superior to principal component analysis for this purpose. Juices from two recently developed grapefruit hybrids were classified similarly to unpasteurized grapefruit juices from commercial cultivars.

Beverages↗
PubMed2004

Genotyping using single nucleotide polymorphism, fluorescence spectroscopy and pattern recognition.

This paper describes a method for genetic screening using single nucleotide polymorphism. Fluorescence spectra with an excitation frequency of 488 nm are recorded over a range of 550 to 660 nm of fragments of human DNA together with two fluorescent probe dyes attached to specific primers, one for each type of allele and a background dye, prepared using the Taqman reaction. The fluorescence spectra are monitored and principal components analysis used to separate spectra into three groups, which are visually identified as allele 1 (wild type), allele 2 (mutant) and mixed allele by comparison to reference samples. Malahanobis distance using 4 principal components are used to correctly classify samples into groups.

DNA↗