SEARCH · PubMed Health

Results for “correlation matrix”

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 415 records · Page 23Linked to original sources

PubMed2006

Distribution and possible source of trace elements in the sediment cores of a tropical macrotidal estuary and their ecotoxicological significance.

The paper presents the first document regarding concentration, distribution and possible sources of selected trace elements (Cu, Fe, Mn, Zn, Cr, Co, Ni, Pb, Al, B and Ba) in core sediments (<63 micro particle size) from the lower stretch of Hugli (Ganges) estuary, northeast coast of Bay of Bengal by ICP-AES and EDXRF to evaluate geochemical processes influencing their distribution and possible environmental consequences. The levels of elements showed a wide range of variations in different core depths, in upper and lower intertidal zones as well as among three sampling stations. The most interesting feature of the study is the downward increase of concentrations of majority of the elements reaching overall maximum values at a depth of 20-28 cm in upper littoral zone of the site located in the extreme downstream stretch of the estuary. Values of organic carbon showed very strong positive correlations with most of the elements as revealed by correlation matrix (r) values. The interelemental relationship revealed the identical behavior of element during its transport in the estuarine environment. The overall variation in concentration can be attributed to differential discharge of untreated effluents originating from industrial, agricultural, and aquacultural sources as well as from domestic sewage along with the fishing and boating activities. The resulting compositional dataset was tested by principal component analyses and cluster analyses. Pollution load index (PLI) and index of Geoaccumulation (Igeo) revealed overall low values but the enrichment factors (EFs) for Pb were typically high for all the stations. The mean concentrations of Zn and to some extent Cu exceeded the Effects Range-Low (ER-L) values in the majority of the cases indicating that there may be some ecotoxicological risk to organisms living in sediments. The concentration of the trace elements reported in this work is useful as baselines for comparison in future sediment quality studies.

Carbon↗

PubMed2004

Mapping, profiling and clustering of pressure pain threshold (PPT) in edentulous oral mucosa.

OBJECTIVES: Edentulous oral mucosa involves different tissue types, various innervation and wound healing process. We hypothesized that pressure pain threshold (PPT) of edentulous oral mucosa varies significantly among different regions. The objective of this study is to examine regional differences and correlations of PPT in edentulous oral mucosa. METHODS: Pain threshold (PPT) was measured at 112 sites in 15 edentulous patients using an electric-controlled pressure algometer. PPT mapping was created by the level of PPT, and PPT clustering was undertaken based on the inter-site correlation of PPT. RESULTS: PPT increased from the anterior to posterior alveolus in both maxilla and mandible, but decreased from the anterior palate to the posterior palate. PPT decreased from the ridge crest to the buccal vestibule. The inter-site difference was four fold within the maxilla and 2.4 fold within the mandible. Principal component analysis applied on PPT inter-site correlation matrix revealed that the maxilla and mandible could be differentiated statistically. The maxilla and mandible were divided into three and four clusters, respectively. CONCLUSION: These results demonstrate that different areas of edentulous oral mucosa have different PPT and that the PPT varies proportionally in selected areas, providing useful diagnostic and therapeutic information in removable prosthodontics and a new opportunity for understanding pain underneath the denture.

Aged↗

PubMed2005

Occurrence and distribution of polycyclic aromatic hydrocarbons in reclaimed water and surface water of Tianjin, China.

Persistent organic pollutants (POPs) such as polycyclic aromatic hydrocarbons (PAHs) are of great concern due to their persistence, bioaccumulation and toxic effects. In this work, 16 PAHs included in the US Environmental Protection Agency's (EPA) priority pollutant list were analyzed using solid-phase extraction-gas chromatography-mass spectrometry (SPE-GC-MS) with a selected ion monitoring (SIM) mode. Reclaimed water and surface water sampling was undertaken in Tianjin, northern China. Total PAH concentrations varied from 1800 to 35,000 ng/L in surface waters (main rivers, tributaries, ditches, etc.) with mean value of 14,000 ng/L and from 227 to 600 ng/L in reclaimed water with mean value of 352 ng/L, respectively. The PAH profiles were dominated by low molecular weight PAHs (two- and three-ring components) in reclaimed water samples and surface water samples. These indicated that PAHs in reclaimed water and surface water might origin from oil or sewage contamination (petrogenic input). To elucidate sources, molecular indices based on indices among phenanthrene versus anthracene and fluoranthene versus pyrene were used to evaluate the possible source (pyrogenic and petrogenic sources, respectively) of PAH contamination in reclaimed water and surface water. The collected data showed that petrogenic input was predominant at almost all the stations investigated. To discriminate pattern differences and similarities among samples, principal component analysis (PCA) was performed using a correlation matrix. PCA revealed the latent relationships among all the surface water stations investigated and confirmed our analytical results. The analysis results of the ratios and PCA in this study showed that the ratios and PCA could be applied to the surface water investigation to some extent.

China↗

PubMed2006

Patterning of geographic variation in Middle Pleistocene Homo frontal bone morphology.

A quantitative assessment of the frontal bone morphology of a sample of Middle Pleistocene hominins was undertaken in order to address questions regarding their population structure and evolutionary history. Outline tracings of the frontal bones of forty-seven fossil crania were obtained, and size-standardized measurements were then computed using an Elliptical Fourier analysis of these tracings. Principal component scores of the Fourier harmonic amplitudes were derived and served as a quantitative representation of the morphology of the frontal bone. Morphological, geographical, and temporal distance matrices were then constructed between each pair of fossils. A partial Mantel matrix correlation test was performed between morphological and geographical distance matrices, controlling for temporal distance, in order to determine if the pattern of geographical differentiation in features of the frontal bone of mid-Pleistocene Homo followed that of an isolation-by-distance model of population structure. The results of the partial Mantel tests indicate that the overall patterning of differentiation in the features of the frontal bone cannot best be explained by a population structure shaped by isolation-by-distance. Additionally, various aspects of the frontal bone quantified here follow different patterns of geographical differentiation, suggesting that a mosaic pattern of evolution holds true for characters within one cranial region and not just for those between regions.

Animals↗

PubMed2004

Estimation of neurophysiological parameters from the waking EEG using a biophysical model of brain dynamics.

This paper presents the results from using electroencephalographic (EEG) data to estimate the values of key neurophysiological parameters using a detailed biophysical model of brain activity. The model incorporates spatial and temporal aspects of cortical function including axonal transmission delays, synapto-dendritic rates, range-dependent connectivities, excitatory and inhibitory neural populations, and intrathalamic, intracortical, corticocortical and corticothalamic pathways. Parameter estimates were obtained by fitting the model's theoretical spectrum to EEG spectra from each of 100 healthy human subjects. Statistical analysis was used to infer significant parameter variations occurring between eyes-closed and eyes-open states, and a correlation matrix was used to investigate links between the parameter variations and traditional measures of quantitative EEG (qEEG). Accurate fits to all experimental spectra were observed, and both inter-subject and between-state variability were accounted for by the variance in the fitted biophysical parameters, which were in turn consistent with known independent experimental and theoretical estimates. These values thus provide physiological information regarding the state. transitions (eyes-closed vs. eyes-open) and phenomena including cortical idling and alpha desynchronization. The parameters are also consistent with traditional qEEG, but are more informative, since they provide links to underlying physiological processes. To our knowledge, this is the first study where a detailed biophysical model of the brain is used to estimate neurophysiological parameters underlying the transitions in a broad range (0.25-50 Hz) of EEG spectra obtained from a large set of human data.

Awareness↗

PubMed2004

Sparse distributed memory using N-of-M codes.

An analysis is presented of a sparse distributed memory (SDM) inspired by that described by Kanerva [Kanerva, P. (1988). Sparse distributed memory. Cambridge, MA: MIT Press] but modified to facilitate an implementation based on spiking neurons. The memory presented here employs sparse binary N-of-M codes, unipolar binary synaptic weights and a simple Hebbian learning rule. It is a two-layer network, the first (fixed) layer being similar to the 'address decoder' in Jaeckel's [Jaeckel, L.A. (1989). A class of designs for a sparse distributed memory. RIACS Technical Report 89.30, NASA Ames Research Centre] 'hyperplane' variant of Kanerva's SDM and the second (writeable) 'data store' layer being a correlation matrix memory as first proposed by Willshaw et al. [Willshaw, D. J., Buneman, O.P., & Longuet-Higgins, H.C. (1969). Non-holographic associative memory. Nature, 222, 960-962]. The resulting network is shown to have good storage efficiency and is scalable. The analysis is supported by numerical simulations and gives results that enable the configuration of the memory to be optimised for a range of noiseless and noisy environments.

Association Learning↗

PubMed2005

Adaptive algorithms for first principal eigenvector computation.

The paper presents a unified framework to derive and analyze 10 different adaptive algorithms, some well-known, to compute the first principal eigenvector of the correlation matrix of a random vector sequence. Since adaptive principal eigenvector algorithms have originated from a diverse set of disciplines, including ad hoc methods, it is necessary to examine them in a unified framework. In a common framework consisting of five steps, we analyze the derivation, convergence, and rate results for many well-known algorithms as well as two new adaptive algorithms. In the process, we offer fresh perspectives on the known algorithms, and derive new results for others. The common framework also allows us to comparatively study the 10 algorithms. Finally, we show experimental results to support our analyses.

Algorithms↗

PubMed2005

Subjective experiences and the psychopathological dimensions in schizophrenia.

The aim of this article was to explore the relationships between subjective experience (SE) and objective symptoms in schizophrenia. Exploratory principal component analysis was used to determine the latent organization of the variables. A group of 310 chronic patients with schizophrenia who met ICD-10 criteria for F20 schizophrenic disorder were included in the study. SE and objective symptoms were rated using, respectively, the 24-item version of the Frankfurt Complaint Questionnaire (FCQ-24) and the Positive and Negative Syndrome Scale (PANSS). An exploratory principal component analysis was performed on the correlation matrix comprising items from both the FCQ-24 and the PANSS. Using several guidelines to select the number of factors, the exploratory principal component analysis yielded a six-factor solution with no overlap of the significant factor loadings for the items from each scale. These six factors represent, respectively, the subjective, negative, positive, disorganization, hostility and anxious-depressive dimensions of the schizophrenic phenomenology. The findings support the view that SE is a construct that is separate and distinct from the objective symptomatology in schizophrenia.

Adult↗

PubMed2005

Factor solution of the BPRS-expanded version in schizophrenic outpatients living in five European countries.

RATIONALE: The expanded version of the Brief Psychiatric Rating Scale (BPRS-E) has improved the instrument's coverage and interrater reliability, but there is little knowledge on its subsyndromes. OBJECTIVES: To assess: (1) whether there are common underlying BPRS-E subscales in patients living in different countries and (2) if this is the case, whether these subscales behave the same in all populations and, if not, what are the differences over these populations. METHODS: Data are part of the EPSILON study, a collaborative project carried out in Denmark, England, Holland, Italy and Spain. A random representative sample of 404 adult patients with a ICD-10 diagnosis of schizophrenia who have been in contact with mental health services of a defined catchment area in each site were assessed. Simultaneous component analysis (SCA) was used to find component weights that optimally explain the variance of the variables in different populations simultaneously. RESULTS: Symptom severity differed significantly among the five EPSILON sites in 12 out of 24 BPRS-E items, but a common component solution could be found. It explained 48.8% of the variance and gave four well-interpretable components: manic excitement/disorganization, depression/anxiety, negative and positive symptoms. Each component's internal consistency and intercomponent correlation matrix differed significantly among sites. The four components mean score differed significantly among sites for negative symptoms and depression/anxiety. CONCLUSIONS: In spite of the heterogeneity of symptom's severity in the various countries, the way symptoms cluster in schizophrenia is rather stable cross-culturally. Data demonstrate that to explore schizophrenia a third component, including mania/disorganization items, is necessary beside the positive-negative symptom dimensions. The subscales derived from these analyses can be readily used in clinical trials and epidemiological studies.

Adult↗

PubMed1998

Anthropometric variability, equipment usability and musculoskeletal pain in a group of nurses in the Western Cape.

This study examined the anthropometry and anthropometric fit of a group of nurses in Western Cape private hospitals. Anthropometric variables were measured using a sample of nurses and a correlation matrix generated. All nurses were given a questionnaire concerned with operational problems in the work environment and musculoskeletal pain. The nurses reported numerous problems in the working environment, including lumbar backache, inadequate space and equipment that caused bodily discomfort. There were consistent, statistically significant associations between the frequency of occurrence of these problems and the anthropometric data indicating that the problems were caused or amplified by body size variability and were not simply general usability problems which would affect all nurses irrespective of their body dimensions.

Adult↗

PubMed2003

Functional and effective frontotemporal connectivity and genetic risk for schizophrenia.

BACKGROUND: Functional neuroimaging and electrophysiologic studies have found disturbed frontotemporal interaction in schizophrenia. We sought to determine whether abnormalities of frontotemporal connectivity are trait markers of genetic risk for schizophrenia. METHODS: We investigated 64 schizophrenia patients, 79 of their clinically unaffected siblings, and 88 unrelated normal controls with an auditory oddball electroencephalogram (EEG) evoked potential paradigm. We measured: 1) frontotemporal event-related EEG-coherence (i.e. a measure of functional connectivity); and 2) we performed structural equation modeling of the effective connectivity between the frontal P300 and temporoparietal P300-amplitude. RESULTS: Schizophrenic patients and their siblings showed a reduction of frontotemporal coherence. At peak activation during the P300 time-window, a negative ("inhibitory") frontotemporal path coefficient was found in normal controls, whereas a positive coefficient was seen in schizophrenic patients with siblings being intermediate. Intra-class correlations between sib-pairs and relative risk estimates of the applied connectivity measures were non-significant. Topographic correlation matrix analyses suggested that the altered functional and effective frontotemporal connectivity indirectly reflect regional abnormalities of increased activation variance. CONCLUSIONS: Impaired interaction of the frontotemporal macro-circuit indirectly reflects genetically determined abnormalities of frontal and temporoparietal microcircuits. The reasons why frontotemporal connectivity appears to be a poor predictor of genetic risk for schizophrenia are discussed.

Adult↗

PubMed1991

Microscopic theory of the dielectric properties of proteins.

This paper investigates the microscopic mechanisms of charge screening in proteins. The screening of an arbitrary perturbing charge density by a protein and its surrounding solution is characterized by a generalized susceptibility, which is approximately given by the mean dipole-dipole correlation matrix of the system. This susceptibility is a microscopic quantity; the sum of its matrix elements gives the macroscopic susceptibility of continuum electrostatics. When screening of a single perturbing point charge is considered, this susceptibility reduces to a scalar quantity, dependent on position within the protein. The contribution of the positional degrees of freedom of the protein atoms can be estimated from molecular dynamics simulations. This contribution gives rise to large spatial variations of the susceptibility, whose significance for protein function is discussed. The model is applied to the small alpha helix deca-alanine, and to the electron-transfer protein cytochrome c. The results agree qualitatively with previous normal mode calculations. The importance, and the large spatial variations, of charge screening by deca-alanine suggest that dielectric screening may play a role in the binding of charged ligands by helices. In cytochrome c, the dielectric susceptibility in response to a point charge is at a minimum in the central heme region, resulting in a lowering of the reorganization free energy for charge transfer to and from the heme.

Biophysical Phenomena↗

PubMed1997

Molecular dynamics study of time-correlated protein domain motions and molecular flexibility: cytochrome P450BM-3.

Time-correlated atomic motions were used to characterize protein domain boundaries from atomic coordinates generated by molecular dynamics simulations. A novel application of the dynamical cross-correlation matrix (DCCM) analysis tool was used to help identify putative protein domains. In implementing this new approach, several DCCM maps were calculated, each using a different coordinate reference frame from which protein domain boundaries and protein domain residue constituents could be identified. Cytochrome P450BM-3, from Bacillus megaterium, was used as the model protein in this study. The analyses indicated that the simulated protein comprises three distinct domain regions; in contrast, only two protein domains were identified in the original crystal structure report. Specifically, the DCCM analyses showed that the F-G helix region was a separate domain entity and not a part of the alpha domain, as previously designated. The simulations demonstrated that the domain motions of the F-G helix region effected both the size and shape of the enzyme active site, and that the dynamics of the F-G helix domain could possibly control access of substrate to the binding pocket.

Bacillus megaterium↗

PubMed2000

An empirical approach to characterizing trunk muscle coactivation using simulation input modeling techniques.

Accurately describing trunk muscle coactivation is fundamental to quantifying the spine reaction forces that occur during lifting tasks and has been the focus of a great deal of research in the spine biomechanics literature. One limitation of previous approaches has been a lack of consideration given to the variability in these coactivation strategies. The research presented in this paper is an empirical approach to quantifying and modeling trunk muscle coactivation using simulation input modeling techniques. Electromyographic (EMG) data were collected from 28 human subjects as they performed controlled trunk extension exertions. These exertions included isokinetic (10 and 45 degrees /s) and constant acceleration (50 degrees /s/s) trunk extensions in symmetric and asymmetric (30 degrees ) postures at two levels of trunk extension moment (30 and 80Nm). The EMG data were collected from the right and left pairs of the erector spinae, latissimus dorsi, rectus abdominis, external obliques and internal obliques. Each subject performed nine repetitions of each combination of independent variables. The data collected during these trials were used to develop marginal distributions of trunk muscle activity as well as a 10x10 correlation matrix that described how the muscles cooperated to produce these extension torques. These elements were then combined to generate multivariate distributions describing the coactivation of the trunk musculature. An analysis of these distributions revealed that increases in extension moment, extension velocity and sagittal flexion angle created increases in both the mean and the variance of the distributions of the muscular response, while increases in the rate of trunk extension acceleration decreased both the mean and variance of the distributions of activity across all muscles considered. Increases in trunk asymmetry created a decrease in mean of the ipsi-lateral erector spinae and an increase in the mean of all other muscles considered, but there was little change in the variance of these distributions as a function of asymmetry.

Acceleration↗

PubMed1995

The state of body surface mapping in Japan.

In Japan, body surface mapping (BSM) started in 1974. A huge amount of data has been accumulated regarding basic researches and clinical applications. Recent work on BSM in Japan is summarized here, with the goals of establishing a normal database and diagnostic criteria by using the standardized mapping system. The standard systems used in Japan are the HPM-7100 and the VCM-3000, manufactured by Fukuda-Denshi (Tokyo, Japan) under the supervision of a committee of the Japanese Circulation Society. The number of leads in this system is 87 (59 on front, 28 on back). As a basic study, a computer simulation was carried out on bundle branch block with myocardial infarction (MI), on late potentials in MI, and finally, on the solution of the inverse problem. The database of 606 normal subjects was established regarding age and sex, and a "departure index" (the grade of deviation from normal: the difference between a patient's data the normal mean divided by the normal SD) was proposed. Using the departure index, diagnostic criteria were proposed for the ischemic site, MI site, hypertrophic site of the ventricle, etc. The origin of the ventricular premature contractions was determined by the site of minima and maxima of the QRS and QRST isointegral maps. The site of accessory pathways was determined by the site of minimum less than -0.15 mV on the BSM. For the prediction of patients prone to ventricular tachycardia (VT), several approaches were tried such as multipolar patterns of QRST isointegral maps, Wigner distribution, late potentials with relation to endo- or epicardial delayed potentials, body surface distribution of specific frequency band (25-50 Hz) obtained from fast Fourier transform analysis, and nondipolarity of the QRST isointegral map. To improve the ablation procedure of VT, the author developed a technique to determine the precise location of the VT focus in pace mapping using a correlation matrix between VT and pace maps. To ensure the longevity of the BSM, a reduction of the number of leads has been proposed. The usefulness of BSM has been confirmed and the technique accepted in Japan for daily clinical diagnosis.

Action Potentials↗

PubMed2001

The Family Response Questionnaire: a new scale to assess the responses of family members to people with chronic fatigue syndrome.

OBJECTIVE: Family responses to patients with chronic fatigue syndrome (CFS) may influence the course of the disorder and family members themselves are likely to be adversely affected. However, the beliefs and responses of relatives of CFS patients have been under-researched. The aim of this study was to produce an easy-to-administer questionnaire to assess the responses of family members to people with CFS. METHODS: Seventy-eight people, all close relatives of (physician-diagnosed) CFS sufferers, completed the first version of the Family Response Questionnaire (FRQ). RESULTS: Examination of the correlation matrix and a cluster analysis of the items support four scales rather than the original five. The four response scales were labelled: sympathetic-empathic, active engagement, rejecting-hostile, and concern with self. Measures of test-retest and internal reliability were high. Participants found the items both comprehensible and relevant to their experiences of living with people with CFS. CONCLUSION: The new version of the FRQ will be useful in further examination of the responses of CFS on individuals and their families.

Adolescent↗

PubMedDate not supplied

Determination of polychlorobiphenyls in Venice Lagoon sediments.

Polychlorinated biphenyl (PCBs) congeners were measured in 14 sediment samples collected at five sites in the Venice Lagoon selected on the basis of a supposed diversity of inputs and of pollution levels. The PCBs were determined after a sonication assisted extraction by gas chromatography mass spectrometry (GCMS). The sum of the congener concentrations determined in the samples range from 4.05 to 239.15 ng/g on a dry weight basis. The concentration values are very variable both comparing the sites and comparing different samples from the same site and can be connected to the sand percentage in the sediment samples. The correlation matrix obtained from data matrix using the congener concentrations as variables shows high values, mostly between 0.964 and 1, suggesting that the pattern of the PCB congeners and the ratios among the concentrations in Venice Lagoon sediments are more or less constant; the samples differ only in the concentration level.

Environmental Monitoring↗

PubMedDate not supplied

Clinical rating scales in suicide risk assessment.

This study explores the usefulness of clinical rating scales in the assessment of suicidal risk in an urban psychiatric teaching hospital. Admission for clinically evaluated suicide risk was the outcome variable because actual suicide occurs rarely. Six clinical scales identified high-risk patients: the Modified SAD PERSONS scale, revised Beck Depression Inventory, Beck Anxiety Inventory, Beck Hopelessness Scale, Beck Scale for Suicidal Ideation (BSS), and the High-Risk Construct Scale (NEW). It was hypothesized that patients who scored highly on the clinical scales were more likely to be admitted. Five of the scales had previously established psychometric properties, while one was new and untested. For our patient population, the established scales had 100% sensitivity and negative predictive value, but lower specificity and positive predictive value (range = 38-90% & 28-71%). We performed a correlation matrix and regression analysis to determine which scale(s) best predicted admission based upon suicidal concerns. The previously untested NEW scale was the best predictor followed by the BSS. Clinical rating scales cannot predict suicide in the individual and strict cut-off scores should not be used to dictate admission to hospital. However, the information provided can be a valuable adjunct to suicide risk assessment in psychiatric and non-psychiatric emergency settings

Adolescent↗