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At least 253 records · Page 14Linked to original sources

PubMed2004

Representing the behavior of partially coherent optical systems by using overcomplete basis sets.

A technique is described for representing the behavior of partially coherent optical systems by using overcomplete basis sets. The scheme is closely related to Gabor function theory. Through singular-value decomposition it is shown that if E is a matrix containing the sampled basis functions, then all of the information needed for optical calculations is contained in S = EE(dagger) and R = E(dagger)E. For overcomplete sets, S can be inverted to give a dual basis set, E = S(-1)E, which can be used to find the correlation matrix elements A of a sampled bimodal expansion of the spatial coherence function. Overcomplete correlation matrices can be scattered easily at optical components. They can be used to determine (i) the natural modes of a field; (ii) the total power in a field, Pt = Tr[RA]; (iii) the power coupled between two fields, A and B, that are in different states of coherence, Pc = Tr[RARB]; and (iv) the entropy of a field, Q = Tr[Zsigmar(I-Z)r/r], where Z = RA/Tr[RA].

Journal Article↗

PubMed1988

Multivariate diallel analysis of ethanol withdrawal symptoms in mice.

Mice from five highly inbred strains were crossed in a complete diallel design. Five hundred and fifty-five offspring were given a liquid diet containing ethanol as their sole food source for 9 days in an attempt to induce dependence. At 6 hr postwithdrawal on day 10, the mice were given a battery of physiological and behavioral measures designed to assess the symptoms of withdrawal. Littermate data were aggregated separately by sex and the aggregate litter mean data was employed in a multivariate extension of Hayman's diallel analysis. Hypothesis sums of squares and cross-products were tested against pooled-within-cell sums of squares and cross-products using Wilk's lambda as a criterion. For each sex, a highly significant additive effect was found, with some evidence for dominance effects as well, suggesting the raw materials are present for successful genetic selection. There was some evidence for dominance effects as well, but no evidence for maternal and other reciprocal effects was found for the set of seven measures. Composites derived from the additive and general dominance hypotheses correlation matrices and error correlation matrix were compared with a composite index currently being used in a multivariate selection study of ethanol dependence. Total ethanol consumption during the exposure period was positively correlated with low dependence between strains, and negatively correlated with measures of low dependence within cells.

Alcohol Drinking↗

PubMed2000

Foliage echoes: a probe into the ecological acoustics of bat echolocation.

The research reported here aims at understanding the biosonar system of bats based on the properties of its natural inputs (ecological acoustics). Echoes from foliages are studied as examples of ubiquitous, natural targets. The echo properties and their qualitative relationship to plant architecture are described. The echoes were found to be profoundly stochastic and in general neither Gaussian nor stationary. Consequently, features useful for discrimination of such target classes will be confined to estimated random process parameters. Several such statistical signal features which are sufficiently invariant to allow a classification of the used example plants were identified: the characteristic exponent and the dispersion of an alpha-stable model for the amplitude distribution, a crest factor defined as the ratio of maximum squared amplitude and signal energy, the dispersion of the first threshold passage distribution, the structure of the correlation matrix, and a nonstationarity in sound channel gain. Discrimination error probability could be reduced by combining features pairwise. The best combination was the crest factor and the correlation coefficient of a log-linear model of the time-variant sound channel gain; it yielded an estimated Bayes risk of 6.9% for data pooled from different views.

Acoustics↗

PubMed2002

[Obesity--a risk factor].

The nutritional status of a selected population--859 male members of the Fire Rescue Service from 12 districts in the Czech Republic--was assessed in 1997 and 1998. The study provides extensive information on selected anthropometrical and biochemical parameters, especially on those, which are generally used as risk indices for the origin and development of cardiovascular disease (CVD): body mass index (BMI), body fat percentage (b. fat), waist circumference (waist), serum concentrations of total cholesterol (Tchol), HDL- and LDL-cholesterol (HDL-chol, LDL-chol), triacylglyceroles (TAG) and the atherogenic index (AI). As far as lipid parameters were concerned, increased serum levels were estimated in 30.4% (TAG), 54% (Tchol) and 60.9% (LDL-chol) of volunteers. Decreased serum levels of HDL-chol were found in 38.2% of volunteers. An AI higher than 3.5 a.u. was calculated for 79.9% of all subjects in study while an AI higher than 5.0 a.u. was calculated for 45.3% of all subjects. An AI higher than 3.5 a.u. was found in 62% of males with normal weight, in 85% of overweight males and in 92% of obese males. The results of the study proved the considerable prevalence of the overweightness and obesity in the male population group that was followed: according to the calculated BMI, 49.5% of volunteers were estimated to be overweight and 16.3% to be obese. The study concept made it possible to reveal the relationships among the anthropometrical and biochemical parameters followed. The correlation matrix documents a statistically significant dependence among the BMI or waist values and the serum concentrations of Tchol, LDL-chol, TAG and AI. A significant negative correlation was found between the HDL-chol serum concentration and the BMI or waist values. The variance analysis results (the estimated lipid parameter values were divided into groups according to BMI and waist categories) document a statistically significant increase in serum Tchol, LDL-chol, TAG and AI in age categories over 35 years in comparison with the category of men under 25 years of age. For Tchol and LDL-chol a statistically significant increase had already been found in the 25-35 year age category. In comparison with the normal weight category, Tchol serum levels and AI values were statistically significantly higher in both the overweight and obese categories. Statistically significant increase was proven for the TAG and LDL-chol serum levels in both the overweight II. gr. and obese categories. A statistically significant decrease in comparison with the normal weight category was found in the HDL-chol serum levels of both the overweight and obesity categories. In the same way, an increase in Tchol and LDL-chol, TAG serum concentrations and AI values in higher and high risk CVD categories (according to the waist circumference value) was found in comparison with the low CVD risk category.

Adult↗

PubMed1985

The relation of serum calcium and immunoparathormone levels to parathyroid size and weight in primary hyperparathyroidism.

This study was designed to determine whether the serum calcium or immunoparathormone (iPTH) level would be of value in predicting the size or weight of the parathyroid gland in patients with single-gland enlargement caused by primary hyperparathyroidism. Ninety-two patients who underwent parathyroidectomy with removal of a single enlarged gland at the North Carolina Memorial Hospital (1974 to 1984) were reviewed. The preoperative calcium and immunoparathormone levels were correlated to the weight and calculated volume of the removed gland. The calcium level was found to be significantly associated with parathyroid gland weight and volume (p less than 0.001), as determined by linear regression analysis. Despite the statistical association, the correlation coefficient (calculated with the Pearson correlation matrix) was low, 0.16 for the relation of calcium to gland weight and 0.25 for the relation of calcium to calculated gland volume. The calculated coefficients of correlation of iPTH (three different assays) to gland weight and volume were similarly low. These findings demonstrate a variable relationship between the preoperative serum calcium level or the iPTH level to the weight or volume of the enlarged hyperfunctioning parathyroid gland. Identification of the pathologic parathyroid gland(s) in primary hyperparathyroidism cannot be based on a perceived relation of preoperative calcium or iPTH levels to the size of the enlarged glands.

Adolescent↗

PubMed1998

Severity of symptoms of depression and anxiety as predictors of duration of psychotherapy.

The present study explored predictors of the duration of therapy exclusive of outcome utilizing data on 77 patients at St. John's University Center for Psychological Services. Measures of time in therapy were the total number of sessions attended and the number of sessions attended within the first six months of therapy. A bivariate Pearson product-moment correlation matrix was constructed, comprised of measures for time in therapy, severity of symptom measures, treatment modality (psychodynamic or cognitive-behavioral), age, and sex. There was a significant correlation between scores on state anxiety and the total number of sessions as well as between scores on state anxiety and number of sessions attended within six months, but no other correlations between measures of severity of symptoms and time in therapy were significant (p > .05). The results indicate that severity of symptoms does not significantly predict the duration of therapy.

Adult↗

PubMed2004

Analysis of data with multiple sources of correlation in the framework of generalized estimating equations.

This paper is motivated by a study of physical activity participation habits in African American women with three potential sources of correlation among study outcomes, according to method of assessment, timing of measurement, and intensity of physical activity. To adjust for the multiple sources of correlation in this study, we implement an approach based on generalized estimating equations that models association via a patterned correlation matrix. We present a general algorithm that is relatively straightforward to program, an analysis of our physical activity study, and some asymptotic relative efficiency comparisons between correctly specifying the correlation structure vs ignoring two sources of correlation in the analysis of data from this study. The efficiency comparisons demonstrate that correctly modeling the correlation structure can prevent substantial losses in efficiency in estimation of the regression parameter.

Algorithms↗

PubMed2006

Singular value decomposition of genome-scale mRNA lengths distribution reveals asymmetry in RNA gel electrophoresis band broadening.

We describe the singular value decomposition (SVD) of yeast genome-scale mRNA lengths distribution data measured by DNA microarrays. SVD uncovers in the mRNA abundance levels data matrix of genes x arrays, i.e., electrophoretic gel migration lengths or mRNA lengths, mathematically unique decorrelated and decoupled "eigengenes." The eigengenes are the eigenvectors of the arrays x arrays correlation matrix, with the corresponding series of eigenvalues proportional to the series of the "fractions of eigen abundance." Each fraction of eigen abundance indicates the significance of the corresponding eigengene relative to all others. We show that the eigengenes fit "asymmetric Hermite functions," a generalization of the eigenfunctions of the quantum harmonic oscillator and the integral transform which kernel is a generalized coherent state. The fractions of eigen abundance fit a geometric series as do the eigenvalues of the integral transform which kernel is a generalized coherent state. The "asymmetric generalized coherent state" models the measured data, where the profiles of mRNA abundance levels of most genes as well as the distribution of the peaks of these profiles fit asymmetric Gaussians. We hypothesize that the asymmetry in the distribution of the peaks of the profiles is due to two competing evolutionary forces. We show that the asymmetry in the profiles of the genes might be due to a previously unknown asymmetry in the gel electrophoresis thermal broadening of a moving, rather than a stationary, band of RNA molecules.

Evolution, Molecular↗

PubMed1995

Multivariate analysis of fears in dental phobic patients according to a reduced FSS-II scale.

This study analyzed and assessed dimensions of a questionnaire developed to measure general fears and phobias. A previous factor analysis among 109 dental phobics had revealed a five-factor structure with 22 items and an explained total variance of 54%. The present study analyzed the same material using a multivariate statistical procedure (LISREL) to reveal structural latent variables. The LISREL analysis, based on the correlation matrix, yielded a chi-square of 216.6 with 195 degrees of freedom (P = 0.138) and showed a model with seven latent variables. One was a general fear factor correlated to all 22 items. The other six factors concerned "Illness & Death" (5 items), "Failures & Embarrassment" (5 items), "Social situations" (5 items), "Physical injuries" (4 items), "Animals & Natural phenomena" (4 items). One item (opposite sex) was included in both "Failures & Embarrassment" and "Social situations". The last factor, "Social interaction", combined all the items in "Failures & Embarrassment" and "Social situations" (9 items). In conclusion, this multivariate statistical analysis (LISREL) revealed and confirmed a factor structure similar to our previous study, but added two important dimensions not shown with a traditional factor analysis. This reduced FSS-II version measures general fears and phobias and may be used on a routine clinical basis as well as in dental phobia research.

Adult↗

PubMed2004

Patterns of phenotypic covariation and correlation in modern humans as viewed from morphological integration.

Proportionality of phenotypic and genetic distance is of crucial importance to adequately focus on population history and structure, and it depends on the proportionality of genetic and phenotypic covariance. Constancy of phenotypic covariances is unlikely without constancy of genetic covariation if the latter is a substantial component of the former. If phenotypic patterns are found to be relatively stable, the most probable explanation is that genetic covariance matrices are also stable. Factors like morphological integration account for such stability. Morphological integration can be studied by analyzing the relationships among morphological traits. We present here a comparison of phenotypic correlation and covariance structure among worldwide human populations. Correlation and covariance matrices between 47 cranial traits were obtained for 28 populations, and compared with design matrices representing functional and developmental constraints. Among-population differences in patterns of correlation and covariation were tested for association with matrices of genetic distances (obtained after an examination of 10 Alu-insertions) and with Mahalanobis distances (computed after craniometrical traits). All matrix correlations were estimated by means of Mantel tests. Results indicate that correlation and covariance structure in our species is stable, and that among-group correlation/covariance similarity is not related to genetic or phenotypic distance. Conversely, genetic and morphological distance matrices were highly correlated. Correlation and covariation patterns were largely associated with functional and developmental factors, which probably account for the stability of covariance patterns.

Alu Elements↗

PubMed1995

Validity of three clinical performance assessments of internal medicine clerks.

PURPOSE: To analyze the construct validity of three methods to assess the clinical performances of internal medicine clerks. METHOD: A multitrait-multimethod (MTMM) study was conducted at the Case Western Reserve University School of Medicine to determine the convergent and divergent validity of a clinical evaluation form (CEF) completed by faculty and residents, an objective structured clinical examination (OSCE), and the medicine subject test of the National Board of Medical Examiners. Three traits were involved in the analysis: clinical skills, knowledge, and personal characteristics. A correlation matrix was computed for 410 third-year students who completed the clerkship between August 1988 and July 1991. RESULTS: There was a significant (p < .01) convergence of the four correlations that assessed the same traits by using different methods. However, the four convergent correlations were of moderate magnitude (ranging from .29 to .47). Divergent validity was assessed by comparing the magnitudes of the convergence correlations with the magnitudes of correlations among unrelated assessments (i.e., different traits by different methods). Seven of nine possible coefficients were smaller than the convergent coefficients, suggesting evidence of divergent validity. A significant CEF method effect was identified. CONCLUSION: There was convergent validity and some evidence of divergent validity with a significant method effect. The findings were similar for correlations corrected for attenuation. Four conclusions were reached: (1) the reliability of the OSCE must be improved, (2) the CEF ratings must be redesigned to further discriminate among the specific traits assessed, (3) additional methods to assess personal characteristics must be instituted, and (4) several assessment methods should be used to evaluate individual student performances.

Clinical Clerkship↗

PubMed1993

Adhesion and invasion potential of rat prostatic cancer cells: correlation with metastatic potential.

This investigation examined the ability of low-metastatic AT-1 and high-metastatic ML and MLL cell lines to adhere to a monolayer of bovine aortic endothelial cells and fibronectin substratum and penetrate a matrigel basement membrane matrix. Cell area, shape factor, and motility as influenced by fibronectin were also examined using these cell lines. The ability of these cells to adhere to fibronectin and traverse matrigel matrix correlated with their metastatic potential. In addition, fibronectin increases cell circularity and reduces cell area as metastatic potential increases within AT-1 to ML or MLL cell lineages.

Animals↗

PubMed2004

Semiclassical tunneling splittings from short time dynamics: Herman-Kluk-propagation and harmonic inversion.

We investigate a recently proposed method [J. Chem. Phys. 108, 9206 (1998)] to obtain tunneling splittings from short time cross-correlation matrices that were propagated according to the semiclassical propagator of Herman and Kluk. The energy levels were extracted by harmonic inversion of the cross-correlation matrix using the filter diagonalization technique. The aim of this study is twofold: First, the short time behavior of the Herman-Kluk-propagator and the meaning of using cross-correlation matrices rather than autocorrelation functions is addressed. Numerical examples are given for one- and two-dimensional model potentials. Second, the performance of the method is investigated for a system with considerable anharmonicity and coupling. Here the proton transfer in 3,7-dichlorotropolone is considered using an ab initio reaction surface Hamiltonian approach. For this example also the extension to more dimensions is critically discussed.

Journal Article↗

PubMed1999

Detection of protein fold similarity based on correlation of amino acid properties.

An increasing number of proteins with weak sequence similarity have been found to assume similar three-dimensional fold and often have similar or related biochemical or biophysical functions. We propose a method for detecting the fold similarity between two proteins with low sequence similarity based on their amino acid properties alone. The method, the proximity correlation matrix (PCM) method, is built on the observation that the physical properties of neighboring amino acid residues in sequence at structurally equivalent positions of two proteins of similar fold are often correlated even when amino acid sequences are different. The hydrophobicity is shown to be the most strongly correlated property for all protein fold classes. The PCM method was tested on 420 proteins belonging to 64 different known folds, each having at least three proteins with little sequence similarity. The method was able to detect fold similarities for 40% of the 420 sequences. Compared with sequence comparison and several fold-recognition methods, the method demonstrates good performance in detecting fold similarities among the proteins with low sequence identity. Applied to the complete genome of Methanococcus jannaschii, the method recognized the folds for 22 hypothetical proteins.

Amino Acid Sequence↗

PubMed1996

A nonverbal signal in voices of interview partners effectively predicts communication accommodation and social status perceptions.

Derivations from nonverbal communications accommodation theory are tested, and this knowledge is extended both theoretically and methodologically. Fast fourier transform and statistical analysis of a low-frequency nonverbal signal-in voices from 25 dyadic interviews between a talk show host and his guests revealed voice convergence between partners. Correlation coefficients from comparisons of partners' voice spectra and factor analysis of the correlation matrix showed that lower status partners accommodated their voices to higher status partners via the nonverbal signal. Student ratings of the social status of the same talk show host and guests were correlated with factor loadings, thereby providing convergent validity of the nonverbal signal as a predictor of social status perceptions and accommodation.

Dominance-Subordination↗

PubMed2000

Factor structure of the College Adjustment Scales.

The present study examined the underlying structure of the College Adjustment Scales via principal components analysis. A correlation matrix of the nine subscales showed significant multicolinearity. A subsequent principal components analysis demonstrated that one factor accounted for 57% of the total variance and that the majority of subscales were moderately correlated with this single factor. The results suggest that the College Adjustment Scales may measure the same underlying construct and that the clinical distinctions implied by subscale scores should be regarded with caution. Conclusions are constrained by sample size and demographic characteristics, but the results suggest the need for further empirical validation of the College Adjustment Scales, which may be useful in college counseling centers.

Adaptation, Psychological↗

PubMed1977

Relation of food consumption to cancer mortality in Japan, with special reference to international figures.

The present study was designed to examine the epidemiological association of food consumption with cancer mortality in Japan, if any, in comparison with similar examinations in developed countries including Japan, in a search for dietary factors in cancer etiology. Whereas food consumption patterns in Japan was believed to be specific among developed countries, this study revealed that the correlation matrix among major foods both for international and Japanese data made it possible to categorize these foods into two groups with some similar patterns, since there should be observed a positive or negative correlation for each pair of foods. The patterns for correlation of food consumption to cancer mortality in Japan were found to be considerably different from those in developed countries, and this suggested that the epidemiological association between the two in Japan, if any, could be specifically evaluated from that in develop countries. The urban-type region for food consumption in Japan, however, indicated a possible westernization for the relation of food consumption to cancer mortality as well as for food consumption patterns, whereas the traditional Japanese region for food consumption did not indicate any similarity with westernization for the relationship between food consumption and cancer mortality, as well as for food consumption patterns. The above findings also suggested that there might be a possible significance for the regionalization of Japan in such studies, and that the urbanization of food consumption patterns in Japan would show that this country has a similar pattern of association between food consumption and cancer mortality as observed among developed countries in Europe and/or North America.

Dairy Products↗

PubMed1987

Analysis of the glycopeptides derived from the extracellular matrix secreted by cultured bovine aortic smooth muscle cells.

Modulation of smooth muscle cell behaviour in culture has been associated with changes in the extracellular matrix. In the present study cultures of bovine aortic smooth muscle cells were compared in the rapidly proliferating and confluent phases of growth. The extracellular matrix was similar in both phases of growth and consisted of glycoproteins ranging from molecular weight 20,000 to over 200,000. The glycopeptides derived from these components displayed several differences. N-linked heteropolysaccharides of the biantennary and complex (more than two branches) types were predominant in the matrix of the confluent phase. Larger amounts of high mannose glycopeptides were present in the preparations from proliferating cells. O-Glycosidic glycopeptides were minor components in both preparations, but a slight increase was noted in the confluent phase of growth. Some of the changes in glycopeptides were interpreted in terms of the levels of the major components of the matrix such as the interstitial procollagens and fibronectin. The results indicate that processing of oligosaccharides associated with secreted glycoproteins of the extracellular matrix correlates with the state of growth of smooth muscle cells in culture.

Animals↗