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PubMed2005

Correlation between 2 interstitial cystitis symptom instruments.

PURPOSE: Two statistically validated interstitial cystitis (IC) symptom instruments have been used in clinical research. In this study we report what is to our knowledge the first direct comparison of the University of Wisconsin Symptom Instrument (UWI) with the O'Leary-Sant instruments, that is the IC Symptom Index (ICSI) and IC Problem Index (ICPI). MATERIALS AND METHODS: A convenience sampling of 107 patients with IC evaluated at the urology clinic at our institution from March through August 2000 were asked to complete ICSI, ICPI and UWI. The scores were analyzed and graphed. RESULTS: Mean ICSI, ICPI and UWI scores +/- SD were 12.6 +/- 4.3, 10.5 +/- 3.8 and 25.5 +/- 10.8, respectively. UWI and ICSI scores correlated at r = 0.80 (p <0.01) and ICSI/ICPI scores correlated at r = 0.83 (p <0.01). ICSI and ICPI contain 4 symptom-problem pairs. There are relevant differences in the correlation of symptom severity (ICSI question) and its associated problem (ICPI question). The symptom of urgency correlated best with the associated problem (r = 0.84), followed by nocturia (r = 0.82), pain (r = 0.70) and frequency (r = 0.68). CONCLUSIONS: The ICSI and UWI symptom instruments correlate strongly in a large population of patients with IC. The data presented will aid in interpreting the literature. A relatively poor correlation between pain symptom-problem pairs in the O'Leary-Sant instruments is probably an artifact of wording. The word pressure appears in ICPI but not in ICSI. We suggest using parallel wording of the pain symptom-problem pair containing the identical phrase, burning, pain, discomfort or pressure, to improve the ICSI/ICPI correlation and more accurately reflect the clinical condition.

Adult↗

PubMed2005

Correlation between urethral sphincter activity and Valsalva leak point pressure at different bladder distentions: revisiting the urethral pressure profile.

PURPOSE: We determined the correlation between Valsalva leak point pressure (LPP) and the urethral pressure profile (UPP) in urodynamically selected patients with stress urinary incontinence (SUI) as well as the interference of bladder volume on this correlation. MATERIALS AND METHODS: A total of 450 consecutive women with SUI were clinically evaluated and underwent urodynamic study. Inclusion criteria were urodynamically demonstrable SUI with normal bladder compliance, sensitivity and capacity. Severe pelvic prolapse, detrusor overactivity and a pattern suggestive of obstruction were excluded. Urodynamic study was performed using a 7Fr 4 channel membrane catheter. LPP was determined at mid bladder capacity and UPP was determined at 50 ml, between 200 and 250 ml, and at bladder capacity. RESULTS: A total of 200 women fulfilled the selection criteria, of whom 30, 114 and 56 had a LPP of 60 or less, between 60 and 120, and greater than 120 cm H2O, respectively. Except for age and the number of pads the 3 groups were well matched in clinical and bladder urodynamic parameters. A progressive correlation of LPP with maximum urethral closure pressure was found when UPP was performed at 50 ml (r = 0.305, p <0.0001), at 250 ml (r = 0.483, p <0.0001) and at maximum bladder filling (r = 0.561, p <0.0001). Urethral functional length did not show a correlation with LPP at a bladder distention of 50 ml (r = 0.117, p = 0.100) or 200 ml (r = 0.167, p = 0.019) but there was a minor correlation at bladder capacity (r = 0.234, p = 0.002). CONCLUSIONS: There is a significant correlation between maximum urethral closure pressure and LPP. Patients with a LPP of 60 cm H2O or less have a shorter urethral functional length and lower sphincter activity. Patients with SUI have a more remarkable correlation between UPP and Valsalva LPP when UPP is determined after filling the bladder to more than 200 ml.

Aged↗

PubMed2006

Correlative study of iron accumulation in liver, myocardium, and pituitary assessed with MRI in young thalassemic patients.

Clinical complications resulting from unevenly iron accumulation in individual organs of patients with beta-thalassemia major can affect both expectancy and quality of life. Magnetic resonance imaging (MRI) offers a quantitative, noninvasive, accurate method for estimating iron levels in various tissues, not easily accessible with other techniques. The aim of this study was to evaluate and correlate the level of iron accumulation in different organs (anterior pituitary, myocardium, and liver) assessed with MRI, in children and young adults with beta-thalassemia major. Thirty children and young adults (13 female and 17 male patients) with homozygous beta-thalassemia, treated conventionally, were studied with hepatic, myocardial, and hypophyseal MRI. For liver and myocardium, we calculated the natural logarithm of the signal-to-air ratio in flash 2-dimensional sequences with electrocardiogram gating, whereas for anterior pituitary, the signal intensity was measured in sagittal T2 sequences. All scans were performed within 3 months. In 13 patients, data regarding liver iron concentrations (LIC) assessed by percutaneous liver biopsy were available. The mean of serum ferritin concentrations for 1 year before scans was calculated for each patient. MRI values in myocardium and liver showed a significant negative correlation to age (r=-0.73 and -0.69, respectively). For pituitary MRI, a linear regression with age was recorded in patients over 14 years of age (r=-0.67), whereas a relatively increased signal intensity reduction was recorded in pubertal subjects. Mean serum ferritin concentrations ranged from 252 to 5872 mug/L with an average of 1525+/-1047 mug/L. No statistical significant correlation was noted between mean ferritin levels versus liver, pituitary, and cardiac MRI values (r=-0.49, -0.28, and -0.1, respectively). Mean LIC values assessed by percutaneous biopsy were 13.76+/-11.6 mg/g of dry tissue. A statistically significant negative correlation was observed between liver MRI readings and LIC determined by biopsy (r=-0.89). None of the 3 organs studied with MRI were significantly correlated to each other. Pituitary to liver MRI values and liver to myocardial MRI values were moderately correlated (r=0.34 and 0.42, respectively). Pituitary MRI was not correlated at all to myocardial MRI (r=-0.001). In conclusion, iron accumulation in thalassemic patients is a procedure progressing with age, which seems to act independently in different organs. MRI represents a reliable, noninvasive method for assessing iron overload in various tissues, non-easily accessible with other techniques. Regular scanning, to recognize preclinically excessive iron deposits and intensified chelation therapy, can prevent serious and fatal complications.

Adolescent↗

PubMed2005

Quantitative genetics and behavioural correlates of digit ratio in the zebra finch.

A recent study on a captive zebra finch population suggested that variation in digit ratio (i.e. the relative length of the second to the fourth toe) might be an indicator of the action of sex steroids during embryo development, as is widely assumed for human digits. Zebra finch digit ratio was found to vary with offspring sex, laying order of eggs within a clutch, and to predict aspects of female mating behaviour. Hence, it was proposed that the measurement of digit ratio would give insights into how an individual's behaviour is shaped by its maternal environment. Studying 500 individuals of a different zebra finch population I set out to: (1) determine the proximate causes of variation in digit ratio by means of quantitative genetics and (2) to search for phenotypic and genetic correlations between digit ratio, sexual behaviour and aspects of fitness. In contrast to the earlier study, I found no sexual dimorphism in digit ratio and no effect of either laying order or experimentally altered hatching order on digit ratio. Instead, I found that variation in digit ratio was almost entirely additive genetic, with heritability estimates ranging from 71 to 84%. The rearing environment (from egg deposition to independence) explained an additional 5-6% of the variation in digit ratio, but there was no indication of any maternal effects transmitted through the egg. I found highly significant phenotypic correlations (and genetic correlations of similar size) between digit ratio and male song rate (positive correlation) as well as between digit ratio and female hopping activity in a choice chamber (negative correlation). Rather surprisingly, the strength of these correlations differed significantly between subsequent generations of the same population, illustrating how quickly such correlations can appear and disappear probably due to genotype-environment interactions.

Animals↗

PubMed2001

Model of correlated sequential adsorption of colloidal particles.

We present results of a model of sequential adsorption in which the adsorbing particles are correlated with the particles attached to the substrate. The strength of the correlations is measured by a tunable parameter sigma. The model interpolates between free ballistic adsorption in the limit sigma-->infinity and a strongly correlated phase, appearing for sigma-->0 and characterized by the emergence of highly ordered structures. The phenomenon is manifested through the analysis of several magnitudes, as the jamming limit and the particle-particle correlation function. The effect of correlations in one dimension manifests in the increased tendency to particle chaining in the substrate. In two dimensions the correlations induce a percolation transition, in which a spanning cluster of connected particles appears at a certain critical value sigma(c). Our study could be applicable to more general situations in which the coupling between correlations and disorder is relevant, as for example, in the presence of strong interparticle interactions.

Journal Article↗

PubMed2001

Precollisional velocity correlations in a hard-disk fluid with dissipative collisions.

Velocity correlations are studied in granular fluids, modeled by the inelastic hard sphere gas. Making a density expansion of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy for the evolution of the reduced distributions, we predict the presence of precollisional velocity correlations. They are created by the propagation through correlated sequences of collisions (ring events) of the velocity correlations generated after dissipative collisions. The correlations have their origin in the dissipative character of collisions, being always present in granular fluids. The correlations, that manifest microscopically as an alignment of the velocities of a colliding pair produce modifications of collisional averages, in particular, the virial pressure. The pressure shows a reduction with respect to the elastic case as a consequence of the velocity alignment. Good qualitative agreement is obtained for the comparison of the numerical evaluations of the obtained analytical expressions and molecular dynamics results that showed evidence of precollisional velocity correlations [R. Soto and M. Mareschal, Phys. Rev. E 63, 041303 (2001)].

Journal Article↗

PubMed2001

Mode-coupling theory for multiple-point and multiple-time correlation functions.

We present a theoretical framework for higher-order correlation functions involving multiple times and multiple points in a classical, many-body system. Such higher-order correlation functions have attracted much interest recently in the context of various forms of multidimensional spectroscopy, and have found an intriguing application as proposed measures of dynamical heterogeneities in structural glasses. The theoretical formalism is based upon projection operator techniques that are used to isolate the slow time evolution of dynamical variables by expanding the slowly evolving component of arbitrary variables in an infinite, "multilinear" basis composed of the products of slow variables of the system. Using the formalism, a formally exact mode coupling theory is derived for multiple-point and multiple-time correlation functions. The resulting expressions for higher-order correlation functions are made tractable by applying a rigorous perturbation scheme, called the N-ordering method, which is exact for systems with finite correlation lengths in the thermodynamic limit. The theory is contrasted with standard mode coupling theories in which the noise or fluctuating force appearing in the generalized Langevin equation is assumed to be Gaussian, and it is demonstrated that the non-Gaussian nature of the fluctuating forces leads to important contributions to higher-order correlation functions. Finally, the higher-order correlation functions are evaluated analytically for an ideal gas system for which it is shown that the mode coupling theory is exact.

Journal Article↗

PubMed2002

Pattern formation on nonuniform surfaces by correlated random sequential absorptions.

The pattern formation on nonuniform surfaces by correlated-random sequential absorption (CRSA) process has been investigated by computer simulations. The nonuniform surfaces are represented by percolation clusters with probabilities p(s) and p(s) stands for the nonuniform degree of surfaces. The interactions between the particles and the defects in surfaces are involved by introducing a sticking coefficient s. When s-->0, the CRSA process is controlled by the absorption of surfaces and the correlation between particles. With the correlation increasing from a weak limit to a strong one, the cluster consisting of absorbed particles changes from the dispersed pattern of site percolation to correlated percolation, and then to Leath percolation clusters. When s-->1 and p(s)-->p(c), the CRSA process is dominated by the absorption of the defects, where p(c) is the threshold of percolations. The patterns appear randomly dispersed in spite of the correlation. With the decrease of s and increase of p(s), the interaction controlling the CRSA process changes from the absorption of defects to that of surface and the correlation between particles gradually. For the system s-->0, the transition correlation exponent alpha(c)=d(s), where d(s) is the fractal dimension of the percolation surfaces.

Journal Article↗

PubMed2002

Anomalous scaling of a passive scalar advected by the turbulent velocity field with finite correlation time: two-loop approximation.

The renormalization group and operator product expansion are applied to the model of a passive scalar quantity advected by the Gaussian self-similar velocity field with finite, and not small, correlation time. The inertial-range energy spectrum of the velocity is chosen in the form E(k) proportional, variant k(1-2 epsilon ), and the correlation time at the wave number k scales as k(-2+eta). Inertial-range anomalous scaling for the structure functions and other correlation functions emerges as a consequence of the existence in the model of composite operators with negative scaling dimensions, identified with anomalous exponents. For eta> epsilon, these exponents are the same as in the rapid-change limit of the model; for eta< epsilon, they are the same as in the limit of a time-independent (quenched) velocity field. For epsilon =eta (local turnover exponent), the anomalous exponents are nonuniversal through the dependence on a dimensionless parameter, the ratio of the velocity correlation time, and the scalar turnover time. The nonuniversality reveals itself, however, only in the second order of the epsilon expansion and the exponents are derived to order epsilon (2), including anisotropic contributions. It is shown that, for moderate order of the structure function n, and the space dimensionality d, finite correlation time enhances the intermittency in comparison with both the limits: the rapid-change and quenched ones. The situation changes when n and/or d become large enough: the correction to the rapid-change limit due to the finite correlation time is positive (that is, the anomalous scaling is suppressed), it is maximal for the quenched limit and monotonically decreases as the correlation time tends to zero.

Journal Article↗

PubMed2004

Time correlation functions of hard sphere and soft sphere fluids.

We explore the transition between soft particle fluids of increasing steepness to the hard sphere limit. We analyze the analytic forms of the time correlation functions used in determining transport coefficients in Green-Kubo formulas for fluids composed of particles interacting through a repulsive r(-n) potential. We focus on the steeply repulsive n--> infinity limit where the potential tends to the hard sphere interaction. Dufty [Mol. Phys. 100, 2331 (2002)] developed a theoretical framework that can be used to characterize the transition from a steeply repulsive continuous potential toward the hard sphere potential for the shear stress time correlation function. This function was shown to consist of a rapidly decaying contribution (which is singular in the steeply repulsive limit) and a slowly decaying nonsingular part which can be reasonably well represented by Enskog's prediction on times of order and in excess of the mean collision time. We extend this treatment to the bulk viscosity and thermal conductivity. We focus on the bulk viscosity (pressure) correlation function as it is purely singular for hard spheres, and has no kinetic or cross term contributions in this limit. There is no relaxation of this correlation function on the mean collision or Enskog time scale for hard spheres. We show that it is not possible to represent the steeply repulsive behavior of this function entirely in terms of a sech function, i.e., C(B)(t)=sech(a(n)t/tau(n)), where a(n) is a numerical factor, t is time, and tau(n) is a relaxation time proportional to n(-1). An additional singular function, which we call w(t), is required to obtain the correct short-time behavior of C(B)(t) and the Enskog value for the bulk viscosity. With this additional function, the value of a(n) in the n--> infinity limit is a(n)=square root of 2 which is consistent with the second moment of the time expansion of the time correlation function. We compute this function for large n and extrapolate it to n--> infinity, determining one possible analytic form. The shear stress correlation function also gives a(n)=square root of 2 in the hard sphere limit for the singular part when the sech and w functions are used. This function has a nonsingular component, even in the hard sphere limit. We explore various forms for the crossover function X(t/tau(n)) introduced by Dufty, which weights the limiting singular and nonsingular contributions to C(S)(t) particularly at intermediate times. The qualitative behavior for the heat flux time correlation function (used to obtain the thermal conductivity) is much the same as the shear case. The w(t) derived by several self-consistent extrapolations appears, within the simulation statistics, to be the same for the bulk and shear viscosity, and for the thermal conductivity cases.

Journal Article↗

PubMed2004

Random matrix theory analysis of cross correlations in financial markets.

We confirm universal behaviors such as eigenvalue distribution and spacings predicted by random matrix theory (RMT) for the cross correlation matrix of the daily stock prices of Tokyo Stock Exchange from 1993 to 2001, which have been reported for New York Stock Exchange in previous studies. It is shown that the random part of the eigenvalue distribution of the cross correlation matrix is stable even when deterministic correlations are present. Some deviations in the small eigenvalue statistics outside the bounds of the universality class of RMT are not completely explained with the deterministic correlations as proposed in previous studies. We study the effect of randomness on deterministic correlations and find that randomness causes a repulsion between deterministic eigenvalues and the random eigenvalues. This is interpreted as a reminiscent of "level repulsion" in RMT and explains some deviations from the previous studies observed in the market data. We also study correlated groups of issues in these markets and propose a refined method to identify correlated groups based on RMT. Some characteristic differences between properties of Tokyo Stock Exchange and New York Stock Exchange are found.

Journal Article↗

PubMed2005

Many-body correlations versus mode-coupling effects in the dynamics of dense gases.

Time dependent contributions due to the triplet and quadruplet correlation functions have been combined with microscopically determined contribution due to the pair correlation function for the transverse stress correlation function. Comparison of the results with simulation data shows that contributions due to two- and three-body static correlation functions are sufficient to understand the viscous dynamics of dense gases. However, close to the triple point, it becomes necessary to include the contribution due to the four-body correlation function. The contribution due to the mode coupling effect has been contrasted with the contribution due to three- and four-body correlation functions. It is noted that the mode coupling contribution plays a similar role as that due to many-body correlation functions.

Journal Article↗

PubMed2006

Broad peak in the dx2-y2 superconducting correlation length as a function of hole concentration in the two-dimensional t-J model.

We have calculated high temperature series to 12th order in inverse temperature for singlet superconducting correlation functions of the 2D t-J model with s, dx2-y2, and dxy symmetry pairs. Our calculations differ from previous work by removing disconnected pieces from the original four-point correlator and by treating the resulting pairing correlator as a matrix. We find the correlation length for dx2-y2 pairing grows significantly with decreasing temperature and develops a broad peak as a function of doping around delta=0.25 for T/J=0.25 at J/t=0.4. The correlation lengths for s and dxy symmetry remain small and do not display peaks. Antiferromagnetic spin correlations at low doping act to suppress the dx2-y2 and dxy superconducting correlation lengths.

Journal Article↗

PubMed1999

Correlation between structural parameters of garnet and garnet-like structures.

Statistical analysis of structural parameters of garnet and garnet-like structures retrieved from the Inorganic Crystal Structure Database has revealed strong correlations between them. The degree of correlation depends on doping site and garnet type. Structural parameters are not equally sensitive to changes imposed by doping. The strongest correlation exists between the unit-cell parameter and the doping-ion radius. In the case of doping at the dodecahedral sites, the most sensitive parameter is the shortest dodecahedral distance. Principal component analysis (PCA) clearly shows that the first component explains most of the variation of structural data. It has a geometric basis and correlates with the effective radii of the doping ion. Partial correlation helps to identify the strongest relations between pairs of variables when the influence of other structural variables on them is controlled. It appears that in some cases partial correlation has a different sign when compared with the results of the standard correlation technique.

Journal Article↗

PubMed2006

Modeling of muscle motor unit innervation process correlation and common drive.

Concurrently active motor units (MUs) of a given muscle can exhibit a certain degree of synchronous firings, and a certain degree of common variation in their firing rates. The former property is referred to as motor unit synchrony in the literature, which is termed motor unit innervation process (MUIP) correlation in this study. The latter is referred to as motor unit common drive and can be quantified by the common drive coefficient, which is the correlation coefficient between the smoothed firing rates of the two MUs. Both properties have important roles and implications in the generation and resulting characteristics of the myoelectric signal and for the development of signal processing algorithms in myoelectric signal (MES) applications. In order to study these implications and characteristics, in this paper estimation procedures are developed to quantify the degree of MUIP correlation and common drive as functions of physiological parameters. Also, the interaction between MUIP correlation and motor unit common drive is studied in a physiologically realistic simulation model. Neurons modeled by Hodgkin-Huxley systems form the framework of the simulation model in which excitation and synaptic characteristics can be modified. MUIP correlation and common drive degree and interaction are studied through a number of simulations. To support the simulation results, experimental in vivo motor unit trains were collected at low levels of contraction from 11 subjects, and decomposed into the constituent unit trains giving 50 concurrently active motor unit pairs. The simulation demonstrated that the innervation process correlation coefficient is controlled primarily by the postsynaptic conductance, gsyn, and was less than 0.05 mS/cm2 for realistic values of gsyn. The common drive was found to be controlled by the exciting neuron input with no statistically significant interaction between it and the MUIP correlation. The experimental data gave results in close agreement with those of the simulation.

Action Potentials↗

PubMedDate not supplied

Correlation statistics for cDNA microarray image analysis.

In this paper, correlation of the pixels comprising a microarray spot is investigated. Subsequently, correlation statistics, namely, Pearson correlation and Spearman rank correlation, are used to segment the foreground and background intensity of microarray spots. The performance of correlation-based segmentation is compared to clustering-based (PAM, k-means) and seeded-region growing techniques (SPOT). It is shown that correlation-based segmentation is useful in flagging poorly hybridized spots, thus minimizing false-positives. The present study also raises the intriguing question of whether a change in correlation can be an indicator of differential gene expression.

Artificial Intelligence↗

PubMed2006

Correlation filters with controlled scale response.

Correlation filtering methods are becoming increasingly popular for image recognition and location. The recent introduction of optimal tradeoff circular harmonic function filters allowed the user to specify the response of a correlation filter to in-plane rotation distortion. In this paper we introduce a new correlation filter design that can provide a user-specified response to in-plane scale distortion. The design is based on the Mellin radial harmonic (MRH) transform and incorporates multiple harmonics into the correlation filter for improved discrimination capability. Additionally, the filter design minimizes the average correlation energy in order to achieve sharp correlation peaks, and thus we refer to these filters as minimum average correlation energy Mellin radial harmonic (MACE-MRH) filters. We present underlying theory, a MACE-MRH filter design method, and numerical simulation results.

Algorithms↗

PubMedDate not supplied

Multifield-graphs: an approach to visualizing correlations in multifield scalar data.

We present an approach to visualizing correlations in 3D multifield scalar data. The core of our approach is the computation of correlation fields, which are scalar fields containing the local correlations of subsets of the multiple fields. While the visualization of the correlation fields can be done using standard 3D volume visualization techniques, their huge number makes selection and handling a challenge. We introduce the Multifield-Graph to give an overview of which multiple fields correlate and to show the strength of their correlation. This information guides the selection of informative correlation fields for visualization. We use our approach to visually analyze a number of real and synthetic multifield datasets.

Journal Article↗