A log-Birnbaum-Saunders regression model with asymmetric errors

This paper introduces a skewed log-Birnbaum-Saunders regression model based on the skewed sinh-normal distribution proposed by Leiva et al. [A skewed sinh-normal distribution and its properties and application to air pollution, Comm. Statist. Theory Methods 39 (2010), pp. 426-443]. Some influence methods, such as the local influence and generalized leverage, are presented. Additionally, we derived the normal curvatures of local influence under some perturbation schemes. An empirical application to a real data set is presented in order to illustrate the usefulness of the proposed model.

Analysis of NDVI time series using cross-correlation and forecasting methods for monitoring sugarcane fields in Brazil

Brazil is the largest sugarcane producer in the world and has a privileged position to attend to national and international market places. To maintain the high production of sugarcane, it is fundamental to improve the forecasting models of crop seasons through the use of alternative technologies, such as remote sensing. Thus, the main purpose of this article is to assess the results of two different statistical forecasting methods applied to an agroclimatic index (the water requirement satisfaction index; WRSI) and the sugarcane spectral response (normalized difference vegetation index; NDVI) registered on National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA-AVHRR) satellite images. We also evaluated the cross-correlation between these two indexes. According to the results obtained, there are meaningful correlations between NDVI and WRSI with time lags. Additionally, the adjusted model for NDVI presented more accurate results than the forecasting models for WRSI. Finally, the analyses indicate that NDVI is more predictable due to its seasonality and the WRSI values are more variable making it difficult to forecast.

Application of the log-conformation tensor to three-dimensional time-dependent free surface flows

The numerical simulation of flows of highly elastic fluids has been the subject of intense research over the past decades with important industrial applications. Therefore, many efforts have been made to improve the convergence capabilities of the numerical methods employed to simulate viscoelastic fluid flows. An important contribution for the solution of the High-Weissenberg Number Problem has been presented by Fattal and Kupferman [J. Non-Newton. Fluid. Mech. 123 (2004) 281-285] who developed the matrix-logarithm of the conformation tensor technique, henceforth called log-conformation tensor. Its advantage is a better approximation of the large growth of the stress tensor that occur in some regions of the flow and it is doubly beneficial in that it ensures physically correct stress fields, allowing converged computations at high Weissenberg number flows. In this work we investigate the application of the log-conformation tensor to three-dimensional unsteady free surface flows. The log-conformation tensor formulation was applied to solve the Upper-Convected Maxwell (UCM) constitutive equation while the momentum equation was solved using a finite difference Marker-and-Cell type method. The resulting developed code is validated by comparing the log-conformation results with the analytic solution for fully developed pipe flows. To illustrate the stability of the log-conformation tensor approach in solving three-dimensional free surface flows, results from the simulation of the extrudate swell and jet buckling phenomena of UCM fluids at high Weissenberg numbers are presented. (C) 2012 Elsevier B.V. All rights reserved.

Correlation of the Physicochemical and Structural Properties of pDNA/Cationic Liposome Complexes with Their in Vitro Transfection

In this study, we characterized the conventional physicochemical properties of the complexes formed by plasmid DNA (pDNA) and cationic liposomes (CL) composed of egg phosphatidylcholine (EPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) (50/25/25% molar ratio). We found that these properties are nearly unaffected at the studied ranges when the molar charge ratio (R-+/-) between the positive charge from the CL and negative charge from pDNA is not close to the isoneutrality region (R-+/- = 1). However, the results from in vitro transfection of HeLa cells showed important differences when R-+/- is varied, indicating that the relationships between the physicochemical and biological characteristics were not completely elucidated. To obtain information regarding possible liposome structural modifications, small-angle X-ray scattering (SAXS) experiments were performed as a function of R-+/- to obtain correlations between structural, physicochemical, and transfection properties. The SAXS results revealed that pDNA/CL complexes can be described as being composed of single bilayers, double bilayers, and multiple bilayers, depending on the R-+/- value. Interestingly, for R-+/- = 9, 6, and 3, the system is composed of single and double bilayers, and the fraction of the latter increases with the amount of DNA (or a decreasing R-+/-) in the system. This information is used to explain the transfection differences observed at an R-+/- = 9 as compared to R-+/- = 3 and 6. Close to the isoneutrality region (R-+/- = 1.8), there was an excess of pDNA, which induced the formation of a fraction of aggregates with multiple bilayers. These aggregates likely provide additional resistance against the release of pDNA during the transfection phenomenon, reflected as a decrease in the transfection level. The obtained results permitted proper correlation of the physicochemical and structural properties of pDNA/CL complexes with the in vitro transfection of HeLa cells by these complexes, contributing to a better understanding of the gene delivery process.

The log-exponentiated generalized gamma regression model for censored data

For the first time, we introduce a generalized form of the exponentiated generalized gamma distribution [Cordeiro et al. The exponentiated generalized gamma distribution with application to lifetime data, J. Statist. Comput. Simul. 81 (2011), pp. 827-842.] that is the baseline for the log-exponentiated generalized gamma regression model. The new distribution can accommodate increasing, decreasing, bathtub- and unimodal-shaped hazard functions. A second advantage is that it includes classical distributions reported in the lifetime literature as special cases. We obtain explicit expressions for the moments of the baseline distribution of the new regression model. The proposed model can be applied to censored data since it includes as sub-models several widely known regression models. It therefore can be used more effectively in the analysis of survival data. We obtain maximum likelihood estimates for the model parameters by considering censored data. We show that our extended regression model is very useful by means of two applications to real data.

Nursing care time and quality indicators for adult intensive care: correlation analysis

The objective of this quantitative, correlational and descriptive study was to analyze the time the nursing staff spends to assist patients in Adult Intensive Care Units, as well as to verify its correlation with quality care indicators. The average length of time spent on care and the quality care indicators were identified by consulting management instruments the nursing head of the Unit employs. The average hours of nursing care delivered to patients remained stable, but lower than official Brazilian agencies' indications. The correlation between time of nursing care and the incidence of accidental extubation indicator indicated that it decreases with increasing nursing care delivered by nurses. The results of this investigation showed the influence of nursing care time, provided by nurses, in the outcome of care delivery.

Pancreatic iron stores assessed by magnetic resonance imaging (MRI) in beta thalassemic patients

Purpose: To assess the correlation between MRI findings of the pancreas with those of the heart and liver in patients with beta thalassemia; to compare the pancreas T2* MRI results with glucose and ferritin levels and labile plasma iron (LPI). Materials and methods: We retrospectively evaluated chronically transfused patients, testing glucose with enzymatic tests, serum ferritin with chemiluminescence, LPI with cellular fluorescence, and T2* MRI to assess iron content in the heart, liver, and pancreas. MRI results were compared with one another and with serum glucose, ferritin, and LPI. Liver iron concentration (LIC) was determined in 11 patients' liver biopsies by atomic absorption spectrometry. Results: 289 MRI studies were available from 115 patients during the period studied. 9.4% of patients had overt diabetes and an additional 16% of patients had impaired fasting glucose. Both pancreatic and cardiac R2* had predictive power (p < 0.0001) for identifying diabetes. Cardiac and pancreatic R2* were modestly correlated with one another (r(2) = 0.20, p < 0.0001). Both were weakly correlated with LIC (r(2) = 0.09, p < 0.0001 for both) and serum ferritin (r(2) = 0.14, p < 0.0001 and r(2) = 0.03, p < 0.02, respectively). None of the three served as a screening tool for single observations. There is a strong log-log, or power-law, relationship between ratio of signal intensity (SIR) values and pancreas R2* with an r(2) of 0.91. Conclusions: Pancreatic iron overload can be assessed by MRI, but siderosis in other organs did not correlate significantly with pancreatic hemosiderosis. (C) 2011 Elsevier Ireland Ltd. All rights reserved.

A log-linear regression model for the beta-Birnbaum-Saunders distribution with censored data

The beta-Birnbaum-Saunders (Cordeiro and Lemonte, 2011) and Birnbaum-Saunders (Birnbaum and Saunders, 1969a) distributions have been used quite effectively to model failure times for materials subject to fatigue and lifetime data. We define the log-beta-Birnbaum-Saunders distribution by the logarithm of the beta-Birnbaum-Saunders distribution. Explicit expressions for its generating function and moments are derived. We propose a new log-beta-Birnbaum-Saunders regression model that can be applied to censored data and be used more effectively in survival analysis. We obtain the maximum likelihood estimates of the model parameters for censored data and investigate influence diagnostics. The new location-scale regression model is modified for the possibility that long-term survivors may be presented in the data. Its usefulness is illustrated by means of two real data sets. (C) 2011 Elsevier B.V. All rights reserved.

ANTERIOR SHOULDER INSTABILITY: CORRELATION BETWEEN MAGNETIC RESONANCE ARTHROGRAPHY, ULTRASOUND ARTHROGRAPHY AND INTRAOPERATIVE FINDINGS

The purpose of the present study was to determine ultrasound (US) arthrography diagnostic accuracy in patients with recurrent shoulder dislocation by comparing US arthrography and magnetic resonance arthrography (MRA) with intraoperative findings. Fifty-six consecutive patients with diagnosis of chronic anterior instability of the shoulder were evaluated for assessment of bone and soft tissue lesions by three radiologists. Twenty-five cases were confirmed by surgery. Sensitivity, specificity, inter-and intraobserver agreement were calculated. Ultrasound sensitivity ranged from 20% to 100% and specificity from 25% to 90%. MRA sensitivity ranged from 80% to 100% and specificity from 50% to 100%. Interobserver agreement was good for MRA (0.54-0.70) and fair for US arthrography (0.19-0.40). Despite a higher interobserver variability for US arthrography than for MRA, our results indicate that US is capable of demonstrating bone and soft tissue lesions related to chronic instability of the shoulder in the presence of intra-articular fluid. (E-mail: marcelo_simao@hotmail.com) (C) 2012 World Federation for Ultrasound in Medicine & Biology.

Exact correlation functions in particle-reaction models with immobile particles

Exact results on particle densities as well as correlators in two models of immobile particles, containing either a single species or else two distinct species, are derived. The models evolve following a descent dynamics through pair annihilation where each particle interacts once at most throughout its entire history. The resulting large number of stationary states leads to a non-vanishing configurational entropy. Our results are established for arbitrary initial conditions and are derived via a generating function method. The single-species model is the dual of the 1D zero-temperature kinetic Ising model with Kimball-Deker-Haake dynamics. In this way, both in finite and semi-infinite chains and also the Bethe lattice can be analysed. The relationship with the random sequential adsorption of dimers and weakly tapped granular materials is discussed.

Ligand- and Structure-Based Drug Design Strategies and PPAR delta/alpha Selectivity

Peroxisome-proliferator-activated receptors are a class of nuclear receptors with three subtypes: a, ? and d. Their main function is regulating gene transcription related to lipid and carbohydrate metabolism. Currently, there are no peroxisome-proliferator-activated receptors d drugs being marketed. In this work, we studied a data set of 70 compounds with a and d activity. Three partial least square models were created, and molecular docking studies were performed to understand the main reasons for peroxisome-proliferator-activated receptors d selectivity. The obtained results showed that some molecular descriptors (log P, hydration energy, steric and polar properties) are related to the main interactions that can direct ligands to a particular peroxisome-proliferator-activated receptors subtype.

Second-trimester soft markers: relation to first-trimester nuchal translucency in unaffected pregnancies

Objective Genetic sonography following first-trimester combined screening appears to increase substantially detection rates for Down syndrome but it relies on the unproved assumption of independence between these tests. In this study we aimed to investigate the relationship between first-trimester nuchal translucency (NT) and a series of second-trimester soft markers and structural defects in unaffected pregnancies. Methods NT measurement in the first trimester was followed by second-trimester scan (18 to 23 + 6 weeks) including examination for three categorical markers (intracardiac echogenic foci, hyperechogenic bowel and structural defects) and measurement of nasal bone length, nuchal-fold thickness, femur length, humerus length, renal pelvis diameter and prenasal thickness. All continuous variables were expressed in multiples of the median (MoM) for gestation and correlation coefficients between log-transformed NT and second-trimester variables were calculated. In addition, frequencies of soft markers and structural defects in cases with increased NT were compared to those with normal NT, using MoM cut-offs. Results In a dataset of 1970 cases, NT was significantly correlated (P < 0.05) with all second-trimester continuous variables, the correlation being strongest for nuchal-fold thickness (r = 0.10). There was a higher frequency of cases with second-trimester nuchal-fold thickness above the 97.5th centile (10.7 vs. 2.2%) and hyperechogenic bowel (2.4 vs. 0.1%) in cases with increased NT. Conclusions Straightforward reassessment of risk using likelihood ratios derived from the second-trimester genetic sonogram might lead to inaccurate estimates. Multivariate models using continuous second-trimester variables might be preferable in sequential screening strategies. Copyright. 2012 ISUOG. Published by John Wiley & Sons, Ltd.

A Poisson mixed model with nonnormal random effect distribution

In this paper, we propose a random intercept Poisson model in which the random effect is assumed to follow a generalized log-gamma (GLG) distribution. This random effect accommodates (or captures) the overdispersion in the counts and induces within-cluster correlation. We derive the first two moments for the marginal distribution as well as the intraclass correlation. Even though numerical integration methods are, in general, required for deriving the marginal models, we obtain the multivariate negative binomial model from a particular parameter setting of the hierarchical model. An iterative process is derived for obtaining the maximum likelihood estimates for the parameters in the multivariate negative binomial model. Residual analysis is proposed and two applications with real data are given for illustration. (C) 2011 Elsevier B.V. All rights reserved.

Atopic dermatitis: correlation between non-damaged skin barrier function and disease activity

Background Atopic dermatitis (AD) is a chronic dermatosis, predominant in childhood, characterized by pruritus and eczematous-type lesions with xerosis as the prominent clinical sign. Objectives To analyze the correlation between biophysical measurements of skin barrier function and other assessment criteria of clinical severity according to Rajka and Langelands criteria. Methods Biophysical measurements [transepidermal water loss (TEWL) and corneometry] were obtained from 120 patients with the diagnosis of AD. Serum levels of IgE were also evaluated. Results A significant correlation between corneometry, TEWL, and clinical severity of AD was found. Data showed an inverse correlation between corneometry, TEWL, and AD severity, and a significant difference (P < 0.001) between mean of corneometry and TEWL and AD severity (mild, moderate, and severe). As for IgE levels, corneometry had significant negative correlation, in contrast with TEWL, which showed a significant positive correlation (P < 0.001). Conclusion Biophysical measurements of skin barrier in non-lesional skin of AD may work as an evaluation factor for AD severity.

Sulcus anatomy and diameter in pseudophakic eyes and correlation with biometric data: Evaluation with a 50 MHz ultrasound biomicroscope

PURPOSE: To evaluate the sulcus anatomy and possible correlations between sulcus diameter and white-to-white (WTW) diameter in pseudophakic eyes, data that may be important in the stability of add-on intraocular lenses (IOLs). SETTING: University Eye Hospital, Tuebingen, Germany. DESIGN: Case series. METHODS: In pseudophakic eyes, the axial length (AL) and horizontal WTW were measured by the IOLMaster device. Cross-sectional images were obtained with a 50 MHz ultrasound biomicroscope on the 4 meridians: vertical, horizontal (180 degrees), temporal oblique, and nasal oblique. Sulcus-to-sulcus (STS), angle-to-angle (ATA), and sclera-to-sclera (ScTSc) diameters were measured. The IOL optic diameter (6.0 mm) served as a control. To test reliability, optic measurements were repeated 5 times in a subset of eyes. RESULTS: The vertical ATA and STS diameters were statistically significantly larger than the horizontal diameter (P=.0328 and P=.0216, respectively). There was no statistically significant difference in ScTSc diameters. A weak correlation was found between WTW and horizontal ATA (r = 0.5766, P<.0001) and between WTW and horizontal STS (r = 0.5040, P=.0002). No correlation was found between WTW and horizontal ScTSc (r = 0.2217, P=.1217). CONCLUSIONS: The sulcus anatomy had a vertical oval shape with the vertical meridian being the largest, but it also had variation in the direction of the largest meridian. The WTW measurements showed a weak correlation with STS. In pseudophakic eyes, Soemmerring ring or a bulky haptic may affect the ciliary sulcus anatomy.