Optimal conditions for the wetting balance test

Wetting balance tests of copper sheets submerged in tin solder baths were carried out in a completely automatic wetting balance. Wetting curves were examined for three different values of sheet thickness and four different solder bath temperatures. Most of the wetting curves showed a distorted shape relative to that of a standard curve, preventing calculation of important wetting parameters, such as the wetting rate and the wetting force. The wetting tests showed that the distortion increased for a thicker sheet thickness and a lower solder bath temperature, being the result of solder bath solidification around the submerged sheet substrate. (C) 2008 Elsevier B.V. All rights reserved.

Residuals for log-Burr XII regression models in survival analysis

In this paper, we compare three residuals to assess departures from the error assumptions as well as to detect outlying observations in log-Burr XII regression models with censored observations. These residuals can also be used for the log-logistic regression model, which is a special case of the log-Burr XII regression model. For different parameter settings, sample sizes and censoring percentages, various simulation studies are performed and the empirical distribution of each residual is displayed and compared with the standard normal distribution. These studies suggest that the residual analysis usually performed in normal linear regression models can be straightforwardly extended to the modified martingale-type residual in log-Burr XII regression models with censored data.

A log-extended Weibull regression model

A bathtub-shaped failure rate function is very useful in survival analysis and reliability studies. The well-known lifetime distributions do not have this property. For the first time, we propose a location-scale regression model based on the logarithm of an extended Weibull distribution which has the ability to deal with bathtub-shaped failure rate functions. We use the method of maximum likelihood to estimate the model parameters and some inferential procedures are presented. We reanalyze a real data set under the new model and the log-modified Weibull regression model. We perform a model check based on martingale-type residuals and generated envelopes and the statistics AIC and BIC to select appropriate models. (C) 2009 Elsevier B.V. All rights reserved.

Log-modified Weibull regression models with censored data: Sensitivity and residual analysis

This paper proposes a regression model considering the modified Weibull distribution. This distribution can be used to model bathtub-shaped failure rate functions. Assuming censored data, we consider maximum likelihood and Jackknife estimators for the parameters of the model. We derive the appropriate matrices for assessing local influence on the parameter estimates under different perturbation schemes and we also present some ways to perform global influence. Besides, for different parameter settings, sample sizes and censoring percentages, various simulations are performed and the empirical distribution of the modified deviance residual is displayed and compared with the standard normal distribution. These studies suggest that the residual analysis usually performed in normal linear regression models can be straightforwardly extended for a martingale-type residual in log-modified Weibull regression models with censored data. Finally, we analyze a real data set under log-modified Weibull regression models. A diagnostic analysis and a model checking based on the modified deviance residual are performed to select appropriate models. (c) 2008 Elsevier B.V. All rights reserved.

On estimation and influence diagnostics for zero-inflated negative binomial regression models

The zero-inflated negative binomial model is used to account for overdispersion detected in data that are initially analyzed under the zero-Inflated Poisson model A frequentist analysis a jackknife estimator and a non-parametric bootstrap for parameter estimation of zero-inflated negative binomial regression models are considered In addition an EM-type algorithm is developed for performing maximum likelihood estimation Then the appropriate matrices for assessing local influence on the parameter estimates under different perturbation schemes and some ways to perform global influence analysis are derived In order to study departures from the error assumption as well as the presence of outliers residual analysis based on the standardized Pearson residuals is discussed The relevance of the approach is illustrated with a real data set where It is shown that zero-inflated negative binomial regression models seems to fit the data better than the Poisson counterpart (C) 2010 Elsevier B V All rights reserved

Regression models for grouped survival data: Estimation and sensitivity analysis

In this study, regression models are evaluated for grouped survival data when the effect of censoring time is considered in the model and the regression structure is modeled through four link functions. The methodology for grouped survival data is based on life tables, and the times are grouped in k intervals so that ties are eliminated. Thus, the data modeling is performed by considering the discrete models of lifetime regression. The model parameters are estimated by using the maximum likelihood and jackknife methods. To detect influential observations in the proposed models, diagnostic measures based on case deletion, which are denominated global influence, and influence measures based on small perturbations in the data or in the model, referred to as local influence, are used. In addition to those measures, the local influence and the total influential estimate are also employed. Various simulation studies are performed and compared to the performance of the four link functions of the regression models for grouped survival data for different parameter settings, sample sizes and numbers of intervals. Finally, a data set is analyzed by using the proposed regression models. (C) 2010 Elsevier B.V. All rights reserved.

Dietary lysine requirement of juvenile pacu Piaractus mesopotamicus (Holmberg, 1887)

Lysine is the reference essential amino acid in fish feeds and usually the most limiting amino acid in feedstuffs. The dietary lysine requirement of juvenile pacu Piaractus mesopotamicus (4.3 g) was determined using five isonitrogenous (32% CP) test diets containing graded levels of lysine (0.9, 1.17, 1.44, 1.69 and 1.96% of dry diet) fed three times a day to four groups of 18 fish for 74 days. Growth, body composition, nutrient retention and hematological parameters of pacu were analyzed. Analysis of variance showed that all growth performance parameters were significantly affected by dietary treatments. The lysine requirements estimated using regression analysis for maximum weight gain and feed efficiency were 1.45 and 1.51% of dry diet, respectively. Nitrogen retention efficiency increased with increasing levels of dietary lysine up to 1.43% (p<0.05). Whole-body protein increased (p<0.05) and whole-body lipid decreased (p<0.05) with increasing dietary lysine level. Thus, the lysine requirement of juvenile pacu was estimated as being 1.4-1.5% of dry diet or 4.4-4.7% of dietary protein. (c) 2009 Elsevier B.V. All rights reserved.

Short communication: Evaluation of an on-farm test to estimate somatic cell count

The objective of this study was to compare the results of an on-farm test, named Somaticell, with results of electronic cell counting and for milk somatic cell count (SCC) among readers. The Somaticell test correctly determined the SCC in fresh quarter milk samples. Correlation between Somaticell and electronic enumeration of somatic cells was 0.92 and. coefficient 0.82. Using a threshold of 205,000 cells/mL, the sensitivity and specificity for determination of intramammary infections were 91.3 and 96.0%, respectively. The SCC was greater for milk samples from which major mastitis pathogens were recovered. Minor variation among readers was observed and most likely associated with the mixing procedure. However, the final analysis indicated that this variation was not significant and did not affect the amount of samples classified as having subclinical mastitis. The on-farm test evaluated in this study showed adequate capacity of determining SCC on quarter milk samples and may be considered as an alternative for on-farm detection of subclinical mastitis.

A Log-Linear Regression Model for the Beta-Weibull Distribution

We introduce the log-beta Weibull regression model based on the beta Weibull distribution (Famoye et al., 2005; Lee et al., 2007). We derive expansions for the moment generating function which do not depend on complicated functions. The new regression model represents a parametric family of models that includes as sub-models several widely known regression models that can be applied to censored survival data. We employ a frequentist analysis, a jackknife estimator, and a parametric bootstrap for the parameters of the proposed model. We derive the appropriate matrices for assessing local influences on the parameter estimates under different perturbation schemes and present some ways to assess global influences. Further, for different parameter settings, sample sizes, and censoring percentages, several simulations are performed. In addition, the empirical distribution of some modified residuals are displayed and compared with the standard normal distribution. These studies suggest that the residual analysis usually performed in normal linear regression models can be extended to a modified deviance residual in the proposed regression model applied to censored data. We define martingale and deviance residuals to evaluate the model assumptions. The extended regression model is very useful for the analysis of real data and could give more realistic fits than other special regression models.

Test procedure for variable rate fertilizer on coffee

The objective was to develop and test a procedure for applying variable rates of fertilizers and evaluate yield response in coffee (Coffea arabica L.) with regard to the application of phosphorus and potassium. The work was conducted during the 2004 season in a 6.4 ha field located in central Sao Paulo state. Two treatments were applied with alternating strips of fixed and variable rates during the whole season: one following the fertilizing procedures recommended locally, and the other based on a grid soil sampling. A prototype pneumatic fertilizer applicator was used, carrying two conveyor belts, one for each row. Harvesting was done with a commercial harvester equipped with a customized volumetric yield monitor, separating the two treatments. Data were analyzed based on geostatistics, correlations and regressions. The procedure showed to be feasible and effective. The area that received fertilizer applications at a variable rate showed a 34% yield increase compared to the area that received a fixed rate. The variable rate fertilizer resulted in a savings of 23% in phosphate fertilizer and a 13% increase in potassium fertilizer, when compared to fixed rate fertilizer. Yield in 2005, the year after the variable rate treatments, still presented residual effect from treatments carried out during the previous cycle.

A split-pot experiment with sorghum to test a root water uptake partitioning model

Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality.

Potassium Soil Test Calibration for Lowland Rice on an Inceptisol

Potassium (K) plays an important role in many physiological and biochemical processes in plants and its adequate use is an important issue for sustainable economic crop production. Soil test-based K fertilizer recommendations are very limited for lowland rice (Oryza sativa L.) grown on Inceptisols. The objective of this study was to calibrate K soil testing for the response of lowland rice (cv. Ipagri 109) to added K. A field experiment was conducted in the farmers` field in the municipality of Lagoa da Confusao, State of Tocantins, central Brazil. The K rates used were 0, 125, 250, 375, 500, and 625 kg K ha-1 applied as broadcast and incorporated during sowing of the first rice crop. Rice responded significantly to K fertilization during 2 years of experimentation. Maximum grain yield of about 6,000 kg ha-1 was obtained with 57 mg K kg-1 soil in the first year and with 30 mg K kg-1 in the second year. This indicated that at low levels of K in the soil, nonexchangeable K was available for plant growth. Potassium use efficiency designated as agronomic efficiency (kg grain produced/kg K applied) decreased significantly in a quadratic fashion with increasing K level in the soil. Agronomic efficiency had a significantly linear association with grain yield. Hence, improving agronomic efficiency with management practices can improve rice yield.

Paclitaxel associated with cholesterol-rich nanoemulsions promotes atherosclerosis regression in the rabbit

A cholesterol-rich nanoemulsion (LDE) that resembles LDL binds to the LDL receptors and after injection into the blood stream may concentrate in cells with LDL receptor overexpression, as occurs in neoplasias and other proliferative processes. Thus, LDE can be used as vehicle to target drugs against those cells. The current study was designed to verify in rabbits whether LDE concentrates in the lesioned rabbit artery and whether a paclitaxel derivative, paclitaxel oleate, associated to LDE could reduce the atherosclerotic lesions. Sixteen male New Zealand rabbits were fed a 1% cholesterol diet for 60 days. Starting from day 30 under cholesterol feeding, eight animals were treated with four weekly intravenous injections of LDE-paclitaxel (4 mg/kg) and eight with four weekly intravenous saline solution injections for additional 30 days. On day 60, the animals were sacrificed for analysis. The uptake of LDE labeled with [C-14]-cholesteryl oleate by the aortic arch of cholesterol-fed rabbits was twice as much that observed in animals fed only regular chow. LDE-paclitaxel reduced the lesion areas of cholesterol-fed animals by 60% and intima-media ratio fourfold and inhibited the macrophage migration and the smooth muscle cell proliferation and invasion of the intima. LDE-paclitaxel treatment had no toxicity. In conclusion, LDE-paclitaxel produced pronounced atherosclerosis regression without toxicity and has shown remarkable potential in cardiovascular therapeutics. (c) 2008 Published by Elsevier Ireland Ltd.

Investigation of the Performance of the Disintegration Test for Dietary Supplements

The aim of this study was to investigate how beaker size, basket assembly, use of disk, and immersion medium impact the disintegration time of dietary supplements. The disintegration times were determined for five tablet and two capsule products. A two-station disintegration tester was used with Apparatus A or Apparatus B as described in the United States Pharmacopeia (USP) chapters, < 701 > and < 2040 >. Two beakers complying with the harmonized specifications were used, one with a volume of 1,000 mL and one with a 1,500-mL volume. The disintegration data were analyzed using ANOVA for the following factors: beaker size, equipment (App A and B) and condition (with/without disk). Two tablet products were not sensitive to any changes in the test conditions or equipment configurations. One product was only partially sensitive to the test conditions. The other products showed impact on the disintegration time for all test conditions. The results revealed that these tablet products might pass or fail current USP disintegration requirements depending on the equipment configuration. Similar results were obtained for the two investigated capsule formulations. One product might fail current USP disintegration requirements if the large beaker was used, but might pass the disintegration requirements when the small beaker was used. Hydroxy propyl methyl cellulose capsules were mostly influenced if sodium instead of a potassium buffer was used as the immersion medium. The results demonstrate that the current harmonized ICH specifications for the disintegration test are insufficient to make the disintegration test into reliable test for dietary supplements.

QSAR Modeling of a Set of Pyrazinoate Esters as Antituberculosis Prodrugs

Tuberculosis is an infection caused mainly by Mycobacterium tuberculosis. A first-line antimycobacterial drug is pyrazinamide (PZA), which acts partially as a prodrug activated by a pyrazinamidase releasing the active agent, pyrazinoic acid (POA). As pyrazinoic acid presents some difficulty to cross the mycobacterial cell wall, and also the pyrazinamide-resistant strains do not express the pyrazinamidase, a set of pyrazinoic acid esters have been evaluated as antimycobacterial agents. In this work, a QSAR approach was applied to a set of forty-three pyrazinoates against M. tuberculosis ATCC 27294, using genetic algorithm function and partial least squares regression (WOLF 5.5 program). The independent variables selected were the Balaban index (I), calculated n-octanol/water partition coefficient (ClogP), van-der-Waals surface area, dipole moment, and stretching-energy contribution. The final QSAR model (N = 32, r(2) = 0.68, q(2) = 0.59, LOF = 0.25, and LSE = 0.19) was fully validated employing leave-N-out cross-validation and y-scrambling techniques. The test set (N = 11) presented an external prediction power of 73%. In conclusion, the QSAR model generated can be used as a valuable tool to optimize the activity of future pyrazinoic acid esters in the designing of new antituberculosis agents.