The exponentiated generalized gamma distribution with application to lifetime data

A four-parameter extension of the generalized gamma distribution capable of modelling a bathtub-shaped hazard rate function is defined and studied. The beauty and importance of this distribution lies in its ability to model monotone and non-monotone failure rate functions, which are quite common in lifetime data analysis and reliability. The new distribution has a number of well-known lifetime special sub-models, such as the exponentiated Weibull, exponentiated generalized half-normal, exponentiated gamma and generalized Rayleigh, among others. We derive two infinite sum representations for its moments. We calculate the density of the order statistics and two expansions for their moments. The method of maximum likelihood is used for estimating the model parameters and the observed information matrix is obtained. Finally, a real data set from the medical area is analysed.

Definition of priority areas for forest conservation through the ordered weighted averaging method

The general objective of this study was to evaluate the ordered weighted averaging (OWA) method, integrated to a geographic information systems (GIS), in the definition of priority areas for forest conservation in a Brazilian river basin, aiming at to increase the regional biodiversity. We demonstrated how one could obtain a range of alternatives by applying OWA, including the one obtained by the weighted linear combination method and, also the use of the analytic hierarchy process (AHP) to structure the decision problem and to assign the importance to each criterion. The criteria considered important to this study were: proximity to forest patches; proximity among forest patches with larger core area; proximity to surface water; distance from roads: distance from urban areas; and vulnerability to erosion. OWA requires two sets of criteria weights: the weights of relative criterion importance and the order weights. Thus, Participatory Technique was used to define the criteria set and the criterion importance (based in AHP). In order to obtain the second set of weights we considered the influence of each criterion, as well as the importance of each one, on this decision-making process. The sensitivity analysis indicated coherence among the criterion importance weights, the order weights, and the solution. According to this analysis, only the proximity to surface water criterion is not important to identify priority areas for forest conservation. Finally, we can highlight that the OWA method is flexible, easy to be implemented and, mainly, it facilitates a better understanding of the alternative land-use suitability patterns. (C) 2008 Elsevier B.V. All rights reserved.

Spatio-temporal modeling of agricultural yield data with an application to pricing crop insurance contracts

This article presents a statistical model of agricultural yield data based on a set of hierarchical Bayesian models that allows joint modeling of temporal and spatial autocorrelation. This method captures a comprehensive range of the various uncertainties involved in predicting crop insurance premium rates as opposed to the more traditional ad hoc, two-stage methods that are typically based on independent estimation and prediction. A panel data set of county-average yield data was analyzed for 290 counties in the State of Parana (Brazil) for the period of 1990 through 2002. Posterior predictive criteria are used to evaluate different model specifications. This article provides substantial improvements in the statistical and actuarial methods often applied to the calculation of insurance premium rates. These improvements are especially relevant to situations where data are limited.

Parametric and nonparametric statistical modelling of crop yield: implications for pricing crop insurance contracts

This article considers alternative methods to calculate the fair premium rate of crop insurance contracts based on county yields. The premium rate was calculated using parametric and nonparametric approaches to estimate the conditional agricultural yield density. These methods were applied to a data set of county yield provided by the Statistical and Geography Brazilian Institute (IBGE), for the period of 1990 through 2002, for soybean, corn and wheat, in the State of Paran. In this article, we propose methodological alternatives to pricing crop insurance contracts resulting in more accurate premium rates in a situation of limited data.

Effectiveness of the standard evaluation method for hydraulic nozzles employed in stored grain protection trials

In stored grains, smaller depositions and great variation with respect to theoretical insecticide doses are frequently found. The objective of this work was to study the effectiveness of the standard method (ISO 5682/1-1996) employed to evaluate hydraulic nozzles used in stored corn and wheat grain protection experiments. The transversal volumetric distribution and droplet spectrum of a model TJ-60 8002EVS nozzle were determined in order to calibrate a spraying system for an application rate of 5 L/t and to obtain theoretical concentrations of 10 and 0.5 mg/kg of fenitrothion and esfenvalerate, respectively. After treatment, the corn and wheat grains were processed and deposition was analyzed by gas chromatography. The type of grain did not have any influence on insecticide deposition and was dependent upon insecticide only. The insecticide deposits on the grains only reached 42.1 and 38.2% of the intended theoretical values for fenitrothion and esfenvalerate concentrations, respectively. These results demonstrate the ineffectiveness of the standard evaluation method for hydraulic nozzles employed in stored grain protection experiments.

Method development and optimization for the determination of selenium in bean and soil samples using hydride generation electrothermal atomic absorption spectrometry

The present investigation is the first part of an initiative to prepare a regional map of the natural abundance of selenium in various areas of Brazil, based on the analysis of bean and soil samples. Continuous-flow hydride generation electrothermal atomic absorption spectrometry (HG-ET AAS) with in situ trapping on an iridium-coated graphite tube has been chosen because of the high sensitivity and relative simplicity. The microwave-assisted acid digestion for bean and soil samples was tested for complete recovery of inorganic and organic selenium compounds (selenomethionine). The reduction of Se(VI) to Se(IV) was optimized in order to guarantee that there is no back-oxidation, which is of importance when digested samples are not analyzed immediately after the reduction step. The limits of detection and quantification of the method were 30 ng L(-1) Se and 101 ng L(-1) Se, respectively, corresponding to about 3 ng g(-1) and 10 ng g(-1), respectively, in the solid samples, considering a typical dilution factor of 100 for the digestion process. The results obtained for two certified food reference materials (CRM), soybean and rice, and for a soil and sediment CRM confirmed the validity of the investigated method. The selenium content found in a number of selected bean samples varied between 5.5 +/- 0.4 ng g(-1) and 1726 +/- 55 ng g(-1), and that in soil samples varied between 113 +/- 6.5 ng g(-1) and 1692 +/- 21 ng g(-1). (C) 2011 Elsevier B.V. All rights reserved.

Validated method for the quantification of artepillin-C in Brazilian propolis

Brazilian propolis contains several phenolic compounds among which 5 diprenyl-4-hydroxycinnamic acid (artepillin-C) is commonly found in areas where flora is rich in Baccharis species. The quantification of artepillin-C has become an important factor as an indicator of Brazilian propolis quality and the compound may be used as a chemical marker for quality control in exportating green propolis. This work was to validate the method and evaluate the content of artepillin-C from 33 samples collected in different Brazilian regions. The method used was HPLC with UV-vis detection and a reversed-phase C-18 Column. The validation parameters studied were: linearity, accuracy, precision, quantification and detection limits. The results obtained were: detection limit = 0.0036 mu g/mL, quantification limit = 0.012 mu g/mL, accuracy = 0.0064 and 0.078, recovery 98-102%. Artepillin-C content varied from 0 to 11% depending on the geographical origin. Propolis from the southeast region presented the highest level of artepillin-C (5.0-11.0%). Whist that from the northeast region did not show any artepillin-C. Copyright (C) 2008 John Wiley & Sons, Ltd.

Enzymatic-spectrophotometric determination of paraquat in urine samples: A method based on its toxic mechanism

Paraquat is a broad-spectrum contact herbicide that has been encountered worldwide in several cases of accidental, homicidal, and suicidal poisonings. The pulmonary toxicity of this compound is related to the depletion of NADPH in the pneumocytes, which is continuously consumed by the reduction/oxidation of paraquat and reductase enzyme systems in the presence of O(2) (redox cycling). Based on this mechanism, an enzymatic-spectrophotometric method was developed for the determination of paraquat in urine samples. The velocity of NADPH consumption was monitored at 340 nm, every 10 s during 15 min. The velocity of NADPH oxidation correlated with the paraquat levels found in samples. The enzymatic-spectrophotometric method showed to be sensitive, making possible the detection of paraquat in urine samples at concentrations as low as 0.05 mg/L.

Development and Characterization of L-Alanyl-L-Glutamine Containing Pellets employing Extrusion-Spheronization Method and Drying Process in Fluidized Bad Equipment.

Development and Characterization of L-Alanyl-L-Glutamine Containing Pellets employing Extrusion-Spheronization Method and Drying Process in Fluidized Bad Equipment"". In this work, five formulations of L-alanyl-L-glutamine (glutamine dipeptide) containing pellets with different drug concentration were developed and evaluated: F1 (9.07%); F2 (17.70%); F3 (27.98%); F4 (37.74%) e F5 (47.53%). Pellets were prepared by extrusion-spheronization method and, further, dried in fluidized bad equipment. The following assays were carried out with the batches obtained: granulometry, friability, true density and morphologic analysis. Between the five formulations evaluated, pellets obtained from F3 present best yield (75.80%), most uniform particle size distribution (89.67% of pellets with size in the range of 0.80 to 1.18), most high true density (2.1634 g/ml) and best aspect (1.0795 +/- 0.0410). Due to these features, pellets obtained from F3 were considered adequate to further polymeric coating process in order to produce a multiparticulate system to prolong L-alanyl-L-glutamine release.

Development of a Stability-Indicating LC Assay Method for Determination of Chloroquine

A simple and rapid development of a stability-indicating LC method for determination of chloroquine diphosphate in the presence of its hydrolysis, oxidative and photolysis degradation products is described. Stress testing showed that chloroquine diphosphate was degraded under basic conditions and by photolytic treatment but was stable under the other stress conditions investigated. Separation of the drug from its degradation products was achieved with a Nova Pack C18 column, 0.01 M PIC B7 and acetonitrile (40:60 v/v) pH 3.6, as mobile phase. Response was linear over the range 0.08-5.70 mu g mL(-1) (r = 0.996), with limits of detection and quantification (LOD and LOQ) of 0.17 and 0.35 mu g mL(-1), respectively.

Obtention and Evaluation of Inclusion Complexes of Furosemide with beta-ciclodextrin and hidroxipropil-beta-ciclodextrin: Effects on Drug`s Dissolution Properties

Obtention and Evaluation of Inclusion Complexes of Furosemide with beta-ciclodextrin and hidroxipropil-beta-ciclodextrin: Effects on Drug`s Dissolution Properties. The purpose of this study was to prepare, characterize and evaluate the dissolution behavior of inclusion complexes of furosemide with beta-cyclodextrin (beta-CD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD). Solid complexes of furosemide with P-CD and-HP-beta-CD were prepared by using a freeze-drying method. Physical mixtures were prepared for comparison. The inclusion complexes were characterized by differential scanning calorimetry (DSC), Infrared (IR) and dissolution test. ""In vitro"" dissolutions assays were performed at pH 1,2; pH 4,5 and pH 6,8 media for a 60 min period. Statistical analysis employing ANOVA and Tukey`s Test, for the dissolution efficiency values (ED%), showed that complexation of furosemide with both cyclodextrins improved significantly ED% of the drug in all tested media, suggesting a minor pH influence on dissolution properties of the drug.

Development and validation of a method for quantitative determination of econazole nitrate in cream formulation by capillary zone electrophoresis

A simple, fast, inexpensive and reliable capillary zone electrophoresis (CZE) method for the determination of econazole nitrate in cream formulations has been developed and validated. Optimum conditions comprised a pH 2.5 phosphate buffer at 20 mmol L(-1) concentration, +30 kV applied voltage in a 31.5 cm x 50 mu m I.D. capillary. Direct UV detection at 200 nm led to an adequate sensitivity without interference from sample excipients. A single extraction step of the cream sample in hydrochloric acid was performed prior to injection. Imidazole (100 mu g mL(-1)) was used as internal standard. Econazole nitrate migrates in approximately 1.2 min. The analytical curve presented a coefficient of correlation of 0.9995. Detection and quantitation limits were 1.85 and 5.62 mu g mL(-1), respectively. Excellent accuracy and precision were obtained. Recoveries varied from 98.1 to 102.5% and intra- and inter-day precisions, calculated as relative standard deviation (RSD), were better than 2.0%. The proposed CZE method presented advantageous performance characteristics and it can be considered suitable for the quality control of econazole nitrate cream formulations. (c) 2008 Elsevier B.V. All rights reserved.

Optimization of preservative system in ophthalmic suspension with dexamethasone and polymyxin B

A simplex-lattice statistical project was employed to study an optimization method for a preservative system in an ophthalmic suspension of dexametasone and polymyxin B. The assay matrix generated 17 formulas which were differentiated by the preservatives and EDTA (disodium ethylene diamine-tetraacetate), being the independent variable: X-1 = chlorhexidine digluconate (0.010 % w/v); X-2 = phenylethanol (0.500 % w/v); X-3 = EDTA (0.100 % w/v). The dependent variable was the Dvalue obtained from the microbial challenge of the formulas and calculated when the microbial killing process was modeled by an exponential function. The analysis of the dependent variable, performed using the software Design Expert/W, originated cubic equations with terms derived from stepwise adjustment method for the challenging microorganisms: Pseudomonas aeruginosa, Burkholderia cepacia, Staphylococcus aureus, Candida albicans and Aspergillus niger. Besides the mathematical expressions, the response surfaces and the contour graphics were obtained for each assay. The contour graphs obtained were overlaid in order to permit the identification of a region containing the most adequate formulas (graphic strategy), having as representatives: X-1 = 0.10 ( 0.001 % w/v); X-2 = 0.80 (0.400 % w/v); X-3 = 0.10 (0.010 % w/v). Additionally, in order to minimize responses (Dvalue), a numerical strategy corresponding to the use of the desirability function was used, which resulted in the following independent variables combinations: X-1 = 0.25 (0.0025 % w/v); X-2 = 0.75 (0.375 % w/v); X-3 = 0. These formulas, derived from the two strategies (graphic and numerical), were submitted to microbial challenge, and the experimental Dvalue obtained was compared to the theoretical Dvalue calculated from the cubic equation. Both Dvalues were similar to all the assays except that related to Staphylococcus aureus. This microorganism, as well as Pseudomonas aeruginosa, presented intense susceptibility to the formulas independently from the preservative and EDTA concentrations. Both formulas derived from graphic and numerical strategies attained the recommended criteria adopted by the official method. It was concluded that the model proposed allowed the optimization of the formulas in their preservation aspect.

Validation of an HPLC analytical method for determination of pancuronium bromide in pharmaceutical injections

Pancuronium bromide is used with general anesthesia in surgery for muscle relaxation and as an aid to intubation. A high performance liquid chromatographic method was fully validated for the quantitative determination of pancuronium bromide in pharmaceutical injectable solutions. The analytical method was performed on an amino column (Luna 150mm4.6mm, 5m). The mobile phase was composed of acetonitrile:water containing 50mmol L-1 of 1-octane sulfonic acid sodium salt (20:80v/v) with a flow rate of 1.0mL min-1 and ultraviolet (UV) detection at 210nm. The proposed analytical method was compared with that described in the British Pharmacopoeia.