A generalized modified Weibull distribution for lifetime modeling

A four parameter generalization of the Weibull distribution capable of modeling a bathtub-shaped hazard rate function is defined and studied. The beauty and importance of this distribution lies in its ability to model monotone as well as non-monotone failure rates, which are quite common in lifetime problems and reliability. The new distribution has a number of well-known lifetime special sub-models, such as the Weibull, extreme value, exponentiated Weibull, generalized Rayleigh and modified Weibull distributions, among others. We derive two infinite sum representations for its moments. The density of the order statistics is obtained. The method of maximum likelihood is used for estimating the model parameters. Also, the observed information matrix is obtained. Two applications are presented to illustrate the proposed distribution. (C) 2008 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.

Material properties and nondestructive evaluation of laminated veneer lumber (LVL) made from Pinus oocarpa and P. kesiya

This study aimed at evaluating the mechanical, physical and biological properties of laminated veneer lumber (LVL) made from Pinus oocarpa Schiede ex Schltdl (PO) and Pinus kesiya Royle ex Gordon (PK) and at providing a nondestructive characterization thereof. Four PO and four PK LVL boards from 22 randomly selected 2-mm thickness veneers were produced according to the following characteristics: phenol-formaldehyde (190 g/m(2)), hot-pressing at 150A degrees C for 45 min and 2.8 N/mm(2) of specific pressure. After board production, nondestructive evaluation was conducted, and stress wave velocity (v (0)) and dynamic modulus of elasticity (E (Md) ) were determined. The following mechanical and physical properties were then evaluated: static bending modulus of elasticity (E (M) ), modulus of rupture (f (M) ), compression strength parallel to grain (f (c,0)), shear strength parallel to glue-line (f (v,0)), shear strength perpendicular to glue-line (f (v,90)), thickness swelling (TS), water absorption (WA), and permanent thickness swelling (PTS) for 2, 24, and 96-hour of water immersion. Biological property was also evaluated by measuring the weight loss by Trametes versicolor (Linnaeus ex Fries) Pilat (white-rot) and Gloeophyllum trabeum (Persoon ex Fries.) Murrill (brown-rot). After hot-pressing, no bubbles, delamination nor warping were observed for both species. In general, PK boards presented higher mechanical properties: E (M) , E (Md) , f (M) , f (c,0) whereas PO boards were dimensionally more stable, with lower values of WA, TS and PTS in the 2, 24, and 96-hour immersion periods. Board density, f (v,0), f (v,90) and rot weight loss were statistically equal for PO and PK LVL. The prediction of flexural properties of consolidated LVL by the nondestructive method used was not very efficient, and the fitted models presented lower predictability.

Preparation and characterization of ethanol-treated silk fibroin dense membranes for biomaterials application using waste silk fibers as raw material

The possibility of producing valued devices from low cost natural resources is a subject of broad interest. The present study explores the preparation and characterization of silk fibroin dense membranes using waste silk fibers from textile processing. Morphology, crystallinity, thermal resistance and cytotoxicity of membranes as well as the changes on the secondary structure of silk fibroin were analyzed after undergoing treatment with ethanol. Membranes presented amorphous patterns as determined via X-ray diffraction. The secondary structure of silk fibroin on dense membranes was either random coil (silk I) or p-sheet (silk II), before and after ethanol treatment, respectively. The sterilized membranes presented no cytotoxicity to endothelial cells during in vitro assays. This fact stresses the material potential to be used in the fabrication of biomaterials, as coatings of cardiovascular devices and as membranes for wound dressing or drug delivery systems. (C) 2010 Elsevier Ltd. All rights reserved.

The influence of crucible material on the DSC thermal analysis compared to freeze-drying microscopy results

The aim of this study was to investigate the influence of different crucible materials on the thermal analysis of binary systems. The thermal properties of two distinct solutions were measured both by Differential Scanning Calorimetry (DSC) and freeze-drying microscopy and the results were compared. The glass transition of the maximally freeze-concentrate (T (g)`) and the eutectic melting temperature (T (eut)) were not influenced by the crucible material. However the heat of fusion (Delta H) involved during the T (eut) as well as the Delta C (p) involved during the T (g)` of the solutions were affected.

Use of diamond-like carbon with tungsten (W-DLC) films as biocompatible material

Diamond-like carbon (DLC), also known as amorphous hydrogenated carbon (a-C:H), are a class of materials with excellent mechanical, tribological and biological properties. When the DLC films are enhanced with other elements, all of these properties can be changed within a certain range. In this work, reactive magnetron sputtering was used to deposit W-DLC (hydrogenated tungsten carbide) films on Ti6A14V (implant material). Many films were made using pure tungsten (99.99%) target and different plasmas processes, with different ratio among argon and methane. It was possible to change the films composition (from pure amorphous carbon to carbon enhanced with tungsten) according to ratio of argon and methane plasma. Between all films processed, the carbon films enhanced with tungsten showed good results in the ""in vitro"" cytotoxicity testing. Raman spectroscopy was used to analyze the chemical bonds kinds and the chemical bonds quantities. The Rutherford Back Scattering (RBS) was used to analyze the films compositions. The chemical inertness was analyzed by scanning voltametry. W-DLC thin films obtained in these processes have low roughness, high chemical resistance, good adhesion and show a high biocompatibility, when compared with common DLC thin films. Hence we have concluded that the tungsten concentrations in the DLC films make an important role to improve the properties of the DLC layers. (C) 2007 Elsevier B.V. All rights reserved.

Re-examination of the anion derivatives of isoflavones by radical fragmentation in negative electrospray ionization tandem mass spectrometry: experimental and computational studies

This paper reports theoretical and experimental studies of gas-phase fragmentation reactions of four naturally occurring isoflavones. The samples were analyzed in negative ion mode by direct infusion in ESI-QqQ, ESI-QqTOF and ESI-Orbitrap systems. The MS/MS and MS(n) spectra are in agreement with the fragmentation proposals and high-resolution analyses have confirmed the formulae for each ion observed. As expected, compounds with methoxyl aromatic substitution have showed a radical elimination of center dot CH(3) as the main fragmentation pathway. A second radical loss (center dot H) occurs as previously observed for compounds which exhibit a previous homolytic center dot CH(3) cleavage (radical anion) and involves radical resonance to stabilize the anion formed. However, in this study we suggest another mechanism for the formation of the main ions, on the basis of the enthalpies for each species. Compounds without methoxy substituent dissociate at the highest energies and exhibit the deprotonated molecule as the most intense ion. Finally, energy-resolved experiments were carried out to give more details about the gas-phase dissociation reaction of the isoflavones and the results are in agreement with the theoretical approaches. Copyright (C) 2011 John Wiley & Sons, Ltd.

Development and Validation of a Simple Method for Routine Analysis of Ractopamine Hydrochloride in Raw Material and Feed Additives by HPLC

A simple method was optimized and validated for determination of ractopamine hydrochloride (RAC) in raw material and feed additives by HPLC for use in quality control in veterinary industries. The best-optimized conditions were a C8 column (250 x 4.6 mm id, 5.0 mu m particle size) at room temperature with acetonitrile-100 mM sodium acetate buffer (pH 5.0; 75 + 25, v/v) mobile phase at a flow rate of 1.0 mL/min and UV detection at 275 nm. With these conditions, the retention time of RAC was around 5.2 min, and standard curves were linear in the concentration range of 160-240 mu g/mL (correlation coefficient >= 0.999). Validation parameters, such as selectivity, linearity, limit of detection (ranged from 1.60 to 2.05 mu g/mL), limit of quantification (ranged from 4.26 to 6.84 mu g/mL), precision (relative standard deviation <= 1.87%), accuracy (ranged from 96.97 to 100.54%), and robustness, gave results within acceptable ranges. Therefore, the developed method can be successfully applied for the routine quality control analysis of raw material and feed additives.

Ca(2+) binding to c-state of adenine nucleotide translocase (ANT)-surrounding cardiolipins enhances (ANT)-Cys(56) relative mobility: A computational-based mitochondrial permeability transition study

The oxidation of critical cysteines/related thiols of adenine nucleotide translocase (ANT) is believed to be an important event of the Ca(2+)-induced mitochondrial permeability transition (MPT), a process mediated by a cyclosporine A/ADP-sensitive permeability transition pores (PTP) opening. We addressed the ANT-Cys(56) relative mobility status resulting from the interaction of ANT/surrounding cardiolipins with Ca(2+) and/or ADP by means of computational chemistry analysis (Molecular Interaction Fields and Molecular Dynamics studies), supported by classic mitochondrial swelling assays. The following events were predicted: (i) Ca(2+) interacts preferentially with the ANT surrounding cardiolipins bound to the H4 helix of translocase, (ii) weakens the cardiolipins/ANT interactions and (iii) destabilizes the initial ANT-Cys(56) residue increasing its relative mobility. The binding of ADP that stabilizes the conformation ""m"" of ANT and/or cardiolipin, respectively to H5 and H4 helices, could stabilize their contacts with the short helix h56 that includes Cys(56), accounting for reducing its relative mobility. The results suggest that Ca(2+) binding to adenine nucleotide translocase (ANT)-surrounding cardiolipins in c-state of the translocase enhances (ANT)-Cys(56) relative mobility and that this may constitute a potential critical step of Ca(2+)-induced PTP opening. (C) 2009 Elsevier B.V. All rights reserved.

Accelerated Stability and Moisturizing Capacity of Emulsions Presenting Lamellar Gel Phase Obtained from Brazilian Natural Raw Material

Oil-in-water (O/W) emulsions containing gel phase were developed with cupuassu and/or cocoa butter from Brazilian ecosystem. They were subjected to storage advanced stability tests (SAST) and to in vivo corneometry evaluation. The evaluated emulsions showed great performance in the evaluated conditions considering that no significant variation was observed. The moisturizing potential was advantageous even without the moisturizing active. The formulation was considered a good cosmetic moisturizing cream and a promise as a drug carrier.

A Computational Framework for Institutional Agency

This paper provides a computational framework, based on Defeasible Logic, to capture some aspects of institutional agency. Our background is Kanger-Lindahl-P\"orn account of organised interaction, which describes this interaction within a multi-modal logical setting. This work focuses in particular on the notions of counts-as link and on those of attempt and of personal and direct action to realise states of affairs. We show how standard Defeasible Logic can be extended to represent these concepts: the resulting system preserves some basic properties commonly attributed to them. In addition, the framework enjoys nice computational properties, as it turns out that the extension of any theory can be computed in time linear to the size of the theory itself.

Substrate-inhibited kinetics with catalyst deactivation in an isothermal CSTR. II. Multiple pseudosteady states and reactor failure

Analytical expressions are derived for the time and magnitude of failure of an isothermal CSTR with substrate-inhibited kinetics, caused by slow catalyst deactivation under three types of parallel and series mechanisms. Reactors operating at high space velocity are found to be most susceptible to early failure and poisoning by product is more dangerous than by reactant. The magnitude of the jump across steady states depends solely on the Langmuir-Hinshelwood kinetic parameters and a detailed analysis of reactor behavior during the jump itself is given.

Two dimensional computational fluid dynamic models for waste stabilisation ponds

Traditional waste stabilisation pond (WSP) models encounter problems predicting pond performance because they cannot account for the influence of pond features, such as inlet structure or pond geometry, on fluid hydrodynamics. In this study, two dimensional (2-D) computational fluid dynamics (CFD) models were compared to experimental residence time distributions (RTD) from literature. In one of the-three geometries simulated, the 2-D CFD model successfully predicted the experimental RTD. However, flow patterns in the other two geometries were not well described due to the difficulty of representing the three dimensional (3-D) experimental inlet in the 2-D CFD model, and the sensitivity of the model results to the assumptions used to characterise the inlet. Neither a velocity similarity nor geometric similarity approach to inlet representation in 2-D gave results correlating with experimental data. However. it was shown that 2-D CFD models were not affected by changes in values of model parameters which are difficult to predict, particularly the turbulent inlet conditions. This work suggests that 2-D CFD models cannot be used a priori to give an adequate description of the hydrodynamic patterns in WSP. (C) 1998 Elsevier Science Ltd. All rights reserved.

A computational study of shock speeds in high-performance shock tubes

This paper describes U2DE, a finite-volume code that numerically solves the Euler equations. The code was used to perform multi-dimensional simulations of the gradual opening of a primary diaphragm in a shock tube. From the simulations, the speed of the developing shock wave was recorded and compared with other estimates. The ability of U2DE to compute shock speed was confirmed by comparing numerical results with the analytic solution for an ideal shock tube. For high initial pressure ratios across the diaphragm, previous experiments have shown that the measured shock speed can exceed the shock speed predicted by one-dimensional models. The shock speeds computed with the present multi-dimensional simulation were higher than those estimated by previous one-dimensional models and, thus, were closer to the experimental measurements. This indicates that multi-dimensional flow effects were partly responsible for the relatively high shock speeds measured in the experiments.