Effect of Different Factors on the Service Life of Concrete Structures in Chloride Environment: A Parametric Study - Part Two

In this paper, the effect of different factors on the service life of reinforced concrete structures in marine environments is investigated through a parametric study. The considered case for the study was the two- dimensional diffusion problem. By solving the selected model for corrosion initiation by Finite Element Method, it has been concluded that, corrosion initiates at corner bars before side bars. Also, concrete elements subjected to two-dimensional diffusion are more susceptible to corrosion initiation than elements subjected to one-dimensional diffusion. Moreover, increase in water to cement ratio by 12.5%-50% in range 0.20-0.40 reduces the service life by 6.2%-31%, and by 5.3%-16.9% for the range 0.40-0.60. And, the increase in concrete cover in the range of 20-40 mm by 12.5% - 50% increases the service life by 5.1%-18.8%, and in the range of 35-60 mm by 2.9%-10.3%. The addition of fly ash and blast-furnace slag increased the service life by 6.35%-69.7% due to increase of age factor by 25%-200%. Furthermore, the addition of silica fume by 5%-15% increases the service life by 21.7%-81.2%. Regarding the environmental factors, increasing of temperature by 25%-75% reduces service life by 4.7%-12.75%, and reducing of relative humidity by 25%-50% increases the life by 17.5%-90.4%.are also given

Effect of Different Factors on the Service Life of Concrete Structures in Chloride Environments: A Parametric Study – Part One

This paper presents a comprehensive parametric study to determine the effect of different factors on the service life of reinforced concrete structures in chloride-laden environment. A model for corrosion initiation is selected and solved numerically by Finite Element Method for one-dimensional diffusion problem. It has been found that increase in water to cement ratio by 12.5%-50% in range of 0.20-0.40reduces the service life by 8%-35%, and by 7.35%-30.5% for the range 0.40-0.60. Also, the increase in concrete cover in the range of 20-35 mm by 14%-42%increases the service life by 8.1%-25.8%, and in the range of 35-60 mm by 7.7%-21.8%.Regarding mineral admixtures, the addition of fly ash and blast-furnace slag resulted in enhances the service life by 8%-70.7% due to increase of age factor by 25%-200%. Moreover,the addition of silica fume by 5%-15% increases the service life by 25.5%-80.6%.Finally, the rise of temperature by 25%-75% reduces the service life by 6.45%-18.7%, and the reduction of relative humidity by 25%-50% increases the life by 21.2%-89%. These values are based on a conservative approach and tend to guide the practice engineer on how these parameters affect service life of concrete structures

The structure of the infinite models in integer programming

The infinite models in integer programming can be described as the convex hull of some points or as the intersection of halfspaces derived from valid functions. In this paper we study the relationships between these two descriptions. Our results have implications for corner polyhedra. One consequence is that nonnegative, continuous valid functions suffice to describe corner polyhedra (with or without rational data)

Mikrosfere ropinirol hidroklorida za polagano oslobađanje: Utjecaj procesnih parametara

An emulsion solvent evaporation method was employed to prepare microspheres of ropinirole hydrochloride, a highly water soluble drug, by using ethylcellulose and PEG with the help of 32 full factorial design. The microspheres were made by incorporating the drug in a polar organic solvent, which was emulsified using liquid paraffin as an external oil phase. Effects of various process parameters such as viscosity of the external phase, selection of the internal phase, surfactant selection and selection of stirring speed were studied. Microspheres were evaluated for product yield, encapsulation efficiency and particle size. Various drug/ethylcellulose ratios and PEG concentrations were assayed. In vitro dissolution profiles showed that ethylcellulose microspheres were able to control release of the drug for a period of 12 h.Mikrosfere ropinirol hidroklorida, ljekovite tvari vrlo dobro topljive u vodi, pripravljene su metodom isparavanja otapala, koristeći etilcelulozu i PEG te 32 potpuno faktorijalno dizajniranje. Mikrosfere su pripravljene na sljedeći način: otopina ljekovite tvari u polarnom organskom otapalu emulgirana je s tekućim parafinom kao vanjskom uljnom fazom. Ispitivan je utjecaj različitih procesnih parametara poput viskoznosti vanjske faze, vrste interne faze i površinski aktivne tvari te brzine miješanja. Za pripravljene mikrosfere određeno je iskorištenje, učinkovitost inkapsuliranja i veličina čestica. Isprobavani su različiti odnosi ljekovite tvari i etilceluloze te koncentracija PEG-a. In vitro pokusi su pokazali da je oslobađanje ljekovite tvari kontrolirano tijekom 12 h

PHB-PEO electrospun fiber membranes containing chlorhexidine for drug delivery applications

Fiber meshes of poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate)/poly(ethylene oxide) (PHB/PEO) with different concentrations of chlorhexidine (CHX) were prepared by electrospinning for assessment as a polymer based drug delivery system. The electrospun fibers were characterized at morphological, molecular and mechanical levels. The bactericidal potential of PHB and PHB/PEO electrospun fibers, with and without CHX, was investigated against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by disk diffusion susceptibility tests. Electrospun fibers containing CHX exhibited bactericidal activity. PHB/PEO-1%CHX displayed higher CHX release levels and equivalent antibacterial activity when compared to PHB/PEO with 5 and 10 wt% CHX. Bactericidal performance of samples with 1 wt% CHX was assessed by Colony Forming Units (CFU), where reductions of 100% and 99.69% against E. coli and S. aureus were achieved, respectively.This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011 and PEST-C/QUI/UIO686/2011. The authors also thank funding from Matepro - Optimizing Materials and Processes", ref. NORTE-07-0124-FEDER-000037", co-funded by the "Programa Operacional Regional do Norte" (ON.2 - O Novo Norte), under the "Quadro de Referencia Estrategico Nacional" (QREN), through the "Fundo Europeu de Desenvolvimento Regional" (FEDER). D.M.C, JP and VS thanks the FCT for the, SFRH/BD/82411/2011, SFRH/BD/64901/2009 and SFRH/BPD/63148/2009 grants respectively. The authors also thank support from the COST Action MP1003, 2010 'European Scientific Network for Artificial Muscles' and to the COST Action MP1206 'Electrospun Nano-fibres for Bio inspired Composite Materials and Innovative Industrial Applications'. The authors also thank prof. Jose Luis Gomez Ribelles from the Unversidad Politecnica de Valencia, Spain, for interesting discussions on these issues

Estimação não-parametrica de volatilidade em modelos continuos

Orientador : Aluisio PinheiroDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação CientificaMestradoMestre em Estatístic

Effective Rheology of Bubbles Moving in a Capillary Tube

We calculate the average volumetric flux versus pressure drop of bubbles moving in a single capillary tube with varying diameter, finding a square-root relation from mapping the flow equations onto that of a driven overdamped pendulum. The calculation is based on a derivation of the equation of motion of a bubble train from considering the capillary forces and the entropy production associated with the viscous flow. We also calculate the configurational probability of the positions of the bubbles.Comment: 4 pages, 1 figur

A QUESTÃO DE ASPECTO NOS TEMPOS VERBAIS EM INGLÊS

Os tempos verbais em inglês são problemáticos para os aprendizes brasilieros. Este texto enfatiza o que subjaz aos tempos verbais em português e contrasta os resultados obtidos com a importância do aspecto na escolha dos tempos, especialmente os tempos do passado, em inglês. Algumas das implicações pragmáticas dessas diferenças são também discutidas. Palavras-chave: tempos verbais, aspecto verbal, ensino-aprendizagem de língua