Rheological behavior of binary aqueous solutions of poly(ethylene glycol) of 1500 g·mol-1 as affected by temperature and polymer concentration

The rheological behavior of poly(ethylene glycol) of 1500 g·mol -1(PEG1500) aqueous solutions with various polymer concentrations (w = 0.05, 0.10, 0.15, 0.20 and 0.25) was studied at different temperatures (T = 283.15, 288.15, 293.15, 298.15 and 303.15) K. The analyses were carried out considering shear rates ranging from (20 to 350) s-1, using a cone-and-plate rheometer under controlled stress and temperature. Classical rheological models (Newton, Bingham, Power Law, Casson, and Herschel-Bulkley) were tested. The Power Law model was shown suitable to mathematically represent the rheological behavior of these solutions. Well-adjusted empirical models were derived for consistency index variations in function of temperature (Arrhenius-type model; R2 > 0.96), polymer concentration (exponential model; R2 > 0.99) or the combination of both (R 2 > 0.99). Additionally, linear models were used to represent the variations of behavior index in the functions of temperature (R2 > 0.83) and concentration (R2 > 0.87). © 2013 American Chemical Society.

Influence of the concentration of polyols on the rheological and spectral characteristics of guar gum

Polyols are widely used as sugar substitutes and provide texture to foods. Guar gum has many applications in food industry such as increasing product viscosity and improving texture. Knowledge of rheological properties of gum/polyol systems is important to permit replacing sugar while maintaining product texture. In this work, rheological properties of 0.1, 0.5 and 1 g/100 g guar solutions containing 10 and 40 g/100 g of maltitol, sorbitol, or xylitol were studied. The behavior of these mixtures was evaluated by steady and oscillatory shear measurements, and after a freezing/thawing cycle. Apparent viscosity of guar solutions increased with addition of polyols and with the increase in their concentrations, except for 40 g/100 g sorbitol addition to 1 g/100 g guar gum, in which the apparent viscosity decreased. Addition of polyols also increased the dynamic moduli of the systems. In mixtures of guar with 40 g/100 g polyol, the phase angle (δ) was below unity, but was dependent on frequency, which is characteristic of concentrated solutions with a certain degree of structuring. FTIR spectroscopy was studied to provide information on possible interactions between guar gum and polyols. Analyses carried out after freezing/thawing showed no changes in the viscoelastic behavior of the solutions. © 2013 Elsevier Ltd.

Rheological, mechanical, and bioadhesive behavior of hydrogels to optimize skin delivery systems

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influence of the rheological behaviour of the lubricant on the appearance of pitting in elastohydrodynamic eegime

This paper analyses the influence of lubricant behaviour on the appearance of pitting. It attempts to study the effect of viscosity?pressure relation, compressibility, film thickness?roughness relation and friction coefficient on pitting failure of the contacting elements.To explain these effects, we first deal with the influence of the oil on the lubrication of the contact using elastohydrodynamic theory and secondly two multiaxial fatigue criteria are used, Crossland criterion and Dang Van criterion, to evaluate the influence of the rheology on the appearance of pitting. Finally, different applications are presented together with a discussion on the results obtained.

Concurrent multi-scale modeling of civil infrastructures for analyses on structural deterioration—Part I : Modeling methodology and strategy

This paper aims to develop the methodology and strategy for concurrent finite element modeling of civil infrastructures at the different scale levels for the purposes of analyses of structural deteriorating. The modeling strategy and method were investigated to develop the concurrent multi-scale model of structural behavior (CMSM-of-SB) in which the global structural behavior and nonlinear damage features of local details in a large complicated structure could be concurrently analyzed in order to meet the needs of structural-state evaluation as well as structural deteriorating. In the proposed method, the “large-scale” modeling is adopted for the global structure with linear responses between stress and strain and the “small-scale” modeling is available for nonlinear damage analyses of the local welded details. A longitudinal truss in steel bridge decks was selected as a case to study how a CMSM-of-SB was developed. The reduced-scale specimen of the longitudinal truss was studied in the laboratory to measure its dynamic and static behavior in global truss and local welded details, while the multi-scale models using constraint equations and substructuring were developed for numerical simulation. The comparison of dynamic and static response between the calculated results by different models indicated that the proposed multi-scale model was found to be the most efficient and accurate. The verification of the model with results from the tested truss under the specific loading showed that, responses at the material scale in the vicinity of local details as well as structural global behaviors could be obtained and fit well with the measured results. The proposed concurrent multi-scale modeling strategy and implementation procedures were applied to Runyang cable-stayed bridge (RYCB) and the CMSM-of-SB of the bridge deck system was accordingly constructed as a practical application.

Concurrent multi-scale modeling of civil infrastructures for analyses on structural deteriorating—Part II : Model updating and verification

This paper is a continuation of the paper titled “Concurrent multi-scale modeling of civil infrastructure for analyses on structural deteriorating—Part I: Modeling methodology and strategy” with the emphasis on model updating and verification for the developed concurrent multi-scale model. The sensitivity-based parameter updating method was applied and some important issues such as selection of reference data and model parameters, and model updating procedures on the multi-scale model were investigated based on the sensitivity analysis of the selected model parameters. The experimental modal data as well as static response in terms of component nominal stresses and hot-spot stresses at the concerned locations were used for dynamic response- and static response-oriented model updating, respectively. The updated multi-scale model was further verified to act as the baseline model which is assumed to be finite-element model closest to the real situation of the structure available for the subsequent arbitrary numerical simulation. The comparison of dynamic and static responses between the calculated results by the final model and measured data indicated the updating and verification methods applied in this paper are reliable and accurate for the multi-scale model of frame-like structure. The general procedures of multi-scale model updating and verification were finally proposed for nonlinear physical-based modeling of large civil infrastructure, and it was applied to the model verification of a long-span bridge as an actual engineering practice of the proposed procedures.

Integrating hardware and software information flow analyses

Security-critical communications devices must be evaluated to the highest possible standards before they can be deployed. This process includes tracing potential information flow through the device's electronic circuitry, for each of the device's operating modes. Increasingly, however, security functionality is being entrusted to embedded software running on microprocessors within such devices, so new strategies are needed for integrating information flow analyses of embedded program code with hardware analyses. Here we show how standard compiler principles can augment high-integrity security evaluations to allow seamless tracing of information flow through both the hardware and software of embedded systems. This is done by unifying input/output statements in embedded program execution paths with the hardware pins they access, and by associating significant software states with corresponding operating modes of the surrounding electronic circuitry.