Evaluation of the characteristics of a viscoelastic material from creep analysis using the universal viscoelastic model. I. Isolation of the elastic component designated as the “Projected Elastic Limit”

In a preceding publication this author introduced a new universal viscoelastic model to describe a definitive relationship between constant strain rate, creep, and stress relaxation analysis for viscoelastic polymeric compounds. One extremely important characteristic of this new model is that it also characterizes secondary creep very well. Because secondary creep is the linear portion of creep after the completion of primary creep, then a straight line with a slope and an intercept can describe secondary creep. To effectively define a straight line in the secondary creep region it was found necessary to obtain averages of the instantaneous slope and the instantaneous intercept strain by averaging over a series of equally spaced data points in the secondary slope region. Most importantly, this average intercept strain was found to be independent of creep stress and creep time. This means that all the secondary creep straight lines must pass through the same intercept creep strain for all creep stresses. The results presented in this study strongly indicate that this secondary creep intercept strain is independent of creep stress and creep time, and appears to increase as the value of the efficiency of yield energy dissipation decreases. Because a decrease in the efficiency of yield energy dissipation, n, appears to correlate with an increase in the elastic solid like character of a material, then it appears that this secondary creep intercept strain should be a direct measure of the strain that the material can survive to retain its full elastic character. Therefore, this secondary creep intercept strain has been designated as the “Projected Elastic Limit” of a given viscoelastic material. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2923–2936, 2003     

Expert judgement on the long term possibilities of conventional emission abatement technologies for passenger cars

Topics in Catalysis - This paper presents the results of a quantitatively substantiated “expert judgement” concerning the potential for further reduction of the exhaust emissions of...     

Theory and application of Agricultural Innovation Platforms for improved irrigation scheme management in Southern Africa

Abstract

Many small-scale irrigation systems are characterized by low yields and deteriorating infrastructure. Interventions often erroneously focus on increasing yields and rehabilitating infrastructure. Small-scale irrigation systems have many of the characteristics of complex socio-ecological systems, with many different actors and numerous interconnected subsystems. However, the limited interaction between the different subsystems and their agents prevents learning and the emergence of more beneficial outcomes. This article reports on using Agricultural Innovation Platforms to create an environment in which irrigation scheme actors can engage, experiment, learn and build adaptive capacity to increase market-related offtake and move out of poverty.     

Stability analysis of bilinear systems under aperiodic sampled-data control

This note considers the problem of local stability of bilinear systems with aperiodic sampled-data linear state feedback control. The sampling intervals are time-varying and upper bounded. It is shown that the feasibility of some linear matrix inequalities (LMIs), implies the local asymptotic stability of the sampled-data system in an ellipsoidal region containing the equilibrium. The method is based on the analysis of contractive invariant sets, and it is inspired by the dissipativity theory. The results are illustrated by means of numerical examples.     

Continuous-time norm-constrained Kalman filtering

This paper considers continuous-time state estimation when part of the state estimate or the entire state estimate is norm-constrained. In the former case continuous-time state estimation is considered by posing a constrained optimization problem. The optimization problem can be broken up into two separate optimization problems, one which solves for the optimal observer gain associated with the unconstrained state estimates, while the other solves for the optimal observer gain associated with the constrained state estimates. The optimal constrained state estimate is found by projecting the time derivative of an unconstrained estimate onto the tangent space associated with the norm constraint. The special case where the entire state estimate is norm-constrained is briefly discussed. The utility of the filtering results developed are highlighted through a spacecraft attitude estimation example. Numerical simulation results are included.     

Hygrothermal aging of rubber‐modified and mineral‐filled dicyandiamide‐cured DGEBA epoxy resin. III. Dielectric spectroscopy investigation

The effects of moisture absorption on the dielectric properties of a rubber‐modified, mineral‐filled, epoxy resin based on the diglycidyl ether of bisphenol A cured with dicyandiamide are reported. Samples of the resin were aged by immersing in deionized water, or 5% w/w NaCl solution, at elevated temperatures. Dielectric measurements were carried out over the frequency range 10^?1 to 6 × 10⁵ Hz. A featureless dielectric spectrum was observed with both real and imaginary dielectric permittivity increasing with the amount of absorbed water. The change in the dielectric properties with absorption of water was independent of presence of salt, temperature of exposure, and aging history, although a hysteresis of the hydration–dehydration process was observed at low frequencies. Two types of absorbed water were observed—water molecularly dispersed within the epoxy matrix and clustered water in spherical microcavities. The time dependence of the real dielectric permittivity measured at 10 kHz was found to closely resemble that of the water absorption, which allowed the activation energy of diffusion to be calculated from both dielectric and gravimetric data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1011–1024, 2002; DOI 10.1002/app.10368     

Formation of Azobenzenes and Azoxybenzenes from the Aqueous Reactions of Anilines and Ozone

Azobenzenes and azoxybenzenes are two of the products identified from the aqueous reaction of anilines with ozone. Aniline concentration and functional groups on the benzene ring of aniline affected the amount of azobenzenes and azoxybenzenes formed; (1) decreasing the aniline concentration significantly increased azobenzene formation, and (2) electron-withdrawing groups increased the formation of its related azobenzene and azoxybenzene, whereas electron-donating groups had the opposite effect.     

Chemistry of hydrogen sulphide under coal liquefaction conditions: 1. Modelling hydrogen transfer catalysis

The work reported here represents initial attempts to develop a complete kinetic and mechanistic understanding of the reaction chemistry of H₂S under coal liquefaction conditions, using both model systems and coal. Hydrogen sulphide was found to promote/catalyse the transfer of hydrogen from tetralin to 2-hydroxyquinoline (2-HOQ). The presence of H₂S can increase the rate of hydrogen transfer from tetralin to 2-HOQ by a factor of 10 compared with the same reaction run in the absence of H₂S. The energy of activation for hydrogen transfer was found to decrease by ≈5 kcal mol⁻¹ in the presence of H₂S. The presence of H₂S was also found to promote loss of oxygen from 2-HOQ to form small amounts of quinoline. No evidence of CC or CN bond cleavage in 2-HOQ was noted under any of the reaction conditions studied. These results suggest that the presence of H₂S reduces the temperatures necessary to promote effective hydrogen transfer from tetralin by 50–75 °C. Moreover, they imply that similar effects occur in H₂S-promoted coal liquefaction.     

Transient measurements of adsorption and diffusion in H-ZSM-5 membranes

A transient permeation method presented here not only determines the adsorption and diffusion properties of the pores that are the transport pathways through zeolite membranes, but nondestructively estimates the effective thickness of the membrane. Transient responses of the permeate concentration to step changes in the feed were measured on two H-ZSM-5 tubular membranes and modeled assuming Maxwell-Stefan diffusion and Langmuir adsorption. The adsorption isotherms determined from these transient measurements at 298 K of N₂ and CO₂ were nearly identical to those measured by calorimetry on H-ZSM-5 powders. The CH₄ isotherm at 298 K was similar to isotherms measured by calorimetry and gravimetric techniques on Na-ZSM-5 and silicalite powders. The similarity of the isotherms indicates that transport of these light gases occurs mainly through zeolite pores. The Maxwell-Stefan diffusion coefficients D_MS depended on concentration and were higher for higher feed partial pressures. Average D_MS values for the two membranes were 7.5, 5 and 1.5×10⁻¹⁰ m²/s for N₂, CH₄, and CO₂, respectively; these are in the same range and order as diffusion coefficients measured in zeolite crystals.     

Surface hydrolysis of filaments based on poly(trimethylene terephthalate) spun at high spinning speeds

The surface alkaline hydrolysis of fibers made from poly(trimethylene terephthalate) (PTT) was studied after extruding the polymer at high spinning speeds from 2000 to 6000 m/min and heat setting in the range of temperatures from 100 to 180°C. Fiber weight loss increased with an increasing heat‐setting temperature but it was also dependent on the spinning speed. Some of the partially hydrolyzed fibers had a well‐developed, hydrophilic surface, and pore size in the range of 0.69 to 1.20 μm. The optimum reaction and morphological conditions for increasing porosity in PTT fibers depends on spinning speed and heat‐setting temperature. A temperature of 180°C is the upper limit for heat‐setting PTT filaments but seems to be the most effective for making porous fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1724–1730, 2004