Freeze-Thaw Treatment of Membrane Concentrates Derived from Kraft Pulp Mill Operations

Freeze thaw was studied as a waste treatment method for concentration and volume reduction of contaminated waste concentrates that are derived from the use of membrane technology in the treatment of high strength Kraft pulp mill effluents. Unidirectional freezing experiments were conducted to simulate seminatural freezing, in which the independent variables—freezing rate, time frozen, storage temperature, concentration, liquid depth, thawing rate and method of thawing—were examined for their relative importance. Method of thawing followed by freezing rate, rate of thawing, storage temperature, and time frozen were identified as the most important independent variables that contribute significantly to treatment performance. Under ideal conditions, freeze thaw was shown to effectively concentrate and separate the constituent matter of alkaline, extraction-stage membrane concentrate to achieve color removals as high as 73% in the top 70% liquid fraction. The results suggest a new field of use for freeze thaw as a waste treatment process for the management of high strength liquid wastes amenable to mechanical coagulation by freezing.     

Fuel use and design analysis of improved woodburning cookstoves in the Guatemalan Highlands

This study examined the fuel use and design of an improved woodburning cookstove (plancha), in comparison to traditional cooking over an open woodfire. These cookstoves had been randomly introduced into population households in the Guatemalan Highlands that had previously used open woodfires. This research consisted of: (1) a 12-household Kitchen Performance Test (KPT) over a 4-day period and (2) single-day participant observation in five households. The KPT monitored fuel consumption and the number, age, and gender of people who were cooked for, while the participant observation was used to form a complete understanding of fuel use patterns and to examine the influence of stove condition and cooking behavior. In spite of fairly low variability in the fuel use data (coefficients of variation of about 0.34) the KPT did not show statistically significant differences in fuel use between the two cooking methods. It is possible that increased study power through a larger sample size may have resulted in a statistically significant difference in favor of the plancha, but it is doubtful that the size of the effect would be of any practical significance. Thus, although other studies have shown that the plancha is extremely effective in reducing indoor air pollution in the study area, the KPT did not indicate that it offered any benefits with respect to fuel use. Practical and experimental recommendations for future cookstove efficiency studies are presented, with directions for continued work in this area.     

Stress-strain response of a cast 319-T6 aluminum under thermomechanical loading

The stress-strain behavior of cast 319-T6 aluminum-copper alloys with three different secondary dendrite arm spacings (SDASs) was studied at high temperatures and under thermomechanical deformation, exposing marked cyclic softening. A two state-variable unified inelastic constitutive model proposed earlier was modified to describe the stress-strain responses of these alloys by considering the variation of hardening and recovery functions of back-stress and drag stress. The SDAS was incorporated in the model as a length-scale parameter, and the material constants were determined systematically from experiments on a cast 319-T6 aluminum with small and large SDASs. The capabilities of the constitutive model were checked by the comparisons of simulations to experiments in the small-strain regime (<0.005). The results show that the model provides successful simulations for material response after thermal exposure at high temperature and cyclic transient stress-strain behavior. The causes of mechanical behaviors at the macro scale are discussed based on microstructural changes during thermal exposure.     

SC and pass transistor combined circuits

The pass-transistor structure provides a powerful tool for the implementation of binary and multiple-valued logic (MVL). Circuit realisation of any general MVL function using literals, MAX and MIN is easy. However, the resulting circuits have certain limitations. A combination of pass transistors (PT) with switched-capacitor (SC) circuits is shown to provide useful improvements.<>     

Discussion of “miscibility gap in Fe-Ni-Al and Fe-Ni-Al-Co Systems” and “Role of Alloying elements in phase decomposition in alnico magnet alloys”

Metallurgical and Materials Transactions A -