The Influence of Surface Chemistry on the Rheology and Flow of Flocculated Particulate Suspensions

Abstract

The role of the surface chemistry of particles in controlling the rheology of flocculated particulate suspensions is discussed. The case is developed for the measurement of the shear yield stress of a suspension of alumina particles and a theoretical interpretation of the yield stress is presented which is able to describe the effect of particle size distribution, solid loading, pH and hence, electrokinetics of the suspension. Scaling of the data to the maximum yield stress at a given volume fraction provides a means of removing particle size and volume fraction related effects and gives information as to the mode of failure in yielding of suspensions and the mode of action of molecular additives.     

Remote sensing of tidal chlorophyll-a variations in estuaries

Simultaneous acquisition of surface chlorophyll-a concentrations for 39 samples from boats and Daedalus 1260 Multispectral Scanner data from a U-2 aircraft was conducted in the northern reaches of San Francisco Bay on 28 August 1980. These data were used to develop regression models for predicting surface chlorophyll-a concentrations over the study area for ebb-tide (8.40 a.m. P.D.T. (Pacific Daylight Time)) and flood-tide (3.10 p.m. P.D.T.) conditions. After selection of a single ‘best fitting’ model for both morning and afternoon data sets, the chlorophyll-a concentration was predicted for ebb and flood tide for the entire study area at approximately 40m × 40m resolution. The predicted spatial display of chlorophyll-a revealed a localized area of high phytoplankton biomass that has been inferred from field surveys and appears to be a common summer phenomenon.

Knowledge of the distribution of phytoplankton and the location of this zone of high biomass is valuable in establishing management policies for this ecologically important estuary. Furthermore, the techniques used here may provide an alternative cost-effective method for assessing water-quality conditions and they may prove useful for studying spatial variations (patchiness) and seasonal variations in phytoplankton biomass in other estuaries and coastal waters.     

CONTROL OF STORAGE‐RELATED PHYSIOLOGICAL DISORDERS OF “D’ANJOU” PEARS BY INTEGRATED REDUCED DOSAGE OF ETHOXYQUIN AND LOW OXYGEN TREATMENTS1

A 1000‐p.p.m. ethoxyquin drench containing 528 p.p.m. thiobendazol (TBZ) fungicide prior to controlled atmosphere (CA) storage effectively controlled the development of superficial scald (SS) for 1 month regular air (RA) storage following 5 months CA storage. The preharvest drench was not effective in controlling the development of SS in fruit returned to RA storage following 7 months CA storage. Application of a 1750‐p.p.m. ethoxyquin line spray (without TBZ) following 5 months CA storage effectively extended the control of SS to 2 months under RA conditions. The 1750 p.p.m. ethoxyquin line spray was effective in controlling SS for 1 month RA storage following an additional 2 months CA storage period. This represents a 36% reduction in the amount of ethoxyquin currently used on fruit stored for short periods of time. Minor, noncommercial amounts of pithy brown core (PBC) developed during storage, demonstrating that 1% O ₂ and 1% CO ₂ in a flow‐through system can be safely utilized for the storage of pears. Growing location (Oregon vs. Washington) made no difference in the sensitivity to CO ₂ injury and packing and handling damage.     

Volatile Flavor Components from Boiled Crayfish (Procambarus clarkii) Tail Meat

The volatile flavor components of boiled red swamp crayfish (Procambarus clarkii) tail meat were characterized by a combination of dynamic headspace concentration on a porous polymer trap, high resolution gas chromatography, mass spectrometry and chromatography-coupled aroma sniffing evaluation. A total of 70 volatile compounds in many different chemical classes were identified and reported for the first time in crayfish tail meat. Various components gave green grassy, woody, buttery, metallic, or sulfur-like aroma characteristics. Most of the sensory characteristics of the individual components in the aromagram agreed well with the identification of the chemical structures eluted within the corresponding chromatographic period. However, several pleasant nutty, meaty and salty-meaty areas in the gas chromatographic aromagram remained unidentified.     

EVALUATION OF SWEET POTATO CULTIVARS AND HEATING METHODS FOR CONTROL OF MALTOSE PRODUCTION, VISCOSITY AND SENSORY QUALITY

Two varieties of sweet potato were subjected to four cooking temperature‐time combinations. A fifth treatment involved adding maltose syrup. Raw comminuted sweet potato mash and cooked sweet potato puree were evaluated for total solids, alcohol insoluble solids, commonly occurring sugars, viscosity (puree only) and for starch gelatinization temperatures. The uncooked Owairaka Red variety was higher in total solids and in alcohol insoluble solids than the Toka Toka Gold. With the exception of the cooked puree with added maltose, baking at 200C resulted in puree with the highest maltose levels. A very fast cooking procedure tended to result in puree with lower levels of maltose and high viscosity. Sensory studies revealed that the Owairaka Red variety produced puree with more viscous and adhesive mouth feel. It was concluded that cooking alone could not be used to optimize both maltose production and viscosity.     

Characterization of New Volatile Compounds in the Neutral Fraction of Roasted Beef Flavor

Volatile flavor compounds were isolated from 190 lb of roasted eye round beef. The neutral fraction of the flavor isolate was subjected to extensive gas chromatographic fractionation and the pure fractions obtained were identified by GC-mass spectrometry. A total of 67 compounds were reported to be new constituents in beef flavor.     

Inhibition of Lipid Oxidation during Processing of Washed, Minced Atlantic Mackerel

An antioxidative system that was designed to maintain heme iron reduced, nonheme iron as an inactive chelate, and provide free radical scavenging in the aqueous and lipid phases, was most effective when added early in the processing of washed, minced mackerel muscle. Mince prepared from mackerel dark muscle showed greater propensity to oxidize than did the mince from light muscle. Washed mince from light muscle in the presence of the antioxidative system showed no loss of odor quality during 24 wk at -20°C. Postmortem age of the mackerel muscle had little effect on initial odor quality of the washed mince.     

A simulation clock-based solution to the frequency domain experiment indexing problem

Frequency domain experiments (FDEs) were introduced to perform system sensitivity analysis for factor screening in complex simulations. Since then, FDEs have been used in simulation optimization, gradient estimation and several other research areas. Central to all FDEs is the Fourier analysis of a sampled data sequence. The choice of an appropriate oscillation index and associated sampling index for the sampled data sequence has been a much researched topic now known in the FDE literature as the indexing problem. In this paper we address the indexing problem by providing some general guidelines on the selection of the oscillation index and considering the implementation of two different indices: the continuous global simulation clock time and an inherently discrete index such as the job index in a simple queuing system. We show that the choice of a discrete oscillation index has to be made in an application-dependent manner and does not generalize well to different discrete-event simulation scenarios. In contrast, because the notion of time underlies all discrete-event simulations, the global simulation clock time is a natural choice for an FDE indexing scheme. Two different schemes for the global simulation clock time are presented. The results are illustrated via different scenarios commonly found in simulations of queuing networks and manufacturing systems.