A Two-Dimensional Approach to Systems Development

Abstract

Although many variables can contribute to the failure of a systems development project, the use of the traditional f one-dimensional systems development life cycle approach is often a major factor in the failure of such an effort This article describes an alternative method— the two-dimensional approach to systems development— and discusses why IS managers should consider adopting this new development approach.     

Inhibition of citral degradation in model beverage emulsions using micelles and reverse micelles

Citral is a flavour component that is widely used in the beverage, food, and fragrance industries. Citral chemically degrades over time in aqueous solutions due to acid catalysed and oxidative reactions, leading to loss of desirable flavour and the formation of off-flavours. We examined the influence of surfactant micelles (Tween 80) in the aqueous phase and reverse micelles (polyglycerol polyricinoleate, PGPR) in the oil phase on the oil–water partitioning and chemical degradation of citral in medium chain triglyceride oil-in-water emulsions. The percentage of citral in the aqueous phase of the emulsions increased with increasing Tween 80 concentration, which was attributed to its incorporation within surfactant micelles. The rate of citral degradation decreased as the Tween 80 concentration was increased from 1% to 5% w/w in both aqueous solutions and in emulsions, suggesting that citral was protected from degradation once it was incorporated into micelles. The presence of reverse micelles (5% or 10% w/w PGPR) in the oil droplets decreased the percentage of citral present within the aqueous phase of the emulsions, suggesting that citral was preferentially incorporated into the reverse micelles. In addition, the presence of reverse micelles increased the chemical stability of citral, possibly because a greater fraction remained within the oil droplets. These results show that micelle or reverse-micelle structures may be used to improve the chemical stability of citral in beverage emulsions.     

Inhibition of Ostwald ripening in model beverage emulsions by addition of poorly water soluble triglyceride oils

Beverage emulsions containing flavor oils that have a relatively high water-solubility are unstable to droplet growth due to Ostwald ripening. The aim of this study was to improve the stability of model beverage emulsions to this kind of droplet growth by incorporating poorly water-soluble triglyceride oils. High pressure homogenization was used to prepare a series of 5 wt% oil-in-water emulsions stabilized by modified starch that had different lipid phase compositions (orange oil : corn oil). Emulsions prepared using only orange oil as the lipid phase were highly unstable to droplet growth during storage, which was attributed to Ostwald ripening resulting from the relatively high water-solubility of orange oil. Droplet growth could be effectively inhibited by incorporating ≥ 10% corn oil into the lipid phase prior to homogenization. In addition, creaming was also retarded because the lipid phase density was closer to that of the aqueous phase density. These results illustrate a simple method of improving the physical stability of orange oil emulsions for utilization in the food, beverage, and fragrance industries.     

Electrical properties of composite gate oxides formed by rapidthermal processing

In this study, oxide stacks formed by combinations of rapid thermal chemical vapor deposition and rapid thermal oxidation have been investigated as gate dielectrics. This was achieved by performing various types of in situ rapid thermal oxidations both prior to and after oxide deposition to form composite stacked structures. The oxidation ambient and temperature was varied to study the effect on electrical properties such as mobility, leakage current, charge trapping, breakdown and hot carrier degradation. It was found that pre-oxidation prior to depositing an oxide results in a composite structure that greatly reduces the defect density by mismatching pores and weak spots in each film. The mobility behavior of these films was also found to be improved over as-deposited oxides. Post-deposition oxidation in O₂ and N₂O was also found to improve the mobility characteristics. Additionally, post-annealing in N₂ O was effective in improving the reliability of deposited oxides. These N₂O annealed films had low interface trap densities, improved high field mobility, very low charge trapping characteristics and enhanced resistance to hot carrier induced interface state generation. These improvements are attributed to 1) the presence of nitrogen at the interface and 2) to the reduction of nitrogen and hydrogen concentrations in the bulk of the oxide. The role of atomic oxygen during the post-anneal in N₂O is discussed along with differences in annealing ambients     

Interactions between display gain and task-induced stress in manual tracking.

"It is important for the human engineer to know how the performance of man-machine systems is affected by factors which stress or overload the human operator… . Five systems, all of which had the same dynamics but differed in display magnification, were employed. Operators were given considerable training on all five systems, after which they were required to control the systems under a series of stressful conditions. Performance was measured both in terms of system error and error at the display. The results indicated that stress increased error in all systems, but the order of merit of the various systems was unchanged by stress. The results are discussed in terms of their relevance to the study of man-machine systems. The pitfalls of purely psychological interpretations of the behavior of tracking systems are outlined." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nonlinear control of competitive mixed‐culture bioreactors via specific cell adhesion

A nonlinear control strategy is developed for competitive mixed‐culture bioreactors in which two cell populations compete for a common growth limiting substrate. A stream is periodically removed from the reactor, and the two cell populations are separated using specific cell adhesion. The steady state corresponding to the desired population fraction is stabilized by discarding faster growing cells and recycling slower growing cells to the reactor. The recycle loop must be operated periodically to allow regeneration of the adhesion column after each separation. As a result, the manipulated input is chosen as the sampling interval during which material is removed from the reactor. The nonlinear controller is designed using a simplified dynamic model that assumes continuous separation of the cell populations. The controller is implemented by calculating the sampling interval that leads to the same amount of material being removed from the reactor as that computed from the continuous control law. A nonlinear, closed‐loop observer is used to generate one‐time‐delay‐ahead predictions of the measured cell concentrations and the unmeasured substrate concentration. The efficacy of the proposed control strategy is evaluated via simulation.     

Investigating the effect of chemical ingredient modifications on the slow cook-off violence of ammonium perchlorate solid propellants on the laboratory scale

ABSTRACT

Rocket propellants that contain ammonium perchlorate (AP) often have a violent response during slow heating. Two laboratory tests have been developed to determine the reaction violence of these materials. The first test was the Combustion Rate Analysis of a Slowly Heated Propellant (CRASH-P) test, which used dynamic pressure sensors to quantify the violence of the reaction. The second test used x-rays to measure physical changes in the propellants before ignition and their reaction violence through the deformation speed of the sample container. For this study, four propellant formulation modification categories were investigated. The propellants were investigated for their reaction violence and sample expansion before ignition.     

Melanin synthesis is associated with changes in hyphopodial turgor, permeability, and wall rigidity in gaeumannomyces graminis var. graminis

Mycelia of Gaeumannomyces graminis var. graminis form large cells called hyphopodia with deeply lobed, melanized walls. Like appressoria produced by other pathogens, hyphopodia develop on hydrophobic surfaces, but it is not clear that hyphopodia function as platforms for host penetration. In appressoria, melanin synthesis is linked to the generation of enormous turgor pressures that provide the necessary force for plant penetration. In the present study, hyphopodial turgor was measured in a wild-type strain of G. graminis var. graminis, a mutant exhibiting constitutive synthesis of melanin (referred to as the dark mutant), and a melanin-deficient strain (thr). These experiments demonstrate that hyphopodia of the wild-type strain generate higher pressures than the dark mutant and that nonmelanized thr hyphopodia generate minuscule internal pressures. Melanization of the wall is also associated with an increase in its rigidity. These data correlate with differences in wall permeability consistent with a recent model for turgor generation by appressoria.