Lipase-catalyzed transesterification of phosphatidylcholine at controlled water activity

The incorporation of a free fatty acid into thesn-1 position of phosphatidylcholine by lipase-catalyzed transesterification was investigated. The thermodynamic water activity of both the enzyme preparation and the substrate solution was adjusted to the same value prior to the reaction. The reaction rate increased with increasing water activity but the yield of modified phosphatidylcholine decreased due to hydrolysis. By using a large excess of the free fatty acid (heptadecanoic acid), the hydrolysis reaction was slowed down, so a higher yield was obtained at a given degree of incorporation. The best results were obtained withRhizopus arrhizus lipase immobilized by adsorption on a polypropylene support. With this preparation, a yield of 60% and nearly 50% incorporation of heptadecanoic acid (100% incorporation in thesn-1 position) was obtained at a water activity of 0.064. The enzyme preparation had good operational stability and position specificity. Little incorporation (<1%) was observed in thesn-2 position, when almost all the fatty acid in thesn-1 position was exchanged.     

Tetranorsesquiterpenoids as Attractants of Yucca Moths to Yucca Flowers

Journal of Chemical Ecology - The obligate pollination mutualism between Yucca and yucca moths is a classical example of coevolution. Oviposition and active pollination by female yucca moths occur...     

Effects of carbon content and solidification rate on thermal conductivity of grey cast iron

The thermal conductivity or diffusivity of pearlitic grey irons with various carbon contents is investigated by the laser flash method. The materials are cast in controlled thermal environments and produced in three dissimilar cooling rates. The cooling rate together with the carbon content largely influence the thermal conductivity of grey iron. Linear relationships exist between the thermal conductivity and the carbon content, the carbon equivalent and the fraction of former primary solidified austenite transformed into pearlite. The work shows that optimal thermal transport properties are obtained at medium cooling rates. Equations describing the thermal conductivity of pearlite,solidified as pre-eutectic austenite, and the eutectic of grey iron are derived. The thermal conductivity of pearlitic grey iron is modeled at both room temperature and elevated temperature with good accuracy.     

Microstructural Investigation of Protective and Non-Protective Oxides on 11% Chromium Steel

FIB, SEM and STEM/EDX were used to investigate X20 stainless-steel samples exposed to dry O₂, or O₂ containing 40% H₂O, with a flow velocity of 0.5 cm/s or 5 cm/s, for 168 hr or 336 hr at 600°C. Thin protective Cr-rich (Cr,Fe)₂O₃ was maintained on the samples exposed to dry O₂, even after 336 hr, and on the sample exposed to O₂/H₂O mixture with the low-flow velocity (0.5 cm/s) for 168 hr. The oxide scale formed in the latter environment contained less Cr, due to Cr loss through CrO₂(OH)₂ evaporation. Breakaway oxidation occurred on the samples exposed in high-gas-flow velocity for shorter time (168 hr) or in low-gas-flow velocity (0.5 cm/s) for longer time (336 hr). The breakaway scales featured a two-layered structure: an outward-growing oxide “island” consisting of almost pure hematite (α-Fe₂O₃), and an inward-growing oxide “crater” consisting of (Cr,Fe)₃O₄. The transition from a thin protective (Cr,Fe)₂O₃ scale to a non-protective thick scale on this martensitic/ferritic steel originated locally and was followed by rapid oxide growth, resulting in a thick scale that covered the whole sample surface.     

The Inhibitive Effect of Traces of SO2 on the Oxidation of Iron

The oxidation of Fe was investigated at 500–700°C in the presence of O₂ with 0–1000 ppm SO₂. The exposures were carried out in a thermobalance and lasted for 24 h. The oxidized samples were investigated by grazing-angle XRD, SEM/EDX, GDOES and XPS. The rate of oxidation of pure iron is slowed down by traces of O₂ in O₂ below 600°C while SO₂ has no effect on oxidation rate at higher temperatures. Exposure to SO₂<600°C resulted in the formation of small amounts of sulfate at the gas/oxide interface. In addition, sulfur, probably sulfide, accumulated at the metal/oxide interface. The influence of SO₂ on oxidation rate is attributed to surface sulfate. The sulfur distribution in the scale is rationalized in terms of the thermodynamic stability of compounds in the Fe–O–S system. Exposure to SO₂ caused the formation of hematite whiskers.     

Improved Quality Output through Computer‐Based Training: An Automotive Assembly Field Study

In this article, two field experiments, conducted in an automotive assembly plant, evaluate how computer‐based training of operational sequences and related quality information can support the assembly performance of the operators. The experiments were performed during the launch of a new vehicle. A comparison was made of learning progress and quality performance between a reference group of operators that only had regular training and a test group for which some of the regular training was replaced with individual computer‐based training. Both quantitative measures of the quality output and questionnaires and observations were used to evaluate the effects of computer‐based training. The results show a clear positive difference in learning progress and improvements in quality output for the test group compared with the reference group. This combined with positive attitudes expressed by the operators and their team leaders shows that this type of training is an effective way to train operators during launches of new vehicles in automotive production.     

Discriminating Conduct: Deploying Systems to Support Awareness in Organizations

Alongside the emergence of the use of fieldwork studies for design there has been a discussion on how best these studies can inform system development. Concerns have been expressed as to whether their most appropriate contribution is a list of requirements or design recommendations. This article explores a recurrent issue that has emerged from fieldwork studies in Computer-Supported Cooperative Work, awareness, and with respect to a particular system development project discusses some of the implications for the development and deployment of one particular kind of technology—image recognition systems—in particular, organizational settings. In the setting in question—surveillance centers or operations rooms—staff utilize a range of practices to maintain awareness. Rather than extending field studies so that they can better assist design, it may be considered how workplace studies can contribute to a respecification of key concepts, like awareness, that are critical to an understanding of how technologies are used and deployed in everyday environments.     

Supporting Roadmapping of Quality Requirements

Would slightly better performance be significantly more valuable from a market perspective? Would significantly better performance be just slightly more expensive to implement? When dealing with performance, usability, reliability, and so on, you often end up in difficult trade-off analysis. You must take into account aspects such as release targets, end-user experience, and business opportunities. At the same time, you must consider what is feasible with the evolving system architecture and the available development resources.Quality requirements are of major importance in the development of systems for software-intensive products. To be successful, a company must find the right balance among competing quality attributes. How should you balance, for example, investments for improved usability of a mobile phone's phone book and better mobile positioning? In the context of quality requirements, decision making typically combines market considerations and design issues in activities such as roadmapping, release planning, and platform scoping. Models that address requirements prioritization in a market-driven context often emphasize functional aspects. (For a comparison of other relevant techniques with Quper, see the sidebar.) Quper provides concepts for reasoning about quality in relation to cost and value and can be used in combination with existing prioritization approaches.     

Plasma-derived proteins in airway defence, disease and repair of epithelial injury

One significant characteristic of the airway mucosa in vivo, that cannot easily be mimicked in vitro, is its microcirculation, which generates a highly dynamic, biologically active milieu of plasma-derived molecules that may pass to the airway lumen in vivo. New data on the mechanisms of airway mucosal exudation indicate that the protein systems of circulating plasma may contribute significantly to the biology and immunology of the lamina propria, its surface epithelium and the luminal surface, not only in injured airways, but also in airways that are activated but display no sign of oedema, epithelial disruption, or increased absorption capacity. We suggest that present knowledge of the mechanisms of plasma exudation, together with rapidly emerging information (not detailed herein) on receptors, target cells and cellular responses to the plasma-derived molecules, must be considered in any realistic model that investigates "immuno-inflammatory" mechanisms of the airway mucosa.     

Effect of set-up error on the dose across the junction of matching cranial-spinal fields in the treatment of medulloblastoma

PURPOSE: The effect of systematic and stochastic setup error on the dose delivered to the gap region for the three field radiation treatment of medulloblastoma is studied. The consequences of such setup error is discussed. METHODS AND MATERIALS: The treatment of medulloblastoma is typically a 3 field technique, in which two lateral cranial fields are matched with a spine field. The x-ray dose delivered to the region between the matched fields depends upon the gap size. The choice of the gap width between the cranial and spinal fields is controversial. It is currently a compromise between minimizing the risk of dose hot spots to the spine, and the associated clinical complications, as well as the magnitude of cold spots (underdosing) across the gap, with the associated risk of disease recurrence. In this paper, we examine the effect of gap width with a moving junction, referred to as "field feathering", on the dose across the field junction for a 6MV photon beam. In addition, we have studied 129 portal films and 40 simulation films to assess the accuracy and precision of patient setup during treatment with a plan involving feathered fields. Selected landmarks observable on both portal and simulation films were identified and the variation in the distances to the field edges measured. The distribution of patient setup error was convoluted with the beam profiles for a 6MV linac. These convoluted field edges were used obtain dose profiles across the gap region as a function of gap separation. The consequences for therapy are discussed. In addition, analysis of patient setup error on an alternative treatment involving beam modifiers to broaden the beam penumbra is discussed. RESULTS: The magnitude of the spatial stochastic and systematic setup error was determined to be approximately three and two millimeters respectively. The dosimetric consequences of patient setup error lead to over and under dosing in the spinal gap region for the three field technique. The degree of under or over dose depends on the nature and magnitude of the patient setup error. CONCLUSIONS: The effect of patient setup error can lead to significant dosimetric errors in the dose to the gap region depending on the magnitude of the setup errors. The effective over and under dose can be compensated by the use beams modifiers such as a beam spoiler or vibrating jaws.