Atomic Energy of Canada Limited

About: Atomic Energy of Canada Limited is a company organization based out in Ottawa, Ontario, Canada. It is known for research contribution in the topics: Neutron & Zirconium alloy. The organization has 4845 authors who have published 4826 publications receiving 102951 citations.

What determines the thickness of a biological membrane.

Abstract: Membrane thickness is thought to play a key role in protein function. Thus understanding the cell's ability to modulate the thickness of its membranes is essential in elucidating the structure/function relationship in biological membranes. We have investigated the influence of cholesterol on the structure of "thin" (diC14:1PC) and "thick" (diC22:1PC) phospholipid bilayers using oriented multibilayers and small angle neutron diffraction. Neutron contrast variation was used to determine the structure factors and the distribution of water across the bilayers. We found that in response to cholesterol, bilayer thickness changed in a similar fashion in both systems. The thickening of bilayers was rationalized in terms of cholesterol's ordering effect on the lipid's acyl chains, which dominates over the other option of rectifying the hydrophobic mismatch, surprisingly even in the case of diC22:1PC and cholesterol.

Growth-curve analysis: a critical reevaluation

Abstract: Growth-curve analysis (Ricklefs 1967) has long enjoyed an ardent following. Recentlyß Brisbin et al. (1987) predicted a bright future for this methodology, but failed to address critical shortcomings of growthcurve analysis and of the Richards (1959) model in particular. They also completely ignored alternatives. Growth-curve analysis is a tool onlyß and not an end in itself. The main question is not which model to use, but whether to use growth-curve analysis at all. For many studies growth-curve analysis is inappropriateß and alternativesß such as simple observedgrowth statistics, may be more effective growth indicators. Although the Richards model with its variable sigmoid shape is intuitively attractiveß other simpler models can be superior for studying growth. There are many reasons growth-curve analysis may not be an ideal methodology. Growth-curve analysis is labor intensive because numerous data are required to satisfy models with several fitted parameters. For passerines, with their short nestling timeß this usually means daily measurement on a rigid schedule so that each nestling is always measured at about the same time. Alternatively, variable time must be taken into account during curve fitting. Growth-curve analysis requires numerous precise data. Small changes in only a single measurement can profoundly affect parameter estimates. Sensitivity depends on the type of model employed, however. High data requirements of growth-curve analysis can stress both parents and nestlings. Frequent disturbances can cause nest abandonment and conse-