Distribution of lipids in non-lamellar phases of their mixtures

We consider a model of lipids in which a head group, characterized by its volume, is attached to two flexible tails of equal length. The phase diagram of the anhydrous lipid is obtained within self-consistent field theory, and displays, as a function of lipid architecture, a progression of phases: body-centered cubic, hexagonal, gyroid, and lamellar. We then examine mixtures of an inverted hexagonal forming lipid and a lamellar forming lipid. As the volume fractions of the two lipids vary, we find that inverted hexagonal, gyroid, or lamellar phases are formed. We demonstrate that the non-lamellar forming lipid is found preferentially at locations which are difficult for the lipid tails to reach. Variations in the volume fraction of each type of lipid tail are on the order of one to ten per cent within regions dominated by the tails. We also show that the variation in volume fraction is correlated qualitatively with the variation in mean curvature of the head-tail interface.Comment: 10 pages, 12 figures (better figures are available upon request), to appear in J. Chem. Phy

The effects of railway investments in a polycentric city

This paper analyses the effect of railway investment on land prices and land use in a polycentric city under various regulatory regimes of land markets. The introduction of a faster mode of transport (train), accessible in discrete locations leads to an extended city size. The stations of the “fast” mode attract dense residential settlements. As a result, the average residential and commercial land rents increase in both the competitive and segmented land market situations, as compared with the “slow” unimodal transport case. When rail investments only serve one particular centre, this leads to the growth of the advantaged centre at the expense of the other centre. Generally speaking, investment in the fast mode results in city growth and increase in rent receipts. However the effect of the investment for individual centres and their corresponding residential areas depends on the underlying land market assumptions and the level of investment. Distorted land markets lead to increases in commercial rents, but this is more than off-set by the decrease in residential land rent

Choice of departure station by railway users

This paper applies a multinomial logit model to the choice of a departure railway station by Dutch railway passengers. This is a relevant theme since about 50% of Dutch railway passengers do not travel via the nearest railway station. The passengers’ choices for departure stations are aggregated at the four digit postal code area level. We applied three functional forms for the underlying systematic utility of a station, namely a linear effect of attributes, cross effect of distance and frequency of service, and a translog formulation on distance and frequency of train services. With 3,498 post code areas and 360 railway stations our analysis found consistent effect sizes for distance, frequency of service, intercity status of the station and the presence of park-and-ride facility on the choice of departure station. The effect of distance on the choice of a departure station declines smoothly. The effect of frequency of service is relatively small compared to the effect of distance. A frequency of service increase by a hundred trains per day is equivalent to being 600 m closer to the station. The Intercity status of the station plays the biggest role in the choice of departure station. It has an equivalent effect of a change in 2 km distance or about a frequency of service of 300 trains per day. In addition, the presence of park-and-ride facility in the station poses a sizable effect in the departure station choice. In most cases its effect reaches about 35% of the intercity status effect

Professionalising purchasing organisations : towards a purchasing development model

How does purchasing develops as a discipline over time in large international organisations? What are the drivers and enablers behind the development of purchasing? Is there an ideal growthpath for purchasing in organisations? These subjects are discussed in this paper by, firstly, providing an overview of current literature and analysing the models which have been published in management literature. Based on our analysis we propose an integrated framework which may help practitioners in developing their future courses of action with regard to purchasing and supply strategy and organisation. Currently, this framework is tested through empirical research