Observations of classical cepheids

The observations of classical Cepheids are reviewed. The main progress that has been made is summarized and some of the problems yet to be solved are discussed. The problems include color excesses, calibration of color, duplicity, ultraviolet colors, temperature-color relations, mass discrepancies, and radius determination

Generalized Multivariate Extreme Value Models for Explicit Route Choice Sets

This paper analyses a class of route choice models with closed-form probability expressions, namely, Generalized Multivariate Extreme Value (GMEV) models. A large group of these models emerge from different utility formulas that combine systematic utility and random error terms. Twelve models are captured in a single discrete choice framework. The additive utility formula leads to the known logit family, being multinomial, path-size, paired combinatorial and link-nested. For the multiplicative formulation only the multinomial and path-size weibit models have been identified; this study also identifies the paired combinatorial and link-nested variations, and generalizes the path-size variant. Furthermore, a new traveller's decision rule based on the multiplicative utility formula with a reference route is presented. Here the traveller chooses exclusively based on the differences between routes. This leads to four new GMEV models. We assess the models qualitatively based on a generic structure of route utility with random foreseen travel times, for which we empirically identify that the variance of utility should be different from thus far assumed for multinomial probit and logit-kernel models. The expected travellers' behaviour and model-behaviour under simple network changes are analysed. Furthermore, all models are estimated and validated on an illustrative network example with long distance and short distance origin-destination pairs. The new multiplicative models based on differences outperform the additive models in both tests

How ions distribute in a drying porous medium: A simple model

Salt crystallization at surfaces is an important problem for buildings and monuments. We do not consider the formation of salt crystals as such, but focus on transport properties of ions in a drying porous medium. We deal with the first phase of the drying process, where the water is still uniformly distributed throughout the medium. An approximate model is presented, which accounts for both convection and diffusion. It is shown that the key parameter is the Peclet number at the evaporating surface, PehL/D, where h, L, , and D are the drying rate, sample size, porosity, and diffusion constant, respectively. When Pe1 (diffusion dominates over convection) the ions remain uniformly distributed throughout the system. Strong accumulation at the evaporating surface occurs for Pe1 (convection dominates over diffusion). Crossover behavior is found for Pe1. Therefore, it is likely that the first crystals will be formed both in the bulk and at the interfaces of the material when Pe1. For high values of Pe the density peak at the evaporating surface will reach the saturation concentration long before it is reached in the bulk of the material. As a consequence, the salt starts to crystallize at the interfaces

Evacuation plan evaluation: Assessment of vehicular evacuation schemes by means of an analytical dynamic traffic model

An evacuation model is posed, combining a dynamic travel demand component, an adaptive travel choice behaviour component, and a dynamic network loading component. The travel demand component considers the primary choice facing the endangered residents, whether to participate in the evacuation, and if so, when to depart. The travel choice behaviour component considers the secondary choice facing the evacuees, where to seek refuge and by which route to travel towards this safe destination. The network loading component considers both the dynamic traffic and hazard conditions, and propagates the evacuees through the infrastructure network. The proposed model can act on a broad spectrum of hazards, as it uses general features to compute the effects of the hazard on the evacuation. Furthermore, the model structure enables the assessment of various categories of evacuation, ranging from voluntary over recommended to mandatory. And, the behavioural responses of the evacuees towards evacuation instructions are modelled, such that instructions can be followed fully, followed in part, or rejected completely. An illustrative example of a hypothetical evacuation shows the principles and possibilities of the posed evacuation model

On the metallicity gradient of the Galactic disk

Aims: The iron abundance gradient in the Galactic stellar disk provides fundamental constraints on the chemical evolution of this important Galaxy component. However the spread around the mean slope is, at fixed Galactocentric distance, larger than estimated uncertainties. Methods: To provide quantitative constraints on these trends we adopted iron abundances for 265 classical Cepheids (more than 50% of the currently known sample) based either on high-resolution spectra or on photometric metallicity indices. Homogeneous distances were estimated using near-infrared Period-Luminosity relations. The sample covers the four disk quadrants and their Galactocentric distances range from ~5 to ~17 kpc. Results: A linear regression over the entire sample provides an iron gradient of -0.051+/-0.004 dex/kpc. The above slope agrees quite well, within the errors, with previous estimates based either on Cepheids or on open clusters covering similar Galactocentric distances. However, once we split the sample in inner (Rg < 8 kpc) and outer disk Cepheids we found that the slope (-0.130+/-0.015 dex/kpc) in the former region is ~3 times steeper than the slope in the latter one (-0.042+/-0.004 dex/kpc). We found that in the outer disk the radial distribution of metal-poor (MP, [Fe/H]<-0.02 dex) and metal-rich (MR) Cepheids across the four disk quadrants does not show a clear trend when moving from the innermost to the external disk regions. We also found that the relative fractions of MP and MR Cepheids in the 1st and in the 3rd quadrant differ at 8 sigma (MP) and 15 sigma (MR) level.Comment: 6 pages, 6 figures, A&A accepte

The influence of the pore structure on the moisture transport in lime plaster-brick systems as studied by NMR

This paper presents an experimental analysis of the porous structure and drying kinetics of lime-based plasters and plaster-brick systems using different methods. The effect of adding a water-repellent admixture (linseed oil) to the plasters was also evaluated. Nuclear Magnetic Resonance (NMR) was used to measure moisture profiles during drying of mono-material plaster specimens and of specimens constituted by the same plasters applied on fired-clay brick. NMR transverse relaxation time was used to examine the pore water distribution. The NMR moisture profiles showed that the drying behaviour of the water-repellent mono-plasters differs slightly from the reference, but when applied on brick, it significantly hinders the drying of the substrate. The results indicated that the addition of linseed oil to the lime plaster has negatively influenced the bonding process and created an hydraulic resistivity for the moisture to flow from the brick to the plaster during drying. This phenomena was mainly atributed to three factors: i) hydrophobization of part of the mortar pores; ii) the development of air bubbles related to entrained air during the mixing process; and iii) the mismatch between the physical-chemical properties of both systems, namely the different pore network and surface energy, which seems to affect the interpenetration of both porous layers.</p

Water and salt transport in plaster/substrate systems

The transport of salt and water during drying has been studied in systems consisting of a substrate covered with either one or two plaster layers. The drying behaviour of these systems was modelled with invasion percolation (IP) algorithms. The model outcomes were compared with experimental results obtained with Nuclear Magnetic Resonance (NMR). It was found that drying behaviour of the plaster layers was strongly influenced by the properties of the substrate. When the substrate has the widest pores, the plaster layers stay wet while the substrate dries out. As a consequence most salt, present in the substrate, moves to the plaster layers and accumulates at the external surface. In the case that the substrate has the smallest pores, the plaster layers dry out first. In this case salts also crystallize in the substrate. Further we have tried to make an accumulating plaster system consisting of two layers on top of a substrate, which would function purely on the basis of differences in pore sizes between the layers. The drying behaviour in the presence of pure water was as predicted by the model. However, in the case of a salt solution the salt modified the drying behaviour such that the accumulation properties of the system were reduced. Therefore, we conclude that for transporting systems tuning the pore-sizes of the layers suffices, but for accumulating systems it seems that additives , for example water repellents, have to be used

The Politics of Sustainability Transitions

info:eu-repo/semantics/publishe

The design of design: A systems approach to Integral Planning and spatial Design in the Dutch Southwest Delta

The mission-oriented turn as proposed in the 2009 Lund declaration advocates ‘research addressing the Grand Challenges of our time, moving beyond the current rigid thematic approaches’. This contribution exposes how such research is taken up in the Dutch ‘Integral Planning and Design in the southwest Delta’ (IPDD) project2, specifying the challenges of spatial design in the context of societal complexity and sustainability transitions. To redefine societies’ challenges is to redefine the task of spatial design, as well as its relations with governance and data management. One of the key questions raised in the project is therefore the following: In what way do the composed nature and complex dynamics of the delta areas on the one hand and the anticipation to future transformations and transitions on the other hand put new demands on the form, function and role of spatial design in reaching synchronized/integrated/interconnected delta area development