Building effective models from sparse but precise data

A common approach in computational science is to use a set of of highly precise but expensive calculations to parameterize a model that allows less precise, but more rapid calculations on larger scale systems. Least-squares fitting on a model that underfits the data is generally used for this purpose. For arbitrarily precise data free from statistic noise, e.g. ab initio calculations, we argue that it is more appropriate to begin with a ensemble of models that overfit the data. Within a Bayesian framework, a most likely model can be defined that incorporates physical knowledge, provides error estimates for systems not included in the fit, and reproduces the original data exactly. We apply this approach to obtain a cluster expansion model for the Ca[Zr,Ti]O3 solid solution.Comment: 10 pages, 3 figures, submitted to Physical Review Letter

A tale of two charters

Charters are official commitments to quality and reform. Belgium introduced its Charter of the User of Public Services in 1993. The federal administration’s Copernicus reform began in 1999 and had a strong external outlook. It therefore may be considered as a second User Charter. In this article we focus on the administrative and political contingencies of the introduction of the two charters in Belgium. We show that actual administrative reform and political attention for administrative reform are distinct phenomena. Variations in political attention for reform depend on crises and on political realignment. Both charters were introduced in a period of disturbed relations between citizens and politics. The introduction of a User Charter and the launch of the Copernicus reform were definitely political events, and not merely administrative ones. A charter was needed to restore citizen-government relations. The charters, as pledges for reform, served as lightning rods for political discontent

A signaling perspective on bureaucratic encounters: How public officials interpret signals and cues

This article provides scholars studying frontline judgements an analytical framework—the signaling perspective—that could be used to examine how street‐level bureaucrats evaluate unobservable citizen‐client properties. It proposes to look not only at the kind of signals and cues officials gather, but also at the interpretive frames used to make sense of them. This offers a valuable contribution to the street‐level bureaucracy literature, which largely focuses on explaining discretionary decision making by looking at the influence of officials' personal preferences or client characteristics, but less on officials' interpretive frameworks to make sense of client characteristics. The analytical framework is illustrated by applying it to existing literature on trustworthiness judgements of social workers and police officers. Different interpretive frames were found from which frontline officials interpret citizen characteristics as signals. The article concludes by offering several avenues for future research.The politics and administration of institutional chang

First-principles study of ternary fcc solution phases from special quasirandom structures

In the present work, ternary Special Quasirandom Structures (SQSs) for a fcc solid solution phase are generated at different compositions, $x_A=x_B=x_C=\tfrac{1}{3}$ and $x_A=\tfrac{1}{2}$, $x_B=x_C=\tfrac{1}{4}$, whose correlation functions are satisfactorily close to those of a random fcc solution. The generated SQSs are used to calculate the mixing enthalpy of the fcc phase in the Ca-Sr-Yb system. It is observed that first-principles calculations of all the binary and ternary SQSs in the Ca-Sr-Yb system exhibit very small local relaxation. It is concluded that the fcc ternary SQSs can provide valuable information about the mixing behavior of the fcc ternary solid solution phase. The SQSs presented in this work can be widely used to study the behavior of ternary fcc solid solutions.Comment: 20 pages, 7 figure

Monitoring van kustbroedvogels in de SBZ-V ‘Kustbroedvogels te Zeebrugge-Heist’ en de westelijke voorhaven van Zeebrugge tijdens het broedseizoen 2013

This report describes the fluctuations in the number of breeding pairs in the Special Protected Area under the Bird Directive ‘Kustbroedvogels te Zeebrugge-Heist’ and in the western port of Zeebrugge. These are by far the most important breeding sites for coastal breeders in Belgium. The quality of the breeding sites and the foraging areas is discussed and advice is given for a better management of the colonies.The populations of terns (Sandwich, Common and Little Tern) and Black-headed Gulls have decreased strongly since 2008 and the breeding success was insufficient for a stable population size. In Zeebrugge all 3 tern species used to exceed the threshold of 1% of their respective biogeographic population considerably. In 2013 only the Common Tern reached this threshold. The decrease is due to persistent problems with land predators. Food availability seemed to play no role in this.Also some scarce species strongly declined in Zeebrugge. Crested Lark and Yellow-legged Gull have totally left the area and the number of Northern Wheatears was reduced to 1 pair in 2013. Also Mediterranean Gull and Kentish Plovers strongly declined during the past decade. Oystercatchers and Common Gull seemed to have stabilised at a level much lower than before. Only the population of Common Ringed Plover is rather stable at about 8 pairs.The populations of Herring and Lesser Black-backed Gulls also strongly declined in 2013. Where Lesser Black-backed gull still exceeds the 1% level (1.8% in 2013), the number of Herring Gulls dropped to 0.8% of the total biogeographic population. This decline is due to disturbance by foxes and a decreased availability of suitable nesting areas

Thermodynamic properties of binary HCP solution phases from special quasirandom structures

Three different special quasirandom structures (SQS) of the substitutional hcp $A_{1-x}B_x$ binary random solutions ($x=0.25$, 0.5, and 0.75) are presented. These structures are able to mimic the most important pair and multi-site correlation functions corresponding to perfectly random hcp solutions at those compositions. Due to the relatively small size of the generated structures, they can be used to calculate the properties of random hcp alloys via first-principles methods. The structures are relaxed in order to find their lowest energy configurations at each composition. In some cases, it was found that full relaxation resulted in complete loss of their parental symmetry as hcp so geometry optimizations in which no local relaxations are allowed were also performed. In general, the first-principles results for the seven binary systems (Cd-Mg, Mg-Zr, Al-Mg, Mo-Ru, Hf-Ti, Hf-Zr, and Ti-Zr) show good agreement with both formation enthalpy and lattice parameters measurements from experiments. It is concluded that the SQS's presented in this work can be widely used to study the behavior of random hcp solutions.Comment: 15 pages, 8 figure