Effective learning hyper-heuristics for the course timetabling problem

Course timetabling is an important and recurring administrative activity in most educational institutions. This article combines a general modeling methodology with effective learning hyper-heuristics to solve this problem. The proposed hyper-heuristics are based on an iterated local search procedure that autonomously combines a set of move operators. Two types of learning for operator selection are contrasted: a static (offline) approach, with a clear distinction between training and execution phases; and a dynamic approach that learns on the fly. The resulting algorithms are tested over the set of real-world instances collected by the first and second International Timetabling competitions. The dynamic scheme statistically outperforms the static counterpart, and produces competitive results when compared to the state-of-the-art, even producing a new best-known solution. Importantly, our study illustrates that algorithms with increased autonomy and generality can outperform human designed problem-specific algorithms.     

The determination of134Cs,137Cs,210Pb,226Ra and228Ra concentrations in nearshore marine sediments and seawater

Multi-radionuclide analyses of coastal marine sediments and seawater can be of considerable value in defining rates and mechanisms of nearshore processes. A preliminary study of¹³⁴Cs,¹³⁷Cs,²¹⁰Pb,²²⁶Ra and²²⁸Ra in the Clyde Sea Area has been performed. A summary of the marine geochemistries of these species and a detailed account of methods involved in their routine analysis are described.     

A Stochastic Analysis of Some Two‐Person Sports

We consider two‐person sports where each rally is initiated by a server, the other player (the receiver) becoming the server when he/she wins a rally. Historically, these sports used a scoring based on the side‐out scoring system, in which points are only scored by the server. Recently, however, some federations have switched to the rally‐point scoring system in which a point is scored on every rally. As various authors before us, we study how much this change affects the game. Our approach is based on a rally‐level analysis of the process through which, besides the well‐known probability distribution of the scores, we also obtain the distribution of the number of rallies. This yields a comprehensive knowledge of the process at hand, and allows for an in‐depth comparison of both scoring systems. In particular, our results help to explain why the transition from one scoring system to the other has more important implications than those predicted from game‐winning probabilities alone. Some of our findings are quite surprising, and unattainable through Monte Carlo experiments. Our results are of high practical relevance to international federations and local tournament organizers alike, and also open the way to efficient estimation of the rally‐winning probabilities.     

Anisotropic diffusion in confined colloidal dispersions: the evanescent diffusivity

We employ an analogy to traditional dynamic light scattering to describe the inhomogeneous and anisotropic diffusion of colloid particles near a solid boundary measured via evanescent wave dynamic light scattering. Following this approach, we generate new expressions for the short-time self- and collective diffusivities of colloidal dispersions with arbitrary volume fraction. We use these expressions in combination with accelerated Stokesian dynamics simulations to calculate the diffusivities in the limit of large and small scattering wave numbers for evanescent penetration depths ranging from four particle radii to one-fifth of a particle radius and volume fractions from 10% to 40%. We show that at high volume fractions, and larger penetration depths, the boundaries have little effect on the dynamics of the suspension parallel to the wall since, to a first approximation, the boundary acts hydrodynamically much as another nearby particle. However, near and normal to the wall, the diffusivity shows a strong dependence on penetration depth for all volume fractions. This is due to the lubrication interactions between the particles and the boundary as the particle moves relative to the wall. These results are novel and comprehensive with respect to the range of penetration depth and volume fraction and provide a complete determination of the effect of hydrodynamic interactions on colloidal diffusion adjacent to a rigid boundary.     

Zur Entwicklung von Schwefelwasserstoff

Ohne Zusammenfassung     

Aspects of magnetogasdynamic flows involving upstream influence effects

Résumé Pour l'analyse mathématique des problèmes concernant l'écoulement d'un fluide en présence d'un champ magnétique dans laquelle les parois nonconductrices existent, on doit considérer la solution des equationsMaxwell dans les régions des parois. Il y a des auteurs qui n'ont pas considéré cette solution, et cet article fait commenter sur quelquesuns des problèmes qui sont déficitaire dans cette matière.

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Sponsored by the Mathematics Research Center, United States Army, Madison, Wisconsin under Contract No.: DA-31-124-ARO-D-462.     

Electrical conductivity of 2,4-dinitrosoresorcinol and its complexes

Electrical conductivity measurements of 2,4-dinitrosoresorcinol (DNR) and its complexes were measured in the temperature range 20–115°C to give faint semiconducting behaviour for these systems. The conductivity values of the bis Co, Ni, Cu and Zn systems indicated that the metal ion forms a bridge between the two ligands facilitating the transfer of current carriers with some degree of delocalization in the excited state. As the iron content in the complexes increased, a gradual increase of electrical conductivity occurred, that might be due to lattice imperfections.