An average case analysis of the minimum spanning tree heuristic for the range assignment problem

We present an average case analysis of the minimum spanning tree heuristic for the range assignment problem on a graph with power weighted edges. It is well-known that the worst-case approximation ratio of this heuristic is 2. Our analysis yields the following results: (1) In the one dimensional case ($d = 1$), where the weights of the edges are 1 with probability $p$ and 0 otherwise, the average-case approximation ratio is bounded from above by $2-p$. (2) When $d =1$ and the distance between neighboring vertices is drawn from a uniform $[0,1]$-distribution, the average approximation ratio is bounded from above by $2-2^{-\alpha}$ where $\alpha$ denotes the distance power radient. (3) In Euclidean 2-dimensional space, with distance power gradient $\alpha = 2$, the average performance ratio is bounded from above by $1 + \log 2$

Annual Report Ant Smelt 2010: A changing role for smelt Osmerus eperlanus in the Lake IJsselmeer and Lake Markermeer foodweb? Climate- and nutrient-induced changes in ecoystem functioning

The smelt project is part of a larger research project that aims at generating, exploring and testing different possible explanations for the observed Autonomous Negative Trends (ANT) in water fowl in Lake Markermeer and Lake IJsselmeer. The smelt populations in both lakes have been in severe decline since 1990. These declines have a large impact on the conservation of water birds relying on smelt as their prey and the fishery both on smelt and on piscivorous fish relying on smelt. In winter time the Lake IJsselmeer area is home to the largest population of waterfowl in Western Europe. The area is therefore considered to be an important Natura-2000 area. Identification of the causes of the observed negative trends will help managers (RWS) to take the appropriate restoration measures and thereby improve the these lakes as habitat for waterfowl

Diversification of prey capture techniques among the piscivores in Lake Tana's (Ethiopia) Labeobarbus species flock (Cyprinidae)

Lake Tana harbours the only known intact species flock of large cyprinid fishes (15 Labeobarbus spp.). One of the most curious aspects of this species flock is the large number (8) of piscivorous species. Cyprinids are not well designed for piscivory (i.e. small slit-shaped pharyngeal cavity, lack of teeth in the oral jaws, lack of a stomach), which raises the question how well adapted these labeobarbs actually are to function as piscivores? In this study we analyse the kinematics of prey capture (by varied combinations of suction, swimming and jaw protrusion) among Lake Tana's piscivorous labeobarbs. Suction feeding kinematics were similar to values reported for other piscivorous fish species. A detailed analysis of several Labeobarbus species displayed distinct types of techniques (overswimming, velocity/volume suction with jaw protrusion) suited to capture elusive prey in different macro-habitats, Lake Tana's Labeobarbus species evolved a wide range of piscivorous predation techniques, a unique scenario for cyprinid fishes

Effects of retro-nasal aroma release on satiation

It is suggested that the brain response of a food odour sensed retro-nasally is related to satiation. The extent of retro-nasal aroma release during consumption depends on the physical structure of a food, i.e. solid foods generate a longer, more pronounced retro-nasal aroma release than liquid foods. The aim of this study was to investigate if a beverage becomes more satiating when the retro-nasal aroma release profile coincides with the profile of a (soft) solid food. In a double-blind placebo-controlled randomised cross-over full factorial design, twenty-seven healthy subjects (fourteen males and thirteen females; aged 16-65 years; BMI 19-37 kg/m(2) were administered aroma profiles by a computer-controlled stimulator based on air dilution olfactometry. Profile A consisted of a profile that is obtained during consumption of normal beverages. Profile B is normally observed during consumption of (soft) solids. The two profiles were produced with strawberry aroma and administered in a retro-nasal fashion, while the subjects consumed a sweetened milk drink. Before, during and after the sensory stimulation, appetite profile measurements were performed. Subjects felt significantly more satiated if they were aroma stimulated with profile B (P = 0.04). After stimulation with sweet strawberry aroma, there was a significant decrease in desire to eat sweet products (P = 0.0001). In conclusion, perceived satiation was increased by altering the extent of retro-nasal aroma release

Recreatieve visserij onder de loep

Hoeveel recreatieve vissers zijn er in Nederland en hoeveel vis vangen deze vissers? Deze op het eerste gezicht simpele vraag is volgens IMARES onderzoeker Martin de Graaf in de praktijk niet eenvoudig te beantwoorden. Vooral het nauwkeurig schatten van het aantal sportvissers en hun vangsten is vaak een lastige opgave

Tetragonal zirconia: Wet chemical preparation, mechanical and electrical properties

Yttria-stabilized zirconia powders were prepared in the composition range of 3 to 13 at% yttria. The hydrolysis-gel precipitation technique was used, starting from metal alkoxides or chlorides. In the composition range between 5 and 10 at% yttria, the materials sintered at 1250°C have a fully tetragonal structure. The density was higher than 95% and the grain sizes can be varied between 0.1 and 0.5μm depending on the preparation conditions. The fracture toughness KIC amounts 6 to 11 MPam but is not dependent on the composition. The transformation toughening mechanism and the properties of the tetragonal phase itself play an important role in the increase of KIC compared with cubic materials. The magnitude of the oxygen-ion conductivity value is comparable with that for cubic materials

Management plan for the natural resources of the EEZ of the Dutch Caribbean

On the 10th of October 2010 the governmental entity known as the Netherlands Antilles is scheduled to cease to exist. Each island will aquire a new status within the kingdom. Following the declaration of an Exclusive Fishery Zone (EFZ) in 1993, an Exclusive Economic Zone (EEZ) has been declared in the Dutch Caribbean on the tenth of June 2010. The EEZ area concerned, is a large expanse of sea which harbours exceptional biodiversity, and represents an important natural renewable resource potential. The Netherlands Antilles, Aruba and The Netherlands have, therefore, opted to draft a management plan for the EEZ. This initiative began in the year 2005 when the first conference regarding the management of the biodiversity in the EEZ was held. The consensus was that despite a fragmented Dutch Caribbean, the EEZ should always be integrally managed. In 2009 the participants of the second conference confirmed the need for common management and developed common goals, principles and a framework for the management of the Dutch Caribbean waters. Resulting from this conference a management plan was drafted, circulated to all stakeholders and discussed on the 1st of June 2010. Based on the input and feedback received, as well as subsequent correspondence, this final management plan was jointly developed

Dense Regular Packings of Irregular Non-Convex Particles

We present a new numerical scheme to study systems of non-convex, irregular, and punctured particles in an efficient manner. We employ this method to analyze regular packings of odd-shaped bodies, not only from a nanoparticle but also both from a computational geometry perspective. Besides determining close-packed structures for many shapes, we also discover a new denser configuration for Truncated Tetrahedra. Moreover, we consider recently synthesized nanoparticles and colloids, where we focus on the excluded volume interactions, to show the applicability of our method in the investigation of their crystal structures and phase behavior. Extensions to the presented scheme include the incorporation of soft particle-particle interactions, the study of quasicrystalline systems, and random packings.Comment: 4 pages, 3 figure