Numerical experiments with the lid driven cavity flow problem

The centerline velocity profiles obtained from the solution of the two- and three-dimensional representations of the lid driven cavity flow problem are compared for different Reynolds numbers. Two configurations were used in this study: a unit cavity and a cavity with an aspect ratio of 2. The Reynolds numbers ranged from 100 to 5000 for all of the configurations studied. A new method of extending the Jacobi collocation technique called spectral difference is developed in this paper together with a unique computational grid. In addition, an iterative method for solving the pressure problem is also developed. This new numerical method allowed the calculation of three-dimensional Navier-Stokes equations to be performed in computers with very modest computational capabilities such as workstations.     

On Synchronous Robotic Networks—Part II: Time Complexity of Rendezvous and Deployment Algorithms

This paper analyzes a number of basic coordination algorithms running on synchronous robotic networks. We provide upper and lower bounds on the time complexity of the move-toward-average and circumcenter laws, both achieving rendezvous, and of the centroid law, achieving deployment over a region of interest. The results are derived via novel analysis methods, including a set of results on the convergence rates of linear dynamical systems defined by tridiagonal Toeplitz and circulant matrices.     

Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors

Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me₃Si)_0.80((CH₂=CH)MeSi)_1.0(MeHSi)_0.35] _n (VPS) or [MeHSiCH₂] _n (MPCS) with [R₂AlNH₂]₃, where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et₂AlNH₂]₃. In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu₂AlNH₂]₃ yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed.     

Impacts of new technologies on media usage and social behaviour in domestic environments

Technological infrastructure at home is changing continuously and is becoming increasingly interconnected. Media devices, including the TV set, provide access to the Internet and offer manifold opportunities to consume media on demand. Additionally, personal devices, such as smartphones, also enable flexible consumption and sharing of media. Questions about how these technologies change the user's media usage and how these changes affect the social structure of a household, however, remain largely unanswered. In order to gain insight into the adoption of new technologies into daily routines, we explored these changes in respect of people's media usage in a qualitative long-term Living Lab study. We will present findings regarding personal routines, flexible integration of new devices into existing practices, influences on households as social systems and related issues in device access and collective use. We will highlight potentials and conflicts regarding device shifts and roles; restrictions in device access; social influences in the living room; and individual changes in media consumption.     

Simulating protection rackets: a case study of the Sicilian Mafia

Protection racketeering groups are powerful, deeply entrenched in multiple societies across the globe, and they harm the societies and economies in which they operate in multiple ways. These reasons make their dynamics important to understand and an objective of both scientific and application-oriented interest. Legal and social norm-based approaches arguably play significant roles in influencing protection racket dynamics. We propose an agent-based simulation model, the Palermo Scenario, to enrich our understanding of these influences and to test the effect of different policies on protection racket dynamics. Our model integrates the legal and the social norm-based approaches and uses a complex normative agent architecture that enables the analysis of both agents’ behaviours and mental normative representations driving behaviour. We demonstrate the usefulness of the model and the benefits of using this complex normative architecture through a case study of the Sicilian Mafia.     

BENCHMARKING RIVER HABITAT IMPROVEMENT

River ecosystems have witnessed a long history of human pressure, particularly the disruption of freshwater fish populations. The awareness of this situation has led to many habitat improvement projects, with a variable degree of success. In natural situations, fish populations co‐inhabit throughout the hydrological cycle with different degrees of adequacy, and the sequence of favourable and unfavourable conditions dictates abiotic constraints and biotic interactions that shape the final biological assemblages. We postulate that a part of unsuccessful restoration results is related to insufficient closeness to the natural habitat conditions of the river type that is to be restored, including the naturally adverse periods. We used the river2d model to predict habitat availability as weighted usable area (WUA) at a degraded site that is to be restored, for two native Mediterranean species and their life stages—the Southwestern nase Iberochondrostoma almacai and the Arade chub Squalius aradensis. We then analysed the yearly evolution of the natural WUA at a nearby reference site. Overall, the reference site exhibited the longest periods during which the WUA was continuously lower than the chosen WUA thresholds for each of the four bioperiods. Considerable divergences from natural habitat availability values can be seen for the spawning, rearing and growth bioperiods. Restoration outcomes can result in appreciable deviations—favourable or unfavourable to fish populations—from the WUA occurring under natural conditions over the course of the year. Restoration should therefore take account of local hydraulic and habitat patterns that govern population dynamics and result in the final fish assemblage. Copyright © 2011 John Wiley & Sons, Ltd.     

Towards reproducibility in recommender-systems research

Numerous recommendation approaches are in use today. However, comparing their effectiveness is a challenging task because evaluation results are rarely reproducible. In this article, we examine the challenge of reproducibility in recommender-system research. We conduct experiments using Plista’s news recommender system, and Docear’s research-paper recommender system. The experiments show that there are large discrepancies in the effectiveness of identical recommendation approaches in only slightly different scenarios, as well as large discrepancies for slightly different approaches in identical scenarios. For example, in one news-recommendation scenario, the performance of a content-based filtering approach was twice as high as the second-best approach, while in another scenario the same content-based filtering approach was the worst performing approach. We found several determinants that may contribute to the large discrepancies observed in recommendation effectiveness. Determinants we examined include user characteristics (gender and age), datasets, weighting schemes, the time at which recommendations were shown, and user-model size. Some of the determinants have interdependencies. For instance, the optimal size of an algorithms’ user model depended on users’ age. Since minor variations in approaches and scenarios can lead to significant changes in a recommendation approach’s performance, ensuring reproducibility of experimental results is difficult. We discuss these findings and conclude that to ensure reproducibility, the recommender-system community needs to (1) survey other research fields and learn from them, (2) find a common understanding of reproducibility, (3) identify and understand the determinants that affect reproducibility, (4) conduct more comprehensive experiments, (5) modernize publication practices, (6) foster the development and use of recommendation frameworks, and (7) establish best-practice guidelines for recommender-systems research.     

Nature and the Nazi Diet 1

This article investigates the role of natural foods and farming in Nazi Germany. Why did the state encourage Germans to eat and farm more naturally? What did “natural” mean in the context of this genocidal regime? By what means were Germans encouraged to take up these practices and to what degree did they do so? This article explores these questions by tracing the assimilation of natural foods and farming to the regime's racial, political, and economic goals. Eating more naturally, Nazi leaders believed, would promote racial health, boost physical performance, and maximize the efficient use of resources, all qualities needed to fight and win the coming war. Natural foods and farming, in short, belonged to the biopolitics of fascist modernity. The article develops this claim in two sections, one on efforts to make German diets more natural, the other on an early form of organic farming known as biodynamics. The conclusion considers the implications of these findings for food historians more generally.     

Optimizing water tanks in water distribution systems by combining network reduction,mathematical optimization and hydraulic simulation

In the last two decades, water consumption in Germany has been decreasing, which causes the water tanks and pipes in water distribution systems to work inefficiently. This paper proposes a method that supports the planning process for tanks in water distribution systems. The method uses a combination of network reduction, mathematical optimization and hydraulic simulation. The mathematical optimization model is a non-convex Mixed Integer Quadratically Constrained Program (MIQCP) that is solved by a piecewise linearization. As this may lead to many binary variables and therefore high computing times, the size of the water distribution system model is reduced before building the optimization model. After applying several network reduction techniques and using a piecewise approximation of the original model, there may be some hydraulic differences between the original network model and the reduced network model. To make sure that the solution obtained in the optimization process is feasible in the original water distribution system model, the solution is verified by a hydraulic simulation. If the solution is not feasible, the reduced model has to be modified and solved again until the hydraulic simulation verifies a solution as feasible. In this paper, each of these processes is described and the results indicate the usefulness of each of them.     

Updated safety analysis of ITER

An updated version of the ITER Preliminary Safety Report has been produced and submitted to the licensing authorities. It is revised and expanded in response to requests from the authorities after their review of an earlier version in 2008, to reflect enhancements in ITER safety provisions through design changes, to incorporate new and improved safety analyses and to take into account other ITER design evolution. The updated analyses show that changes to the Tokamak cooling water system design have enhanced confinement and reduced potential radiological releases as well as removing decay heat with very high reliability. New and updated accident scenario analyses, together with fire and explosion risk analyses, have shown that design provisions are sufficient to minimize the likelihood of accidents and reduce potential consequences to a very low level. Taken together, the improvements provided a stronger demonstration of the very good safety performance of the ITER design.