Off-line synthesis of evolutionarily stable normative systems

Within the area of multi-agent systems, normative systems are a widely used framework for the coordination of interdependent activities. A crucial problem associated with normative systems is that of synthesising norms that will effectively accomplish a coordination task and that the agents will comply with. Many works in the literature focus on the on-line synthesis of a single, evolutionarily stable norm (convention) whose compliance forms a rational choice for the agents and that effectively coordinates them in one particular coordination situation that needs to be identified and modelled as a game in advance. In this work, we introduce a framework for the automatic off-line synthesis of evolutionarily stable normative systems that coordinate the agents in multiple interdependent coordination situations that cannot be easily identified in advance nor resolved separately. Our framework roots in evolutionary game theory. It considers multi-agent systems in which the potential conflict situations can be automatically enumerated by employing MAS simulations along with basic domain information. Our framework simulates an evolutionary process whereby successful norms prosper and spread within the agent population, while unsuccessful norms are discarded. The outputs of such a natural selection process are sets of codependent norms that, together, effectively coordinate the agents in multiple interdependent situations and are evolutionarily stable. We empirically show the effectiveness of our approach through empirical evaluation in a simulated traffic domain.     

Execution infrastructure for normative virtual environments

Virtual Institutions (VIs) have proven to be adequate to engineer applications where participants can be humans and software agents. VIs combine Electronic Institutions (EIs) and 3D Virtual Worlds (VWs). In this context, Electronic Institutions are used to establish the regulations that structure interactions and support software agent participation while Virtual Worlds facilitate human participation. In this paper we propose Virtual Institution eXEcution Environment (VIXEE) as an innovative communication infrastructure for VIs. Using VIXEE to connect Virtual Worlds and EI opens EI to humans, providing a fully operational and comprehensive environment. The main features of the infrastructure are (i) the causal connection between Virtual Worlds and Electronic Institutions, (ii) the automatic generation and update of the VIs' 3D visualization and (iii) the simultaneous participation of users from different virtual world platforms. We illustrate the execution of VIXEE system in a simple eAuction house example and use this example to evaluate the performance of our solution.     

On climate reconstruction using bivalves: three methods to interpret the chemical signature of a shell

To improve our understanding of the climate process and to assess the human impact on current global warming, past climate reconstruction is essential. The chemical composition of a bivalve shell is strongly coupled to environmental variations and therefore ancient shells are potential climate archives. The nonlinear nature of the relation between environmental condition (e.g. the seawater temperature) and proxy composition makes it hard to predict the former from the latter, however. In this paper we compare the ability of three nonlinear system identification methods to reconstruct the ambient temperature from the chemical composition of a shell. The comparison shows that nonlinear multi-proxy approaches are potentially useful tools for climate reconstructions and that manifold based methods result in smoother and more precise temperature reconstruction.     

Adaptive case-based reasoning using retention and forgetting strategies

Case-based reasoning systems need to maintain their case base in order to avoid performance degradation. Degradation mainly results from memory swamping or exposure to harmful experiences and so, it becomes vital to keep a compact, competent case base. This paper proposes an adaptive case-based reasoning model that develops the case base during the reasoning cycle by adding and removing cases. The rationale behind this approach is that a case base should develop over time in the same way that a human being evolves her overall knowledge: by incorporating new useful experiences and forgetting invaluable ones. Accordingly, our adaptive case-based reasoning model evolves the case base by using a measure of “case goodness” in different retention and forgetting strategies. This paper presents empirical studies of how the combination of this new goodness measure and our adaptive model improves three different performance measures: classification accuracy, efficiency and case base size.     

Effect of homogenization conditions on physicochemical properties of chitosan-based film-forming dispersions and films

Film-forming dispersions (FFD) based on high molecular weight chitosan (CH) alone or in combination with oleic acid (OA) were prepared under different homogenization conditions (rotor-stator or rotor stator together with microfluidization at different pressures). Film-forming dispersions (FFD) were characterized in terms of particle size distribution, rheological properties, distribution and ζ-potential. In order to study the impact of the properties of the FFD on the casted films, the water vapour permeability, mechanical properties and microstructure of the dry films were evaluated. Results showed that microfluidization promoted significant changes in the size and surface charge of the FFD particles, which in turn had an impact on the rheological properties of the FFD. The changes were more marked with the increase in microfluidization pressure. As regards film properties, the higher the microfluidization pressure in the FFD, the lower the water vapour permeability values and the stiffer the CH-OA composite films. These results were explained by film microstructure, which was observed by SEM.     

Artificially Linked Ubiquitin Dimers Characterised Structurally and Dynamically by NMR Spectroscopy

As one of the most prevalent post-translational modifications in eukaryotic cells, ubiquitylation plays vital roles in many cellular processes, such as protein degradation, DNA metabolism, and cell differentiation. Substrate proteins can be tagged by distinct types of polymeric ubiquitin (Ub) chains, which determine the eventual fate of the modified protein. A facile, click chemistry based approach for the efficient generation of linkage-defined Ub chains, including Ub dimers, was recently established. Within these chains, individual Ub moieties are connected through a triazole linkage, rather than the natural isopeptide bond. Herein, it is reported that the conformation of an artificially K48-linked Ub dimer resembles that of the natively linked dimer, with respect to structural and dynamic characteristics, as demonstrated by means of high-resolution NMR spectroscopy. Thus, it is proposed that artificially linked Ub dimers, as generated by this approach, represent potent tools for studying the inherently different properties and functions of distinct Ub chains.     

Effect of an epoxy octasilsesquioxane on the thermodegradation of an epoxy/amine system

Polyhedral oligomeric silsesquioxanes (POSS^®) can be added to thermoplastic and thermostable polymers to obtain hybrid materials with only a minor tendency to suffer ignition. The aim of the work reported was to analyse the influence of an octafunctional POSS^® in the pyrolysis of an epoxy/amine system as well as during the combustion process. Thermal degradation of the modified materials, with respect to the unmodified ones, was analysed using thermogravimetric analysis. As the content of POSS^® increased the stability improved and the char/ceramic yields were higher. The Kissinger–Akahira–Sunose method was applied to the modified blends and it showed a decrease in the activation energy with POSS^® content. Empirical kinetic models, as well as generalized master plots, were applied to explain the degradation mechanism for ternary blends. The limiting oxygen index parameter was measured to analyse the fire retardancy effect of POSS^®: it increased from 24.3 to 25.4% with the addition of 2.5 wt% of POSS^®. The mechanism of thermal degradation of the hybrid materials based on an epoxy resin is affected by the presence of the octaepoxy POSS^®. Only small amounts of POSS^® are necessary to enhance the combustion resistance of the system. Copyright © 2009 Society of Chemical Industry     

Effect of essential oils on properties of film forming emulsions and films based on hydroxypropylmethylcellulose and chitosan

Film-forming dispersions (FFD) and films, prepared by incorporating different concentrations of bergamot (BO), lemon (LO) and tea tree (TTO) essential oils into hydroxyproplymethylcellulose (HPMC) and chitosan (CH) were obtained and their physico-chemical properties were characterised. Results showed that the increment of essential oil (EO) content promoted significant changes in the size and surface charge of the FFD particles. As regards the film properties, the higher the EO content, the lower the water vapour permeability and the moisture sorption capacity. In general, the addition of EO into the HPMC or CH matrix leads to a significant decrease in gloss, transparency, tensile strength and elastic modulus of the composite films. Discriminant analyses of obtained data revealed that the polymer type was the main factor which defined the FFD and composite film behaviour. For a given polymer, although both the nature and concentration of the EO influenced FFD behaviour, the concentration played a more important role. In film properties, the discriminant analyses did not reveal different groups associated to the different nature or concentration of the essential oils, although composite films with BO appeared to differ slightly from the rest.     

Scientific output and impact of postdoctoral scientists: a gender perspective

This paper analyses the scientific output and impact of 731 Ph.D. holders who were awarded their doctorate at Spanish universities between 1990 and 2002. The aim was to identify any differences in the amount of scientific output and the impact of publications, in terms of citations, according to gender. The analysis revealed no significant differences in the amount of scientific output between males and females. However, the proportion of female Ph.D. holders with no postdoctoral output was significantly higher than that of their male counterparts, and the median number of papers published after Ph.D. completion was also lower among women. As regards pre- and postdoctoral research, the data showed that early scientific output may be a good predictor of subsequent productivity in both gender groups. The results also indicated that articles by female Ph.D. holders were cited significantly more often, even when self-citations were excluded.