Showing papers by "University of Maribor published in 2010"

Coevolutionary games--a mini review.

Abstract: Prevalence of cooperation within groups of selfish individuals is puzzling in that it contradicts with the basic premise of natural selection. Favoring players with higher fitness, the latter is key for understanding the challenges faced by cooperators when competing with defectors. Evolutionary game theory provides a competent theoretical framework for addressing the subtleties of cooperation in such situations, which are known as social dilemmas. Recent advances point towards the fact that the evolution of strategies alone may be insufficient to fully exploit the benefits offered by cooperative behavior. Indeed, while spatial structure and heterogeneity, for example, have been recognized as potent promoters of cooperation, coevolutionary rules can extend the potentials of such entities further, and even more importantly, lead to the understanding of their emergence. The introduction of coevolutionary rules to evolutionary games implies, that besides the evolution of strategies, another property may simultaneously be subject to evolution as well. Coevolutionary rules may affect the interaction network, the reproduction capability of players, their reputation, mobility or age. Here we review recent works on evolutionary games incorporating coevolutionary rules, as well as give a didactic description of potential pitfalls and misconceptions associated with the subject. In addition, we briefly outline directions for future research that we feel are promising, thereby particularly focusing on dynamical effects of coevolutionary rules on the evolution of cooperation, which are still widely open to research and thus hold promise of exciting new discoveries.

Reward and cooperation in the spatial public goods game

Abstract: The promise of punishment and reward in promoting public cooperation is debatable. While punishment is traditionally considered more successful than reward, the fact that the cost of punishment frequently fails to offset gains from enhanced cooperation has lead some to reconsider reward as the main catalyst behind collaborative efforts. Here we elaborate on the "stick vs. carrot" dilemma by studying the evolution of cooperation in the spatial public goods game, where besides the traditional cooperators and defectors, rewarding cooperators supplement the array of possible strategies. The latter are willing to reward cooperative actions at a personal cost, thus effectively downgrading pure cooperators to second-order free-riders due to their unwillingness to bear these additional costs. Consequently, we find that defection remains viable, especially if the rewarding is costly. Rewards, however, can promote cooperation, especially if the synergetic effects of cooperation are low. Surprisingly, moderate rewards may promote cooperation better than high rewards, which is due to the spontaneous emergence of cyclic dominance between the three strategies.

The Role of Functional Foods, Nutraceuticals, and Food Supplements in Intestinal Health

Abstract: New eating habits, actual trends in production and consumption have a health, environmental and social impact. The European Union is fighting diseases characteristic of a modern age, such as obesity, osteoporosis, cancer, diabetes, allergies and dental problems. Developed countries are also faced with problems relating to aging populations, high energy foods, and unbalanced diets. The potential of nutraceuticals/functional foods/food supplements in mitigating health problems, especially in the gastrointestinal (GI) tract, is discussed. Certain members of gut microflora (e.g., probiotic/protective strains) play a role in the host health due to its involvement in nutritional, immunologic and physiological functions. The potential mechanisms by which nutraceuticals/functional foods/food supplements may alter a host’s health are also highlighted in this paper. The establishment of novel functional cell models of the GI and analytical tools that allow tests in controlled experiments are highly desired for gut research.

Anomalous diffusion modeling by fractal and fractional derivatives

Abstract: This paper makes an attempt to develop a fractal derivative model of anomalous diffusion. We also derive the fundamental solution of the fractal derivative equation for anomalous diffusion, which characterizes a clear power law. This new model is compared with the corresponding fractional derivative model in terms of computational efficiency, diffusion velocity, and heavy tail property. The merits and distinctions of these two models of anomalous diffusion are then summarized.

Evolutionary establishment of moral and double moral standards through spatial interactions.

Abstract: Situations where individuals have to contribute to joint efforts or share scarce resources are ubiquitous. Yet, without proper mechanisms to ensure cooperation, the evolutionary pressure to maximize individual success tends to create a tragedy of the commons (such as over-fishing or the destruction of our environment). This contribution addresses a number of related puzzles of human behavior with an evolutionary game theoretical approach as it has been successfully used to explain the behavior of other biological species many times, from bacteria to vertebrates. Our agent-based model distinguishes individuals applying four different behavioral strategies: non-cooperative individuals (“defectors”), cooperative individuals abstaining from punishment efforts (called “cooperators” or “second-order free-riders”), cooperators who punish non-cooperative behavior (“moralists”), and defectors, who punish other defectors despite being non-cooperative themselves (“immoralists”). By considering spatial interactions with neighboring individuals, our model reveals several interesting effects: First, moralists can fully eliminate cooperators. This spreading of punishing behavior requires a segregation of behavioral strategies and solves the “second-order free-rider problem”. Second, the system behavior changes its character significantly even after very long times (“who laughs last laughs best effect”). Third, the presence of a number of defectors can largely accelerate the victory of moralists over non-punishing cooperators. Fourth, in order to succeed, moralists may profit from immoralists in a way that appears like an “unholy collaboration”. Our findings suggest that the consideration of punishment strategies allows one to understand the establishment and spreading of “moral behavior” by means of game-theoretical concepts. This demonstrates that quantitative biological modeling approaches are powerful even in domains that have been addressed with non-mathematical concepts so far. The complex dynamics of certain social behaviors become understandable as the result of an evolutionary competition between different behavioral strategies.

Heterogeneous aspirations promote cooperation in the prisoner's dilemma game.

Abstract: To be the fittest is central to proliferation in evolutionary games. Individuals thus adopt the strategies of better performing players in the hope of successful reproduction. In structured populations the array of those that are eligible to act as strategy sources is bounded to the immediate neighbors of each individual. But which one of these strategy sources should potentially be copied? Previous research dealt with this question either by selecting the fittest or by selecting one player uniformly at random. Here we introduce a parameter that interpolates between these two extreme options. Setting equal to zero returns the random selection of the opponent, while positive favor the fitter players. In addition, we divide the population into two groups. Players from group select their opponents as dictated by the parameter , while players from group do so randomly irrespective of . We denote the fraction of players contained in groups and by and , respectively. The two parameters and allow us to analyze in detail how aspirations in the context of the prisoner's dilemma game influence the evolution of cooperation. We find that for sufficiently positive values of there exist a robust intermediate for which cooperation thrives best. The robustness of this observation is tested against different levels of uncertainty in the strategy adoption process and for different interaction networks. We also provide complete phase diagrams depicting the dependence of the impact of and for different values of , and contrast the validity of our conclusions by means of an alternative model where individual aspiration levels are subject to evolution as well. Our study indicates that heterogeneity in aspirations may be key for the sustainability of cooperation in structured populations.

Punish, but not too hard: how costly punishment spreads in the spatial public goods game

Abstract: We study the evolution of cooperation in spatial public goods games where, besides the classical strategies of cooperation (C) and defection (D), we consider punishing cooperators (PC) or punishing defectors (PD) as an additional strategy. Using a minimalist modeling approach, our goal is to separately clarify and identify the consequences of the two punishing strategies. Since punishment is costly, punishing strategies lose the evolutionary competition in case of well-mixed interactions. When spatial interactions are taken into account, however, the outcome can be strikingly different, and cooperation may spread. The underlying mechanism depends on the character of the punishment strategy. In the case of cooperating punishers, increasing the fine results in a rising cooperation level. In contrast, in the presence of the PD strategy, the phase diagram exhibits a reentrant transition as the fine is increased. Accordingly, the level of cooperation shows a non-monotonous dependence on the fine. Remarkably, punishing strategies can spread in both cases, but based on largely different mechanisms, which depend on the cooperativeness (or not) of punishers.

Pancreatic beta cell lines and their applications in diabetes mellitus research

Abstract: During the past 30 years great effort has been put into establishing an insulin-secreting beta cell line that retains normal regulation of insulin secretion, but only few of these attempts have been successful. To overcome the limited availability of primary beta cells and to include the principles of the 3Rs into the field of diabetes mellitus research, numerous investigators used X-rays or viruses to induce insulinomas, in vitro transformation, derivation of cells from transgenic mice or even non-islet cells to produce immortalised beta cell lines. The most widely used insulin-secreting cell lines are RIN, HIT, MIN, INS-1 and TC cells. These cells produce insulin and small amounts of glucagon and somatostatin. Some of them are only poorly responsive to glucose, others respond to glucose well, but their concentration-dependence curve is markedly shifted to higher sensitivity. Despite problems associated with beta cell cultures, these cell lines have provided some valuable information about physiological processes. However, an urgent need to establish a "normal" beta cell line of human or pig origin remains.

Aspiring to the fittest and promotion of cooperation in the prisoner's dilemma game.

Abstract: Strategy changes are an essential part of evolutionary games. Here, we introduce a simple rule that, depending on the value of a single parameter $w$, influences the selection of players that are considered as potential sources of the new strategy. For positive $w$ players with high payoffs will be considered more likely, while for negative $w$ the opposite holds. Setting $w$ equal to zero returns the frequently adopted random selection of the opponent. We find that increasing the probability of adopting the strategy from the fittest player within reach, i.e., setting $w$ positive, promotes the evolution of cooperation. The robustness of this observation is tested against different levels of uncertainty in the strategy adoption process and for different interaction networks. Since the evolution to widespread defection is tightly associated with cooperators having a lower fitness than defectors, the fact that positive values of $w$ facilitate cooperation is quite surprising. We show that the results can be explained by means of a negative feedback effect that increases the vulnerability of defectors although initially increasing their survivability. Moreover, we demonstrate that the introduction of $w$ effectively alters the interaction network and thus also the impact of uncertainty by strategy adoptions on the evolution of cooperation.

Time-Delay Compensation by Communication Disturbance Observer for Bilateral Teleoperation Under Time-Varying Delay

Abstract: This paper presents the effectiveness of a time-delay compensation method based on the concept of network disturbance and communication disturbance observer for bilateral teleoperation systems under time-varying delay. The most efficient feature of the compensation method is that it works without time-delay models (model-based time-delay compensation approaches like Smith predictor usually need time-delay models). Therefore, the method is expected to be widely applied to network-based control systems, in which time delay is usually unknown and time varying. In this paper, the validity of the time-delay compensation method in the cases of both constant delay and time-varying delay is verified by experimental results compared with Smith predictor.

Nanoparticle-induced widening of the temperature range of liquid-crystalline blue phases

Abstract: Liquid-crystalline blue phases exhibit exceptional properties for applications in the display and sensor industry. However, in single component systems, they are stable only for very narrow temperature range between the isotropic and the chiral nematic phase, a feature that severely hinders their applicability. Systematic high-resolution calorimetric studies reveal that blue phase III is effectively stabilized in a wide temperature range by mixing surface-functionalized nanoparticles with chiral liquid crystals. This effect is present for two liquid crystals, yielding a robust method to stabilize blue phases, especially blue phase III. Theoretical arguments show that the aggregation of nanoparticles at disclination lines is responsible for the observed effects.

Core Values, Culture and Ethical Climate as Constitutional Elements of Ethical Behaviour: Exploring Differences Between Family and Non-Family Enterprises

Abstract: The research presented in this article aims to contribute both quantitatively and qualitatively to the discussion on family versus non-family businesses’ differences in ethical core values, culture and ethical climate. The purpose of our article is to better understand the association between the degree of involvement of a family in an enterprise and its influence on the enterprise’s core values, culture and ethical climate as the constitutional elements of enterprise ethical behaviour. The research indicates that family as well as non-family enterprises maintain positive attitudes towards the core values with ethical content. Regarding the type and strength of culture as well as the type of ethical climate, our research results indicate significant differences between family and non-family enterprises.

An Empirical Study of Virtual Learning Environment Adoption Using UTAUT

Abstract: When users are presented with a new technology or service, a number of factors influence their decision about how and when they will use it. To measure how students and teachers are going to accept and use a specific e-learning technology or service, an appropriate instrument is needed. In this paper common theories that can be used for measuring students' acceptance of e-learning technologies and services are presented. The Unified Theory of Acceptance and Use of Technology (UTAUT) model was used to develop the measurement instrument. The measurement items have been adapted to Moodle, an open source web-based Virtual Learning Environment (VLE). Empirical data was conducted using an online survey with undergraduate students (n=235). To understand students’ perceptions about using Moodle, the UTAUT research model and hypothesized relationships between UTAUT constructs were empirically tested using the structural equation modeling (SEM) approach. The results indicate that performance expectancy and social influence have a significant impact on students’ attitudes towards using Moodle. Social influence and attitudes toward using are significant determinants of students' behavioral intention. Students’ behavioural intentions were shown to be strong and significant determinant of actual use of Moodle. The implications and limitations of the present study are also discussed.

Impact of delays and rewiring on the dynamics of small-world neuronal networks with two types of coupling

Abstract: We study synchronization transitions and pattern formation on small-world networks consisting of Morris–Lecar excitable neurons in dependence on the information transmission delay and the rewiring probability. In addition, networks formed via gap junctional connections and coupling via chemical synapses are considered separately. For gap-junctionally coupled networks we show that short delays can induce zigzag fronts of excitations, whereas long delays can further detriment synchronization due to a dynamic clustering anti-phase synchronization transition. For the synaptically coupled networks, on the other hand, we find that the clustering anti-phase synchronization can appear as a direct consequence of the prolongation of information transmission delay, without being accompanied by zigzag excitatory fronts. Irrespective of the coupling type, however, we show that an appropriate small-world topology can always restore synchronized activity if only the information transmission delays are short or moderate at most. Long information transmission delays always evoke anti-phase synchronization and clustering, in which case the fine-tuning of the network topology fails to restore the synchronization of neuronal activity.

Synthesis of regional networks for the supply of energy and bioproducts

Abstract: This article presents a method for the synthesis of regional renewable energy supply chains, based on Mixed-Integer Linear Programming (MILP). This method addresses the challenges presented by biomass resources. The main challenges are the distributive and varied availabilities regarding both location and time. This work also aims to maximise the economically viable utilisation of resources, accounting for the competition between energy and food production. A four-layer supply chain superstructure has been developed, which includes the harvesting, preparation, core processing and distribution of products. This considered system’s boundaries involve a region, which is then divided into zones for optimising conversion operations and transportation flows. An MILP model has been formulated with profit maximisation as the optimisation criterion. The environmental impact is evaluated by the carbon footprint. The sensitivity of the optimal solutions is analysed for different regions’ sizes, transportation costs, pre-processing alternatives and the co-production of food and energy.

Comparing general-purpose and domain-specific languages: An empirical study

Abstract: Many domain-specific languages, that try to bring feasible alternatives for existing solutions while simplifying programming work, have come up in recent years. Although, these little languages seem to be easy to use, there is an open issue whether they bring advantages in comparison to the application libraries, which are the most commonly used implementation approach. In this work, we present an experiment, which was carried out to compare such a domain-specific language with a comparable application library. The experiment was conducted with 36 programmers, who have answered a questionnaire on both implementation approaches. The questionnaire is more than 100 pages long. For a domain-specific language and the application library, the same problem domain has been used - construction of graphical user interfaces. In terms of a domain-specific language, XAML has been used and C# Forms for the application library. A cognitive dimension framework has been used for a comparison between XAML and C# Forms.

Advances in surface EMG: recent progress in detection and processing techniques.

Abstract: This article is the first section of a review work structured in three parts and concerning a) advances in surface EMG detection and processing techniques, b) recent progress in surface EMG clinical research applications and, c) myoelectric control in neurorehabilitation. This article deals with the state of the art regarding a) the electrode-skin interface (equivalent circuits, skin treatment, conductive gels), b) signal detection modalities, spatial filters and front-end amplifiers, c) power line interference removal, separation of propagating and non-propagating potentials and removal of outliers from surface EMG signal maps, d) segmentation of surface EMG signal maps, e) decomposition of surface EMG into the constituent action potential trains, and f) relationship between surface EMG and force. The material is presented with an effort to fill gaps left by previous reviews and identify areas open for future research.

Biogas production from maize hybrids.

Abstract: There is an increasing world wide demand for energy crops and animal manures for biogas production. This research project was aimed at optimising anaerobic digestion of maize, using a laboratory digester, and finding out which maturity class of corn and which hybrid of a particular maturity class produces the highest rate of biogas and biomethane. Also the chemical composition of gases was studied. The corn hybrids of FAO 300 – FAO 400, FAO 400 – FAO 500 and FAO 500 – FAO 600 maturity class were tested. Experiments took place in the lab for 35 days within four series of experiments with four repetitions according to the method DIN 38 414. Results show that the highest maturity class of corn (FAO 400, FAO 500) increases the amount of biomethane. The greatest gain of biomethane per hectare according to maturity class is found with hybrids of FAO 400 (7768.4 Nm 3 ha −1 ) and FAO 500 (7050.1 Nm 3 ha −1 ) maturity class. Among the corn hybrids of maturity class FAO 300 – FAO 400, the hybrid PR38F70 gives the greatest production of biomethane per hectare (7646.2 Nm 3 ha −1 ). Among the hybrids of maturity class FAO 400 – FAO 500, the greatest amount of biomethane was achieved by the hybrid PIXXIA (9440.6 Nm 3 ha −1 ). Among the hybrids of maturity class FAO 500 – FAO 600 the hybrid CODISTAR (FAO 500) gives the highest production of biomethane (8562.7 Nm 3 ha −1 ). Production of biomethane varied with corn hybrids from 50 to 60% of produced biogas.

Ultra‐High Surface Area Functional Porous Polymers by Emulsion Templating and Hypercrosslinking: Efficient Nucleophilic Catalyst Supports

Abstract: 4-Dimethylaminopyridine (DMAP) is a highly efficient and important organocatalyst used for a variety of organic reactions, including the acylation and silylation of hindered alcohols, the Baylis–Hillman reaction and the ringopening polymerisation of lactide and other lactones. Heterogeneous versions supported on soluble and crosslinked polymers as well as inorganic nanoparticles have been described. Soluble catalysts and nanoparticles can show high activities but require extra isolation steps for catalyst recycling. On the other hand, catalysts supported on insoluble polymer beads, whilst being simple to recycle, tend to suffer from a drop in activity compared to the homogeneous catalyst. Furthermore, the performance of catalysts supported on gel-type polymer beads is limited by solvent-dependent access to the reactive sites inside the beads. The use of permanently porous (often referred to as macroporous ) polymer beads overcomes these solvent limitations, however reactions with these supports can be slow as mass transfer to the active sites on the internal surface of the porous bead occurs by diffusion only. The mass transport limitations of permanently porous beads can be overcome by using emulsion-templated porous polymers (polyHIPEs), which possess very large pores (1– 100 mm) permitting mass transfer by convection rather than diffusion. PolyHIPE materials are produced from high internal phase emulsions (HIPEs), where the dispersed phase occupies >74 % of the emulsion volume. PolyHIPEs have been prepared from either oil-in-water (o/w) or water-in-oil (w/o) emulsions and have been used in a flow through manner as scavengers, reagents, solid-phase synthesis supports and chromatography media. For polyHIPEs to function as a heterogeneous catalyst support, a high surface area is required. PolyHIPE materials with surface areas up to 690 m g 1 can be prepared by the addition of an organic porogen to the monomer phase together with careful choice of HIPE stabilising surfactant. However the resulting materials are rather weak mechanically. An alternative approach to introducing high surface areas is the hypercrosslinking method. Hypercrosslinked polymers contain a very high density of crosslinks together with molecular-sized pores (micropores), and exhibit important properties such as an ultra-high surface area (up to 2000 m g ) and the ability to sorb large amounts of both thermodynamically good and poor solvents, due to high matrix rigidity and a much reduced degree of chain entanglement. Hypercrosslinked polystyrene, in the form of beads, can be prepared by Lewis acid catalysed post polymerisation crosslinking of poly(4-vinylbenzyl chloride) (pVBC) (Scheme 1). High surface area polyHIPE materials for gas storage have recently been prepared by this method. Hypercrosslinked polyHIPE is a potentially attractive catalyst support material due to the combination in one material of an interconnected network of macropores, facilitating access of reagents to the surface, with an ultra-high surface area produced by the hypercrosslinking induced microporosity. Furthermore, hypercrosslinking VBC polyHIPEs to less than full conversion would leave residual chloromethyl functionality for the attachment of catalysts. In this work, we demonstrate proof of this concept; the hypercrosslinking of VBC polyHIPEs is controlled to leave unreacted benzyl chloride moieties with which to anchor DMAP, leading to a highly efficient, recyclable nucleophilic catalyst (Scheme 1). [a] J. Wall, Prof. N. R. Cameron Department of Chemistry and Biophysical Sciences Institute Durham University South Road, Durham, DH1 3LE (UK) Fax: (+44) 191-3844737 E-mail : n.r.cameron@durham.ac.uk [b] Dr. I. Pulko, Prof. P. Krajnc Faculty of Chemistry and Chemical Engineering University of Maribor Smetanova 17, 2000 Maribor (Slovenia) Fax: (+386)2-2527-774 E-mail : peter.krajnc@uni-mb.si [c] Dr. I. Pulko Polymer Technology College Pod gradom 4, 2380 Slovenj Gradec (Slovenia) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200903043.

Impact of critical mass on the evolution of cooperation in spatial public goods games.

Abstract: We study the evolution of cooperation under the assumption that the collective benefits of group membership can only be harvested if the fraction of cooperators within the group, i.e., their critical mass, exceeds a threshold value. Considering structured populations, we show that a moderate fraction of cooperators can prevail even at very low multiplication factors if the critical mass is minimal. For larger multiplication factors, however, the level of cooperation is highest at an intermediate value of the critical mass. The latter is robust to variations of the group size and the interaction network topology. Applying the optimal critical mass threshold, we show that the fraction of cooperators in public goods games is significantly larger than in the traditional linear model, where the produced public good is proportional to the fraction of cooperators within the group.

Evidence for a new resonance and search for the Y(4140) in the γγ→φJ/ψ process

Abstract: The process gammagamma-->phiJ/psi is measured using a data sample of 825 fb{-1} collected with the Belle detector. A narrow peak of 8.8{-3.2}{+4.2} events, with a significance of 3.2 standard deviations including systematic uncertainty, is observed. The mass and natural width of the structure [named X(4350)] are measured to be [4350.6{-5.1}{+4.6}(stat)+/-0.7(syst)] MeV/c{2} and [13{-9}{+18}(stat)+/-4(syst)] MeV, respectively. The product of its two-photon decay width and branching fraction to phiJ/psi is [6.7{-2.4}{+3.2}(stat)+/-1.1(syst)] eV for J{P}=0{+}, or [1.5{-0.6}{+0.7}(stat)+/-0.3(syst)] eV for J{P}=2{+}. No signal for the Y(4140)-->phiJ/psi structure reported by the CDF Collaboration in B-->K{+}phiJ/psi decays is observed, and limits of Gamma_{gammagamma}(Y(4140))B(Y(4140)-->phiJ/psi)<41 eV for J{P}=0;{+} or <6.0 eV for J{P}=2{+} are determined at the 90% C.L. This disfavors the scenario in which the Y(4140) is a D{s}{*+}D{s}{*-} molecule.

Self-medication among healthcare and non-healthcare students at University of Ljubljana, Slovenia.

Abstract: Objective: To determine the incidence of self-medication among University of Ljubljana students and the effect of the type of curriculum on the pattern of self-medication.

Defector-accelerated cooperativeness and punishment in public goods games with mutations.

Abstract: We study the evolution of cooperation in spatial public goods games with four competing strategies: cooperators, defectors, punishing cooperators, and punishing defectors. To explore the robustness of the cooperation-promoting effect of costly punishment, besides the usual strategy adoption dynamics we also apply strategy mutations. As expected, frequent mutations create kind of well-mixed conditions, which support the spreading of defectors. However, when the mutation rate is small, the final stationary state does not significantly differ from the state of the mutation-free model, independently of the values of the punishment fine and cost. Nevertheless, the mutation rate affects the relaxation dynamics. Rare mutations can largely accelerate the spreading of costly punishment. This is due to the fact that the presence of defectors breaks the balance of power between both cooperative strategies, which leads to a different kind of dynamics.