On the transition to efficiency in Minority Games

The existence of a phase transition with diverging susceptibility in batch Minority Games (MGs) is the mark of informationally efficient regimes and is linked to the specifics of the agents' learning rules. Here we study how the standard scenario is affected in a mixed population game in which agents with the `optimal' learning rule (i.e. the one leading to efficiency) coexist with ones whose adaptive dynamics is sub-optimal. Our generic finding is that any non-vanishing intensive fraction of optimal agents guarantees the existence of an efficient phase. Specifically, we calculate the dependence of the critical point on the fraction $q$ of `optimal' agents focusing our analysis on three cases: MGs with market impact correction, grand-canonical MGs and MGs with heterogeneous comfort levels.Comment: 12 pages, 3 figures; contribution to the special issue "Viewing the World through Spin Glasses" in honour of David Sherrington on the occasion of his 65th birthda

Statistical mechanics and stability of a model eco-system

We study a model ecosystem by means of dynamical techniques from disordered systems theory. The model describes a set of species subject to competitive interactions through a background of resources, which they feed upon. Additionally direct competitive or co-operative interaction between species may occur through a random coupling matrix. We compute the order parameters of the system in a fixed point regime, and identify the onset of instability and compute the phase diagram. We focus on the effects of variability of resources, direct interaction between species, co-operation pressure and dilution on the stability and the diversity of the ecosystem. It is shown that resources can be exploited optimally only in absence of co-operation pressure or direct interaction between species.Comment: 23 pages, 13 figures; text of paper modified, discussion extended, references adde

Algebraic coarsening in voter models with intermediate states

The introduction of intermediate states in the dynamics of the voter model modifies the ordering process and restores an effective surface tension. The logarithmic coarsening of the conventional voter model in two dimensions is eliminated in favour of an algebraic decay of the density of interfaces with time, compatible with Model A dynamics at low temperatures. This phenomenon is addressed by deriving Langevin equations for the dynamics of appropriately defined continuous fields. These equations are analyzed using field theoretical arguments and by means of a recently proposed numerical technique for the integration of stochastic equations with multiplicative noise. We find good agreement with lattice simulations of the microscopic model.Comment: 11 pages, 5 figures; minor typos correcte

Market response to external events and interventions in spherical minority games

We solve the dynamics of large spherical Minority Games (MG) in the presence of non-negligible time dependent external contributions to the overall market bid. The latter represent the actions of market regulators, or other major natural or political events that impact on the market. In contrast to non-spherical MGs, the spherical formulation allows one to derive closed dynamical order parameter equations in explicit form and work out the market's response to such events fully analytically. We focus on a comparison between the response to stationary versus oscillating market interventions, and reveal profound and partially unexpected differences in terms of transition lines and the volatility.Comment: 14 pages LaTeX, 5 (composite) postscript figures, submitted to Journal of Physics

Optimizing evacuation flow in a two-channel exclusion process

We use a basic setup of two coupled exclusion processes to model a stylised situation in evacuation dynamics, in which evacuees have to choose between two escape routes. The coupling between the two processes occurs through one common point at which particles are injected, the process can be controlled by directing incoming individuals into either of the two escape routes. Based on a mean-field approach we determine the phase behaviour of the model, and analytically compute optimal control strategies, maximising the total current through the system. Results are confirmed by numerical simulations. We also show that dynamic intervention, exploiting fluctuations about the mean-field stationary state, can lead to a further increase in total current.Comment: 16 pages, 6 figure

ANALISIS RUGI DAYA DI PENYULANG OEBUFU PT. PLN (PERSERO) ULP KUPANG MENGGUNAKAN ALGORITMA GENETIKA

 The distribution system has a very important role in distributing electrical energy to costumers. Power quality in distribution system can affect the flow of electric distribution. Increase of electrical power demand can affect to power distributing quality like power losses, voltage drop and lower power factor. Load increasing make a reactive current can be up when flow in high resistance conductor as an effect. Installation of capacitor in distribution system is a one of the most efficient method to power losses pressure. This study discusses the optimization of capacitors location and capacity. Genetic algorithm is using as an optimization method. Backward-Forward Sweep Method to be the method of power flow analysis before and after instalation of capacitors to see their effect. Result of genetic algorithm will compare with manual calculation of choosing capacitors to  know how effectively of genetic algorithm. This scheme is tested in Feeder Oebufu on 20 kV distribution system under PT. PLN (Persero) ULP Kupang operation. The test divided into 4 case included: before installation, placement of 1 capacitor, 2 capacitors, and 3 capacitors. Best result got in 3 capacitors simulation. Before installastion of capacitor, the power losses is 771,9928 kW, voltage minimum is 0,9842 pu, and power factor is 0,91257. Placement of 3 capacitors on bus 131 127, and 64 decrease a total power losses to be 31,164 kW, in other hand increase voltage profile around bus locations and power factor to be 0,99257.Sistem distribusi tenaga listrik mempunyai peran penting dalam menyalurkan tenaga listrik ke pelanggan. Kualitas daya pada sistem distribusi mempengaruhi kelancaran distribusi listrik. Peningkatan permintaan daya mempengaruhi kualitas penyaluran daya seperti adanya rugi daya, jaruh tegangan, dan faktor daya rendah. Kenaikan beban mengakibatkan naiknya nilai arus reaktif yang melewati penghantar beresistansi besar. Pemasangan kapasitor pada sistem distribusi adalah salah satu metode yang efisien menekan rugi daya.Pada penelitian ini membahas tentang optimasi lokasi dan kapasitas kapasitor. Algoritma Genetika digunakan sebagai metode optimasi. Metode Backward-Forward Sweep sebagai metode analisa aliran daya sebelum dan sesudah pemasangan kapasitor untuk mengetahui pengaruh pemasangan kapasitor. Hasil dari algoritma genetika dibandingkan dengan perhitungan manual untuk mengetahui keefektifan algoritma. Skema ini diujikan pada Penyulang Oebufu dari sistem distribusi 20 kV yang dioperasikan PT. PLN ULP Kupang.Pengujian dilakukan empat tahap yaitu: sebelum pemasangan, penempatan 1 buah kapasitor, 2 buah, dan 3 buah kapasitor. Hasil terbaik didapat pada pengujian 3 buah kapasitor. Sebelum pemasangan kapasitor rugi daya 771,9928 kW, tegangan minimum 0,9842 pu, faktor daya 0,91257. Pemasangan 3 buah kapasitor di bus 131, 127 dan 64 dapat menurunkan total rugi daya mencapai 31, 1601 kW, menaikkan profil tegangan sekitar bus lokasi dan faktor daya menjadi 0,99257

Effects of noise on convergent game learning dynamics

We study stochastic effects on the lagging anchor dynamics, a reinforcement learning algorithm used to learn successful strategies in iterated games, which is known to converge to Nash points in the absence of noise. The dynamics is stochastic when players only have limited information about their opponents' strategic propensities. The effects of this noise are studied analytically in the case where it is small but finite, and we show that the statistics and correlation properties of fluctuations can be computed to a high accuracy. We find that the system can exhibit quasicycles, driven by intrinsic noise. If players are asymmetric and use different parameters for their learning, a net payoff advantage can be achieved due to these stochastic oscillations around the deterministic equilibrium.Comment: 17 pages, 8 figure

TRANSCRIPTOMIC ANALYSIS OF WHOLE PISTILS AND OVULE CELLS TO IDENTIFY GENES RELATED TO APOSPORY IN HYPERICUM PERFORATUM L.

St. John\u2019s wort (Hypericum perforatum L.) is a medicinal plant that produces important metabolites with antidepressant and anticancer activities. Beside the pharmaceutical interest, recently gained information has shown that H. perforatum is also an attractive model system for the study of aposporous apomixis, that is a reproductive strategy, which, unlike sexual reproduction, permits the inheritance of the maternal genome over generations without genetic recombination events. This asexual mode of seed formation is believed to be a trait with enormous economic and social potential in agriculture. Its innovative use in this area relies upon the idea that indefinitely fixing highly complex genotypes, including hybrid cultivars, through apomixis would have tremendous advantages in plant breeding, biomass and seed production. During the last decades, the understanding of the molecular basis of apomixis in this species has been complicated by the lack of biological data, e.g. genomic or even transcriptomic sequences. The aim of our research project was the sequencing, annotation and comparative investigation of the H. perforatum flower transcriptome, as critical steps toward a better understanding of the genetic control of aposporic and sexual reproduction in the facultative apomict H. perforatum. To this end, next generation sequencing technologies have been used to sequence the flower transcriptomes of obligate sexual and unrelated apomictic H. perforatum genotypes. This approach has enabled the assembly and annotation of large cDNA repositories and their exploitation to design a custom array to be used in flower expression studies. Global gene expression analysis of H. perforatum was initially performed on ovaries collected from sexual and aposporic plant accessions for the purpose of identifying genes and processes potentially associated with apomixis in this model species. Overall, across two selected developmental stages, 224 and 973 unigenes were found to be significantly upand down-regulated. Ontological annotation of differentially expressed genes indicated that terms related to cell cycle, single-organism cellular process DNA (cytosine-5-)-methyltransferase activity, among others, were significantly enriched. In a following step, a laser-capture microdissection approach was adopted in combination the RNA-seq technology with the aim of identifying genes differentially expressed in the ovule cell types primarily involved in the differentiation of the megaspore mother cells and aposporous initials. On the whole, our data suggest that phenotypic expression of apospory is concomitant with the modulation of key genes involved in the sexual reproductive pathway and the responsive to hormonal stimuli. Annotation of all identified flower transcripts as well as their qualitative and quantitative expression data will be presented and critically discussed as they prove a far better understanding of molecular bases of pistil development, embyo sac and egg cell formation in sexual and apomictic H. perforatum

Population structure and evolution of resistance to acetolactate synthase (ALS)-inhibitors in Amaranthus tuberculatus in Italy

6openInternationalBothBackground: Before 2010, Amaranthus tuberculatus (Moq.) J. D. Sauer was barely known to farmers and stakeholders in Italy. Since then, several populations resistant to acetolactate synthase (ALS)-inhibiting herbicides have been collected. In most populations, a known target site resistance-endowing mutation was found, a Trp to Leu substitution at position 574 of the ALS gene, but it was unclear whether they had evolved resistance independently or not. The aims of the work were (i) to elucidate the population structure of Italian ALS-resistant A. tuberculatus populations, and (ii) to analyze the ALS haplotypes of the various populations to determine whether resistance arose multiple times independently. Results: In order to determine the population structure of eight A. tuberculatus populations, eight previously described microsatellite loci were used. Two ancestors were found: three populations derived from one, and five from the other. In the 4-kb ALS region of the genome, including the 2-kb coding region, 389 single nucleotide polymorphisms were found. In silico haplotype estimation was used to reconstruct the sequence of three distinct haplotypes carrying the Trp574Leu mutation. In addition, no mutation was found in 83% of plants of a single population. Conclusions: (i) Resistance must have arisen independently at least three times; (ii) at least one population was already resistant to ALS inhibitors when introduced in Italy; (iii) a single haplotype with a Trp574Leu mutation was shared among six populations, probably because of broad seed dispersal; and (iv) one population likely evolved nontarget site ALS inhibitors resistance.openMilani, A.; Lutz, U.; Galla, G.; Scarabel, L.; Weigel, D.; Sattin, M.Milani, A.; Lutz, U.; Galla, G.; Scarabel, L.; Weigel, D.; Sattin, M