The majority vote (MV) model is a stochastic model for the opinion formation devised as a nonequilibrium version of the Ising model. In its most popular version agents update their opinions at discrete time steps following the opinion of the majority of their neighbors with probability 1-q, where positive q smaller than ½ controls the degree of internal noise. The MV model on regular two- and three-dimensional lattices was shown to exhibit a continuous ordering transition with decreasing q, with the critical exponents belonging to the universality class of the corresponding Ising model. It was also studied and successfully described using the mean-field approximation on various complex networks, in particular on scale-free networks which reflect heterogeneity of human social and economic interactions. In this seminar the above-mentioned basic facts about the MV model are recollected, and certain new results are presented. First, the studies of the MV model on complex networks are extended to the case of multiplex networks in which the agents interact via different communications channels corresponding to independently generated, heterogeneous layers of the multiplex network and make decisions based on the opinions of the majorities of their neighbors within all layers. This model exhibits ordering transition which is quantitatively correctly described in the mean-field approximation. Second, the MV model on complex networks is investigated in which part of agents are anticonformists who with probability 1-q assume opinions opposite to the majority of their neighbors. Numerical evidence for the possibility of the occurrence of a spin-glass-like transition in this model is provided. Finally, response of the MV model to external periodic stimulation is investigated numerically and using the mean-field approximation. Stochastic resonance is observed, i.e., maximization of the response of the model at non-zero level of internal noise.
room 1.03, Pasteura 5 at 17:15

Agata Fronczak (Wydział Fizyki, Politechnika Warszawska)
New ideas in statistical physics – hybrid phase transitions
Water evaporation, melting of snow, loss of magnetic properties of a heated piece of iron, superconductivity - all these phenomena are examples of phase transitions. Explaining the reasons and determining the conditions of phase transition, considered to be the most fascinating property of matter, was one of the greatest challenges of physics of the last century. At that time, many issues related to these phenomena were understood and explained. In particular, it has been shown that despite the great variety of observed changes, they can be divided into two types: discontinuous and continuous. The first one happens suddenly. For example, the transition of water into ice occurs suddenly. At a given pressure and above the melting point, water is fluid and below this temperature it is constant and rigid. There is nothing between one phase and the other - water does not become less fluid before it turns into ice. At the point of change, the density of water changes abruptly. This is not the case of continuous phase transitions, termed critical. It is said that they occur in a turbulent manner. In the vicinity of critical points where these changes occur, the studied systems are extremely susceptible to various fluctuations. In such systems, even a slight change in external parameters, such as temperature, can cause huge changes. Approaching the critical points is apparent from large fluctuations of various internal parameters of the systems studied although the averaged values of these parameters behave continuously - unlike discontinuous transformations.Hybrid variants derive their name from Greek mythology. Mythical hybrids combine unmatched elements (e.g. chimera was a lion's head monster with goat's body). In hybrid phase transitions, such unmatched elements are features of discontinuous and continuous phase transformations, which have previously been thought to not coexist in the same system. During the presentation, I will discuss the properties and examples of hybrid phase transitions [1]. I will also tell about one of the few closely-defined spin models in which such a transition was exactly solved [2]. References:[1] A. Bar, D. Mukamel, Phys. Rev. Lett. 112, 015701 (2014); A. Bar, D. Mukamel, J. Stat. Mech. P11001 (2014); D. Lee, Y.S. Cho, B. Kahang, J. Stat. Mech. 124002 (2016).[2] A. Fronczak, P. Fronczak, A. Krawiecki, Phys. Rev. E 93, 012124 (2016); A. Fronczak, P. Fronczak, Phys. Rev. E 94, 012103 (2016).
room 1.03, Pasteura 5 at 18:15

Grzegorz Link (Wydział Fizyki UW)
A set of practical observations about investing, speculation and how financial markets work, continuation
Na naszym seminarium często skupiamy się na modelach ekonofizycznych i próbie zrozumienia procesów zachodzących na rynkach finansowych od strony teoretycznej. To bardzo ambitne zadanie. W swojej prezentacji sprobuję podejścia komplementarnego - zaprezentuję zestaw praktycznych obserwacji na temat inwestowania i działania rynków finansowych, który zebrałem w ciągu 10 lat obecności na tych rynkach. Będzie to subiektywny zbiór obserwacji, który może stanowić źródło ciekawych tematów dla badacza giełdy, a może też okazać się przydatny dzisiejszym i przyszłym inwestorom.-------------------------------------------------------------------------------------------------------------At our seminar we often focus on econophysical models and try to understand the processes taking place on the financial markets from a theoretical point of view. This is a very ambitious task. In my presentation, I will try a complementary approach - I will present a set of practical observations on investing and the operation of the financial markets that I have gathered over 10 years of presence in these markets. It will be a subjective collection of observations, which may be a source of interesting topics for the stock market researcher, and may also prove useful for today's and future investors.
room 1.03, Pasteura 5 at 18:15

Grzegorz Link (Wydział Fizyki UW)
A set of practical observations about investing, speculation and how financial markets work
Na naszym seminarium często skupiamy się na modelach ekonofizycznych i próbie zrozumienia procesów zachodzących na rynkach finansowych od strony teoretycznej. To bardzo ambitne zadanie. W swojej prezentacji sprobuję podejścia komplementarnego - zaprezentuję zestaw praktycznych obserwacji na temat inwestowania i działania rynków finansowych, który zebrałem w ciągu 10 lat obecności na tych rynkach. Będzie to subiektywny zbiór obserwacji, który może stanowić źródło ciekawych tematów dla badacza giełdy, a może też okazać się przydatny dzisiejszym i przyszłym inwestorom.------------------------------------------------------------------------------------------------------------------------------------At our seminar we often focus on econophysical models and try to understand the processes taking place on the financial markets from a theoretical point of view. This is a very ambitious task. In my presentation, I will try a complementary approach - I will present a set of practical observations on investing and the operation of the financial markets that I have gathered over 10 years of presence in these markets. It will be a subjective collection of observations, which may be a source of interesting topics for the stock market researcher, and may also prove useful for today's and future investors.