Using a phenomenological approach, we analyse the formation and the propagation of the patterns (or 'dissipative structures") in the stock market, the spatial coordinate being the bid-offer spread y, as a function of which the spectrum φof deals is modelled. The stock market will be considered a distributed active medium that is a set of active elements (the brokers) interacting with others through deals (typically a diffusion process). The physical model used is the reaction-diffusion model. The reactive part of the reaction-diffusion equation is developed from a hot-spot mechanism, with a characteristic jump when φ passes the critical value φ_c. Solving the stationary equation according to the Dirichlet boundary conditions, we find the "hot deals" regions, meaning regions of speculative transactions. which can be considered "dissipation" as they do not contribute to the gross national product. The time propagation of these patterns in the one-dimensional space considered could explain the evolution of markets towards speculative bubbles. These are frequently met in the frame of emerging stock markets. Financial data, which illustrate the physical model refer to Romania's stock market, Bucharest S.E.
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